scholarly journals The avian W chromosome is a refugium for endogenous retroviruses with likely effects on female-biased mutational load and genetic incompatibilities

2020 ◽  
Author(s):  
Valentina Peona ◽  
Octavio M. Palacios-Gimenez ◽  
Julie Blommaert ◽  
Jing Liu ◽  
Tri Haryoko ◽  
...  
Keyword(s):  
Gene Dosage ◽  
Endogenous Retroviruses ◽  
Mass Spectrometry Data ◽  
Mutational Load ◽  
W Chromosome ◽  
Entire Genome ◽  
Haldane’S Rule ◽  
Haldane's Rule ◽  
Genome Wide ◽  
Female Specific

SummaryIt is a broadly observed pattern that the non-recombining regions of sex-limited chromosomes (Y and W) accumulate more repeats than the rest of the genome, even in species like birds with a low genome-wide repeat content. Here we show that in birds with highly heteromorphic sex chromosomes, the W chromosome has a transposable element (TE) density of >55% compared to the genome-wide density of <10%, and contains over half of all full-length (thus potentially active) endogenous retroviruses (ERVs) of the entire genome. Using RNA-seq and protein mass spectrometry data, we were able to detect signatures of female-specific ERV expression. We hypothesise that the avian W chromosome acts as a refugium for active ERVs, likely leading to female-biased mutational load that may influence female physiology similar to the “toxic-Y” effect in Drosophila. Furthermore, Haldane’s rule predicts that the heterogametic sex has reduced fertility in hybrids. We propose that the excess of W-linked active ERVs over the rest of the genome may be an additional explanatory variable for Haldane’s rule, with consequences for genetic incompatibilities between species through TE/repressor mismatches in hybrids. Together, our results suggest that the sequence content of female-specific W chromosomes can have effects far beyond sex determination and gene dosage.

scholarly journals The avian W chromosome is a refugium for endogenous retroviruses with likely effects on female-biased mutational load and genetic incompatibilities

2021 ◽  
Vol 376 (1833) ◽  
pp. 20200186
Author(s):  
Valentina Peona ◽  
Octavio M. Palacios-Gimenez ◽  
Julie Blommaert ◽  
Jing Liu ◽  
Tri Haryoko ◽  
...  
Keyword(s):  
Sex Chromosome ◽  
Gene Dosage ◽  
Endogenous Retroviruses ◽  
Mass Spectrometry Data ◽  
Mutational Load ◽  
W Chromosome ◽  
Haldane’S Rule ◽  
Haldane's Rule ◽  
Genome Wide ◽  
Female Specific

It is a broadly observed pattern that the non-recombining regions of sex-limited chromosomes (Y and W) accumulate more repeats than the rest of the genome, even in species like birds with a low genome-wide repeat content. Here, we show that in birds with highly heteromorphic sex chromosomes, the W chromosome has a transposable element (TE) density of greater than 55% compared to the genome-wide density of less than 10%, and contains over half of all full-length (thus potentially active) endogenous retroviruses (ERVs) of the entire genome. Using RNA-seq and protein mass spectrometry data, we were able to detect signatures of female-specific ERV expression. We hypothesize that the avian W chromosome acts as a refugium for active ERVs, probably leading to female-biased mutational load that may influence female physiology similar to the ‘toxic-Y’ effect in Drosophila males. Furthermore, Haldane's rule predicts that the heterogametic sex has reduced fertility in hybrids. We propose that the excess of W-linked active ERVs over the rest of the genome may be an additional explanatory variable for Haldane's rule, with consequences for genetic incompatibilities between species through TE/repressor mismatches in hybrids. Together, our results suggest that the sequence content of female-specific W chromosomes can have effects far beyond sex determination and gene dosage. This article is part of the theme issue ‘Challenging the paradigm in sex chromosome evolution: empirical and theoretical insights with a focus on vertebrates (Part II)’.

scholarly journals Restricted X chromosome introgression and support for Haldane's rule in hybridizing damselflies

2021 ◽  
Author(s):  
Janne Swaegers ◽  
Rosa Ana Sanchez-Guillen ◽  
Pallavi Chauhan ◽  
Maren Wellenreuther ◽  
Bengt Hansson
Keyword(s):  
X Chromosome ◽  
Sex Chromosomes ◽  
Hybrid Zones ◽  
Haldane’S Rule ◽  
Haldane's Rule ◽  
Genome Wide ◽  
Determination System ◽  
Heterogametic Sex ◽  
Sex Determination System ◽  
Genomic Introgression

Contemporary hybrid zones act as natural laboratories for the investigation of species boundaries and allow to shed light on the little understood roles of sex chromosomes in species divergence. Sex chromosomes are considered to function as a hotspot of genetic divergence between species; indicated by less genomic introgression compared to autosomes during hybridisation. Moreover, they are thought to contribute to Haldane's rule which states that hybrids of the heterogametic sex are more likely to be inviable or sterile. To test these hypotheses, we used contemporary hybrid zones of Ischnura elegans, a damselfly species that has been expanding its range into the northern and western regions of Spain, leading to chronic hybridization with its sister species Ischnura graellsii. We analysed genome-wide SNPs in the Spanish I. elegans and I. graellsii hybrid zone and found (i) that the X chromosome shows less genomic introgression compared to autosomes and (ii) that males are underrepresented among admixed individuals as predicted by Haldane's rule. This is the first study in Odonata that suggests a role of the X chromosome in reproductive isolation. Moreover, our data adds to the few studies on species with X0 sex determination system and contradicts the hypothesis that the absence of a Y chromosome causes exceptions to Haldane's rule.

scholarly journals Lack of intrinsic postzygotic isolation in haplodiploid male hybrids despite high genetic distance

2020 ◽  
Author(s):  
Emily E. Bendall ◽  
Kayla M. Mattingly ◽  
Amanda J. Moehring ◽  
Catherine R. Linnen
Keyword(s):  
Genetic Distance ◽  
Genetic Divergence ◽  
Sex Chromosome ◽  
Postzygotic Isolation ◽  
Entire Genome ◽  
Male And Female ◽  
Haldane’S Rule ◽  
Haldane's Rule ◽  
Heterogametic Sex ◽  
High Genetic Distance

AbstractEvolutionary biologists have long been interested in understanding the mechanisms underlying Haldane’s rule. The explanatory theories of dominance and faster-X, which are based on recessive alleles being expressed in the heterogametic sex, have been proposed as common mechanisms. These mechanisms predict that greater hemizygosity leads to both faster evolution and greater expression of intrinsic postzygotic isolation. Under these mechanisms, haplodiploids should evolve and express intrinsic postzygotic isolation faster than diploids because the entire genome is analogous to a sex chromosome. Here, we measure sterility and inviability in hybrids between Neodiprion pinetum and N. lecontei, a pair of haplodiplopids that differ morphologically, behaviorally, and genetically. We compare the observed isolation to that expected from published estimates of isolation in diploids at comparable levels of genetic divergence. We find that both male and female hybrids are viable and fertile, which is less isolation than expected. We then discuss several potential explanations for this surprising lack of isolation, including alternative mechanisms for Haldane’s rule and a frequently overlooked quirk of haplodiploid genetics that may slow the emergence of complete intrinsic postzygotic isolation in hybrid males. Finally, we describe how haplodiploids, an underutilized resource, can be used to differentiate between mechanisms of Haldane’s rule.

scholarly journals Dominance, Epistasis and the Genetics of Postzygotic Isolation

Genetics ◽  
2000 ◽  
Vol 154 (4) ◽  
pp. 1663-1679 ◽  
Author(s):  
Michael Turelli ◽  
H Allen Orr
Keyword(s):  
Maternal Effects ◽  
Drosophila Species ◽  
W Chromosome ◽  
Postzygotic Isolation ◽  
X Chromosomes ◽  
Haldane’S Rule ◽  
Haldane's Rule ◽  
Species Hybrids

Abstract The sterility and inviability of species hybrids can be explained by between-locus “Dobzhansky-Muller” incompatibilities: alleles that are fit on their “normal” genetic backgrounds sometimes lower fitness when brought together in hybrids. We present a model of two-locus incompatibilities that distinguishes among three types of hybrid interactions: those between heterozygous loci (H0), those between a heterozygous and a homozygous (or hemizygous) locus (H1), and those between homozygous loci (H2). We predict the relative fitnesses of hybrid genotypes by calculating the expected numbers of each type of incompatibility. We use this model to study Haldane's rule and the large effect of X chromosomes on postzygotic isolation. We show that the severity of H0 vs. H1 incompatibilities is key to understanding Haldane's rule, while the severity of H1 vs. H2 incompatibilities must also be considered to explain large X effects. Large X effects are not inevitable in backcross analyses but rather—like Haldane's rule—may often reflect the recessivity of alleles causing postzygotic isolation. We also consider incompatibilities involving the Y (or W) chromosome and maternal effects. Such incompatibilities are common in Drosophila species crosses, and their consequences in male- vs. female-heterogametic taxa may explain the pattern of exceptions to Haldane's rule.

scholarly journals The hidden structural variability in avian genomes

2022 ◽  
Author(s):  
Valentina Peona ◽  
Mozes Blom ◽  
Carolina Frankl-Vilches ◽  
Borja Milá ◽  
Hidayat Ashari ◽  
...  
Keyword(s):  
Genetic Variability ◽  
Endogenous Retroviruses ◽  
Nucleotide Polymorphisms ◽  
W Chromosome ◽  
Sequencing Technologies ◽  
Birds Of Paradise ◽  
Long Read ◽  
Female Specific ◽  
Genomic Regions ◽  
Genome Assemblies

Structural variants (SVs) are DNA mutations that can have relevant effects at micro- and macro-evolutionary scales. The detection of SVs is largely limited by the type and quality of sequencing technologies adopted, therefore genetic variability linked to SVs may remain undiscovered, especially in complex repetitive genomic regions. In this study, we used a combination of long-read and linked-read genome assemblies to investigate the occurrence of insertions and dele-tions across the chromosomes of 14 species of birds-of-paradise and two species of estrildid finches including highly repetitive W chro-mosomes. The species sampling encompasses most genera and representatives from all major clades of birds-of-paradise, allowing comparisons between individuals of the same species, genus, and family. We found the highest densities of SVs to be located on the microchromosomes and on the female-specific W chromosome. Genome assemblies of multiple individuals from the same species allowed us to compare the levels of genetic variability linked to SVs and single nucleotide polymorphisms (SNPs) on the W and other chromosomes. Our results demonstrate that the avian W chromosome harbours more genetic variability than previously thought and that its structure is shaped by the continuous accumulation and turn-over of transposable element insertions, especially endogenous retroviruses.

scholarly journals Resurrecting Muller's Theory of Haldane's Rule

Genetics ◽  
1996 ◽  
Vol 143 (1) ◽  
pp. 603-607
Author(s):  
Ling-Wen Zeng
Keyword(s):  
Haldane’S Rule ◽  
Haldane's Rule

scholarly journals Escape from X Chromosome Inactivation and the Female Predominance in Autoimmune Diseases

2021 ◽  
Vol 22 (3) ◽  
pp. 1114
Author(s):  
Ali Youness ◽  
Charles-Henry Miquel ◽  
Jean-Charles Guéry
Keyword(s):  
Autoimmune Diseases ◽  
X Chromosome ◽  
Gene Dosage ◽  
X Chromosome Inactivation ◽  
Chromosome Inactivation ◽  
X Chromosomes ◽  
Female Sex Hormones ◽  
Inactive X Chromosome ◽  
Immune Related Genes ◽  
Female Specific

Women represent 80% of people affected by autoimmune diseases. Although, many studies have demonstrated a role for sex hormone receptor signaling, particularly estrogens, in the direct regulation of innate and adaptive components of the immune system, recent data suggest that female sex hormones are not the only cause of the female predisposition to autoimmunity. Besides sex steroid hormones, growing evidence points towards the role of X-linked genetic factors. In female mammals, one of the two X chromosomes is randomly inactivated during embryonic development, resulting in a cellular mosaicism, where about one-half of the cells in a given tissue express either the maternal X chromosome or the paternal one. X chromosome inactivation (XCI) is however not complete and 15 to 23% of genes from the inactive X chromosome (Xi) escape XCI, thereby contributing to the emergence of a female-specific heterogeneous population of cells with bi-allelic expression of some X-linked genes. Although the direct contribution of this genetic mechanism in the female susceptibility to autoimmunity still remains to be established, the cellular mosaicism resulting from XCI escape is likely to create a unique functional plasticity within female immune cells. Here, we review recent findings identifying key immune related genes that escape XCI and the relationship between gene dosage imbalance and functional responsiveness in female cells.

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