Multiple sources for Sertoli Cells and two Sertoli phenotypes in the adult elasmobranch testis: insight from two species belonging to different Orders

Abstract

Findings presented here for the chondrichthyans <i>Prionace glauca</i> and <i>Isurus oxyrinchus</i> show that the assembly of the spermatocyst and it's attached collecting duct are seamlessly connected developmental phenomena. The cyst's somatic cell component (i.e., Sertoli cells, SCs) and the duct's constituent cells derive both from a common precursor cell type (typically a large oblong cell) found among the A‐spermatogonia in the folliculogenic region. Novel findings show that the co‐developing collecting duct itself serves also as a source of either normal‐looking or basophilic atypical SCs (aSCs), depending on whether the duct–cyst transition remains mitotically active and open, or is sealed. The aSCs arise from accumulating slender basophilic cells at the duct–cyst interface after which the newly formed cyst is sealed. Quantitative analysis of the latter in <i>P. glauca</i> revealed a correlation between the appearance of this aSC in immature cysts and the degenerated testicular condition that displays a gradient of multinucleate cell (MNC) death among spermatogonial cysts. Findings seem to implicate these aSCs in the life–death balance in mature spermatogonial cohorts downstream in the spermatogenic sequence, rather than in newly formed cysts that exhibit low rates of apoptosis. Photomicrographs of developing spermatogonial cysts showing several aSCs interspersed among cytoplasmically linked spermatogonia that are proliferating or have died, seem to suggest that these small SCs may be involved in confining MNC death to a given cyst region under conditions of subthreshold levels of apoptosis such as to ensure cyst recovery in immature spermatogonial cysts.