ISSN:1059-910X    

DOI:10.1002/jemt.1070200102

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

ISSN:1059-910X    

DOI:10.1002/jemt.1070200103

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractIn this review, a few well‐established axioms have been challenged while others were viewed from a new perspective. The extensive literature on the blood‐testis barrier has been scrutinized to help probe its mechanics and hopefully to promote understanding of the constant adaptation of the barrier function to germ cell development. Our principal conclusions are as follows: (1) Although the barrier zonule is topographically located at the base of the seminiferous epithelium it actually encircles the apex of the Sertoli cell. Consequently the long irregular processes specialized in holding and shaping the developing germ cells should be considered as apical appendages analogous to microvilli. (2) The development of the barrier zonule does not coincide with the appearance of a particular class of germ cells. (3) The barrier compartmentalizes the epithelium into only two cellular compartments: basal and lumenal. (4) Although the blood‐testis barrier does sequester germ cells usually considered antigenic, immunoregulator factors other than the physical barrier seem to be involved in preventing autoimmune orchitis. (5) Structurally, a Sertoli cell junctional complex is composed of occluding, gap, close, and adhering junctions. The Sertoli cell membrane segments facing germ cells are presumably included in the continuum of the Sertoli cell junctional complex that extends all over the lateral and apical Sertoli cell membranes. (6) The modulation (i.e., formation and dismantling) of the junctions in a baso‐apical direction is characteristic of the seminiferous epithelium and may be dictated by germ cell differentiation. The formation of tubulobulbar complexes and the following internalization of junction vesicles conceivably represent sequential steps of a single intricate junction elimination process that involves junction membrane segments from different cell types as part of a continual cell membrane recycling system. (7) The preferential association of junctional particles with one or the other fracture‐face reflect a response to various stimuli including seasonal breeding. Changes in the affinity of the particles are generally coincidental with cytoskeletal changes. However, changes in the cytoskeleton are not necessarily accompanied by permeability changes. The number of strands seems to reflect neither the junctional permeability nor the transepithelial resistance. The diverse orientation of the strands seems to be related to the plasticity of the Sertoli cell occluding zonule. (8) Cooperation between all constituents (Sertoli cells, myoid cells, cell substratum, and germ cells) of the epithelium seems essential for the barrier zonule to function in synchrony with the germ cell differentiation. This cooperation ensures that the Sertoli cell barrier zonule is able to continually adapt to the changing requirements of sperma

ISSN:1059-910X    

DOI:10.1002/jemt.1070200104

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractWith 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 breederGalea musteloides. Tissues were studied with transmission electron microscopy and freezefracture 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 con

ISSN:1059-910X    

DOI:10.1002/jemt.1070200105

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractWhen 20‐day‐old rats are placed on a vitamin A deficient diet (VAD) for a period of 10 weeks, the seminiferous tubules are found to contain only Sertoli cells, a few residual A0, A1spermatogonia, and preleptotene spermatocytes (PL). The type A1spermatogonia and PL spermatocytes are arrested in their G2phase. In VAD rats type A2‐A4, intermediate (In) and B spermatogonia and all types of spermatocytes (except PL spermatocytes) and spermatids are eliminated from the seminiferous tubules. Two questions were raised in this investigation: (1) Is there, in VAD rats, any correlation between a breakdown of the blood‐testis barrier (e.g., Sertoli cell tight junctions) and germ cell loss? (2) Is the disappearance of most germinal cells due to their degeneration during spermatogenesis or to a maturation depletion process resulting from an arrest of spermatogenesis at the spermatogonial stage? To investigate these questions four groups of male Sprague‐Dawley rats (20‐days old) were fed a VAD diet for 7 to 12 weeks. The testes were fixed by perfusion with 2.5% glutaraldehyde in 0.1 M sodium cacodylate containing 2% lanthanum nitrate, an electron opaque tracer used to test the patency of Sertoli cell tight junctions. The lanthanum permeated the intercellular space of the basal compartment but was arrested by normal inter—Sertoli cell tight junctions. The seminiferous epithelium showed numerous degenerating germ cells, some being internalized by Sertoli cells as membrane‐bound phagosomes. Thus, these results indicate firstly that inter—Sertoli cell tight junctions remain intact during vitamin A deficiency, and secondly that in a first phase nonviable germinal cells degenerate during spermatogenesis and their residues are actively phagocytosed by Sertoli cells followed by a second phase where the regressed state of the seminiferous epithelium is maintained by a maturation depletion condition resulting from an arrest of spermatogonial proliferation a

ISSN:1059-910X    

DOI:10.1002/jemt.1070200106

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractUsing immunohistochemical techniques both at light and electron microscopic levels, the arrangement and distribution of intermediate filaments in Sertoli cells of normal testis (in rat and human), during pre‐ and postnatal development (in rabbit, rat, and mouse) and under experimental and pathological conditions (human, rat), have been studied and related to the pertinent literature. Intermediate filaments are centered around the nucleus, where they apparently terminate in the nuclear envelope providing a perinuclear stable core area. From this area they radiate to the plasma membranes; apically often a close association with microtubules is seen. Basally, direct contacts of the filaments with focal adhesions occur, while the relationship to the different junctions of Sertoli cells is only incompletely elucidated. In the rat (not in human) a group of filaments is closely associated with the ectoplasmic specializations surrounding the head of elongating spermatids. Both in rat and human, changes in cell shape during the spermatogenic cycle are associated with a redistribution of intermediate filaments. As inferred from in vitro studies reported in the literature, these changes are at least partly hormone‐dependent (vimentin phosphorylation subsequent to FSH stimulation) and influenced by local factors (basal lamina, germ cells). Intermediate filaments, therefore, are suggested to be involved in the hormone‐dependent mechanical integration of exogenous and endogenous cell shaping forces. They permit a cycledependent compartmentation of the Sertoli cell into a perinuclear stable zone and a peripheral trafficking zone with fluctuating shape. The latter is important with respect to the germ cell‐supporting surface of the cell which seems to limit the spermatogenetic potential of the mal

ISSN:1059-910X    

DOI:10.1002/jemt.1070200107

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractThe maximum‐likelihood (ML) method for the quantitative analysis of electron‐microscopic autoradiographs has been shown to be substantially superior to the conventional crossfire (CF) method. It can generate reliable and accurate tracer concentration estimates with far fewer micrographs and produce valid estimates even at counts low enough to preclude the use of the crossfire method while eliminating the need for special ad hoc treatment of narrow membranous structures as well as the secondary verification of the tracer concentration estimates.Despite these significant advantages, the large computational requirements of the ML method has to date hampered its widespread use. In this paper, we present a new line‐integration method that allows us to reduce the computational requirements of the ML method to a point where it becomes feasible to implement it on a small computer system of the type typically available to a laboratory user of EM autoradiography. We present the complete line‐integration method for the particular case of EM autoradiography with tritium, and show how it can be adapted to other isotopes.We have constructed a software package that implements the complete maximum‐likelihood method on the IBM PC class of machines using our line‐integration method. Features of this software package which are of particular importance to the research community are device independence, which makes it usable with a large variety of currently available laboratory equipment, and easy portability of the software and data between different compu

ISSN:1059-910X    

DOI:10.1002/jemt.1070200108

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractAlcian blue (AB) and ruthenium red (RR) effects on ultrastructural preservation of the bacterial cell envelope of methanotrophs are compared. A previous successful method with RR that enhanced preservation of outer envelope layers in two representative methanotroph species is applied to other genera and species of methanotropic bacteria. Alcian blue is substituted for RR in this en bloc protocol. The effect of AB on preservation of these layers is assessed at the ultrastructural level and compared to RR for all species examined. Further, comparison with freeze etch and a fixation in the absence of either RR or AB is made. Both RR and AB are found to aid preservation and help visualize additional components of the cell envelope which are lost or minimized in a standard fixation not employing these cationic reagents. For some species, images obtained are similar between RR and AB procedures and agree with images seen by freeze etch. For other species, AB preserves extended filamentous material that is partially condensed even with the use of RR. Thus, use of AB improves the preservation of outer envelope structure in these organisms equally or more effectively than use of RR.

ISSN:1059-910X    

DOI:10.1002/jemt.1070200109

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

摘要:

AbstractWe describe a temperature‐jump device that permits time‐resolved studies of thin cryo‐transmission electron microscopy specimens. The specimen is rapidly heated to induce a change in microstructure just prior to cryo‐fixation. The apparatus consists of a xenon arc lamp equipped with a shutter controlled by timing circuitry, used in conjunction with an environmental specimen preparation chamber. The specimen is heated by exposure to focused light from the lamp, and then plunged into cryogen. Using a thermocouple constructed from an electron microscope grid, we show that temperature jumps of 30–60 K are achieved with exposure times of 150–450 milliseconds. Micrographs of dimyristoyl phosphatidylcholine (DMPC) vesicles and n‐docosane films, subjected to these exposures, shew that the specimens are still at least 20–30 K above their initial temperature when they contact the cryogen. This method could be applied to a variety of biological and chemical systems which undergo structural changes activated by a rise

ISSN:1059-910X    

DOI:10.1002/jemt.1070200110

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY

ISSN:1059-910X    

DOI:10.1002/jemt.1070200111

出版商:Wiley Subscription Services, Inc., A Wiley Company    

年代:1992

数据来源: WILEY