TY - JOUR
T1 - The avian W chromosome is a refugium for endogenous retroviruses with likely effects on female-biased mutational load and genetic incompatibilities
AU - Peona, Valentina
AU - Palacios-Gimenez, Octavio M.
AU - Blommaert, Julie
AU - Liu, Jing
AU - Haryoko, Tri
AU - Jønsson, Knud A.
AU - Irestedt, Martin
AU - Zhou, Qi
AU - Jern, Patric
AU - Suh, Alexander
PY - 2021/9/13
Y1 - 2021/9/13
N2 - 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.
AB - 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.
KW - Haldane's rule
KW - W chromosome
KW - endogenous retrovirus
KW - sex chromosome
KW - transcriptome
KW - transposable element
UR - http://www.scopus.com/inward/record.url?scp=85111172649&partnerID=8YFLogxK
U2 - 10.1098/rstb.2020.0186
DO - 10.1098/rstb.2020.0186
M3 - Article
VL - 376
JO - Philosophical Transactions of the Royal Society B: Biological Sciences
JF - Philosophical Transactions of the Royal Society B: Biological Sciences
SN - 0962-8436
IS - 1833
M1 - 20200186
ER -