Endocrine control of reproduction in two rhynchocoelan worms

Abstract

This brief review of the reproductive endocrinology in two distant species of Rhynchocoela examines selected results of earlier studies on the heteronemertean, Lineus ruber, and reports current and unpublished research on the hoplonemertean, Amphiporus lactifloreus.

Experimental evidence is presented for existence in the brain of a gonad-inhibiting hormone (GIH) that controls reproduction in male and female worms of both species. In adults deprived of GIH during the quiescent phase of the reproductive cycle, sexual characteristics grow rapidly and precociously; GIH replacement therapy prevents the anticipated sexual development. In L. ruber, the removal of GIH stimulates macromolecular syntheses in sexual target cells of both sexes: RNA synthesis is promoted in young oocytes; DNA synthesis is increased in spermatogonia, and induced in primary spermatocytes; and protein synthesis is significantly increased in gametocytes and sex-specific skin glands. GIH might be a regulating hormone which would inhibit the secretion of sex-specific stimulating substances produced by cells in proximity to the gonads.

Keywords:

• Rhynchocoela
• reproductive endocrinology
• brain hormone
• oogenesis
• sex-specific cells