摘要:

AbstractNitric oxide is a novel intercellular messenger whose role in neuronal development is not yet known. As a first step toward elucidating its developmental function, we examined the pattern of NADPH diaphorase histochemical staining, an indicator of the presence of nitric oxide synthase, in the rat spinal cord at pre and postnatal ages. Some types of neurons expressed diaphorase activity transiently during development. For example, a subset of somatic motor neurons, located in the ventrolateral corner of a few caudal segments of the cervical spinal cord, were diaphorase‐positive beginning on E15, but gradually became diaphorase‐negative by birth. In contrast, other spinal neurons expressed diaphorase activity continuously from development into adulthood. Preganglionic autonomic motor neurons became diaphorase‐positive early in their development, as they were migrating toward their adult positions. Other spinal neurons, such as those in superficial dorsal horn, first expressed diaphorase relatively late in their development, after reaching their final location. The transient expression in some cell types, as well as the early expression in others, suggest that nitric oxide may have an important role(s) during development, which may differ from its functions in the adult nervous system. © 1995 Wiley‐L

ISSN:1058-8388    

DOI:10.1002/aja.1002020302

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

年代:1995

数据来源: WILEY

摘要:

AbstractElucidating how collagen fibril growth is regulated is important in determining how tissues are assembled. Fibrils are deposited as segments. The growth of these segments is an important determinant of tissue architecture, stability, and mechanical attributes. Fibril segments were isolated from developing tendons and their structure characterized. The post‐depositional changes leading to linear and lateral growth of fibrils also were examined. Segments extracted from 14‐day chicken embryo tendons had a mean length of 29 μm. The segments were asymmetric, having a short and a long tapered end. Most of the segments were centrosymmetric with respect to molecular packing. Segments extracted from 12‐to 16‐day tendons had the same structure, but mean segment length increased incrementally due to the addition of an increasingly large population of longer segments. At 17 days of development there was a precipitous increase in segment length. The morphological data indicate that the increase in length was the result of lateral associations among adjacent segments. Analysis demonstrated that this fibril growth was associated with a significant decrease in fibril associated decorin. Using immunoelectron microscopy, decorin was seen to decrease significantly at 18 days of development. When decorin content was biochemically determined, a decrease also was observed. Decorin mRNA also decreased relative to fibrillar collagen mRNA during the same period. These data support the hypothesis that a decrease in fibril‐associated decorin is necessary for fibril growth associated with tissue maturation. Growth through post‐depositional fusion allows for appositional and intercalary growth and would be essential for normal development, growth, and repair. © 1995 Wi

ISSN:1058-8388    

DOI:10.1002/aja.1002020303

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

年代:1995

数据来源: WILEY

摘要:

AbstractMyoD belongs to a family of helix‐loop‐helix proteins that control myogenic differentiation. Transfection of various non‐myogenic cell lines with MyoD transforms them into myogenic cells. In normal embryonic development MyoD is upregulated at the time when the hypaxial musculature begins to form, but its role in the function of adult muscle remains to be elucidated. In this study we examined the cellular locations of MyoD protein in normal and abnormal muscles to see whether the presence of MyoD protein is correlated with a particular cellular behaviour and to assess the usefulness of MyoD as a marker for satellite cells. Adult rats were anaesthetised and their tibialis anterior or soleus muscles either denervated, tenotomised, freeze lesioned, lesioned and denervated, or lesioned and tenotomised. At various intervals after the operations the rats were killed and their muscles removed, snap frozen, and sectioned with a cryostat along with muscles from unoperated neonatal and adult rats. The sections were processed for immunohistochemistry using a rabbit affinity‐purified antibody to recombinant MyoD. MyoD proved to be an excellent marker for active satellite cells; satellite cells in neonatal and regenerating muscles contained high levels of MyoD protein. MyoD positive cells were not observed in the muscles of old adults, in which the satellite cells are fully quiescent. MyoD immunoreactivity was rapidly lost from satellite cell nuclei after they fused into myotubes and was not detected in either sub‐synaptic or non‐synaptic nuclei of mature fibers. Denervation, and to a lesser extent tenotomy, of lesioned muscles induced expression of MyoD in myotubal nuclei. Denervation of normal muscles also upregulated MyoD in muscle fiber nuclei, an effect which was maximal after 3 days. We conclude that MyoD protein is neurally regulated in both myotubes and muscle fibers. © 1995 Wil

ISSN:1058-8388    

DOI:10.1002/aja.1002020304

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

年代:1995

数据来源: WILEY

摘要:

AbstractCyclopamine is a steroidal alkaloid which causes limb and craniofacial defects in many vertebrate species. We have used Xenopus laevis as a model system to characterize the defects caused by cyclopamine at the cellular level. The most dramatic consequence of cyclopamine treatment in theXenopusembryo is a defect in formation of craniofacial cartilage. Much of this cartilage is absent in treated animals. As in avian and mammalian species,Xenopuscraniofacial cartilage is derived primarily from cells of the cranial neural crest. Grafting experiments show that development of the cartilaginous derivatives of the cranial neural crest is impaired after cyclopamine treatment, and this is at least partially due to a direct effect on presumptive crest cells. A culture system was used to determine the cellular response to the drug. Cyclopamine did not block the initial emigration of cells from a neural plate explant. However, cell death is seen in treated cultures after 4 days. Trunk neural crest cells and transformed cell lines are resistant to cyclopamine. We therefore conclude that cyclopamine specifically causes death of cranial neural crest cells and that lethality is likely to account for the teratogenic effects of this compound. © 1995 Wiley‐Liss, I

ISSN:1058-8388    

DOI:10.1002/aja.1002020305

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

年代:1995

数据来源: WILEY

摘要:

AbstractPrevious work has shown that treatment with retinoic acid (RA) can induce malformations in regenerating pectoral and caudal fins. RA‐treated regenerates are narrower than unamputated and regenerated control fins because of a decrease in the distance between rays, and either partial or total fusion of some of them. In order to tackle the issue of how RA induces its teratogenic effects on regenerating fins, and which cell types may be specifically affected by RA, we have examined the cellular changes occurring in early regenerates following treatment with retinoids. The work presented here shows for the first time that RA induces significant apoptosis in the wound epidermis, but not in the mesenchyme, of a regenerating appendage, besides inhibiting blastema development as reported in other species. We also show that RA does not retard regeneration by inhibiting accumulation of blastemal cells, but probably by impairing their ability to migrate distal to the amputation plane. This effect is rapidly reversed by discontinuing the treatment, and within 24 hr of removing the drug, blastema development is well advanced. By this time the teratogenic effects induced by RA are already apparent. A correlation between the length of the apical ectodermal ridge (AER) and the number of digits formed has been demonstrated in developing limb buds. We therefore suggest that RA‐induced patterning abnormalities in regenerating fins are the consequence of a reduction in the size of the wound epidermis, due to increased cell death, which would affect patterning of the underlying mesenchyme. © 1995 Wiley‐Lis

ISSN:1058-8388    

DOI:10.1002/aja.1002020306

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe development of basal laminas was examined in immunohistochemical sections of chicken leg muscle spindles from embryonic day (E) 13 to 8 weeks postnatal. Fragments of basal laminas as seen with immunostaining for isoforms of laminin were already observed in E6 muscles. When clusters of intrafusal myotubes were first recognized at E13‐14, they were surrounded by basal laminas which were incomplete both in terms of coverage and molecular composition. More mature basal lamina tubes individually enclosed young myofibers at E18. Afterents made contact with myotubes, synaptic portions of basal laminas at myosensory junctions reacted strongly with antibodies against s‐laminin and chondroitin sulfate proteoglycan, while extrasynaptic portions were negative or reacted only weakly. At synaptic basal laminas of neuromuscular junctions heparin sulfate proteoglycan and s‐laminin became prominent after E16. Contrary to the early presence of basal lamina proteins around intrafusal fibers, initial deposition of basal lamina proteins in the outer spindle capsule was not recognized until E17‐18, and significant amounts were not detected until postnatal week 1. Unlike intrafusal basal laminas, capsular basal laminas developed no distinct specialized regions; however, molecular compositions of intrafusal and capsular basal laminas were similar. © 1995 Wiley

ISSN:1058-8388    

DOI:10.1002/aja.1002020307

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

年代:1995

数据来源: WILEY

摘要:

AbstractClusterin/TRPM‐2 is a sulfated glycoprotein that is expressed in many tissues. Independently cloned and isolated by several laboratories, it bears many names, and has been shown to be involved in many processes. These include cell‐cell adhesion and aggregation, inhibition of complement cytolysis, programmed cell death and apoptosis, tissue remodeling, and terminal differentiation. The hair follicle undergoes cycles of growth, regression, and rest, which involve both tissue remodeling and programmed cell death. To identify whether clusterin expression is involved in hair growth and cycling, we studied the expression of clusterin throughout the hair cycle. We demonstrate that clusterin is expressed during the growth phase of the hair cycle. We found no correlation between clusterin expression and the apoptotic regression of the hair follicle. Using immunohistochemistry we localized clusterin to the inner root sheath of the follicle. This suggests that clusterin might be involved in the morphogenesis and differentiation of the hair follicle. We propose that clusterin has a role in the maintenance of the layered structure of the hair follicle, and in the interactions between the inner root sheath and both the outer root sheath and the hair shaft. © 1995 Wiley‐Lis

ISSN:1058-8388    

DOI:10.1002/aja.1002020308

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe neurofibromatosis type 1 (NF1) gene encodes a tumor suppressor protein, termed neurofibromin, which is expressed predominantly in neurons, Schwann cells, oligodendrocytes, and leukocytes. There are at least three isoforms of neurofibromin produced by the alternative use of exons 23a and 48a. Previously we described the identification of anNF1mRNA isoform containing an additional 54 nucleotides from exon 48a (type 3NF1) in human skeletal, cardiac and smooth muscle tissues by reverse‐transcribed (RT)‐PCR. To extend our initial observations, we have produced high titer chicken IgY antibodies which specifically recognize this muscle‐specific neurofibromin isoform. AnNF1cDNA was generated containing human exon 48a sequences and expressed as a fusion protein in bacteria. The muscle‐specific neurofibromin antibodies detected this exon 48a fusion protein by Western immunoblotting. Immunoprecipitation using these type 3 neurofibromin antibodies also specifically detected a 250 kDa protein in human and rat muscle tissues. Type 3 neurofibromin was found in rat heart and muscle, but not in live, brain, kidney or spleen with levels of expression declining after postnatal day 7. Expression of totalNF1RNA during rat embryonic development was detected at high levels in E15 heart, tongue, and limb bud. In addition, using type 2 neurofibromin‐specific antibodies, the existence of a fourth isoform of neurofibromin (type 4 neurofibromin) containing both exon 23a and 48a sequences was demonstrated in rat heart muscle tissues. The identification of two muscle‐specific isoforms of neurofibromin expands our definition of this important tumor suppressor protein and suggests additional roles for neurofibromin in muscle development and differentiation. © 1995 Wil

ISSN:1058-8388    

DOI:10.1002/aja.1002020309

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

年代:1995

数据来源: WILEY

摘要:

AbstractWe have analysed the endogenous retinoids present in whole mouse embryos from day 9 to day 14 of development and in individual components of the embryo at two stages, day 10.5 and day 13, by HPLC. We can only detect two retinoids, all‐trans‐RA (tRA) and all‐trans‐retinol (t‐retinol), and t‐retinol is 5‐10‐fold in excess over tRA. We cannot detect 9‐cis‐RA or any didehydroretinoids; thus mammalian embryos seem to differ in their retinoid content from other embryos such as chick,Xenopus, and fish. The levels of tRA do not change significantly over the 6 days of development analysed, whereas t‐retinol rises sharply as the liver develops. Within the embryo, tRA is present at high levels in the developing spinal cord and at very low levels in the forebrain; indeed there is a gradient of endogenous tRA from the forebrain to the spinal cord. Other parts of the embryo had intermediate levels of tRA. When a teratogenic dose of RA was administered to day 10.5 embryos, the levels of tRA present in individual tissues of the embryo rose dramatically—from 175‐fold to 1,400‐fold—and the levels rose in all tissues not in any exclusive areas. We then determined which areas of the embryo were malformed by such a teratogenic dose. The lower jaw, palate, vertebrae, tail, and limbs were consistently abnormal, and since these areas received a dose of tRA no higher than any other it was concluded that cell‐specific factors must determine the teratogenic response of these tissues. We then considered whether cellular retinoic acid‐binding protein I or II (CRABP I or II) played any role in this response by determining their relative levels in each of the tissues analysed. There was no correlation between the presence of CRABP I and II and the distribution of administered RA. Neither was there a clear correlation in detail between the presence of CRABP I and II and the sites of teratogenesis. We therefore conclude that other factors, for example, nuclear factors, must be responsible for the teratogenic respo

ISSN:1058-8388    

DOI:10.1002/aja.1002020310

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

年代:1995

数据来源: WILEY

ISSN:1058-8388    

DOI:10.1002/aja.1002020301

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

年代:1995

数据来源: WILEY