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

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.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.Desert hedgehog (DHH) is a member of the hedgehog gene family which act as secreted intercellular signal transducers [1]. Hedgehog was first identified as a segment polarity gene in Drosophila and has since been identified as a key regulator of pattern formation in embryonic and adult development in many vertebrate and invertebrate species. In addition, the hedgehog gene has undergone duplications in both invertebrates and vertebrates to produce a number of orthologues [2-6]. Mammals have three hedgehog orthologues, Sonic (Shh), Indian (Ihh), and desert (Dhh) hedgehog [3,4,7-9]. All three share a striking homology with the Drosophila orthologue [10]. Each mammalian orthologue has a unique, largely non-overlapping expression pattern, except in the gut where Ihh and Shh ar