1. ^*University of Tennessee, Memphis, Department of Obstetrics and Gynecology, Division of Reproductive Genetics, Molecular Genetics Laboratories, Memphis, Tennessee 38105, USA
2. ^†Department of Genetics and Human Variation, La Trobe University, Bundoora, Victoria 3083, Australia

Abstract

THE mammalian subclass Theria consists of infraclasses Meta-theria (marsupials) and Eutheria ('placentals') which diverged from each other 120–150 million years before present¹ (Myr BP). Both infraclasses have Y chromosome-dependent testis determination but direct molecular evidence linking the Metatherian and Eutherian Y chromosomes is lacking. Comparative analyses indicate that three mammalian genes have remained Y-linked for at least 80 Myr, since the divergence of the Eutherian orders from a common ancestor. These are Zfy, a gene encoding a transcription factor of the zinc-finger type²; Sry, the putative primary testis-determining gene³; and Ubely (formerly Sby or Als9Y-l), a candidate for the mouse spermatogenesis gene Spy, encoding a ubiquitin-activating enzyme El homologue^4,5. Although in mar-spials Zfy homologues are autosomal⁶, a Y homologue of Sry has recently been isolated⁷. We report here the identification of a functional marsupial Y-linked homologue of the murine Ube1y gene establishing that Metatherian and Eutherian Y chromosomes diverged from a common ancestor. This extreme conservation indicates that Ube1y plays a critical role in male development.