Pre- and post-natal differentiation of the hamster Leydig cell

Basement membrane and epithelial features of fetal-type Leydig cells in rat and human testis

The basement membranes of developing Leydig cells in fetal and newborn testis of rat were studied by ultrastructural and immunocytochemical methods. Fetal-type Leydig cells in prenatal rats were organized in irregularly outlined groups in the interstitium and were extensively surrounded by ultrastructurally identifiable basement membranes and immunocytochemically localized laminin and collagen type IV. Prenatal Leydig cell precursors had small patches of laminin and collagen type IV on their surfaces, which indicated that changes in extracellular matrix took place during their differentiation to mature fetal-type Leydig cells. Additionally, ultrastructural evidence was obtained for a basement membrane surrounding the fetal human Leydig cells similar to that in fetal rats. Soon after birth the rat fetal-type cells gathered into distinct clusters surrounded by delicate envelope cells and a discontinuous basement membrane. Basement-membrane structures, laminin, and collagen type IV were observed between the clustered cells as well. The basement membranes covering large cell surface areas of the fetal-type Leydig cells in fetal and newborn rats differed from those of the adult-type cells, which, according to our earlier study, are covered only by small patches of basement membrane. The difference between the basement membranes of the fetal- and adult-type rat Leydig cells further supports the concept of two different Leydig cell populations. The earlier findings of the epithelial nature of the Leydig cells agree with the observation of basement membranes in the Leydig cells.

Patchy basement membrane of rat Leydig cells shown by ultrastructural immunolabeling

Rat testes were examined by conventional and immunolabeling transmission electron microscopy. Ultrastructurally identifiable continuous basement membranes were found around seminiferous tubules and the interstitial capillaries. Patches of basement membrane were, additionally, found on free surfaces of Leydig cells, between two Leydig cells, and in macrophage-Leydig cell contact sites. The ultrastructural findings were confirmed by immunocytochemical localization of laminin and collagen type IV in the same areas. A close association between the capillary basement membranes and the surfaces of perivascular Leydig cells was also observed. The possible basement membrane-mediated interactions of Leydig cells with other testicular structures, together with the novel bioactive products and regulators of Leydig cells, support the role of these cells as exceptionally complex regulatory centers of testicular functions.

Testicular involution following optic enucleation: the Leydig cell

The testes of Syrian hamsters underwent pronounced involution within six weeks after blinding. The seminiferous tubules were devoid of all stages of spermatid development and mature spermatozoa were absent from the tubule lumina. The diameter of of the Leydig cells was 25% less than that of controls. Examination with the electron microscope revealed thick bundles of collagen fibrils interspersed between Leydig cells and surrounding Leydig cells in the blinded hamsters. The Leydig cell nuclei were shrunken and highly infolded. Lipid droplets that were often seen in normal Leydig cells were absent in the involuting Leydig cells. The size of the Golgi complex and the amount of smooth endoplasmic reticulum were reduced. Results of the present experiment confirm that inactivity of the Leydig cells is the reason for the decline in serum testosterone levels in blinded hamsters.