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.