Figure 1.

The physiological relationship along the hypothalamic-pituitary-testicular axis that regulates testicular function, and the intimate structural relationship between Sertoli and germ cells in the seminiferous epithelium during spermatogenesis. A) This is a schematic drawing that shows the hormonal regulation of spermatogenesis in the testis via the hypothalamic-pituitary-testicular axis. LHRH released from the hypothalamus stimulates the production of LH and FSH by the pituitary gland, which in turn regulates Leydig and Sertoli cell functions, residing in the interstitium and the seminiferous epithelium, respectively. Testosterone (T) and inhibin (and others, e.g., follistatin) released by Leydig and Sertoli cells, respectively, provide the necessary feed-back loops to maintain the endogenous levels of LH and FSH to regulate spermatogenesis. Any changes in the homeostasis of these hormones can perturb spermatogenesis. For instance, a reduction of intra-testicular T level can suppress spermatid (step 8 and beyond) adhesion, leading to spermatid depletion from the epithelium without disrupting the blood-testis barrier (BTB) integrity.^60–62 The right panel represents a stage II–VI seminiferous tubule dissected from the testis by using a transilluminating stereomicroscope as described.¹ B) A semi-thin cross-section from an adult rat testis showing a seminiferous tubule at stage V of the epithelial cycle, illustrating the intimate relationship between Sertoli (SC) and different germ cells (e.g., sg, spermatogonium; SP, pachytene spermatocyte; RS, round spermatid; es, elongating/elongate spermatid) that constitute the seminiferous epithelium, resting on the basement membrane (see asterisks). C) A schematic drawing of the seminiferous epithelium that illustrates germ cells at different stages of their development are associated with Sertoli cells via specialized cell junctions, such as AJ, apical ectoplasmic specialization (apical ES) and desmosome-like junctions (DJ), and apical tubulobulbar complex (apical TBC). The BTB, which is composed of tight junction (TJ), basal ES, basal TBC, DJ, and AJ, anatomically divides the seminiferous epithelium into the basal and adluminal compartments. However, the BTB must “open” to accommodate the movement of preleptotene spermatocytes across the barrier at stage VIII of the epithelial cycle.⁷ This figure was prepared based on recent findings and reviews in the field.^6,17,45,110 Bar in (B), 10 μm.