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Open Access Research article

A novel MSMB-related microprotein in the postovulatory egg coats of marsupials

Stephen Frankenberg*, Jane Fenelon, Bonnie Dopheide, Geoff Shaw and Marilyn B Renfree

Author Affiliations

ARC Centre of Excellence for Kangaroo Genomics and Department of Zoology, University of Melbourne, Parkville, Victoria, Australia

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BMC Evolutionary Biology 2011, 11:373  doi:10.1186/1471-2148-11-373

Published: 30 December 2011

Abstract

Background

Early marsupial conceptuses differ markedly from those of eutherian mammals, especially during cleavage and early blastocyst stages of development. Additionally, in marsupials the zona pellucida is surrounded by two acellular layers, the mucoid coat and shell, which are formed from secretions from the reproductive tract.

Results

We report the identification of a novel postovulatory coat component in marsupials, which we call uterinesecreted microprotein (USM). USM belongs to a family of disulfide-rich microproteins of unconfirmed function that is found throughout deuterostomes and in some protostomes, and includes β-microseminoprotein (MSMB) and prostate-associated microseminoprotein (MSMP). We describe the evolution of this family in detail, including USM-related sequences in other vertebrates. The orthologue of USM in the tammar wallaby, USM1, is expressed by the endometrium with a dynamic temporal profile, possibly under the control of progesterone.

Conclusions

USM appears to have evolved in a mammalian ancestor specifically as a component of the postovulatory coats. By analogy with the known properties of MSMB, it may have roles in regulating sperm motility/survival or in the immune system. However, its C-terminal domain is greatly truncated compared with MSMB, suggesting a divergent function.