摘要:

AbstractBone cells compose a population of cells of heterogeneous origin but restricted function with respect to matrix formation, mineralization, and resorption. The local, mesenchymal origin of the cells which form the skeleton contrasts with their extraskeletal, hemopoietic relatives under which bone resorption takes place. However, the functions of these two diverse populations are remarkably related and interdependent. Hone cell regulation, presently in its infancy, is a complicated cascade involving a plethora of local and systemic factors, including some components of the skeletal matrices and other organ systems. Thus, any understanding of bone cell regulation is a key ingredient in understanding not only the development, maintenance, and repair of the skeleton but also the prevention and treatment of skeletal disorders.

ISSN:0002-9106    

DOI:10.1002/aja.1001830102

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

年代:1988

数据来源: WILEY

摘要:

AbstractPrevious examination of dividing cells in the isthmus of the mouse pyloric antrum by using semithin (0.5‐μm‐thick) Epon sections revealed that the prophasic condensation of chromosomes began early in the DNA‐synthesizing (S) stage. In order to examine whether the same observation could be made in other proliferating cell types, the crypt base columnar ceils in mouse duodenum and the hepatocytes of the rat 48 hr after partial hepatectomy were investigated by morphologic and radioautographic techniques.When crypt base columnar cells were studied in semi‐thin Epon sections, the four phases of mitosis showed the characteristic features described by classical cytologists. Moreover, the proportion of cells in prophase and telophase was high. To relate the mitotic phases to the stages of the cell cycle, the “frequency of labeled mitoses method” provided the duration of the cell cycle, 12.3 hr, and of the S stage, 7.3 hr. From the frequency of the occurrence of mitotic phases, it was estimated that metaphase lasted 0.3 hr and anaphase 0.11 hr, in line with previous estimates. However, the durations of prophase and telophase were long, 5.9 and 1.9 hr, respectively. The whole mitotic process took over 8 hr. From the duration of prophase and cycle stages, it was calculated that 67% of the S stage was occupied by prophasic cells. In fair agreement with this estimate, 68% of the labeled cells 10 min after a3H‐thymidine injection were found to be in prophase.In regenerating hepatocytes, the morphological features and frequency of prophase and telophase cells were similar to those observed in duodenal crypt cells. While the cycle time was not measured and, therefore, the duration of cycle stages and mitotic phases could not be estimated, it is likely that their duration would be of the same order of magnitude.In conclusion, the mitotic process in duodenal crypt cells takes over 8 hr. Moreover, the crypt cells, like antral isthmal cells, show features of early prophase soon after they enter the S stag

ISSN:0002-9106    

DOI:10.1002/aja.1001830103

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

年代:1988

数据来源: WILEY

摘要:

AbstractThe development of the small intestine in the insectivoreSuncus murinuswas noted during the period from 21 days' gestation to 20 clays after birth. At 21 days of gestation, the proximal small intestine exhibited the beginning of villus formation, whereas the distal small intestine preserved the stratified epithelium. Stratified epithelium in the distal small intestine changed into a single layer by 24 days' gestation. At 26 day's gestation, each epithelial cell was immature; but by 28 days mature‐looking epithelial colls were found. The shape of the villi changed from cuboid to columnar during the same period. The connective‐tissue cores of the villi began to develop at 7 days after birth in the proximal small intestine and at 15 days after birth in the distal small intestine. Crypts appeared at 15 days after birth.Endocytosis of epithelial cells took place at 28 days of gestation. In the proximal small intestine, supranuclear vesicle clusters were observed first at birth; they began to decrease both in number and size at 10 days' gestation and then disappeared completely by 20 days after birth. In the distal small intestine, large supra‐nuclear vacuoles were observed first at 28 days of gestation. Although these vacuoles invariably were found up to 15 days after birth, they also disappeared completely by 20 days. Epithelial cells showed a structure similar to those of the adult after we

ISSN:0002-9106    

DOI:10.1002/aja.1001830104

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

年代:1988

数据来源: WILEY

摘要:

AbstractThe development and modulation of Sertoli cell junctions was studied in newborn and adult mink during the active and inactive spermatogenic phases. The techniques used were electron microscopy of freeze‐fractured replicas and thin sections of tissues infused with horseradish peroxidase as a junction permeability tracer. In the newborn, freeze‐fractured developing junctions had either spherical or fibrillar particles. In addition, Junctional domains where particles were associated preferentially with the E‐face, and others where particles were associated preferentially with the P‐face, were found developing either singly or conjointly within a given membrane segment, thus yielding a heterogeneous Junctional segment. Coincidently with the development of a tubular lumen and the establishment of a competent blood‐testis barrier, Junctional strands were composed primarily of particulate elements associated preferentially with the E‐face. In adult mink during active spermatogenesis, cell junctions were found on the entire lateral Sertoli cell plasma membrane from the basal to the luminal pole of the cell. In the basal third of the Sertoli cell, membranous segments that faced a spermatogonium or a migrating spermatocyte displayed forming tight, gap, and adherens junctions. In the middle third, abutting membrane segments localized above germ cells were involved in continuous zonules and in adherens junctions. In the apical or luminal third, the zonules were discontinuous, and the association of Junctional particles with the E‐face furrow was lost. Gap junctions increased in both size and numbers. Junctional vesicles that appeared as annular gap and tight‐junction profiles in thin sections or as hemispheres in freeze‐fracture replicas were present. Reflexive tight and gap junctions were formed through the interaction of plasma membrane segments of the same Sertoli cell. Internalized Junctional vesicles were also present in mature spermatids. During the inactive spermatogenic phase, cell junctions were localized principally in the basal third of the Sertoli cell; Junctional strands resembled those of the newborn mink. During the active spermatogenic phase, continuous zonules were competent in blocking passage of the protein tracer. During the inactive phase the blood‐testis barrier was incompetent in blocking entry of the tracer into the seminiferous epithelium. It is proposed that modulation of the Sertoli cell zonules being formed at the base and dismantled at the apex of the seminiferous epithelium follows the direction of germ cell migration and opposes the apicobasal direction of junction formation reported for most epithelia. The arrest of spermatogenesis coincides with dramatic changes in the dynamic modifications of S

ISSN:0002-9106    

DOI:10.1002/aja.1001830105

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

年代:1988

数据来源: WILEY

ISSN:0002-9106    

DOI:10.1002/aja.1001830101

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

年代:1988

数据来源: WILEY