Mammalian eggs are surrounded by an extracellular matrix called zona pellucida (ZP). In eutherian mammals, this coat is formed of three or four glycoproteins (ZP1 to ZP4). Mus musculus is the only eutherian species in which ZP is formed by three glycoproteins Zp1, Zp2, and Zp3; Zp4 being a pseudogene. Zp4 has been lost in the Mus lineage after it diverged from Rattus. However, it is still unknown when this loss occurred precisely. In this work, the status of Zp4 in several murine rodents has been tested by phylogenetic, molecular, and proteomic analyses. Our results showed that Zp4 pseudogenisation is restricted to the subgenus Mus; that diverged around 6 MYA.
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