The Silkworm Z Chromosome Is Enriched in Testis-Specific Genes

Arunkumar, Kallare P.; Mita, Kazuei; Nagaraju, Javaregowda

doi:10.1534/genetics.108.099994

Cited by 95 publications

(92 citation statements)

References 55 publications

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“…These studies did not take into account the lack or incompleteness of dosage compensation in birds Itoh et al 2007) so a word of caution is needed regarding the patterns. However, genes that become up-regulated in adult ovary are under-represented on chicken Z (Mank and Ellegren 2009), and an over-representation of testis-specific genes on Z is seen in the female heterogametic silkworm (Arunkumar et al 2009), in agreement with the observations reported herein.…”

Section: Discussionsupporting

confidence: 91%

Emergence of male-biased genes on the chicken Z-chromosome: Sex-chromosome contrasts between male and female heterogametic systems: Figure 1.

Ellegren¹

2011

Genome Res.

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There has been extensive traffic of male-biased genes out of the mammalian and Drosophila X-chromosomes, and there are also reports of an under-representation of male-biased genes on the X. This may reflect an adaptive process driven by natural selection where an autosomal location of male-biased genes is favored since male genes are only exposed to selection one-third of the time when X-linked. However, there are several alternative explanations to ''out-of-the-X'' gene movement, including mutational bias and a means for X-linked genes to escape meiotic sex chromosome inactivation (MSCI) during spermatogenesis. As a critical test of the hypothesis that genomic relocation of sex-biased genes is an adaptive process, I examined the emergence, and loss, of genes on the chicken Z-chromosome, i.e., a female heterogametic system (males ZZ, females ZW ). Here, the analogous prediction would be an emergence of male-biased genes onto, not a loss from, the Z-chromosome because Z is found more often in males than autosomes are. I found that genes expressed in testis but not in ovary are highly over-represented among genes that have emerged on the Z-chromosome during avian evolution. Moreover, genes with male-biased expression are similarly over-represented among new Z-chromosomal genes. Interestingly, genes with female-biased expression have more often moved from than to the Z-chromosome. These observations show that male and female heterogametic organisms display opposing directionalities in the emergence and loss of sex-biased genes on sex chromosomes. This is consistent with theoretical models on the evolution of sexually antagonistic genes in which new mutations are at least partly dominant.

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Section: Discussionsupporting

confidence: 91%

Emergence of male-biased genes on the chicken Z-chromosome: Sex-chromosome contrasts between male and female heterogametic systems: Figure 1.

Ellegren¹

2011

Genome Res.

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“…In addition, the question of sexual antagonism has been extensively addressed in the perspective of how selection maintains genes with differential benefit to males and females in sex linkage, and how this process contributes to sex chromosome evolution. Among other examples, the recent acquisition of 'male beneficial' genes by the mammalian X (Zhang et al, 2010), the abundance of testis-specific genes on the silkworm Z (Arunkumar et al, 2009), the close linkage of sexually selected colour genes to sex-determination loci in cichlids (Lande et al, 2001) and the presence of loci coding for male courtship display traits, involved in behavioural isolation, in the stickleback neosex chromosome (Kitano et al, 2009), all support sexually antagonistic gene content as an important factor in the evolutionary history of both ancestral and more recently derived sex chromosome systems. In birds, chromosome 4a contains the SOX3 gene, considered as a possible ancestral precursor of the male determination gene SRY.…”

Section: Discussionmentioning

confidence: 99%

Evidence of a neo-sex chromosome in birds

et al. 2011

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“…For unknown reasons, the Z chromosome carries an overproportionate number of genes solely expressed in the testis (Arunkumar et al 2009;Walters and Hardcastle 2011).…”

Section: Constituents Of the Z Chromosomementioning

confidence: 99%