skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: Unique structure and positive selection promote the rapid divergence of Drosophila Y chromosomes
Y chromosomes across diverse species convergently evolve a gene-poor, heterochromatic organization enriched for duplicated genes, LTR retrotransposons, and satellite DNA. Sexual antagonism and a loss of recombination play major roles in the degeneration of young Y chromosomes. However, the processes shaping the evolution of mature, already degenerated Y chromosomes are less well-understood. Because Y chromosomes evolve rapidly, comparisons between closely related species are particularly useful. We generated de novo long-read assemblies complemented with cytological validation to reveal Y chromosome organization in three closely related species of the Drosophila simulans complex, which diverged only 250,000 years ago and share >98% sequence identity. We find these Y chromosomes are divergent in their organization and repetitive DNA composition and discover new Y-linked gene families whose evolution is driven by both positive selection and gene conversion. These Y chromosomes are also enriched for large deletions, suggesting that the repair of double-strand breaks on Y chromosomes may be biased toward microhomology-mediated end joining over canonical non-homologous end-joining. We propose that this repair mechanism contributes to the convergent evolution of Y chromosome organization across organisms.  more » « less
Award ID(s):
1844693
PAR ID:
10382224
Author(s) / Creator(s):
; ; ; ;
Date Published:
Journal Name:
eLife
Volume:
11
ISSN:
2050-084X
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; (, PLOS Genetics)
    Meiklejohn, Colin (Ed.)
    Sex chromosomes often evolve unique patterns of gene expression during spermatogenesis. In many species, sex-linked genes are downregulated during meiosis in response to asynapsis of the heterogametic sex chromosome pair (meiotic sex chromosome inactivation; MSCI). This process has evolved convergently across many taxa with independently derived sex chromosomes. Our understanding how quickly MSCI can evolve and whether it is connected to the degree of sequence degeneration remains limited. Teleost fish are a noteworthy group to investigate MSCI because sex chromosomes have evolved repeatedly across species, often over short evolutionary timescales. Here, we investigate whether MSCI occurs in the threespine stickleback fish (Gasterosteus aculeatus), which have an X and Y chromosome that evolved less than 26 million years ago. Using single-cell RNA-seq, we found that the X and Y chromosomes do not have a signature of MSCI, maintaining gene expression across meiosis. Using immunofluorescence, we also show the threespine stickleback do not form a condensed sex body around the X and Y, a feature of MSCI in many species. We did not see patterns of gene content evolution documented in other species with MSCI. Y-linked ampliconic gene families were expressed across multiple stages of spermatogenesis, rather than being restricted to post-meiotic stages, like in mammals. Our work shows MSCI does not occur in the threespine stickleback fish and has not shaped the evolution of the Y chromosome. In addition, the absence of MSCI in the threespine stickleback suggests this process may not be a conserved feature of teleost fish, despite overall sequence degeneration and structural evolution of the Y chromosome, and argues for additional investigation in other species. We also observed testis-dependent differences in coding and expression evolution for X-linked genes, revealing evidence of testis specific faster-X effect and gene-by-gene dosage compensation. 
    more » « less
  2. ; ; ; ; ; ; (, Genome Research)
    Sex chromosome dosage compensation is a model to understand the coordinated evolution of transcription; however, the advanced age of the sex chromosomes in model systems makes it difficult to study how the complex regulatory mechanisms underlying chromosome-wide dosage compensation can evolve. The sex chromosomes ofPoecilia pictahave undergone recent and rapid divergence, resulting in widespread gene loss on the male Y, coupled with complete X Chromosome dosage compensation, the first case reported in a fish. The recent de novo origin of dosage compensation presents a unique opportunity to understand the genetic and evolutionary basis of coordinated chromosomal gene regulation. By combining a new chromosome-level assembly ofP. pictawith whole-genome bisulfite sequencing and RNA-seq data, we determine that the YY1 transcription factor (YY1) DNA binding motif is associated with male-specific hypomethylated regions on the X, but not the autosomes. These YY1 motifs are the result of a recent and rapid repetitive element expansion on theP. pictaX Chromosome, which is absent in closely related species that lack dosage compensation. Taken together, our results present compelling support that a disruptive wave of repetitive element insertions carrying YY1 motifs resulted in the remodeling of the X Chromosome epigenomic landscape and the rapid de novo origin of a dosage compensation system. 
    more » « less
  3. ; ; ; ; ; ; (, Genome Biology and Evolution)
    Schaack, Sarah (Ed.)
    Abstract Sex chromosomes diverge after the establishment of recombination suppression, resulting in differential sex-linkage of genes involved in genetic sex determination and dimorphic traits. This process produces systems of male or female heterogamety wherein the Y and W chromosomes are only present in one sex and are often highly degenerated. Sex-limited Y and W chromosomes contain valuable information about the evolutionary transition from autosomes to sex chromosomes, yet detailed characterizations of the structure, composition, and gene content of sex-limited chromosomes are lacking for many species. In this study, we characterize the female-specific W chromosome of the prairie rattlesnake (Crotalus viridis) and evaluate how recombination suppression and other processes have shaped sex chromosome evolution in ZW snakes. Our analyses indicate that the rattlesnake W chromosome is over 80% repetitive and that an abundance of GC-rich mdg4 elements has driven an overall high degree of GC-richness despite a lack of recombination. The W chromosome is also highly enriched for repeat sequences derived from endogenous retroviruses and likely acts as a “refugium” for these and other retroelements. We annotated 219 putatively functional W-linked genes across at least two evolutionary strata identified based on estimates of sequence divergence between Z and W gametologs. The youngest of these strata is relatively gene-rich, however gene expression across strata suggests retained gene function amidst a greater degree of degeneration following ancient recombination suppression. Functional annotation of W-linked genes indicates a specialization of the W chromosome for reproductive and developmental function since recombination suppression from the Z chromosome. 
    more » « less
  4. ; ; ; ; ; ; (, Molecular Ecology)
    Abstract Sex determination, the developmental process by which sexually dimorphic phenotypes are established, evolves fast. Evolutionary turnover in a sex determination pathway may occur via selection on alleles that are genetically linked to a new master sex determining locus on a newly formed proto‐sex chromosome. Species with polygenic sex determination, in which master regulatory genes are found on multiple different proto‐sex chromosomes, are informative models to study the evolution of sex determination and sex chromosomes. House flies are such a model system, with male determining loci possible on all six chromosomes and a female‐determiner on one of the chromosomes as well. The two most common male‐determining proto‐Y chromosomes form latitudinal clines on multiple continents, suggesting that temperature variation is an important selection pressure responsible for maintaining polygenic sex determination in this species. Temperature‐dependent fitness effects could be manifested through temperature‐dependent gene expression differences across proto‐Y chromosome genotypes. These gene expression differences may be the result ofcisregulatory variants that affect the expression of genes on the proto‐sex chromosomes, ortranseffects of the proto‐Y chromosomes on genes elswhere in the genome. We used RNA‐seq to identify genes whose expression depends on proto‐Y chromosome genotype and temperature in adult male house flies. We found no evidence for ecologically meaningful temperature‐dependent expression differences of sex determining genes between male genotypes, but we were probably not sampling an appropriate developmental time‐point to identify such effects. In contrast, we identified many other genes whose expression depends on the interaction between proto‐Y chromosome genotype and temperature, including genes that encode proteins involved in reproduction, metabolism, lifespan, stress response, and immunity. Notably, genes with genotype‐by‐temperature interactions on expression were not enriched on the proto‐sex chromosomes. Moreover, there was no evidence that temperature‐dependent expression is driven by chromosome‐widecis‐regulatory divergence between the proto‐Y and proto‐X alleles. Therefore, if temperature‐dependent gene expression is responsible for differences in phenotypes and fitness of proto‐Y genotypes across house fly populations, these effects are driven by a small number of temperature‐dependent alleles on the proto‐Y chromosomes that may havetranseffects on the expression of genes on other chromosomes. 
    more » « less
  5. ; ; ; ; (, Genome Biology and Evolution)
    Abstract Our understanding on the interplay between gene functionality and gene arrangement at different chromosome scales relies on a few Diptera and the honeybee, species with quality reference genome assemblies, accurate gene annotations, and abundant transcriptome data. Using recently generated ‘omic resources in the monarch butterfly Danaus plexippus, a species with many more and smaller chromosomes relative to Drosophila species and the honeybee, we examined the organization of genes preferentially expressed at broadly defined developmental stages (larva, pupa, adult males, and adult females) at both fine and whole-chromosome scales. We found that developmental stage–regulated genes do not form more clusters, but do form larger clusters, than expected by chance, a pattern consistent across the gene categories examined. Notably, out of the 30 chromosomes in the monarch genome, 12 of them, plus the fraction of the chromosome Z that corresponds to the ancestral Z in other Lepidoptera, were found enriched for developmental stage–regulated genes. These two levels of nonrandom gene organization are not independent as enriched chromosomes for developmental stage–regulated genes tend to harbor disproportionately large clusters of these genes. Further, although paralogous genes were overrepresented in gene clusters, their presence is not enough to explain two-thirds of the documented cases of whole-chromosome enrichment. The composition of the largest clusters often included paralogs from more than one multigene family as well as unrelated single-copy genes. Our results reveal intriguing patterns at the whole-chromosome scale in D. plexippus while shedding light on the interplay between gene expression and chromosome organization beyond Diptera and Hymenoptera. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email