Academic literature on the topic 'Sex determination in animals'

SummaryIn many reptiles, sex determination is temperature-sensitive. This phenomenon has been shown to take place in the laboratory as well as in nature, but its effect on natural populations remains questionable. In the turtle Emys orbicularis, the effects of temperature override a weak mechanism of genetic sex determination which is revealed in incubation at pivotal temperature. At this temperature, the sexual phenotype is concordant with the expression of the serologically defined H-Y antigen (H-Ys) in non-gonadal tissues; males are H-Ys negative (H-Y−) whereas females are H-Ys positive (H-Y+). To estimate the importance of sexual inversion (sexual phenotype and H-Ys expression discordant) in populations of Brenne (France), the frequencies of male and female sexual phenotypes among H-Ys phenotypes were determined. The frequencies of sex reversed individuals are low, only 6 % of phenotypic females being H-Y− and 11 % of phenotypic males being H-Y+. According to these data, two theoretical models have been constructed to estimate the contribution to sex determination of individuals in relation to their genotype. The first model excludes any influence of incubation temperature and sexual phenotype on the fitness of individuals. The second one considers that these parameters influence fitness because this model has been previously shown to favour environmental sex determination. In both models, it appears that sex determination can be viewed as genotypic and monogenic with some individuals sexually inverted by theaction of temperature. One category of homozygous animals differentiates mainly into one sex, and the heterozygous animals differentiate mainly into the other sex. The second category of homozygotes has a low frequency in the populations and can differentiate as male or female without high constraint. Then it is estimated that in Brenne approximately 83% of the eggs are incubated in conditions allowing the genetic component to influence sex determination.

Sex-lethal (Sxl) is the master switch gene for somatic sex determination in Drosophila melanogaster. In XX animals, Sxl becomes activated and imposes female development; in X(Y) animals, Sxl remains inactive and male development ensues. A switch gene for sex determination, called F, has also been identified in the housefly, Musca domestica. An active F dictates female development, while male development ensues when F is inactive. To test if the switch functions of Sxl and F are founded on a common molecular basis, we isolated the homologous Sxl gene in the housefly. Though highly conserved in sequence, Musca-Sxl is not sex-specifically regulated: the same transcripts and protein isoforms are expressed in both male and female animals throughout development. Musca-Sxl is apparently not controlled by the primary sex-determining signal and, thus, is unlikely to correspond to the F gene. Ectopic expression of Musca-SXL protein in Drosophila does not exert any noticeable effects on the known target genes of endogenous Sxl. Instead, forced overexpression of the transgene eventually results in lethality of both XY and XX animals and in developmental abnormalities in some escaper XY animals. Similar results were obtained with the Sxl homologue of Ceratitis capitata (Saccone, G., Peluso, I., Artiaco, D., Giodano, E., Bopp, D. and Polito, L. C. (1998) Development 125, 1495–1500) suggesting that, in these non-drosophilid species, Sxl performs a function different from that in sex determination.

In the first two papers of this volume, the genetic control of sex determination in Caenorhabditis and Drosophila is reviewed by Hodgkin and by Nöthiger & Steinmarin-Zwicky, respectively. Sex determination in both cases depends on the ratio of X chromosomes to autosomes, which acts as a signal to a cascade of règulatory genes located either on autosomes or on the X chromosome. The state of activity of the last gene in the sequence determines phenotypic sex. In the third paper, Erickson & Tres describe the structure of the mouse Y chromosome and the polymorphisms that have been detected in different mouse species and strains. As in all mammals, the Y carries the primary male-determining locus; autosomal genes may also be involved in sex determination, but they must act down-stream from the Y-linked locus.

Abstract In Caenorhabditis elegans triploid animals with two X chromosomes (symbolized 3A;2X) are males. However, these triploid males can be feminized by making them mutant for recessive dosage compensation mutations, by adding X chromosome duplications or by microinjecting particular DNA sequences termed feminizing elements. None of these treatments affects diploid males. This study explores several aspects of these treatments in polyploids. The dosage compensation mutants exhibit a strong maternal effect, such that reduction of any of the dosage compensation gene functions in the mother leads to sex reversal of 3A;2X animals. Likewise, all X chromosome duplications tested cause both sex reversal and intersexual development of many 3A;2X animals. Microinjected feminizing element DNA does not cause extensive sex reversal, but does result in intersexual development in 3A;2X animals. Neither X chromosome duplications nor microinjected feminizing elements show that extreme maternal effect of the dosage compensation mutants, although there is indirect evidence for a maternal effect of the feminizing elements. In particular, very little feminizing element DNA needs to be microinjected in order to feminize triploid males, far less than what is needed for stable inheritance, implying that feminizing elements can work within the mother's gonad. However, even very high concentrations of microinjected feminizing elements do not affect sex determination in diploid males, suggesting that they are not part of the numerator of the X/A ratio. In addition, no pair of X chromosome duplications feminizes diploid males, suggesting that none of these duplications contains a numerator of the X/A ratio. Instead, I infer that an X-linked locus, as yet undefined, must be present in two copies for hermaphrodite development to ensue or that the two X chromosomes might interact.

Animals determine their sex genetically (GSD: genetic sex determination) and/or environmentally (ESD: environmental sex determination). Medaka (<i>Oryzias latipes</i>) employ a XX/XY GSD system, however, they display female-to-male sex reversal in response to various environmental changes such as temperature, hypoxia, and green light. Interestingly, we found that 5 days of starvation during sex differentiation caused female-to-male sex reversal. In this situation, the metabolism of pantothenate and fatty acid synthesis plays an important role in sex reversal. Metabolism is associated with other biological factors such as germ cells, HPG axis, lipids, and epigenetics, and supplys substances and acts as signal transducers. In this review, we discuss the importance of metabolism during sex differentiation and how metabolism contributes to sex differentiation.

Thesis (Ph.D.) - University of Glasgow, 2008.
Ph.D. thesis submitted to the Division of Molecular Genetics, Institute of Biomedical and Life Sciences, University of Glasgow, 2008. Includes bibliographical references. Print version also available.

Much of what we know about temperature-dependent sex determination (TSD) in reptiles stems from constant temperature incubation studies in the laboratory. In recent years, as TSD studies moved into the field it became evident that TSD was much more complex than previously thought. The present study attempted to reveal the complexity of TSD, as it relates to other features of the species' biology and physical characteristics tractable only in the field, such as fluctuations in incubation temperature and reproductive life history. To this end I studied the ecology of the turtle Carettochelys insculpta, a TSD species inhabiting the wet-dry tropics of northern Australia from 1996 to 1998. I tested hypotheses associated with movements, activity, behaviour, reproduction, nest site choice, nest temperatures, embryonic survival, embryonic aestivation, hatch-ling sex ratios, and emergence in the species. Each of these was also considered in the context of the influence of the wet-dry tropics. Compared to other turtles inhabiting lotic habitats, C. insculpta occupied considerably larger home ranges, covering up to 10 km of river. Of previously published factors influencing home range size, low productivity of the (micro) habitat may best explain the extensive home ranges in C. insculpta. Patchiness and low nutrient value of the chief food (aquatic vegetation) of C. insculpta may force turtles to cover large expanses of river to acquire sufficient energy for growth and reproduction. Females were more active, moved farther, and occupied larger home ranges than males. Home ranges of females comprised 1-4 activity centres, many of which were associated with thermal springs. I suggest that females may exhibit increased activity and movements relative to males because of sexual inequality in parental investment, where food is particularly limiting (e.g., in species with biennial reproduction). Biennial reproduction in the population allowed the examination of the influence of reproductive condition on home range size, movements, and activity. Reproductive condition did not influence home range or activity, but gravid turtles moved father between successive sightings than non-gravid females. Individual data corroborate these findings, with females moving farther between successive sightings while gravid compared to while spent. Contrary to previous reports, turtles did not appear to move into estuarine areas or lowland flood plains during the wet season, but moved into the riparian forest and possibly into wetlands adjacent to the main channel in the vicinity of their dry season home ranges. During the study I documented the turtles' use of small, localized thermal springs discharging from the river bottom. Dataloggers attached to the carapace to monitor ambient water temperatures recorded the frequency and duration of thermal spring use by individuals. Turtles used the thermal springs frequently during the winter (4-6 months) when river temperatures were lower than that of the thermal springs (8 = 29 � 0.52� C). Turtles often utilized thermal springs for several consecutive hours, leaving the springs only to surface for air. Thermal springs may be derived from ground water (which maintains a temperature equivalent to the annual mean air temperature), rather than from a specific geothermal heat source. Nine of 19 radio-telemetered adult females were seen to use thermal springs, of which seven were gravid and two non-gravid. Thus, gravid turtles may seek thermal springs more than non-gravid turtles. Frequency, duration, and timing of usage collectively suggest active thermoregulation as the primary function of thermal spring use. Utilization of thermal springs probably permits turtles to be more active in cooler months, which may enhance growth rates and accumulation of energy for reproduction. Onset of nesting along river stretches with thermal springs preceded nesting in a stretch not known to have thermal springs by 24 days. Thus, I speculate that by warming themselves on thermal springs in the months prior to nesting, turtles may have accelerated follicular development and nested earlier. Female C. insculpta matured at ca. 6 kg body mass (38.0 cm carapace length, 30.5 cm plastron length). Turtles produced egg sizes and clutch sizes similar to that of other turtle species of similar size. Turtles reproduced every second year, but produced two clutches in each breeding year, ca. 40 days apart. Thus, it appeared that females were energy limited, possibly due to the low available energy content of the dry season diet (aquatic vegetation). Life history theory predicts that if some costly behaviour is associated with reproduction, skipping years could reduce that cost and allow savings to be directed into future reproduction. The present study revealed no obvious accessory behaviour in the population. Within years, clutch mass did not differ between early (first) and late (second) clutches. However, earlier clutches tended to have more and smaller eggs per clutch but than later clutches, a new finding for turtles that has been demonstrated in lizards and other animals. Because the study spanned both years with 'big' and 'small' wet seasons, I was able to examine how the magnitude of the wet season influenced reproductive characteristics. Following big wet seasons turtles produced larger, heavier, and more eggs per clutch than they did after small wet seasons. Relationships among body size, egg size, and clutch size were evident after two big wet seasons but not apparent after two small wet seasons. Collectively, annual variation in reproductive characteristics and current life history theory suggest that a big wet season is a plentiful time for the turtles. I investigated beach selection of nesting pig-nosed turtles (Carettochelys insculpta) along a 63 km stretch of river in 1997 and 1998. I used three classes of beaches to examine beach choice: beaches with nests, beaches with only crawls, andbeaches without nests or crawls. Across these beach types I compared aspect, solar exposure, temperature, substrate moisture, height, water depth at approach, and the height of cohesive sand. I located 82 nesting beaches with 221 nests, and identified 171 potential nesting beaches based on previously published criteria. Beaches with nests had a greater substrate moisture content and corresponding higher cohesive sand line (hereafter CSL) than beaches without nests. Beaches with nests also had a higher CSL than beaches with only crawls. Apparently, turtles could not excavate a nest chamber above the CSL due to loose substrate consistency causing sand to fall in on itself. Turtles could only nest at low elevations below the CSL on beaches with lower substrate moisture. Turtles apparently avoided nesting on these beaches due to the higher probability of nest flooding, as corroborated by a concurrent study. Beach temperatures increased with a seasonal increase in air temperatures, and were influenced by aspect and total angle of solar exposure. Temperatures did not differ among beaches with nests, beaches with only crawls, and beaches without crawls or nests. Therefore, there was no indication that turtles were manipulating offspring sex through choice of nesting beach. However, turtles may be manipulating sex by nesting in areas with particular thermal characteristics within beaches. Two related aspects of hatchling emergence were studied. Using emergence phenology data, nest temperatures, historical weather data, and a developmental model, I tested the hypothesis that delayed hatching occurred in C. insculpta, and that such a delay would allow hatchlings to time their emergence to match the onset of the wet season. Hatchling C. insculpta emerged, on average, 17 days later than dates predicted from a developmental model. Combined with observations of hatchlings remaining in eggs until emergence, these results confirmed delayed hatching in nature. This delay was synchronized with initial river rises associated with the onsetof wet season rains, and is consistent with published criteria for embryonic aestivation. On a diel scale, I generated predictions of two potentially competing models for nocturnal emergence in hatchling turtles, based on the knowledge that air temperatures decrease with season during the emergence period. A test of those predictions for C. insculpta produced ambiguous results. However, further analysis indicated that C. insculpta, and probably other nocturnally emerging turtle species, respond to a decline in diel temperature rather than an absolute temperature. The former would ensure nocturnal emergence, while the latter is experienced during the day as well as at night. Nocturnal emergence may be associated with nesting in open microhabitats. The 'decision' of when and where to nest can influence both offspring survival and hatchling sex ratios in animals with temperature-dependent sex determination (TSD). Knowledge of how these maternal attributes influence the incubation environment is an important first step in hypothesizing why TSD evolved in a particular species. 1 studied the influence of nest site choice and timing of nesting on embryonic survival and hatchling sex ratios. Predation and flooding were the major sources of embryonic mortality. Embryonic survival was influenced by both lay date and nest site choice: In one year when nesting began later, nests laid later and at lower elevations were destroyed by early wet season river rises. In other years early nesting precluded flood mortality. However, turtles did not nest at the highest available elevations. I hypothesized that turtles were unable to nest at higher elevations because the sand was dry and not cohesive. A field experiment demonstrated that turtles were constrained to nest at lower elevations where they could construct a nest chamber. A mathematical model predicting hatchling sex from fluctuating temperatures was applied to temperature data from 102 natural nests. Resultsconfirmed a type la pattern of TSD, whereby males are produced from cooler temperatures and females from warmer temperatures. The principal determinant of hatchling sex was lay date. Clutches laid earlier in the season produced mainly males, while later clutches yielded mostly females, due to seasonal ramping of air and sand temperatures. However, nest site choice also exerted an influence on hatchling sex. Female-producing clutches were deposited at higher elevations than male-producing clutches. The onset of nesting was not influenced by water temperatures, but may have been related to the magnitude of the previous wet season(s). Turtles nested earlier after two 'big' wet seasons and later following two 'small' wet seasons. This pattern indicates that the wet season is a plentiful time for the turtles. Adaptive 'differential fitness' models for the evolution of TSD have recently been reviewed and clarified. The differential fitness model that best fits C. insculpta is the 'timematching' model, whereby one sex benefits more than the other from early hatching. Male C. insculpta hatched 2-3 weeks earlier then females, on average. Benefit to early hatching males and, therefore, the ultimate selective mechanism (e.g., growth, time to mature) is unknown. Obtaining such data will likely prove difficult in such a long-lived species. A recent adaptive explanation for the evolution and maintenance of temperaturedependent sex determination (TSD) in reptiles rests upon the assumption that mothers can predict or manipulate offspring sex. I postulated that four physiological and behavioural criteria must be met in order for this assumption to be valid: (1) a strong correlation must exist between substrate temperatures during nest site choice and nest temperatures during the period of development when sex is determined in the egg (thermosensitive period = TSP). (2) Assuming that (1) is possible, mothers would need to be capable of correcting for temporal factors obscuring the predictable thermalcharacteristics of nest sites. This could be accomplished in two ways. By contracting nesting times mothers could assess the relative temperatures of alternate nest sites with some accuracy. A protracted distribution of nesting times could greatly reduce a mother's ability to distinguish between, for example, a cooler nest site at a warmer time and a warmer nest site at a cooler time. Alternatively, mothers would need to be able to incorporate temporal changes in nest site temperatures. (3) Sufficient variation in thermal profiles among nest sites, relative to the breadth of temperatures producing both sexes (pivotal temperatures), would be necessary. For example, if most nests produced both sexes, then depth of the eggs would be the deciding factor determining sex, leaving little opportunity for nest site choice to produce one sex or the other. (4) Mothers would need access to nest sites spanning a range of thermal profiles in order to produce either offspring sex. To this end, home range size relative to the number and location of nesting beaches should be important. I tested these four predictions in Carettochelys insculpta, a beach nesting turtle with TSD, using three years of field data on nest site choice, nesting times, thermal characteristics of nests, hatchling sex ratios, and movements of nesting turtles. A strong positive correlation existed between assessable substrate temperatures at nest site choice and mean daily TSP temperatures in all three years. However, the proportion of explained variation was highly variable among years, and low in 1998. Accordingly, the proportion of nests in which substrate temperatures at nest site choice predicted offspring sex correctly was low in 1998 (48- 62 %, depending on treatment of the data). Nesting times were normally distributed, and combined with diel changes in nest site temperatures greatly reduce a turtle's ability to distinguish between sites that would produce different sexes. Considerable among-clutch variation in thermal profiles to produce variable sex ratios existed, agreeing with other studies on turtles. Radiotelemetry indicated that home rangesencompassed several nesting beaches with differing thermal profiles, indicating scope for producing the desired sex. However, the seasonal increase in air temperatures resulted in an overriding effect of mostly males being produced in early (first) clutches and mainly females being produced in late (second) clutches. Collectively, the results suggest that C. insculpta mothers would find it difficult to predict, and therefore, manipulate hatchling sex, supporting the conventional notion that TSD mothers have little or no control over offspring sex.

The mechanism of sex determination and the development control of the life-cycle of the gastro-intestinal parasite, Strongyloides ratti was investigated using a combination of genetic and parasitological techniques. Parasitological analysis investigated the effects of intra- and extra-host factors on the development of the free-living phase of the life cycle. An initial analysis of the distribution of infective stages among host faecal pellets showed that they were significantly overdispersed and well described by the negative binomial distribution. This overidspersion was found to occur over a wide range of infection intensities and to increase significantly during infection. Further investigation, coupled with an artificial selection experiment, suggested the existence of two discrete developmental switches; an intra-host sex determination switch and an extra-host free-living female/directly developing iL3 development conversion. Analysis of the effects of host immunity on these developmental switches clarified the way in which the composition of the free-living phase varies over the course of an infection. Increasing host immunity results in a greater proportion of female larvae developing into free-living females rather than into directly developing iL3s. Further evidence suggested that the increase in proportion of female larvae that develop into free-living females with increased host immunity is due to an increased temperature sensitivity of the free-living female/directly developing iL3 developmental conversion. Increasing host immunity also alters the sex ratio, resulting in a greater proportion of larvae developing into free-living males. In addition, increased parasitic female age appears to increase the proportion of larvae that develop into free-living males, but does not increase the proportion of female larvae that develop into free-living females. In conclusion, this thesis has used a combined parasitological and genetic approach to investigate the mechanism of sex determination of S. ratti. This understanding now allows a rational view of the S. ratti life-cycle to be presented. These findings are discussed in relation to previous studies of Strongyloides spp. and further questions raised by this work are discussed.

Effective reproduction is essential for species survival. Sexual reproduction depends upon functional gonads and reproductive ducts. Zebrafish (Danio rerio) is a popular model organism, but the genetic basis of zebrafish sex determination, gonad development, and reproductive tract development are not fully understood, and understanding this basis could inform about the evolutionary conservation of these genes and the use of zebrafish to investigate and treat reproductive diseases. In chapter I, I give a overview of sex determination systems, gonad development, and reproductive duct development in mammals and fish, and ask how sex is determined and how reproductive ducts develop in zebrafish. In chapter II, I used genome wide association studies (GWAS) to investigate if the genetic basis of sex determination in a variety of zebrafish strains -- two ‘wild-type’ strains cultured for about 30 years in the lab, and four ‘natural’ strains, wild-type strains isolated directly or recently from nature in India -- and identified a sex-associated region on zebrafish chromosome 4 in natural zebrafish strains that was lacking in the lab strains. In chapter III, I investigated whether or not wnt4a is important for zebrafish ovarian development, and found that wnt4a is expressed in the early bipotential gonad and that loss of wnt4a results in male-biased sex ratios, indicating that wnt4a is important for zebrafish ovarian development. In chapter IV, I investigated whether or not wnt4a is important for male reproductive duct development, and found that loss of wnt4a slows the formation of male reproductive ducts and prevents the male fused ducti deferens from connecting to the genital orifice in zebrafish males. Results further showed that wnt4a is expressed in tissue around the site where this connection should occur before and after the connection is formed, revealing a novel wnt4a phenotype in zebrafish that hasn’t been seen thus far, and indicating that wnt4a is necessary for proper male reproductive duct development in zebrafish. This dissertation contains both published and unpublished co-authored material.

Orientador: Rafael Henrique Nóbrega
Resumo: A decisão sobre se uma gônada bipotencial se desenvolverá em um testículo ou em um ovário é considerado um estágio crítico na diferenciação sexual dos vertebrados. A administração de esteróides exógenos durante este período pode afetar essa plasticidade, promovendo a diferenciação sexual na direção feminina ou masculina. Dessa forma, o objetivo desta tese foi avaliar os efeitos do tratamento de 17β-estradiol no desenvolvimento de Astyanax altiparanae (lambari), através de análises histológicas e de análises de expressão genica de possíveis genes envolvidos em vias masculinas e femininas. Para isso, larvas com gônadas indiferenciadas foram alimentadas com Artemia contendo diferentes concentrações de estradiol durante 28 dias, desde o 1 dia pós-eclosão (dpe) até o período que precede a diferenciação gonadal. Nossos resultados mostraram que o E2 modificou o fenotípo e a relação sexual histológica e, surpreendentemente, induziu intersexo com com a presença de óvulos nos testículos nas concentrações de 2 e 6 mg de E2/kg de alimento. Esses dados são uma evidência clara de que o tratamento utilizado não foi suficiente para induzir a reversão completa do sexo em A. altiparanae. Em termos de expressão gênica, o tratamento com E2 (6 mg/kg de alimento) produziu uma notável plasticidade gonadal entre machos e fêmeas aos 90 dias após a eclosão (dph). Os machos, denominados “machos resistentes ao estradiol”, superexpressaram os genes masculinos, como dmrt1, sox9 e amh. Dessa forma, nó... (Resumo completo, clicar acesso eletrônico abaixo)
Abstract: The decision whether a bipotential gonad will become a testis or ovary is considered a critical stage in vertebrate sex determination. Administration of exogenous steroids can affect this plasticity by skewing the sex gonadal differentiation towards a male or female. The aim of this study is to evaluate the effects of 17β-estradiol (E2) diet on Astyanax altiparanae (lambari) development, focusing on the gonadal development and gene expression analysis of possible candidate genes involved in either male or female pathways. Larvae with undifferentiated gonads were fed with steroid diet containing different concentrations of E2 during 28 days, from the mouth opening until a period that precedes the gonadal differentiation. Animals were sampled at 90 days post-hatching (dhp) for histology and gene expression analysis. Our results showed that E2 disrupted both phenotypic and histological sex ratios, and surprisingly, induced intersex with testis-ova in the concentrations of 2 and 6 mg E2/Kg food. This data is a clear evidence that the treatment used was not enough to induce complete sex reversal in A. altiparanae. However, in terms of gene expression, E2 (6mg/Kg food) induced a remarkable gonadal plasticity between males and females at 90 dph. The males, named as E2 resistant males, overexpressed the male-biased genes, such as dmrt1, sox9 and amh. We suggested that these males were able to resist the E2-induced feminization by the expression of genes related to testis differentiat... (Complete abstract click electronic access below)
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La molécule de l’éthylène (C2H4) est le régulateur principal du sexe chez les cucurbites. Essentiellement, l’éthylène est connu pour son rôle promoteur dans le développement des carpelles et un rôle inhibiteur des étamines dans les fleurs du melon. L’interaction entre les biosynthétique gènes de l’éthylène (CmACS7, CmACS11, et CmACO3) et le facteur de transcription CmWIP1 détermine différentes formes du sexe chez le melon. Le rôle de ces gènes est bien étudié chez le melon. Cependant, le mécanisme qui contrôle l’initiation et la coordination de formation des étamines et des carpelles dans la fleur reste ambigu. En reposant sur l’importance de l’éthylène dans l’expression du sexe chez le melon, j’ai focalisé sur l’identification des gènes impliqués dans la voie signalisation éthylène-sexe. Au cours de la thèse, le criblage des mutants altérés dans la réponse à l’exogène éthylène nous facilitait d’identifier des nouveaux gènes impliqués dans la détermination du sexe chez la famille de Cucurbitacée. Pendant ma thèse j’ai isolé plus de 10 mutants insensibles à l’éthylène de différentes populations du melon. Deux mutants ont été isolés de deux populations monoïques indépendantes. Ces deux mutants provoquent une transition partielle et complète au melon andromonoïque dans la génération M2, respectivement. Un de ces deux mutants a été identifié et caractérisé. Deux autres mutants gsn106 et vat233 ont été criblés de deux populations andromonoïque, provoquent une transition complète et partielle à androïque melon, respectivement. En utilisant le séquençage à haute débit et les analyses génétiques j’ai essayé de cloner et caractériser ces gènes mutants. Par ailleurs, des autres mutants insensibles à l’éthylène sont en cours d’être phénotypes pour le phénotype du sexe. L’isolation et caractérisation des nouveaux gènes impliqués dans le déterminisme du sexe nous aidera pour mettre en place un model clair explant comment le sexe est contrôlé chez les plantes
Ethylene (C2H4) is an important phytohormone in plants and the main sex regulator in the family Cucurbitaceae. As known, the ethylene promotes the carpel development and inhibits the stamens in the melon flower (Cucumis melo L.). The interplay of the biosynthesis genes (CmACS7, CmACS11, et CmACO3) and the transcription factor CmWIP1 generates different sexual forms in melon. The role of these genes in the sex expression is well studied. However, the mechanism that controls the initiation and coordination of stamen and carpel development in the flower remains ambiguous. Based on the importance of the ethylene in the sex determination, I aimed to isolate novel genes involved in the pathway ethylene-sex in the melon (Cucumis melo L.). For this purpose, I used the response to exogenous ethylene in the etiolated seedlings (known as the triple response phenotype) to isolate ethylene-insensitive mutants. During my thesis I isolated more than 10 ethylene-insensitive mutants from six EMS-mutagenised melon populations. Some of these mutants induced changes in the sex expression of the melon. . Two mutants were isolated from two independent monoecious populations (female and male flowers on the same plant) and induced a partial and a complete sexual transition to the andromonoecious melon in the second generation M2, respectively. One of them was cloned and characterized using Omics tools. Two other mutants (gsn106) and (vat233) screened from two independent andromonoecious melon (bisexual and male flowers on the same plant) populations, induced complete and partial sexual transitions into androecy (only male flowers), respectively. Using Next-Generation Sequencing (NGS) and the genetic analysis, we are trying to clone and characterise these mutants (gsn106) and (vat233). In the same way, we continue to observe others promising ethylene-insensitive mutants (vat306, vat175, and vat230) for the sex phenotype. The isolation and characterisation of novel genes involved in the sex determination will permit to provide a new and clear model explains of the sex determination mechanism in plants

Chez les mammifères, la détermination sexuelle résulte dans le développement d’un individu mâle ou femelle. Le développement correct de deux sexes dimorphiques dotés d’organes reproductifs fonctionnels est primordial pour la survie des espèces. La détermination sexuelle chez les mammifères a une base génétique et les deux sexes sont génétiquement distincts dés la fertilisation. Les embryons féminins possèdent deux chromosomes X et les masculins un chromosome X et un Y. L’expression de SRY déclenche le développement testiculaire en assurant une expression stable et prolongée du gène SOX9 dans les cellules somatiques de la gonade masculine. Dans les gonades féminines, l’expression de SOX9 est activement réprimée et permet le développement ovarien. Ces événements sont placés en haut de la cascade de détermination sexuelle mais, même si beaucoup de facteurs ont été identifiés, beaucoup restent encore ignorés ou mal connus. Pour identifier de nouveaux facteurs génétiques qui contrôlent la détermination sexuelle chez l’Homme j’ai étudié plusieurs individus ayant des troubles de détermination sexuelle (DSD) - troubles congénitaux où le développement sexuel chromosomique, gonadique ou anatomique est atypique. Pendant ma thèse, mon but a été de mieux comprendre le rôle de trois gènes – NR5A1, GATA4 et FOG2 – dans le développement et fonction des gonades. Mutations dans NR5A1 sont associées à une insuffisance ovarienne précoce et à une infertilité masculine. Mutations dans GATA4 et FOG2 sont associées à des cas de 46,XY DSD avec ou sans phénotype cardiaque. Mes résultats ont démontré le rôle de ces gènes dans la cascade de détermination sexuelle chez l’Homme

In atherosclerotic arterial tissue, cholesterol is delivered to smooth muscle cells by low-density lipoprotein (LDL) and to macrophages via modified LDL. The reasons for accumulation of excess lipid are unknown although increased uptake of C and CE occurs in regions of arterial de-endothelialisation. We now report that the positioning of a silastic collar containing saline around the outside of arteries induces accumulation of C and CE within those tissues. 9 rabbits were separated into 3 groups, each group was fed a normal laboratory chow, 2 groups were supplemented with lg/day cholesterol; these rabbits were used for C and CE determinations. Three parallel groups of rabbits were set up for histological analysis. At day O, under anaesthesia, a silastic collar was* placed around the left carotid artery. The collar was filled with saline and carefully sealed without causing constriction of the vessel. The vessels were replaced and the animals allowed to recover. After 14 days the carotids from animals for C and CE determination were rapidly removed and divided up into a region from the middle of the collar, a region proximal to the collar and a distal region. The tissues were freeze clamped in liquid nitrogen and lipids extracted with C and CE determined for each region. The carotids for histological analysis were perfuse-fixed in situ and similarly subdivided.We conclude 1) Animals fed high cholesterol accumulate more C than CE within arterial tissue, furthermore this accumulation is greater than in animals fed a normal diet 2) In both normal diet and high cholesterol fed animals an enhanced accumulation of C + CE occurs within arteries with a collar 3) CE appears to be preferentially accumulated within the collar region.

Grand Canyon National Park is all about time and timescales. Time is the currency of our daily life, of history, and of biological evolution. Grand Canyon’s beauty has inspired explorers, artists, and poets. Behind it all, Grand Canyon’s geology and sense of timelessness are among its most prominent and important resources. Grand Canyon has an exceptionally complete and well-exposed rock record of Earth’s history. It is an ideal place to gain a sense of geologic (or deep) time. A visit to the South or North rims, a hike into the canyon of any length, or a trip through the 277-mile (446-km) length of Grand Canyon are awe-inspiring experiences for many reasons, and they often motivate us to look deeper to understand how our human timescales of hundreds and thousands of years overlap with Earth’s many timescales reaching back millions and billions of years. This report summarizes how geologists tell time at Grand Canyon, and the resultant “best” numeric ages for the canyon’s strata based on recent scientific research. By best, we mean the most accurate and precise ages available, given the dating techniques used, geologic constraints, the availability of datable material, and the fossil record of Grand Canyon rock units. This paper updates a previously-published compilation of best numeric ages (Mathis and Bowman 2005a; 2005b; 2007) to incorporate recent revisions in the canyon’s stratigraphic nomenclature and additional numeric age determinations published in the scientific literature. From bottom to top, Grand Canyon’s rocks can be ordered into three “sets” (or primary packages), each with an overarching story. The Vishnu Basement Rocks were once tens of miles deep as North America’s crust formed via collisions of volcanic island chains with the pre-existing continent between 1,840 and 1,375 million years ago. The Grand Canyon Supergroup contains evidence for early single-celled life and represents basins that record the assembly and breakup of an early supercontinent between 729 and 1,255 million years ago. The Layered Paleozoic Rocks encode stories, layer by layer, of dramatic geologic changes and the evolution of animal life during the Paleozoic Era (period of ancient life) between 270 and 530 million years ago. In addition to characterizing the ages and geology of the three sets of rocks, we provide numeric ages for all the groups and formations within each set. Nine tables list the best ages along with information on each unit’s tectonic or depositional environment, and specific information explaining why revisions were made to previously published numeric ages. Photographs, line drawings, and diagrams of the different rock formations are included, as well as an extensive glossary of geologic terms to help define important scientific concepts. The three sets of rocks are separated by rock contacts called unconformities formed during long periods of erosion. This report unravels the Great Unconformity, named by John Wesley Powell 150 years ago, and shows that it is made up of several distinct erosion surfaces. The Great Nonconformity is between the Vishnu Basement Rocks and the Grand Canyon Supergroup. The Great Angular Unconformity is between the Grand Canyon Supergroup and the Layered Paleozoic Rocks. Powell’s term, the Great Unconformity, is used for contacts where the Vishnu Basement Rocks are directly overlain by the Layered Paleozoic Rocks. The time missing at these and other unconformities within the sets is also summarized in this paper—a topic that can be as interesting as the time recorded. Our goal is to provide a single up-to-date reference that summarizes the main facets of when the rocks exposed in the canyon’s walls were formed and their geologic history. This authoritative and readable summary of the age of Grand Canyon rocks will hopefully be helpful to National Park Service staff including resource managers and park interpreters at many levels of geologic understandings...