Y chromosome may be disappearing in humans/mammals, new study finds

Amazing stuff! Are we going to follow the fate of the spiny rats of Japan or the mole voles of eastern Europe? 😊

"... Y chromosomes continue to gradually disappear across different mammal species, a new study found. ...
Researchers estimated that the Y chromosome has lost over 900 active genes over 166 million years – the time period that human beings and the Australian Platypus have been evolving separately. At this rate, genes linked to Y chromosomes will be extinct in 11 million years. ...
The mole voles of eastern Europe and the spiny rats of Japan no longer have Y chromosomes, as they have completely disappeared as a result of evolution. Spiny rats, an endangered species native to several Japanese islands, managed to produce as males and females regardless due to a change in the rat’s chromosome 3. It remains unclear how the mole vole has evolved past Y chromosomes, though researchers will use the discoveries in spiny rats to continue researching. ..."

From the significance and abstract:

"Significance

The evolution of differentiated sex chromosomes has been intensively studied over many decades to address questions, not only about the sex-determining mechanism, but also on the genetic changes to sex chromosomes. A crucial question concerns sex chromosome turnover, whereby a novel sex gene defines a new pair of sex chromosomes, leading to rapid degradation of the sex-specific element. Mammals possess an extremely stable XY chromosome system, in which the Y has almost completely degraded. Exceptional mammals that have recently lost this degraded Y are of unique value for studies of the process of sex chromosome turnover in mammals. Our findings open the way to investigating Y-loss and the earliest evolutionary changes that repurposed an autosome into a new sex chromosome.

Abstract

Mammalian sex chromosomes are highly conserved, and sex is determined by SRY on the Y chromosome. Two exceptional rodent groups in which some species lack a Y chromosome and Sry offer insights into how novel sex genes can arise and replace Sry, leading to sex chromosome turnover. However, intensive study over three decades has failed to reveal the identity of novel sex genes in either of these lineages. We here report our discovery of a male-specific duplication of an enhancer of Sox9 in the Amami spiny rat Tokudaia osimensis, in which males and females have only a single X chromosome (XO/XO) and the Y chromosome and Sry are completely lost. We performed a comprehensive survey to detect sex-specific genomic regions in the spiny rat. Sex-related genomic differences were limited to a male-specific duplication of a 17-kb unit located 430 kb upstream of Sox9 on an autosome. Hi-C analysis using male spiny rat cells showed the duplicated region has potential chromatin interaction with Sox9. The duplicated unit harbored a 1,262-bp element homologous to mouse enhancer 14 (Enh14), a candidate Sox9 enhancer that is functionally redundant in mice. Transgenic reporter mice showed that the spiny rat Enh14 can function as an embryonic testis enhancer in mice. Embryonic gonads of XX mice in which Enh14 was replaced by the duplicated spiny rat Enh14 showed increased Sox9 expression and decreased Foxl2 expression. We propose that male-specific duplication of this Sox9 enhancer substituted for Sry function, defining a novel Y chromosome in the spiny rat."

Y chromosome may be disappearing in humans, new study finds - The Jerusalem Post While most mammals have an X and Y chromosome-based system similar to that of humans, many species have seen a gradual decline in Y chromosomes.

Turnover of mammal sex chromosomes in the Sry-deficient Amami spiny rat is due to male-specific upregulation of Sox9 (no public access)