Ancestral coelomates possessed homologs of several
of the hormones that are important in higher vertebrates such as oxytocin,
GHRH, and insulin. Coelomates also share nuclear receptors, a gene family
which includes receptors for estrogen and testosterone.
A number of peptides similar to oxytocin/vasotocin are known in invertebrates
such as Arg-conopressin-S in mollusks, Lys-conopressin-G in mollusks,
cephalotocin in mollusks, annetocin in annelids, Lom-DH in arthropods,
and Stp-OLP in tunicates. Mollusk conopressin genes are homologous to
those of vasoticn/oxytocin in vertebrtates (Hoyle, 1998; Youson, 1999;
Kesteren, 1992). In worms, annetocin functions in egg-laying and the contraction
of neprhidia (which propel both wastes and gametes) (Ivell, 1999).
GHRH is produced by the hypothalamus to affect the secretion of growth
hormone from the pituitary. Homologs of gene family members are known
in flies. It is also a paracrine/autocrine hormone produced by the lung
and gastrointestinal tract. Beta cells and the insulin they secrete are
known in basal deuterostomes and some protostomes (Hoar). Mollusks have
an insulin-like protein and the insect hormone bombyxin is also similar
to insulin. (Chan, 1990).
Ftz-F1, a protein which activates the ftz homeodomain gene in Drosophila
which is involved in the segmentation of the embryo is a member of the
nuclear receptor superfamily. Some members of the family only contain
the DNA-binding region of the mammalian nuclear hormone receptors (such
Knirps and Embryonic gonald) while Ftz-F1 possesses both the DNA-binding
and ligand binding domains found in the mammalian hormone receptors (Lavorgna,