Chaves-Pozo Elena, Mulero Victoriano, Meseguer José, García Ayala Alfonsa
Department of Cell Biology, Faculty of Biology, University of Murcia, Campus Universitario de Espinardo, 30100 Murcia, Spain.
Biol Reprod. 2005 Mar;72(3):593-601. doi: 10.1095/biolreprod.104.036103. Epub 2004 Nov 17.
The gilthead seabream is a protandrous hermaphrodite seasonal breeding teleost with a bisexual gonad that offers an interesting model for studying the testicular regression process that occurs in both seasonal testicular involution and sex change. Insofar as fish reproduction is concerned, little is known about cell renewal and elimination during the reproductive cycle of seasonal breeding teleosts with asynchronous spermatogenesis. We have previously described how acidophilic granulocytes infiltrate the testis during postspawning where, surprisingly, they produce interleukin-1beta, a known growth factor for mammalian spermatogonia, rather than being directly involved in the elimination of degenerative germ cells. In this study, we are able to discriminate between spermatogonia stem cells and primary spermatogonia according to their nuclear and cytoplasmic diameters and location in the germinal epithelium, finding that these two cell types, together with Sertoli cells, proliferate throughout the reproductive cycle with a rate that depends on the reproductive stage. Thus, during spermatogenesis the spermatogonia stem cells, the Sertoli cells, and the developing germ cells (primary spermatogonia, A and B spermatogonia, and spermatocytes) in the germinal compartment, and cells with fibroblast-shaped nuclei in the interstitial tissue proliferate. However, during spawning, the testis shows few proliferating cells. During postspawning, the resumption of proliferation, the occurrence of apoptotic spermatogonia, and the phagocytosis of nonshed spermatozoa by Sertoli cells lead to a reorganization of both the germinal compartment and the interstitial tissue. Finally, the proliferation of spermatogonia increases during resting when, unexpectedly, both oogonia and oocytes also proliferate. This proliferative pattern was correlated with the gonadosomatic index, testicular morphology, and testicular and gonad areas, suggesting that complex mechanisms operate in the regulation of gonocyte proliferation in hermaphrodite fish.
金头鲷是一种雄性先熟的雌雄同体季节性繁殖硬骨鱼，具有两性性腺，为研究季节性睾丸退化和性转变过程中发生的睾丸退化过程提供了一个有趣的模型。就鱼类繁殖而言，对于具有异步精子发生的季节性繁殖硬骨鱼在生殖周期中的细胞更新和清除知之甚少。我们之前已经描述了嗜酸性粒细胞在产卵后如何浸润睾丸，令人惊讶的是，它们产生白细胞介素-1β，这是一种已知的哺乳动物精原细胞生长因子，而不是直接参与退化生殖细胞的清除。在这项研究中，我们能够根据精原干细胞和初级精原细胞的核直径、细胞质直径以及它们在生发上皮中的位置来区分这两种细胞，发现这两种细胞类型与支持细胞一起在整个生殖周期中增殖，增殖速率取决于生殖阶段。因此，在精子发生过程中，生发区的精原干细胞、支持细胞和发育中的生殖细胞（初级精原细胞、A 型和 B 型精原细胞以及精母细胞）以及间质组织中具有成纤维细胞形状细胞核的细胞会增殖。然而，在产卵期间，睾丸中增殖细胞很少。在产卵后，增殖的恢复、凋亡精原细胞的出现以及支持细胞对未排出精子的吞噬导致生发区和间质组织的重新组织。最后，在静止期精原细胞的增殖增加，出乎意料的是，卵原细胞和卵母细胞也会增殖。这种增殖模式与性腺体指数、睾丸形态以及睾丸和性腺面积相关，表明在雌雄同体鱼类中，性腺细胞增殖的调节存在复杂机制。
