In vertebrate reproductive endocrinology estrogens play a pivotal role via binding to estrogen receptors (ER). In invertebrates, however, the origin and relevance of estrogens remains unclear. It is believed that ER orthologs are lost within the ecdysozoan clade since, within protostomes, ER receptor genes and proteins have only been found in molluscs. But, evidence exists from environmental regulations and testing programs that endocrine disrupting industrial chemicals with estrogenic-activity (xenoestrogens) affect the development and differentiation of some insects and crustaceans.
We try to identify an estrogen receptor in the amphipod crustacean Gammarus fossarum, an ecdysozoan. A crustacean species is chosen for the ancient origin of this taxon in the earlier Cambrian period, as part of the great radiation of coelomate animals that occurred at that time.
Our preliminary data on the identification, sex-specific expression, and induction of an ERα orthologous protein in an ecdysozoan species reveal that sex steroid receptors have evolved also in (at least part of the) arthropods and nematodes. In contrast to the ER ortholog from Aplysia californica (which seems to be similar to the fish ERα), the gammarid ERα protein seems to be structrally similar to the mammalian ERα and has estrogen-dependent functional activity.