Molecular cloning of estrogen receptor α of the Nile crocodile

Estrogens are essential for normal reproductive activity in female and male vertebrates. In female reptiles, they are essential for ovarian differentiation during a critical developmental stage. To understand the molecular mechanisms of estrogen action in the Nile crocodile (Crocodylus niloticus), we have isolated cDNA encoding the estrogen receptor α (ERα) from the ovary. Degenerate PCR primers specific to ER were designed and used to amplify Nile crocodile cDNA from the ovary. The full-length Nile crocodile ERα cDNA was obtained using 5′ and 3′ rapid amplification cDNA ends (RACE). The deduced amino acid sequence of the Nile crocodile ERα showed high identity to the American alligator ERα (98%), caiman ER (98%), lizard ER (82%) and chicken ERα (92%), although phylogenetic analysis suggested profound differences in the rate of sequence evolution for vertebrate ER sequences. Expression of ERα was observed in the ovary and testis of juvenile Nile crocodiles. These data provide a novel tool allowing future studies examining the regulation and ontogenic expression of ERα in crocodiles and expands our knowledge of estrogen receptor evolution.