GONADOTROPIC AND THYROTROPIC CELLS FROM THE MEDITERRANEAN YELLOWTAIL (SERIOLA-DUMERILII, RISSO, 1810) - IMMUNOCYTOCHEMICAL AND ULTRASTRUCTURAL CHARACTERIZATION

Background: Gonadotropins GTH I and GTH II from the pituitary of Medit erranean (M.) yellowtail (Seriola dumerilii) were isolated and charact erized, and antisera to the whole GTH II molecule (anti-My alpha,beta GTH II) and to its beta-subunit (anti-My beta GTH II) were obtained. A t the light microscopic level, anti-My alpha,beta GTH II reacted with My beta GTH II-immunoreactive cells (GTH II cells), thyroid-stimulatin g hormone (TSH) cells, and a third cell population, which could have b een GTH I cells. The aim of this study was the ultrastructural charact erization of GTH and TSH cells in M. yellowtail using the immunogold m ethod in order to provide a basis for future research into reproductio n of this species. Methods: Pituitaries from mature male and female sp ecimens reared in captivity were disected out and processed for electr on microscopy. The immunogold method was carried out by using anti-My alpha,beta GTH II, anti-My alpha,beta GTH II preabsorbed with the alph a subunit of the M. yellowtail GTH (My alpha GTH-subunit), anti-My bet a GTH II, anti-human (h) alpha,beta TSH, and anti-h beta TSH sera to r eveal gonadotropic and thyrotropic cells. Results: M. yellowtail gonad otropic cells were very heterogeneous with regard to their size, shape , and ultrastructural features. Cells were found with numerous, round, variably electron-dense, secretory granules and globules; others were found with their cytoplasm occupied mostly by dilated cisternae of ro ugh endoplasmic reticulum (RER) and scarce secretory granules; and oth er intermediate cell forms were found that showed varying proportions of secretory granules and dilated RER. The secretory granules and glob ules were immunogold labeled with anti-My alpha,beta GTH II, and the r eaction was weaker in the latter. A similar immunogold-labeling patter n was found with anti-My beta GTH II and with anti-My alpha,beta GTH I I preabsorbed with the My alpha GTH-subunit, although some cells that showed the same ultrastructural features described above were not immu nogold labeled and could have been GTH I cells. Thyrotropic cells had small, round, secretory granules of medium or high electron density th at were immunogold labeled with anti-My alpha,beta GTH II, anti-h alph a,beta TSH, and anti-h beta TSH sera, but not with anti-My beta GTH II or anti-My alpha,beta GTH II serum preabsorbed with the My alpha GTH- subunit. All of the cell forms described for gonadotropes and thyrotro pes were also found in a state of involution. Conclusions: Gonadotrope s that are of a single morphological type but that vary in ultrastruct ure are present in the pituitary of captive M. yellowtail. GTH II-and putative GTH I-producing cells were distinguishable from one another a nd from TSH cells by their different reactions to anti-My alpha,beta G TH II, anti-My beta GTH II, and anti-My alpha,beta GTH II preabsorbed with the My alpha GTH-subunit. (C) 1998 Wiley-Liss, Inc.