Cremaster Muscle Myogenesis in the Tip of the Rat Gubernaculum Supports Active Gubernacular Elongation During Inguinoscrotal Testicular Descent

PurposeCryptorchidism is a common abnormality and normal testicular descent is controlled by the gubernaculum. The cremaster may originate from abdominal muscles during gubernacular eversion or alternatively it may develop inside the gubernaculum. We studied cremaster myogenesis to determine how it develops.Materials and MethodsCoronal sections of the pelvis were prepared from male Sprague-Dawley® rats and from males treated prenatally with the antiandrogen flutamide at embryonic day 19, and postnatal days 10, 19 and 35 after receiving ethical approval. Immunohistochemical stains were prepared for Ki67, Pax-7, myogenin, myosin heavy chain 7, Myh1, Myh2, Myh4, embryonic myosin, and slow and cardiac troponin T. Cell counts of the 1) gubernacular tip, 2) proximal gubernaculum/cremaster muscle and 3) adjacent abdominal wall are shown as a percent of positive fibers or positive cells per area.ResultsThroughout embryonic day 19, and postnatal days 10 and 19 proliferation (Ki67) was maximal at the gubernacular tip (p <0.001), as were muscle stem cells markers (Pax-7 p <0.05), early myogenesis (myogenin p <0.001) and immature muscle (Myh7, and slow and cardiac troponin T p <0.0001). In contrast, secondary (fast twitch, Myh1, 2 and 4) fibers were more common in abdominal muscles (p <0.0001). Differences in muscle maturity and composition decreased with time. Flutamide treated rats showed more cellular proliferation than controls postnatally on postnatal day 10 (p <0.001) as well as persistent immature embryonic myosin at the tip from postnatal day 19 (p <0.05).ConclusionsResults show that the rat cremaster muscle is more immature at the gubernacular tip, consistent with myogenesis occurring in the gubernaculum during migration to the scrotum, as proposed in humans.