Toshio Nagano

Some observations on the fine structure of the sertoli cell in the human testis

SummaryThe Sertoli cells of the human testis were studied by means of electron microscope. The membranous structures, lipid droplets and filamentous components in the cytoplasm were described. Of membranous structures, the lamellar body which consists of the fenestrated agranular reticulum was noted. Two types of filaments were observed. One was thin and similar to the tonofilaments. The other was thick and distributed in the periphery of the cytoplasm. Possible function of the lamellar body with lipid droplets and of the filaments was discussed.The materials used in this study were selected from scores of testicular biopsies of different aged men. Thorough observations were made on such materials that appeared to be normal or contained slightly less mature spermatids, judging from histological examinations.

Freeze-fracture observations on the intercellular junctions of Sertoli cells and of Leydig cells in the human testis.

SummaryNormal and feminized human testes were examined by means of freeze-fracture. In both cases, the junctional complexes between adjacent Sertoli cells show a unique characteristic feature. Many parallel linear occluding junctions are located circumferentially around the cell surface at the level of the nucleus. They are more than forty in number over one Sertoli cell surface. In the A face, the particles are not prominent on the ridge of the junctions. Instead, they are clearly seen in the center of the groove of the junctions on the B face. Gap junctions consisting of particle aggregation are not found between the Sertoli cells.The gap junctions between the Leydig cells are frequently observed in both normal and feminized testes. They are round or elliptic in contour and about several micrometers in diameter. The particles, about 8 nm in diameter, are closely packed to form a quasi-hexagonal pattern. The pits are found on the B face corresponding to the particle aggregation.

Development of tight junctions in the caput epididymal epithelium of the mouse.

Abstract The course of development of the epithelial tight junctions of the Wolffian duct and the caput epididymal principal cells in the mouse were examined by freeze-fracture. The histogenesis of the epididymis is briefly described. In the 12-day embryo, tight junction meshworks surround the entire circumference of the columnar cells in the juxtaluminal position. During fetal life, the strands are more discontinuous than those of postnatal mice, and two or more strands frequently run together. Up to 10 days of age, the basal compartments of the tight junctions are much larger than the luminal ones. Marked increases in both the number of strands and the depth of the tight junctions appear by 20 days. Strands with a terminal loop are often observed up to 16 days, except for the newborn stage, suggesting that the formation of the terminal loop is related to the active elongation of the strands. The tight junctions increase greatly in number and depth near three-cell junctions. Up to 20 days, the strands anastomose frequently, with no particular orientation to the cell axis. After 20 to 37 days, the direction of the strands becomes parallel to the luminal surface, with a decreased number of anastomoses as the lumen widens. In the adult, the number of sealing strands is about 10 within the depth of the tight junctions. Free-ended strands are seen in all stages examined. The formation of the tight junction meshworks is discussed in the light of the findings during the development.

Morphogenesis of tight junctions in the peritoneal mesothelium of the mouse embryo.

SummaryThe peritoneal mesothelium of mouse embryos (12 to 18 day of gestation) was studied by freeze-fracture and in sections in order to reveal the initial formation of the tight junctions. Freeze-fracture observations showed three types of tight junctions. Type I consists of belt-like meshworks of elevations on the P face and of shallow grooves on the E face. No tight junctional particle can be seen either on the elevations or in the grooves. Type II shows rows of discontinuous particles on the elevations on the P face. Type III consists of strands forming ridges on the P face. On the E face, the grooves of Type II and III appear to be narrower and sharper than those of Type I. Quantitatively, Type I junctions are most numerous during the early stages (day 12–13) of embryonic development, while Type III junctions become more common in the later stages, and are the only type seen by day 18. Observations on sections, however, fail to distinguish between the three types.The results suggest that an initial sign of tight junction formation is close apposition of the two cell membranes in the junctional domain, without tight junctional particles. Later, the particles appear to be incorporated in the tight junctions and the strands form by fusion of the particles.

Cell to cell relationships in the seminiferous epithelium in the mouse embryo.

SummaryGerm cells and Sertoli cells in embryonic mouse testes (day 14 to 20 of gestation) were examined by sectioning and freeze-fracture. Intercellular cytoplasmic bridges between the germ cells are observed in day 14 and older embryos. Membrane specializations with dense fuzzy material similar to the socalled “desmosome-like structures” are found between Sertoli cells and germ cells. A cell contact area with dense opposed membranes is also found between adjacent germ cells. Asymmetrical dense fuzzy lining of both Sertoli and germ cell membranes is noted. Pinocytotic pits or caveolae are frequently found in the Sertoli cell membrane. Between adjacent Sertoli cells, gap junctions of various sizes and focal meshworks of the occluding junctions are found. Most of the occluding junctional particles are located in the center of the grooves in the E face, and are similar to those in postnatal and adult Sertoli cell junctions. In addition, on both fractured faces there are ridges and grooves devoid of particles which are continuous with occluding junctions with particles, suggesting an initial stage in the formation of occluding junctions of the Sertoli cells. Particles gathered at the site of desmosome-like structures are present on the P face of the Sertoli cell.

Contacts between regenerating axons and the Schwann cells of sciatic nerve segments grafted to the optic nerve of adult rats

SummaryThe relation between Schwann cells, basal laminae and axons during retinal ganglion cell regeneration was studied by using cellular, acellular and partially acellular sciatic nerve autografts into the optic nerve. Acellular grafts were achieved by temporary compression which eliminates living Schwann cells and axons. The compressed sciatic nerve together with the intact portion was used as a partially acellular graft. The compressed portion was anastomosed to the optic nerve and the intact portion was situated distally. After 3–21 days post-operation, the grafts were studied by thin sectioning and freeze-fracture. Axons were seen to regenerate into cellular grafts in contact with Schwann cells after one week, but not into acellular grafts for the entire period. In the partially acellular grafts, regenerating axons were first observed after two weeks and were always in contact with Schwann cells migrating from the intact portion. Moreover, membrane specializations, fuzzy materials in the space between apposed membranes, and putative tight junctions, were found between regenerated axons including growth cone and Schwann cells, and between adjoining Schwann cells. An extensive meshwork of putative tight junctions was displayed between reforming perineurial cells surrounding the groups of Schwann cells and associated axons. Gap junctions were seen between adjoining Schwann cells, and between reforming perineurial cells. These results suggest that the axonal contact with Schwann cell surfaces plays an important role in retinal ganglion cell regeneration.

An electron microscopic observation on the cross-striated fibrils occurring in the human spermatocyte.

SummaryCross-striated fibrils associated with the centriole were found in a presumed young spermatocyte of the human biopsy material. This resembles the structure in the ciliary rootlets already reported in some ciliated epithelia. Probable nature of this structure is briefly discussed.

Immunohistochemical localization of cell adhesion molecules and cell‐cell contact proteins during regeneration of the rat optic nerve induced by sciatic nerve autotransplantation

The central nervous system neurons of adult mammals are known to regenerate into peripheral nerve autograft. The localization of cell adhesion molecules and cell‐cell contact proteins were studied during axonal regeneration induced by sciatic nerve autotransplantation.

Fine structural relation between the Sertoli cell and the differentiating spermatid in the human testis.

SummaryThe structural relationship between the Sertoli cell and the developing spermatid was studied with the electron microscope. In the contact area of the Sertoli cell with the anterior part of the developing spermatid, a filamentous structure is observed. This structure consists of fine tubular filaments about 100 Å in diameter associated with dense material. The functional significance of the structure is discussed.

Cell Junctions in the Seminiferous Tubule and the Excurrent Duct of the Testis: Freeze-Fracture Studies

Publisher Summary This chapter describes the morphological observations of intercellular junctions in the seminiferous tubule and the excurrent duct system of mammalian testes as revealed by freeze fracturing. The junctions in the nonmammalian testes are also described. The seminiferous epithelium resting on the seminiferous tubule consists of two cellular populations: spermatogenic cells and Sertoli cells. These originate from different germinal layers during histogenesis. All generations of the clonal spermatogenic cells are connected with each other by the cytoplasmic bridges to form syncytia until spermiation. The Sertoli cells or supporting cells never divide in the adult testis and are separated by their cell membranes as individual cells. Intercellular junctions among the epithelial lining cells other than the Sertoli cells are recognized as the terminal bar by light microscopy. The junctional complexes of the epithelial cells lining the excurrent duct system are situated in the juxtaluminal area of the cell. More comparative, experimental, and clinicopathological studies on the junctional complexes would be necessary to understand the blood–testis barrier and the environments of the excurrent duct system.