Endocrine Control of Spermatogenesis in Teleost Fish

Abstract

Very different testicular structures and spermatogenetic patterns have been found in fish of the teleost group. Two types of structures may be identified: (i) a tubular type with no lumen (in cyprinodonts); the cysts migrate from the blind end to the vas efferens during the process of spermatogenesis; (ii) a lobular type having a central lumen receiving the spermatozoa released from cysts which remain stationary along the lobule during spermatogenesis. Different spermatogenetic patterns are distinguished in salmonids and cyprinids. In the latter (carp. &Ivprinus ccarpio. and goldfish, Cciras.sius crur-atus). sonme germ cell types (e.g. type B spermatogonia and spermatozoa) are present throughout the year, allowing nearly continuous production of good-quality sperm. Studies of their endocrine patterns suggest that the GTH involved is controlled by external (mainly temperature but also photoperiod) and gonadal factors. The GTH stimulates androgen production and eventually controls spermatogenesis and spernmiation. In salmonids, the two major events of the testicular cycle, spermatogenesis and spermiation, are temporally separated by a stage of spcmsatozoal "maturation" during which the spermatozoa undergo physiological changes. Sperm quality declines during the period of spe'rmiation. The initiation of a new spermatogenetic cycle seems possible only when the spermatozoa have been eliminated from the testis. either by the normal process of spermiation or by intratesticular resorption. This also illustrates the spatias independence of spermatogenesis and spermiation. ' The endocrine pattern of spermatogenesis in saimonids is similar to that in carp but seems different as regards spermiation. This spermiation process includes two steps, initiation and amplification, which require different GTH levels and steroid balance. Among the steroids, I 1-ketotestosterone is the major androgen found in the plasma, but its superiority over other androgens in regard to spernsiation remains to be demonstrated. Environmental factors (photoperiodic changes and temperature) may act directly on the central nervous system to control gonadotropin secretion. Temperature may also directly influence the gonad, somatic or germ cells, and steroid metabolism which acts either locally on the gonad or more centrally. The regulation of spermatogenesis in fish appears to be more subtle than previously believed. Major unknowns are whether there is a second GTH and, if so, its site of action; which steroids are directly involved in the control of sperinatogeriesis in the lobules, and which are the target cells; and which factors regulate testicular size and which pituitary GTH secretion. Finally, the poor yield of spermiation is intriguing and requires further study, considering its practical implication in fish-farming.

Histological Study of the Seminiferous Epithelium in the Japanese Rat Snake, Elaphe Climacophora: Identification of Spermatogonium.

“…The latter finding indicates that spermatogonia of the snakes were located on the Sertoli cell processes, not on the basement membrane. Similar observations have been reported in fishes and amphibians, where their primary spermatogonia might be surrounded by cyst cells (Sertoli cells) [2,4]. The present findings are summarized schematically as in Fig.…”

“…In teleost fishes and amphibians (anamniotes) [2,4], spermatogonia are surrounded by cyst cells (Sertoli cells) and spermatogenic cells show no attachment to the basement membrane throughout spermatogenesis. On the other hand, in birds [16] and mammals, spermatogonia of stem cells lie flat on the basement membrane.…”

A microencapsulated analog of LH-RH accelerates maturation but without stimulating sex reversal in the protandrous black porgy, Acanthopagrus schlegeli

“…Elevated concentrations of plasma T were observed in black porgy by injection of DAla 6 , des-Gly 10 LH-RH ethylamide (without microencapsulation) during the prespawning season (Chang ef al, 1991 The effects of prolonged stimulation by the released LH-RH analog might affect the production of gonadal steroids in black porgy. T, 11-KT, 17a-OH P and 17a, 20p-dihydroxy-4-pregnen-3-one (17a, 20p-diOH P) are involved in spermatogenesis, spermiation and oocyte maturation in fish (Billard et al, 1982;Young et al, 1986). Because of the unavailability of assays for 17a, 20p-diOH P, 11-KT and black porgy gonadotropin, only T, E2 and 17a-OH P were measured in the present study.…”

CARACTERIZACIÓN BIOLÓGICA DE LAS GONADOTROFINAS DE LUBINA (Dicentrarchus labrax) Y DESARROLLO DE HERRAMIENTAS BIOTECNOLÓGICAS E INMUNOLÓGICAS PARA SU ESTUDIO

“…Espermatogonias (sg), espermatocitos (sct), espermátidas (std), espermatozoides (sz), cistes o espermatocistes (C), lumen lobular (lu), membrana basal (mb), fibroblastos (fi). Adaptado de Billard et al (1982).…”

“…El testículo de tipo lobular es el más común entre los teleósteos Perciformes y está compuesto por numerosos lóbulos ramificados y anastomosados entre si. En cada uno de estos lóbulos, las células de Sertoli engloban clones de células germinales en el mismo estado de desarrollo (Billard et al, 1982;Pudney, 1995) formando las unidades funcionales del testículo donde tiene lugar la espermatogénesis, los espermatocistes. El espermatociste más simple lo constituye una sola cé-lula germinal o espermatogonia rodeada por una o dos células de Sertoli que se encargan de suministrar el entorno necesario para su supervivencia, proliferación y diferenciación.…”