Journal of Neuroscience, Vol 6, 2026-2036, Copyright © 1986 by Society for Neuroscience
Egg-laying hormone genes of Aplysia: evolution of the ELH gene family
JR Nambu and RH Scheller
Evolution of the egg-laying hormone (ELH) gene family was examined in the
genus Aplysia using genomic Southern blotting, gene cloning, and
immunocytochemical techniques to identify and characterize homologous
sequences. Most of the species examined have fewer than the 4-5 ELH-
related genes present in the A. californica genome (Mahon et al., 1985;
Scheller et al., 1983). In A. parvula there are 2 ELH genes, and unlike A.
californica, no sequences were found to encode the A or B peptides. The 2
A. parvula ELH genes share at least 90% DNA sequence homology, while the
homology between the A. parvula and A. californica ELH genes is 71%. The
structural organization of the A. parvula ELH precursor is quite similar to
the ELH precursor of A. californica, with all but one of the potential
proteolytic cleavage sites conserved. The overall amino acid homology
between the A. parvula and A. californica ELH precursors is 66%; however,
the alpha and beta bag cell peptides, as well as ELH, are more highly
conserved, suggesting that these peptides have important physiological and
behavioral roles within both Aplysia species. Immunocytochemical studies
indicate that the A. parvula ELH genes are expressed in 2 bag-cell-like
clusters of about 40 neurons each in the abdominal ganglion. There does not
appear to be an atrial gland in A. parvula; however, ELH-immunoreactive
peripheral neurons and their processes are observed along the perimeter of
the large hermaphroditic duct.