LEECH EGG-LAYING-LIKE HORMONE - STRUCTURE, NEURONAL DISTRIBUTION AND PHYLOGENY

Cells immunoreactive to antisera specifically directed against Lymnaea stagnalis caudo dorsal cells egg-laying hormone (CDCH) or against alp ha- and beta-peptides (CDCP), encoded on the egg-laying hormone precur sor, were detected in central nervous system (CNS) of the rhynchobdell id leech Theromyzon tessulatum. A co-localization of the CDC-like horm one and CDC-like peptides was found in T. tessulatum as in L. stagnali s CNS. approximate to 45 immunoreactive cells to the anti-CDCH were de tected in leech brain but this number varies according to the stage of the animal life cycle, i.e. it reaches a maximum just before egg-layi ng while after it decreases to 2-3 cells. CDCH and alpha-CDCP epitopes recognized by anti-CDCH and anti-alpha-CDCP were contained in neurose cretory granules. Following an extensive purification, including HPGPC and reverse-phase HPLC, the CDC-like hormone contained in the T. tess ulatum CNA was isolated. The sequence (GSGVSNGGTEMIQLSHIRERQRYWAQDNLRR RFLEK-amide) was established by a combination of automated Edman degra dation, arginyl-endopeptidase digestion, electrospray mass spectrometr y measurement and carboxypeptidase A treatment. The results demonstrat e that the peptide recognized by the anti-CDCH in the leech CNS posses ses 27.8, 37.2 and 47.2% sequence identity with Aplysia parvula, Lymna ea stagnalis and Aplysia californica ELH, respectively. This molecule was named the leech egg-laying-like hormone (L-ELH). The secondary str ucture prediction of the L-ELH and all mollusks ELH, revealed the exis tence of a conserved segment (segment 29-34) in a strong helicoidal be nd that might be important for receptor recognition and/or activation. This finding constitutes the first biochemical characterization of an egg-laying hormone in other invertebrates than mollusks. (C) 1997 Els evier Science B.V.