{"status":"ok","message-type":"work","message-version":"1.0.0","message":{"indexed":{"date-parts":[[2026,2,19]],"date-time":"2026-02-19T08:27:17Z","timestamp":1771489637940,"version":"3.50.1"},"reference-count":48,"publisher":"Frontiers Media SA","license":[{"start":{"date-parts":[[2025,3,20]],"date-time":"2025-03-20T00:00:00Z","timestamp":1742428800000},"content-version":"vor","delay-in-days":0,"URL":"https:\/\/creativecommons.org\/licenses\/by\/4.0\/"}],"content-domain":{"domain":["frontiersin.org"],"crossmark-restriction":true},"short-container-title":["Front. Cell Dev. Biol."],"abstract":"<jats:p>Understanding the origin and fate of sex chromosomes has been one of the most intriguing questions in biology. In therian (marsupial and eutherian) mammals, most species are characterized by a heteromorphic XX female XY male sex chromosome system. It is commonly accepted that they originated from a pair of autosomes after gaining a sex-determining function, leading to recombination suppression and subsequent Y chromosome degeneration. Unlike eutherian sex chromosomes which share a pseudo-autosomal region (PAR), the marsupial sex chromosomes are typically tiny and lack any homology. However, there is a lack of empirical evidence on biological systems that represent early stages of sex chromosome differentiation. Here, we describe the meiotic dynamics of an XY<jats:sub>1<\/jats:sub>Y<jats:sub>2<\/jats:sub> system in the greater bilby (<jats:italic>Macrotis lagotis<\/jats:italic>: family Thylacomyidae) that resulted from a fusion between an autosome and the ancestral X chromosome. We compared the similarities and differences in the regulation of meiosis in two other Australian marsupial species with different sex chromosome systems: the tammar wallaby (<jats:italic>Macropus eugenii<\/jats:italic>: family Macropodidae) and the fat-tailed dunnart (<jats:italic>Sminthopsis crassicaudata<\/jats:italic>: family Dasyuridae), both with the ancestral XY system. We performed a cytological analysis of meiotic prophase I, including the study of chromosome synapsis, double strand break formation (as a proxy of recombination) and meiotic sex chromosome inactivation. Our results suggest that the neo-PAR in the greater bilby represents an early stage of differentiation, providing new insights into sex chromosome evolution.<\/jats:p>","DOI":"10.3389\/fcell.2025.1562403","type":"journal-article","created":{"date-parts":[[2025,3,20]],"date-time":"2025-03-20T09:44:57Z","timestamp":1742463897000},"update-policy":"https:\/\/doi.org\/10.3389\/crossmark-policy","source":"Crossref","is-referenced-by-count":1,"title":["Meiotic dynamics in a unique Australian marsupial provide new insights into the evolution of neo-sex chromosomes in the early stages of differentiation"],"prefix":"10.3389","volume":"13","author":[{"given":"Laia","family":"Mar\u00edn-Gual","sequence":"first","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"Carolyn J.","family":"Hogg","sequence":"additional","affiliation":[],"role":[{"role":"author","vocabulary":"crossref"}]},{"given":"J. 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