The early recovery phase from spontaneous testicular degeneration in the blue shark, Prionace glauca: Large oblong interstitial cells and the clearance of redundant spermatid-associated Sertoli cells

Abstract

The blue shark (Prionace glauca) maintains voluminous seminal vesicles year-round. And yet, the diametrically arranged testis’s successive rows of spherical germ/ Sertoli cell units (spermatocysts) reveal a gradient of cyst stage-specific, Sertoli cell-only phagocytic clearing activities some time after the spontaneous appearance of protracted, massive multinucleate spermatogonial death seen in summer-mating individuals. Herewith novel findings concerning a hitherto unknown though distinctive interstitial cell type, here termed an oblong reticular-patterned (ORP) cell, observed in both western North Atlantic and Mediterranean Sea blue sharks and that showed cyst-encircling behaviors around far-progressed, phagocytically cleared, earlier spermiogenesis-arrested cysts. The proportion of ORP-positive cysts that were engaged in, or showed completed Sertoli phagocytic clearing of spermatids was significantly (P < 0.01) 3-fold greater in the early recovery phase condition than in the testis condition showing massive multinucleate death. The Sertoli nuclei were the last contents to disappear in the ORP-encased cyst. Bar the odd ORP cell-aggregation at the mature pole, the fully recovered testis sampled in late August lacked all the above. Perusal of a single testicular cross-section showing the diametrically radiating, successive rows of cyst stages facilitates the simultaneous scrutiny of cellular rearrangements in prespermatogenesis at the testis’s immature pole and that of the conclusion of spermatogenesis at the mature pole. Scrutiny of the dynamic stromal environment where cysts are formed at the immature pole revealed the distinctive and insidious ORPs among not-yet sequestered primary spermatogonia, which allude to their alternative fate as future Sertoli cells proper.