The multiple sex chromosomes of platypus and echidna are not completely identical and several share homology with the avian Z

Abstract

Echidna sex chromosomes <p>A comparative study of the karyotype of the short-beaked echidna shows that monotremes appear to have a unique XY sex chromosome system that shares some homology with the avian Z.</p> Abstract Background: Sex-determining systems have evolved independently in vertebrates. Placental mammals and marsupials have an XY system, birds have a ZW system. Reptiles and amphibians have different systems, including temperature-dependent sex determination, and XY and ZW systems that differ in origin from birds and placental mammals. Monotremes diverged early in mammalian evolution, just after the mammalian clade diverged from the sauropsid clade. Our previous studies showed that male platypus has five X and five Y chromosomes, no SRY, and DMRT1 on an X chromosome. In order to investigate monotreme sex chromosome evolution, we performed a comparative study of platypus and echidna by chromosome painting and comparative gene mapping.

Disruption of FEM1C-W gene in zebra finch: evolutionary insights on avian ZW genes

“…One of the candidate avian sex determination genes, DMRT1, is localized on chromosome X5 in platypus. In human, the FEM1C gene is localized on human 5q22.3, close to the DMXL1 locus (5q23.1; Rens et al 2007). FEM1C and DMXL1 have remained in a syntenic block during mammalian and avian evolution.…”

“…FEM1C and DMXL1 have remained in a syntenic block during mammalian and avian evolution. The DMXL1 gene is on platypus chromosome X5 near DMRT1 (Rens et al 2007), but FEM1C is not found in the platypus genome database (http://www.ensembl.org). Although both DMRT1 and FEM1C relate to the sex determination in fly and nematode, their role in birds and platypus are unknown even though they are situated on the sex chromosomes where a testis-determining role could be favored.…”

“…The ancestral chromosomes of avian sex chromosomes are different from those of eutherian mammals and snakes (Fridolfsson et al 1998;Nanda et al 1999;Matsubara et al 2006), although recent evidence indicates surprising shared gene content of the avian Z and monotreme X chromosomes (Rens et al 2007). The gene content of the Z chromosome appears to have changed little during avian evolution, as shown by comparative painting analysis (Itoh and Arnold 2005;Nishida-Umehara et al 2007;Tsuda et al 2007), even in Ratites (Struthioniformes) which are considered to be an ancestral avian species whose sex chromosomes are morphologically relatively undifferentiated (Ogawa et al 1998;Shetty et al 1999).…”

Did sex chromosome turnover promote divergence of the major mammal groups?

“…The other monotreme family, the echidnas, also have a sex chromosome chain but it consists of only nine elements, with the tiny terminal Y 5 fused onto another Y 55. Chromosome painting and gene mapping shows that four of the five XY pairs in the echidna chain are the same, but the fifth is represented by an autosome in platypus.…”

Mammalian X homolog acts as sex chromosome in lacertid lizards

“…In any case, more robust testing of the hypotheses of the ancestral sex determination and on the evolution of sex-determining mechanisms in amniotes is largely precluded by our very limited knowledge about the homology of sex chromosomes and sex-determining genes among particular groups. The homology of sex chromosomes can be inferred from the knowledge of the gene content of sex chromosomes; however, it has been identified in only a few amniote lineages such as viviparous mammals (see, for example, Kohn et al, 2004) and monotremes (see, for example, Rens et al, 2007), birds (see, for example, Zhou et al, 2014), several turtle species (see, for example, Kawagoshi et al, 2012Kawagoshi et al, , 2014, advanced snakes (Matsubara et al, 2006;Vicoso et al, 2013;Rovatsos et al, 2015), iguanas (see, for example, Alföldi et al, 2011;Rovatsos et al, 2014a-c), a gecko (Kawai et al, 2009) and recently also a lacertid lizard (Srikulnath et al, 2014).…”