Evidence of Hβ58, a Gene Involved in Mammalian Placental Development, in the Three-toed Skink, Chalcides chalcides(Squamata: Scincidae), a Viviparous Placentotrophic Reptile

The Hβ58 gene, whose disruption in mice causes reabsorption of the embryo at 9.5 days post-conception, is believed to be essential for development of the placenta. Although the Hβ58 gene is well conserved in some Amniota, nothing is known about its presence in reptiles, some species of which have developed a chorioallantoic placenta. In this work, we investigated the expression of Hβ58 mRNA and protein in the three-toed skink, Chalcides chalcides. Hβ58 protein expression was found in the uterine epithelium beginning from the peri-ovulatory stage. However, it increased strongly at the moment of placental formation, when a high level of expression of mRNA and protein was also observed in the extra-embryonic membranes. The expression of Hβ58 mRNA and protein was maintained, although to a lesser degree, in the placenta during late pregnancy. It was also present in the early embryo. Finally, cloning and sequencing of a gene fragment revealed strong homology of the reptile gene with that of mammals. The high degree of conservation of the gene in amniote vertebrates and its presence in a viviparous squamate reptile (as in mammals) indicates an important role of this gene in the chorioallantoic placenta formation and development.