Syntheses of nucleic acids during spermatogenesis in Nereis diversicolor (annelida polychaeta): a quantitative autoradiographic study

Endocrine and environmental control of reproduction in Polychaeta

In Polychaeta, as in many invertebrates, reproduction is controlled by both environmental and endocrine factors. Although the effects of environmental factors on reproductive behaviour are briefly discussed, this review focuses on the endocrinology of reproduction. As Nereidae are the most intensively studied polychaetes, their epigamic monotelic strategy is discussed first in this review. Although a large number of physiological observations have been made, biochemical data have been greatly lacking until recent years, except, however, for the recent isolation of several pheromones. These substances, such as uric acid and L-cysteine gluthathione disulfide, occur widely and must be present at high concentrations in order to exert their physiological effects. Results obtained from iteroparous species are also considered. The stolonization strategy of Syllidae, the control of vitellogenesis in Nephtyidae, Phyllodocidae, Polynoidae, and Cirratulidae, and the regulation of gamete maturation in Arenicolidae and Pectinariidae are discussed. As with Nereidae, our knowledge of endocrine control is mainly based on experimental data, since only sperm-maturation factor in the genus Arenicola has been identified. Therefore, despite numerous interesting experimental studies in which functional roles for polychaete reproductive hormones have been described, their nature, their primary targets, and their mechanism of action are unfortunately still largely unknown.

Endocrine regulation of spermatogenesis in Nereis diversicolor (annelida polychaeta): experimental study of the control of meiotic differentiation

In Nereidae, spermatogenesis is regulated by a hormone secreted by the supraesophageal ganglion (brain hormone). The hormonal concentration decreases with worm age. Spermatogonial proliferation in young worms proceeds under a high hormonal level whereas differentiation of spermatozoa in aged worms occurs in the absence of brain hormone. Spermatogonia were removed from the endocrine influence of the brain in vitro by the organ culture method. Isolated parapodia produced spermatozoa after 13 days. Control cultures were obtained by associating a parapodium with the prostomium of a young worm. It seems that the brain hormone inhibits the spermatocyte differentiation since removal of the brain results in increased RNA synthesis, followed by DNA replication, meiosis, and spermiogenesis (Bertout, '83). Modalities of the hormonal control of meiosis, especially at the level of the RNA syntheses related to meiotic differentiation, were investigated. Effects of reintroducing the hormonal influence during meiotic differentiation were studied through parapodium-prostomium associations at various time after the brain inhibition has been lifted. Effects or RNA inhibitors (actinomycin D, alpha-amanitin, cordycepin) were also tested. The results lead us to propose a hypothesis according to which brain hormone would interfere with molecular events related to the transition from the stage of spermatogonial proliferation (mitotic behavior) to the stage of meiotic differentiation (meiotic behavior).