Steroids are widely dispersed throughout the animal kingdom where they act as regulators of numerous biochemical and physiological processes.
In vertebrates, the nuclear receptor superfamily contains
receptor proteins with specific affinity to estrogens,
androgens, progestins, glucocorticoids, mineralocorticoids
and thyroid hormones. Besides of them, estrogenrelated
receptor proteins (ERRs) and the ecdysone receptors of the
invertebrate ecdysozoans belong to the nuclear receptor
superfamily.
Three
of the above-mentioned ligand groups (estrogens, androgens,
and progestins) are usually addressed by the term ‘‘sex
steroids’’ since they are involved in sex-specific
regulation of molecular processes. 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.