Symposium proposal | |
Organizer: | Masafumi Nozawa (Tokyo Metropolitan University) |
Co-organizer: | Wen-Juan Ma (The University of Kansas) |
A remarkable diversity of sex-determination systems and diverse rate of sex chromosome differentiation have been documented across the tree of life. Recent advancement in sequencing technologies has enabled us to sequence genomes, transcriptomes, and epigenomes in divergent groups of non-model organisms with various levels of sex chromosome divergence, which has in turn made it possible to tackle the underlying genetic and molecular basis of complex and divergent sex-determination mechanisms. In this context, this symposium aims to broadly cover the recent findings on the evolution and genomic bases of sex-determination mechanisms, as well as evolutionary genomics of sex chromosomes. The three invited speakers will discuss about the evolution of sex determination and sex chromosomes in various animal groups, from vertebrates to insects. A few more speakers working on the evolutionary genetics and genomics of sex determination and sex chromosomes in other eukaryotic groups will be selected to broaden the topics. We also would like to discuss the future directions on the evolutionary studies of sex determination and sex chromosomes. |
S2-1
Sex-biased genome evolution
Melissa A Wilson1
1Center for Evolution and Medicine, Arizona State University
2School of Life Sciences, Arizona State University
2School of Life Sciences, Arizona State University
One of the X chromosomes in genetic females is silenced by a process called X chromosome inactivation (XCI). Variation in XCI across the placenta may contribute to observed sex differences and variability in pregnancy outcomes. However, XCI has predominantly been studied in human adult tissues. Here we sequenced and analyzed DNA and RNA from two locations from 30 full-term pregnancies. Implementing an allele specific approach to examine XCI, we report evidence that XCI in the human placenta is patchy, with large patches of either silenced maternal or paternal X chromosomes. Further, using similar measurements, we show that this is in contrast to adult tissues, which generally exhibit mosaic X-inactivation, where bulk samples exhibit both maternal and paternal X chromosome expression. Further, by comparing skewed samples in placenta and adult tissues, we identify genes that are uniquely silenced or expressed in the placenta compared to adult tissues highlighting the need for tissue-specific maps of XCI.
S2-2
Mobile elements mediate the evolution of sex chromosome dosage compensation of nucleolar organizing regions (NORs) in turtles with male (XX/XY) and female (ZZ/ZW) heterogamety
Nicole Valenzuela1, Eugenia Elisabet Montiel1, Daleen Badenhorst1
1Iowa State University
The nucleolar organizing region (NOR) is the genome compartment where genes coding for the 18S, 5.8S and 28S ribosomal subunits are located. Expression of these genes leads to ribosome biogenesis which is needed for protein synthesis. Specifically, metabolic and cell growth demands impose a costly demand that is met by rDNA copy number and activity. Here we examine the activity of ribosomal DNA clusters that constitute the NORs in several turtles, with emphasis on taxa whose NORs are sex-linked and suffer a gene dose imbalance between the sexes, which may occur when genes are lost from the Y or W due to the lower recombination between sex chromosomes. We describe the location and activity of NORs in 13 turtles, seven of them for the first time. Results reveal instances of upregulation and silencing of rDNA in turtles with sex chromosomes, some commonality in the mechanisms of rDNA regulation in turtles with autosomal and sex-linked NORs, and the involvement of R2 retrolements in the evolution of NOR dosage compensation in turtles. We discuss how our findings contribute to the ongoing debate about the existence, diversity and evolution of sex chromosome dosage compensation.
S2-3
House fly proto-Y chromosomes affect myriad temperature-dependent phenotypes
Richard P Meisel1
1University of Houston
House fly (Musca domestica) has a polygenic sex determination system, with master male and female determining loci identified on all six chromosomes. The two most common male-determining proto-Y chromosomes form north-south clines on multiple continents. This natural distribution suggests that the proto-Y chromosomes confer opposing temperature-dependent fitness effects, and that these context-dependent selection pressures are responsible for the maintenance of the polymorphism. I will present evidence that the house fly proto-Y chromosomes do indeed affect physiology and behavior in a temperature-dependent manner that is consistent with their clinal distributions. I will further show how we have used RNA-seq to identify candidate differentially expressed genes that underly temperature-dependent phenotypes. This analysis revealed a differentially expressed gene that affects male mating behavior in a way that is conserved between house fly and Drosophila, and I will show how this gene is regulated by proto-Y chromosome genotype.
S2-4
Dynamic turnrovers of sexual systems, sex chromosomes and sex-linked gene expression of worms
Yifeng Wang1, Qi Zhou1
1Life Sciences Institute, Zhejiang University
Sex is prevalent among metazoans yet its mechanisms of transition with hermaphroditism and related turnovers of sex chromosomes remain obscure. To address this, we study here genomes and transcriptomes of 13 flatworm and 41 roundworm species, some of which display recent transitions between hermaphroditism and separate sexes (gonochorism). We newly identified the sexually differentiated regions of 17 roundworm species. Lineage-specific translocations of ancestral sex chromosomes originated in the ancestor of Rhabditida or clade I species to different autosomes at different phylogenetic nodes have recurrently formed 'neo-sex' chromosomes, which exhibit signatures of stepwise recombination suppression ('evolutionary strata') similar to those of vertebrate sex chromosomes. All the studied roundworm species have a distorted expression ratio between sexes and between autosomes and sex chromosomes in males, particularly in species with a biased sex ratio, indicating incomplete dosage compensation. Comparison between hermaphroditic or androdiecious (e.g., Caenorhabditis elegans) species to their gonochoristic relatives uncovered transitions from the former to the latter with ZW sex chromosomes (e.g., schistosomes) involves masculinization and defeminization of gene expression in the gonads, while the reverse transition from the species with XY sex chromosomes involves the opposite expression changes. Our work illuminates the origin of sex and the dynamic turnovers of sex chromosomes and gene expression in the two clades of worms, and the newly identified sex-linked genes can have great impact on the future study of controlling of some of the parasites.
S2-5
Structural mutations, antagonism, and differential use of multiple Y alleles shape sex determination in ecomorphs of an African crater lake cichlid
Tyler Linderoth1, Hannah Munby1, Bettina Fischer1, Gregoire Vernaz2, Alexandra M. Tyers3, Benjamin P. Ngatunga4, Asilatu Shechonge4, Martin J. Genner5, George F. Turner3, Richard Durbin1,6
1Department of Genetics, University of Cambridge, Cambridge, UK
2Wellcome/CRUK Gurdon Institute, University of Cambridge, Cambridge, UK
3School of Natural Sciences, Bangor University, Bangor, UK
4Tanzania Fisheries Research Institute, Dar es Salaam, Tanzania
5School of Biological Sciences, University of Bristol, Bristol, UK
6Wellcome Sanger Institute, Hinxton, Cambridge, UK
2Wellcome/CRUK Gurdon Institute, University of Cambridge, Cambridge, UK
3School of Natural Sciences, Bangor University, Bangor, UK
4Tanzania Fisheries Research Institute, Dar es Salaam, Tanzania
5School of Biological Sciences, University of Bristol, Bristol, UK
6Wellcome Sanger Institute, Hinxton, Cambridge, UK
African cichlid fishes are famous for remarkably high rates of speciation but also have some of the fastest evolving sex determination systems in vertebrates, begging the question of whether these phenomena are related. Answering this is challenging because little is known in cichlids about how new sex-determining (SD) variants arise, which evolutionary forces shape their trajectories, and at what demographic scales they evolve. We gained major insights into all of the above by identifying three distinct coexisting XY systems in Astatotilapia calliptera from Lake Masoko, a small crater lake in Tanzania containing two ecomorphs of this species, using full genome data from 647 individuals. All of the Y alleles exist on recombining chromosomes. Two of the Y alleles derive from structural mutations on chromosome 7 that increase expression of the gonadal somatic derived factor gene (gsdf); the first is a tandem duplication of the entire gsdf gene observed throughout much of the Lake Malawi haplochromine cichlid radiation, and the second is a 5kb transposable element (TE) insertion directly upstream of gsdf. Another 700bp TE insertion on chromosome 19 characterizes the third Y allele, pointing to a potentially important role for TEs in generating new SD systems. Males belonging to the deep-water benthic ecomorph exclusively use the gsdf duplication, whereas all three Y alleles operate in the littoral ecomorph, in which they act antagonistically in terms of body size among males with different amounts of benthic admixture. This antagonism in the face of ongoing admixture may be important for sustaining multifactorial sex determination in Lake Masoko and demonstrates that genetic interactions between Y alleles and genetic background can potentially affect fitness.