Vitellogenesis and its control in malacostracan crustacea

Abstract

Vitellogenesis in the amphipod Orchestia gammarella, in natantian decapods and probably in other Malacostraca involves two phases, primary and secondary vitellogenesis. Oogenesis from oogonia to the end of primary vitellogenesis is a continuous process. The primary proteic vitellus is endogenous. The secondary vitellogenesis takes place during the reproductive season. Fully grown primary follicles are surrounded by a permanent follicular tissue (secondary folliculogenesis). The resulting secondary follicles grow synchronously until ovulation. A tubular network has been observed in secondary follicle cells of prawns. The prominent feature of secondary vitellogenesis is the uptake of vitellogenin by the oocytes. This vitellogenin is synthesized by the fat body. Secondary vitellogenesis is controlled by neurohormones that have not yet been isolated and whose modalities of action still remain unclear. In Decapoda, the classical gonad-inhibiting hormone or GIH released by the sinus glands inhibits secondary vitellogenesis and the synthesis of vitellogenin. In Isopoda, vitellogenesis-inhibiting hormone is synthesized by neurosecretory cells in the median part of the protocerebrum. In Amphipoda, neurosecretory cells of this region secrete a neurohormone inducing secondary folliculogenesis and triggering secondary vitellogenesis. The neurohormones would control the formation of functional secondary follicles during the reproductive season.Other hormones are involved in control of secondary vitellogenesis. In Peracarida molting hormone is necessary for a normal synthesis of vitellogenin and the uptake of this protein by growing oocytes. In the amphipod Orchestia gammarella secondary folliculogenesis requires a low titer of ecdysteroids which characterizes postecdysis. The correlation between molt cycle and secondary vitellogenesis would be established in this way. After secondary folliculogenesis, the secondary follicle cells become endocrine and secrete the vitellogenin-stimulating ovarian hormone (VSOH). © 1985 the American Society of Zoologists.