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SC secrete different types of proteases, protease inhibitors, hormones, energy substrates, growth factors, paracrine factors, and extracellular matrix components. Proteases and protease inhibitors from SC participate in ST maintenance, repair, growth, remodeling, and restructuring. Protease inhibitors are required for germ cell translocation across the blood–testis barrier and for spermiation [52]. Moreover, protease inhibitors are involved in assembly and disassembly of cellular junctions in the ST [53].

SC secrete adluminal fluid and maintain a specific environment for differentiation of germ cells toward lumen of the ST [33]. FSH‐regulated functions of SC include transfer of testosterone and glucose and germ cell nurturing by provision of lactate and pyruvate. Under the influence of FSH and androgens, SC secrete proteins necessary for germ cells and interstitial cells of the testes and secrete androgen binding proteins to ensure bioavailability of androgens [54, 55]. Inhibin and activins from SC act on the hypothalamic–pituitary–gonadal axis and also on Leydig cells [56]. The iron carrier protein, transferrin, is produced by SC and its concentration in seminal plasma is correlated with fertility and spermatogenic capacity in the bull [57]. SC co‐cultured with germ cells stimulate DNA and RNA synthesis in the germ cells [58]. Seminiferous growth factor is involved in spermatogonial proliferation, nerve growth factor is required for DNA synthesis in preleptotene spermatocytes, and insulin‐like growth factor‐1 helps in germ cell differentiation [59].

The germ cells residing in the adluminal compartment cannot receive nutrients directly from blood due to the blood–testis barrier. The spermatocytes and spermatids in the adluminal compartment are nursed by amino acids, carbohydrates, lipids, vitamins, and metal ions from SC [34].