Observations on the blood-testis barrier in a frog and a salamander

An ultrastructural study of testes permeability in sea urchins, Strongylocentrotus intermedius

Permeability of testes in sea urchins, Strongylocentrotus intermedius, was investigated by using an electron-opaque tracer, lanthanum nitrate. This tracer is able to enter the basal compartment of germinative epithelium, where developing germ cells are located. However, its ability to penetrate the gonadal lumen was reduced. An incomplete permeability barrier between the basal compartment and the gonadal lumen is supposed to exist in testes of S. intermedius.

Reptilian spermatogenesis: A histological and ultrastructural perspective

Until recently, the histology and ultrastructural events of spermatogenesis in reptiles were relatively unknown. Most of the available morphological information focuses on specific stages of spermatogenesis, spermiogenesis, and/or of the mature spermatozoa. No study to date has provided complete ultrastructural information on the early events of spermatogenesis, proliferation and meiosis in class Reptilia. Furthermore, no comprehensive data set exists that describes the ultrastructure of the entire ontogenic progression of germ cells through the phases of reptilian spermatogenesis (mitosis, meiosis and spermiogenesis). The purpose of this review is to provide an ultrastructural and histological atlas of spermatogenesis in reptiles. The morphological details provided here are the first of their kind and can hopefully provide histological information on spermatogenesis that can be compared to that already known for anamniotes (fish and amphibians), birds and mammals. The data supplied in this review will provide a basic model that can be utilized for the study of sperm development in other reptiles. The use of such an atlas will hopefully stimulate more interest in collecting histological and ultrastructural data sets on spermatogenesis that may play important roles in future nontraditional phylogenetic analyses and histopathological studies in reptiles.

Size-selective junctional barrier and Ca(2+)-independent cell adhesion in the testis of Cynops pyrrhogaster: expression and function of occludin

In urodeles which has testicular structure different from that in mammals, blood-testis barrier was reported to exist like in mammals. However, molecular and functional analyses of the components of the blood-testis barrier in urodeles have not been reported yet. Toward elucidation of the barrier functions and their molecular components in newt testis, we aimed to isolate occludin cDNAs and obtained two kinds of occludin partial cDNAs (occludin 1 and 2) encoding the putative second extracellular loop. Immunoblot and immunofluorescence studies using antibodies against peptides each corresponding to a part of the second extracellular loop of occludin 1 and 2, and those against beta-catenin and zonula occludens-1 (ZO-1) showed that occludin, as well as beta-catenin and ZO-1, was expressed not only in Sertoli cells but also in germ cells throughout all the stages from spermatogonia to elongate spermatids. Tracer experiments revealed a size-selective barrier which allows small molecules ( approximately 500 Da) to get into cysts through Sertoli cells' barrier, but not larger ones (>1.9 kDa) in the stages from spermatogonia to almost mature sperm. No occludin peptides corresponding to a part of the second extracellular loop destroyed the junctional barrier, while both the peptides and antibodies significantly inhibited reaggregation of the dissociated testicular cells which was to a large extent Ca(2+)-independent. These results indicate that the second extracellular loop of occludin is involved in cell adhesion rather than in size-selective barrier in newt testis, though the possibility cannot be excluded that the peptides were not long enough to inhibit the barrier function.

Functional demonstration of the ability of a primary spermatogonium as a stem cell by tracing a single cell destiny in Xenopus laevis

In Xenopus, although primary spermatogonium (PG), the largest cell in the testis, is believed to be spermatogonial stem cell by histological observations, functional evidence has never been obtained. In the present study, we first indicated that culture of juvenile testis in a medium supplemented with follicle stimulating hormone resulted in no proliferation of PG. In this culture system, early secondary spermatogonia could undergo mitotic divisions with a concomitant decrease in their size, so that they became distinguishable in size from PG. Because the subcutaneous environment of juveniles permitted aggregates of the dissociated testicular cells to reconstruct the normal testis structure, we next inserted a genetically marked PG isolated from cultured testes into the aggregate and transplanted it subcutaneously. In this system, 73.9% of the aggregates contained a marked PG. When we observed the aggregates 12 weeks after transplantation, most aggregates (70.0%) contained marked PG that had self-renewed. Among these, fully growing aggregates contained many spermatogenic cells at the later developmental stage. These results suggested that isolated PG from the cultured testes had the ability as stem cells, and that purification of the spermatogenic stem cells became reliable in Xenopus.

Nickel nitrate: a new junction permeability tracer for the study of the blood-testis barrier

With the purpose of evaluating a new intercellular tracer, nickel-K ferrocyanide, we compared results yielded by lanthanum with information provided by nickel. This was done in the seminiferous epithelium of Holtzman rats of several postnatal ages and in a wild local seasonal breeder Galea musteloides. Tissues were studied with transmission electron microscopy and freeze-fracture replications. Nickel tracing proved to delineate cell contours more intensely and less interruptedly than lanthanum. With regard to seasonal variations in adult galea, the limits of the barrier were similar to those described in other mammals: spermatogonia, preleptotene, and leptotene spermatocytes were surrounded by the tracer in the basal compartment. The zygotenepachytenes were contained in the lumenal compartment and tracers were stopped at the inter-Sertoli cell tight junctions. During the inactive spermatogenic phase in winter, the seminiferous epithelium contained Sertoli cells and occasional germ cells, never beyond the spermatocyte stage. The tracer filled intercellular spaces, indicating that the barrier was incompetent. Some resting germ cells showed nuclear hyperchromasia, karyolysis, organelle loss, cell shrinkage, and cell fusion leading to a multinucleated cells. The inter-Sertoli tight junctions were scanty and had randomly oriented and discontinuous junctional strands. Moreover, inter-Sertoli cell gap junctions proliferated. During the active spermatogenic phase in summer, junctions were numerous. Their junctional strands were parallel to each other, and continuous.

Ultrastructure and possible function of giant crystalloids in the Sertoli cell of the juvenile and adult koala (Phascolarctos cinereus)

Sertoli cells of the juvenile and adult koala testis exhibit a unique morphology due to their large nuclei and in particular, a remarkable abundance of large cytoplasmic crystalloid inclusions. Numerous crystalloid subunits in immature Sertoli cells are aggregated into distinct clusters where by assembly and union, they form large slender crystalloids consisting of an ordered substructure of filaments and tubules. Adult Sertoli cells contain large numbers of basally-positioned crystalloids up to 60 micron in length and the observations suggest a possible mechanism for their growth from collections of tubules assembled together within membrane-bound inclusions. The trunk and adluminal cytoplasm of the adult Sertoli cell also contains crystalloids, usually single, positioned between germ cells or their excess residual cytoplasm. Following sperm release, crystalloids are not shed from the seminiferous epithelium but are retained within the apical Sertoli cell cytoplasm. Although their subsequent fate could not be determined crystalloids did not show evidence of breakdown or phagocytosis by the Sertoli cell, suggesting that they may be reutilized and possibly function to stabilize the association between Sertoli cell cytoplasm and the developing germ cells.

Development of the blood-testis barrier in the domestic fowl (Gallus domesticus)

The formation of the blood-testis barrier (BTB) in the domestic fowl was studied at the electronmicroscopic level employing lanthanum as a tracer. No effective barrier could be demonstrated in testes before puberty, although several components of the Sertoli junctional complex such as focal tight junctions and desmosomes were already existent. The time of onset of meiosis after hatching showed great individual variation and meiosis did not occur synchronously in the tubules of a given testis. An effective barrier could first be detected in tubules containing early spermatids, and in which spermatogonia and primary spermatocytes at the leptotene stage were still within the open compartment. Thus, barrier formation was correlated with the occurrence of haploid germ cells. Complete compartmentation of seminiferous tubules, leaving only spermatogonia within the open compartment, was attained in tubules containing elongated spermatids of the maturation phase. In these tubules, primary spermatocytes at the leptotene stage were situated in an intermediate compartment.