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Open Access Research article

Desert hedgehog is a mammal-specific gene expressed during testicular and ovarian development in a marsupial

William A O'Hara1, Walid J Azar2, Richard R Behringer3, Marilyn B Renfree24 and Andrew J Pask1234*

Author affiliations

1 Department of Molecular and Cellular Biology, The University of Connecticut, Storrs CT 06269, USA

2 Department of Zoology, The University of Melbourne, Victoria 3010, Australia

3 Department of Genetics, The University of Texas M. D. Anderson Cancer Center, Houston, TX 77030, USA

4 The Australian Research Council Centre of Excellence in Kangaroo Genomics, Australia

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Citation and License

BMC Developmental Biology 2011, 11:72  doi:10.1186/1471-213X-11-72

Published: 1 December 2011

Abstract

Background

Desert hedgehog (DHH) belongs to the hedgehog gene family that act as secreted intercellular signal transducers. DHH is an essential morphogen for normal testicular development and function in both mice and humans but is not present in the avian lineage. Like other hedgehog proteins, DHH signals through the patched (PTCH) receptors 1 and 2. Here we examine the expression and protein distribution of DHH, PTCH1 and PTCH2 in the developing testes of a marsupial mammal (the tammar wallaby) to determine whether DHH signalling is a conserved factor in gonadal development in all therian mammals.

Results

DHH, PTCH1 and PTCH2 were present in the marsupial genome and highly conserved with their eutherian orthologues. Phylogenetic analyses indicate that DHH has recently evolved and is a mammal-specific hedgehog orthologue. The marsupial PTCH2 receptor had an additional exon (exon 21a) not annotated in eutherian PTCH2 proteins. Interestingly we found evidence of this exon in humans and show that its translation would result in a truncated protein with functions similar to PTCH1. We also show that DHH expression was not restricted to the testes during gonadal development (as in mice), but was also expressed in the developing ovary. Expression of DHH, PTCH1 and PTCH2 in the adult tammar testis and ovary was consistent with findings in the adult mouse.

Conclusions

These data suggest that there is a highly conserved role for DHH signalling in the differentiation and function of the mammalian testis and that DHH may be necessary for marsupial ovarian development. The receptors PTCH1 and PTCH2 are highly conserved mediators of hedgehog signalling in both the developing and adult marsupial gonads. Together these findings indicate DHH is an essential therian mammal-specific morphogen in gonadal development and gametogenesis.

Keywords:
Sex determination; sexual differentiation; gene expression; marsupial; Macropus eugenii.