摘要:

AbstractCD24 is a signal transducing molecule on the surface of most human B cells, murine immature T cells, myeloid and erythroid lineage cells. We isolated rat CD24 gene from embryonic brain cDNA library and characterized the gene expression during rat embryogenesis. Rat CD24 cDNA is homologous to murine and human CD24 gene with respect to the structure of signal peptide, N‐glycosylation sites, and possible glycosyl phosphatidylinositol (GPI) linker attaching site, suggesting that rat CD24 is a transducing glycorprotein anchoring membrane via GPI linker. In the developing embryo, in situ hybridization analyses revealed that CD24 transcript was detected in primitive ectoderm, mesoderm, and ventral endoderm of day 9 postcoitum (p.c.) embryo. In central nervous systems CD24 transcript was strongly expressed in postmitotic cells of spinal cord, hindbrain, midbrain, and forebrain from day 11 p.c. embryo to day 21 p.c. embryo but was dramatically down regulated in adult brain. Furthermore, expression was also detected in epithelium during development of non‐neural tissues, such as intestinal mucosal epithelium, nasal epithelium, ductal epithelium of salivary gland, bronchial epithelium, renal tubular epithelium, and hair follicles. In tooth development, where correct epithelium requires epithelial‐mesechymal interactions, CD24 mRNA was specifically induced in mesenchymal cells differentiating into odontoblast in dental papilla, suggesting the pivotal role of CD24 molecule in cell differentiations in vivo. We suggest that CD24 gene may encode the core peptide molecule of 31 kDa GPI linked molecule which has been known to be important in the migration of neurons on astroglial processes during development. © 1993 Wiley‐L

ISSN:1058-8388    

DOI:10.1002/aja.1001980102

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

年代:1993

数据来源: WILEY

摘要:

AbstractPlatelet‐derived growth factor (PDGF) affects proliferation and differentiation of chicken limb bud mesoderm in vitro. However, no PDGF receptor has been characterized in the chicken wing bud in vivo. In this study, we used reverse transcription PCR (rtPCR), Northern blot analysis, and Western blot analysis to identify a molecule, in the developing wing bud, which represents the chicken homolog of the PDGFα receptor. The chicken PDGFα receptor mRNA was present in both mesoderm and ectoderm and all stages of the developing limb bud examined. Cultured limb bud mesoderm also expressed the PDGFα receptor transcript. In addition, the PDGFα receptor protein was present in whole limb buds and cultured limb bud mesoderm. Expression of the PDGFα receptor in cultured mesoderm was independent of the presence of ectoderm cells. The relative sizes of both the mRNA and protein for the PDGFα receptor in the chicken limb bud were similar to mammalian counterparts. Using similar approaches, neither the mRNA nor protein representing the chicken homolog of the PDGFβ receptor was detected. These data demonstrate for the first time that a PDGFα receptor is present in the embryonic chicken limb bud and may help regulate growth and differentiation of the embryonic limb. © 1993 Wiley

ISSN:1058-8388    

DOI:10.1002/aja.1001980103

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

年代:1993

数据来源: WILEY

摘要:

AbstractCultured stellate reticulum cells isolated from rat mandibular molars respond to incubation in EGF by increasing their level of expression of TGF‐β1mRNA. Northern blots showed that incubation in EGF for 6 hours stimulated over a two‐fold increase in TGF‐β1mRNA in the cells. In contrast, indicating that TGF‐β1does not have an autocrine effect on these cells. Immunocytochemistry showed that EGF receptor was present on the surface of many but not all of the cultured stellate reticulum cells. Because EGF does stimulate premature eruption of teeth, it is possible that its effect on the stellate reticulum region of the enamel organ would be to stimulate synthesis of TGF‐β1mRNA which, in turn, could lead to increased synthesis of TGF‐β1by these cells. The cells do contain the TGF‐β1protein as revealed by immunocytostaining. The newly synthesized TGF‐β1may exert its effect on the adjacent dental follicle to either initiate the onset of the cellular events of tooth eruption or to increase the secretion of extracellular matrix proteins by the follicle for formation of the periodontal ligament.

ISSN:1058-8388    

DOI:10.1002/aja.1001980104

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

年代:1993

数据来源: WILEY

摘要:

AbstractCongenital megacolon develops in transgenic mice that overexpress the homeobox‐containing gene,Hoxa‐4. The current study was done to identify abnormlities of the terminal colon that might account for the phenotype. The terminal bowel of transgenic mice was compared with that of control and lethal spotted (ls/ls) mice, a strain in which megacolon also develops. The terminal colon of the transgenic mice contained fewer ganglia than that of controls, but was hypoganglionic, rather than aganglionic like that ofls/lsmice. The neurons present in the adult transgenic colon were sifnificantly increased in size and a subset of very large neurons(>40 μm in maximum diameter) were observed. Electron microscopic studies of young adult transgenic mice revealed that the ganglia and nerves of the myenteric plexus had the ultrastructure of extraenteric peripheral nerve rather than that of the enteric nervous system (ENS). The myenteric ganglia in the transgenic animals contained Schwann cells associated with a basal lamina that enveloped axons completely and individually, instead of glia. Although collagen is excluded from the ganglia and thin nerve fibers of the normal ENS, a collagen‐containing endoneurium surrounded each of the axon‐Schwann cell units of the abnormal nerve fibers of the transgenic mice were located in these nerve bundles rather than in ganglia. There were smooth muscle abnormalities in the terminal bowel of the transgenic mice. Wide gaps were present in the longitudinal muscle of the transgenic mice; these gaps contained ganglia that were in contact with the adventitia. These longitudinal smooth muscle cells were more irregular than those of controls and they contained fewer puncta adherens; moreover, a larger proportion of the volume of the cytoplasm of transgenic smooth muscle cells was occupied by organelles. Finally, an extensive thickening and reduplication of the basal lamina surrounding the smooth muscle cells of the muscularis mucosa was observed in the transgenic colon and resembled that found inls/lsmice. These data suggest that both smooth muscle and the innervation of the terminal bowel of neonatalHoxa‐4transgenic mice are structurally abnormal. Although some of the abnormalities seen inHoxa‐4transgenic mice are similar to those which arise inls/lsmice, the two conditions are not identical. In both animals, the data are consistent with the hypothesis that the defects arise as a result of a defective interaction between the precursors of enteric neurons and smooth muscle. © 1993 Wi

ISSN:1058-8388    

DOI:10.1002/aja.1001980105

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

年代:1993

数据来源: WILEY

摘要:

AbstractLittle is known about the cellular mechanisms that cause some cells to stop dividing while leaving neighboring cells free to continue dividing. Such events occur during development of theXenopusRetina; all cells of the embryonic eyebud are mitotic, but by stage 37 (St 37), only cells at the ciliary margin continue to proliferate as neighboring cells become post‐mitotic. The mechanisms that control these different proliferative fates remain unknown. One possibility is that total cell number regulates the initial number of proliferative cells at the ciliary margin. To test this hypothesis, we reduced the cell number by surgically removing a portion of the embryonic eyebud, including part of the prospective proliferative zone. Cell counts confirmed that the numbers of both the mitotic, undifferentiated cells and the post‐mitotic, differentiated cells were reduced following the partial ablation. A regression analysis suggested that the initial number of undifferentiated cells was a fixed proportion of the total number, but that this proportion was increased by the partial ablation. This increase occurred for all stages that the partial ablation was performed, from early optic vesicle to mid optic cup stages. The proportion of undifferentiated cells was normal in sham‐operated retinas, indicating that the increase in partially ablated retinas was induced by tissue removal and not by wound healing. Analyses of clones derived from single precursors, labeled with a fluorescent lineage tracer, indicated that the rate of proliferation was the same in partially ablated and sham‐operated retinas. Measurements of bromodeoxyuridine incorporation directly confirmed that at the ciliary margin cell division time was unchanged after partial ablation. Our observations are most consistent with the hypothesis that the proportion of undifferentiated cells was increased because cells that would have become post‐mitotic remained proliferative after the partial ablation. Furthermore, cell‐cell interactions most likely play a major role in controlling the initial number of proliferative cells in the tadpole retina. © 1993 Wil

ISSN:1058-8388    

DOI:10.1002/aja.1001980106

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

年代:1993

数据来源: WILEY

摘要:

AbstractChick embryos cultured on a curved substratum show a transient enlargement of the posterior neuropore (PN), mimicking the temporary delay of PN closure as seen in the curly tail (ct) mouse mutant (van Straaten et al. [1993] Development 117:1163–1172). In the present study the PN enlargement in the chick embryo was investigated further with a high definition light microscope (HDmic), allowing high resolution viewing of living embryos in vitro. The temporary PN enlargement appeared due to considerable reopening of the raphe of the posterior neural tube, which was followed by reclosure after several hours. The raphe was subsequently studied in detail. It appeared very irregular, with small zones of apposed, open and fused neural folds. During closure, these raphe features shifted posteriorly. A distinct fusion sequence between surface epithelium and neuroepithelium was not seen. During experimental reopeining of the raphe in vitro, small bridges temporarily arose, broke and disapeared quickly; they likely represented the first adhesion sites between the neural folds. More prominent adhesion sites partly detached, resulting in bridging filopodia‐like connections; they probably represented the first anteroposterior locations of neural fold fusion. Our observations in the living chick embryo in vitro thus show that the caudal neural tube has an irregular raphe with few adhesion sites, which can be readily reopened. As a result of the irregularity, the PN does not close zipper‐like, but button‐like by forming multiple closure sites. © 1993 Wiley

ISSN:1058-8388    

DOI:10.1002/aja.1001980107

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

年代:1993

数据来源: WILEY

ISSN:1058-8388    

DOI:10.1002/aja.1001980101

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

年代:1993

数据来源: WILEY