Query: sex determination

title: Temperature dependent sex determination in vertebrates
abstract: Edited by the world's foremost authorities on the subject, with essays by leading scholars in the field, this work shows how the sex of reptiles and many fish is determined not by the chromosomes they inherit but by the temperature at which incubation takes place. This open monograph is made available by Smithsonian Scholarly Press. Print copies are available for purchase through our distributor and Amazon.

title: The histone demethylase KDM6B regulates temperature dependent sex determination in a turtle species
abstract: Making males and back again Temperature dependent sex determination occurs in many reptilian species. An epigenetic mechanism is presumed to be at work, but thus far it has not been identified. Ge et al. show that in the red eared slider turtle, an epigenetic modifier, the histone demethylase KDM6B, binds to the promoter of the dominant male gene to activate male development (see the Perspective by Georges and Holleley) Knock down the expression of KDM6B, and embryos destined to be male turn into females. Science, this issue p. 645; see also p. 601 Epigenetic modification of a male determining gene facilitates how fertilized egg incubation temperature determines sex in red eared sliders. Temperature dependent sex determination is a notable model of phenotypic plasticity. In many reptiles, including the red eared slider turtle Trachemys scripta elegans (T. scripta) the individual's sex is determined by the ambient temperature during egg incubation. In this study, we show that the histone H3 lysine 27 (H3K27) demethylase KDM6B exhibits temperature dependent sexually dimorphic expression in early T. scripta embryos before the gonad is distinct. Knockdown of Kdm6b at 26degC (a temperature at which all offspring develop into males) triggers male to female sex reversal in >80% of surviving embryos. KDM6B directly promotes the transcription of the male sex determining gene Dmrt1 by eliminating the trimethylation of H3K27 near its promoter. Additionally, overexpression of Dmrt1 is sufficient to rescue the sex reversal induced by disruption of Kdm6b. This study establishes causality and a direct genetic link between epigenetic mechanisms and temperature dependent sex determination in a turtle species.

title: Transitions in sex determination and sex chromosomes across vertebrate species
abstract: Despite the prevalence of sexual reproduction across eukaryotes, there is a remarkable diversity of sex determination mechanisms. The underlying causes of this diversity remain unclear, and it is unknown whether there are convergent trends in the directionality of turnover in sex determination mechanisms. We used the recently assembled Tree of Sex database to assess patterns in the evolution of sex determination systems in the remarkably diverse vertebrate clades of teleost fish, squamate reptiles and amphibians. Contrary to theoretical predictions, we find no evidence that the evolution of separate sexes is irreversible, as transitions from separate sexes to hermaphroditism occur at higher rates than the reverse in fish. We also find that transitions from environmental sex determination to genetic sex determination occur at higher rates than the reverse in both squamates and fish, suggesting that genetic sex determination is more stable. However, our data are not consistent with the hypothesis that heteromorphic sex chromosomes are an "evolutionary trap." Rather, we find similar transition rates between homomorphic and heteromorphic sex chromosomes in both fish and amphibians, and to environmental sex determination from heteromorphic vs. homomorphic sex chromosome systems in fish. Finally, we find that transitions between male and female heterogamety occur at similar rates in amphibians and squamates, while transitions to male heterogamety occur at higher rates in fish. Together, these results provide the most comprehensive view to date of the evolution of vertebrate sex determination in a phylogenetic context, providing new insight into long standing questions about the evolution of sexual reproduction.

title: Diverse and variable sex determination mechanisms in vertebrates
abstract: Sex is prevalent in nature and sex determination is one of the most fundamental biological processes, while the way of initiating female and male development exhibits remarkable diversity and variability across vertebrates. The knowledge on why and how sex determination mechanisms evolve unusual plasticity remains limited. Here, we summarize sex determination systems, master sex determining genes and gene regulatory networks among vertebrates. Recent research advancements on sex determination system transition are also introduced and discussed in some non model animals with multiple sex determination mechanisms. This review will provide insights into the origin, transition and evolutionary adaption of different sex determination strategies in vertebrates, as well as clues for future perspectives in this field.

title: ZNRF3 functions in mammalian sex determination by inhibiting canonical WNT signaling
abstract: Sex determination involves antagonistic interactions between the testis determining (SRY SOX9 FGF9) and ovary promoting (RSPO1 WNT/b catenin FOXL2) pathways, but the underlying molecular mechanisms remain unclear. We show that ZNRF3, an E3 ubiquitin ligase that inhibits WNT signaling and is a direct target of RSPO1 mediated membrane clearance, is testis determining in mice. Testis determination defects in the absence of ZNRF3 arise due to ectopic canonical WNT signaling in XY gonads at the sex determining stage. We identify human ZNRF3 sequence variants in cases of 46,XY disorders of sex development with XY female presentation. In vitro functional assays show that these variants disrupt ZNRF3 function. Our data reveal a sex determining role for ZNRF3 and indicate that interactions between ZNRF3 and RSPO1 regulate mammalian sex determination. Mammalian sex determination is controlled by the antagonistic interactions of two genetic pathways: The SRY SOX9 FGF9 network promotes testis determination partly by opposing proovarian pathways, while RSPO1/WNT b catenin/FOXL2 signals control ovary development by inhibiting SRY SOX9 FGF9. The molecular basis of this mutual antagonism is unclear. Here we show that ZNRF3, a WNT signaling antagonist and direct target of RSPO1 mediated inhibition, is required for sex determination in mice. XY mice lacking ZNRF3 exhibit complete or partial gonadal sex reversal, or related defects. These abnormalities are associated with ectopic WNT/b catenin activity and reduced Sox9 expression during fetal sex determination. Using exome sequencing of individuals with 46,XY disorders of sex development, we identified three human ZNRF3 variants in very rare cases of XY female presentation. We tested two missense variants and show that these disrupt ZNRF3 activity in both human cell lines and zebrafish embryo assays. Our data identify a testis determining function for ZNRF3 and indicate a mechanism of direct molecular interaction between two mutually antagonistic organogenetic pathways.

title: Characterization of a large sex determination region in Salix purpurea L. (Salicaceae)
abstract: Dioecy has evolved numerous times in plants, but heteromorphic sex chromosomes are apparently rare. Sex determination has been studied in multiple Salix and Populus (Salicaceae) species, and P. trichocarpa has an XY sex determination system on chromosome 19, while S. suchowensis and S. viminalis have a ZW system on chromosome 15. Here we use whole genome sequencing coupled with quantitative trait locus mapping and a genome wide association study to characterize the genomic composition of the non recombining portion of the sex determination region. We demonstrate that Salix purpurea also has a ZW system on chromosome 15. The sex determination region has reduced recombination, high structural polymorphism, an abundance of transposable elements, and contains genes that are involved in sex expression in other plants. We also show that chromosome 19 contains sex associated markers in this S. purpurea assembly, along with other autosomes. This raises the intriguing possibility of a translocation of the sex determination region within the Salicaceae lineage, suggesting a common evolutionary origin of the Populus and Salix sex determination loci.

title: Vertebrate sex determination: evolutionary plasticity of a fundamental switch
abstract: The discovery of the Sry gene in 1990 triggered a revolution in our understanding of sex determination. More recently, advances in non model organisms have been fuelled by the rapid evolution of affordable genome and transcriptome technologies. This Review considers the unusual plasticity in the bipotential system of sex determination and some of the diverse mechanisms that have evolved to control this critical developmental decision, including strong genetic pathways, environmental influences and epigenetic regulation. Ideas emerging from model and non model organisms that suggest that sex determination operates as an antagonistic network with the emergent property of bistability are discussed.

title: A high quality assembly of the Nile Tilapia (Oreochromis niloticus) genome reveals the structure of two sex determination regions
abstract: BackgroundTilapias are the second most farmed fishes in the world and a sustainable source of food. Like many other fish, tilapias are sexually dimorphic and sex is a commercially important trait in these fish. In this study, we developed a significantly improved assembly of the tilapia genome using the latest genome sequencing methods and show how it improves the characterization of two sex determination regions in two tilapia species. homozygous clonal XX female Nile tilapia (Oreochromis niloticus) was sequenced to 44X coverage using Pacific Biosciences (PacBio) SMRT sequencing. Dozens of candidate de novo assemblies were generated and an optimal assembly (contig NG50 of 3.3Mbp) was selected using principal component analysis of likelihood scores calculated from several paired end sequencing libraries. Comparison of the new assembly to the previous O. niloticus genome assembly reveals that recently duplicated portions of the genome are now well represented. The overall number of genes in the new assembly increased by 27.3% including a 67% increase in pseudogenes. The new tilapia genome assembly correctly represents two recent vasa gene duplication events that have been verified with BAC sequencing. At total of 146Mbp of additional transposable element sequence are now assembled, a large proportion of which are recent insertions. Large centromeric satellite repeats are assembled and annotated in cichlid fish for the first time. Finally, the new assembly identifies the long range structure of both a ~9Mbp XY sex determination region on LG1 in O. niloticus, and a ~50Mbp WZ sex determination region on LG3 in the related species O. aureus.ConclusionsThis study highlights the use of long read sequencing to correctly assemble recent duplications and to characterize repeat filled regions of the genome. The study serves as an example of the need for high quality genome assemblies and provides a framework for identifying sex determining genes in tilapia and related fish species.

title: Population viability at extreme sex ratio skews produced by temperature dependent sex determination
abstract: For species with temperature dependent sex determination (TSD) there is the fear that rising temperatures may lead to single sex populations and population extinction. We show that for sea turtles, a major group exhibiting TSD, these concerns are currently unfounded but may become important under extreme climate warming scenarios. We show how highly female biased sex ratios in developing eggs translate into much more balanced operational sex ratios so that adult male numbers in populations around the world are unlikely to be limiting. Rather than reducing population viability, female biased offspring sex ratios may, to some extent, help population growth by increasing the number of breeding females and hence egg production. For rookeries across the world (n 75 sites for seven species) we show that extreme female biased hatchling sex ratios do not compromise population size and are the norm, with a tendency for populations to maximize the number of female hatchlings. Only at extremely high incubation temperature does high mortality within developing clutches threaten sea turtles. Our work shows how TSD itself is a robust strategy up to a point, but eventually high mortality and female only hatchling production will cause extinction if incubation conditions warm considerably in the future.

title: Sex Determination, Sex Chromosomes, and Karyotype Evolution in Insects
abstract: Insects harbor a tremendous diversity of sex determining mechanisms both within and between groups. For example, in some orders such as Hymenoptera, all members are haplodiploid, whereas Diptera contain species with homomorphic as well as male and female heterogametic sex chromosome systems or paternal genome elimination. We have established a large database on karyotypes and sex chromosomes in insects, containing information on over 13000 species covering 29 orders of insects. This database constitutes a unique starting point to report phylogenetic patterns on the distribution of sex determination mechanisms, sex chromosomes, and karyotypes among insects and allows us to test general theories on the evolutionary dynamics of karyotypes, sex chromosomes, and sex determination systems in a comparative framework. Phylogenetic analysis reveals that male heterogamety is the ancestral mode of sex determination in insects, and transitions to female heterogamety are extremely rare. Many insect orders harbor species with complex sex chromosomes, and gains and losses of the sex limited chromosome are frequent in some groups. Haplodiploidy originated several times within insects, and parthenogenesis is rare but evolves frequently. Providing a single source to electronically access data previously distributed among more than 500 articles and books will not only accelerate analyses of the assembled data, but also provide a unique resource to guide research on which taxa are likely to be informative to address specific questions, for example, for genome sequencing projects or large scale comparative studies.