Abstract
In an ultrastructural immunocytochemical study we investigated the development of the gonadotropic cells in the pituitary of two to six months old male African catfish in relation to testicular development. In this period, pituitary and testicular tissue samples were collected on five occasions (groups I–V). Blood samples could only be taken from the fish in groups III–V. The testicular development was divided in three stages i.e., immature (only spermatogonia, group I), early (spermatogonia and spermatocytes, groups II and III) and advanced (all germ cell stages including spermatozoa, groups IV and V) spermatogenesis. 11-Ketotestosterone blood levels were low, except for the last group. Antisera were raised against the complete catfish α,βGTH-II, as well as to the separate α- and β-subunits of catfish GTH-II. In the proximal pars distalis of immature fish, undifferentiated cells, somatotrops, putative thyrotrops (pTSH) and putative gonadotrops (pGTH) were found. In the two latter, secretory granules were labeled with anti-αGTH, but not with anti-βGTH-II. pTSH- and pGTH-cells were distinguished on the basis of the size of their secretory granules. During early spermatogenesis, two classes of putative gonadotrops could be distinguished. One type had the same immunocytochemical and ultrastructural characteristics as in immature fish; the secretory granules in the second cell type, which was more abundant, were also immunopositive for anti-βGTH-II. The mean volume of the secretory granules in these GTH-II cells was three times larger than that in the early appearing pGTH-cells. In addition, the later appearing GTH-II cells contained large inclusions, known as globules. These structures labeled with anti-αβGTH-II and with anti-βGTH-II, but not with anti-αGTH. It is assumed that the globules are involved in a differential storage and/or breakdown of the GTH-II subunits. During advanced spermatogenesis the two gonadotropic cell types could still be distinguished, but the early appearing pGTH-cell type was scarce. The present observations permit the conclusion that the early appearing cells may be GTH-I cells. However, definitive proof about their identity depends on the availability of antibodies or cDNA probes specific for GTH-I.
Résumé
A l'aide d'une étude d'immunocytochimie ultrastructurale, nous avons suivi chez le poisson chat africain mâle âgé de 2 à 6 mois le développement des cellules gonadotropes hypophysaires en relation avec celui des testicules. Pendant cette période, 5 prélèvements hypophysaires et testiculaires ont été effectués (groupe I–V) alors que les prélèvements sanguins n'ont pu être pratiqués que dans les groupes III–V. Le développement testiculaire a été divisé en 3 stades c'est à dire immature (spermatogonies seulement, groupe I), début de spermatogenèse (spermatogonies et spermatocytes, groupe II et III), spermatogenèse avancée (tous les stades de cellules germinales incluant les spermatozïdes, groupe IV et V). Les niveaux sanguins en 11-ketotestostèrone étaient bas excepté dans le dernier groupe. Des anticorps ont été fabriqués contre l'α,βGtH-II et les sousunités α et β de GtH-II de poisson chat. Dans la partie proximale distale de l'hypophyse du poisson immature, des cellules indifférenciées, des cellules somatotropes, des cellules putatives thyrotropes (pTSH) et gonadotropes (pGtH) ont été trouvées. Dans les deux derniers types cellulaires, des granules de sécrétion ont été marqués avec l'anti-αGtH mais pas avec l'antiβ-GtHII. Les cellules présumées à TSH et GtH ont été distinguées par la taille des granules de sécrétion. Pendant le début de la spermatogenèse, 2 classes de cellules gonadotropes putatives ont pu être distinguées. Un type a les mêmes caractéristiques immunocytochimiques et ultrastructurales que chez les immatures; les granules de sécrétion dans le second type cellulaire, qui était plus abondant, répondaient aussi immunopositivement à l'anti-βGtHII. Le volume moyen des granules de sécrétion de ces cellules à GtHII était 3 fois supérieur à celui des cellules putatives à GtH apparaissant tôt. De plus, les cellules à GtHII apparaissant tardivement contiennent de grandes inclusions, connues sous le nom de globules. Ces structures étaient marquées avec l'anti-αβGtHII et avec l'anti-βGtHII, mais pas avec l'anti-αGtH. Il a été supposé que les globules sont impliqués dans un stockage différentiel et/ou destruction des sous-unités de GthII. Pendant les stades plus avancés de la spermatogenèse les 2 typev gonadotropes pouvaient encore être distingués, mais les cellules putatives à GtH apparaissant tôt étaient rares. Les présentes observations permettent de supposer que les cellules à GtH apparaissant tôt peuvent être des cellules à GtHI. Cependant, la preuve définitive de leur identité dépend de la disponibilité d'anti-GtHI ou de cDNAs spécifiques de la GtHI.
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Zandbergen, M.A., van Branden, C.A., Schulz, R.W. et al. GTH-cells in the pituitary of the African catfish, Clarias gariepinus, during gonadal maturation: an immuno-electron microscopical study. Fish Physiol Biochem 11, 255–263 (1993). https://doi.org/10.1007/BF00004573
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DOI: https://doi.org/10.1007/BF00004573