摘要:

AbstractTo elucidate mechanisms underlying gap junction‐mediated intercellular communication in epidermal keratinocytes, we have examined the expression of four connexin genes, Cx26, Cx31.1, Cx37, and Cx43, in fetal (embryonic day 17–18), newborn (post‐natal day 0), and mature rat skin. Northern analyses of total skin RNA showed that levels of Cx26, Cx37, and Cx43 mRNAs remained relatively constant throughtout the three developmental stages examined, whereas Cx31.1 mRNA was 15–30 times more abundant in mature skin than in fetal skin. Antibodies specifically recognizing these connexin proteins were then used in conjunction with a recently described amplification technique to immunohistochemically stain sections of paraffin embedded rat tail epidermis. We show that Cx26, Cx31.1, Cx37, and Cx43 display overlapping but distinct patterns of expression within the keratinocyte cell layers of developing and mature epidermis. © 1994 Wiley

ISSN:1058-8388    

DOI:10.1002/aja.1002000102

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

年代:1994

数据来源: WILEY

摘要:

AbstractIn this study I describe the distribution of one variant of retinoic acid receptor‐β (RAR‐β), the RAR‐β2 isoform, during the stages before organogenesis of the chick embryo. Unlike the situation in older embryos, at these stages its distribution does not differ qualitatively from that of all RAR‐β transcripts. During the presomite headfold stage, RAR‐β2 transcripts are simultaneously upregulated in two different locations. These locations define positional identities within the anlage of the chick alimentary tract and within the central nervous system (CNS). As development proceeds the transcript expression maintains its spatial restriction within those two regions. At presomite stages RAR‐β2 transcripts are enriched within the proamnion, which contains the presumptive foregut and precardiac cells; somewhat later it is present within the foregut endoderm at the site where foregut and the lateral amniocardiac vesicles fuse to form the coelom and cardiac tube. As the foregut continues its caudal extension, RAR‐β2 expression defines an anteroposterior boundary at the level of the pharynx within the alimentary tract. The second expression site of RAR‐β2 mRNA first appears within the posterior neural plate at the level where Hensen's node commences its caudal regression. This boundary lies at the border between the future rhombomeres 5 and 6 within the hindbrain. Expression of RAR‐β2 transcripts is also spatially restricted within some migrating cranial neural crest cells. The expression of RAR‐β2 in cranial neural crest cells is consistent with what is known about the mechanisms by which cranial neural crest cell fate is determined. These data support the hypothesis that retinoids may contribute to positional specification of anteroposterior body axis, and perhaps also to the formation and identity of the developing alimentary tract and heart

ISSN:1058-8388    

DOI:10.1002/aja.1002000103

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe autosomal recessive murine mutationweaver(wv) affects postnatal differentiation in at least three neuronal populations in the brain: dopamine‐containing neurons in the midbrain, and granule and Purkinje cells in the cerebellum. Neuronal populations vulnerable to the actions ofweaverdie in the midst of development. In addition, homozygous weaver males are sterile. We show by a histological analysis of epididymides and testes that the cause of male sterility in weaver is lack of sperm. The epididymides of the adult weaver mice examined were devoid of sperm, and few seminiferous tubules in the adult weaver's testes contained elongated spermatids. Most tubules were marked by moderate to severe degeneration of the seminiferous epithelium. A developmental study showed that the mutant phenotype emerged after the third postnatal week. By postnatal day 28, the development of weaver sperm lagged behind that of the wild‐type and some seminiferous tubules contained degenerating germ cells. By postnatal day 35, terminal differentiation of spermatids appeared to be arrested in many tubules and degeneration of the seminiferous epithelium was widespread. The heterozygotes were unaffected at all ages sampled. We conclude that the normal allele at the weaver locus is necessary for spermiogenesis and the maintenance of spermatogenesis. © 1994 Wiley‐Lis

ISSN:1058-8388    

DOI:10.1002/aja.1002000104

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

年代:1994

数据来源: WILEY

摘要:

AbstractDuring development, limb‐bud mesenchymal cells carry out complex spatiotemporal patterns of growth and differentiation. Tissue and organ culture facilitate analysis of environmental influences on these cell behaviors, allowing their partial dissection into exogenous and endogenous components. Two factors that complicate such in vitro analyses are the heterogeneity of the cultured cells and imprecise knowledge of culture medium composition. Limb mesenchyme comprises a heterogenous cell population with important regional differences in cell type. Dividing the limb into subregions helps limit the cellular heterogeneity and using chemically defined, serum‐free medium allays concerns about medium composition. In the present study, mesenchyme from different regions along the anteroposterior and proximodistal axes of stage 21–22 and stage 23–24 chick wing buds was grown in high‐density microtiter cultures in chemically defined and in serum‐containing medium. Fourday cultures of the various regions were compared in terms of culture morphology and the accumulation of Alcian blue‐positive cartilage matrix and DNA. The results demonstrate stage‐ and region‐dependent differences in the in vitro growth, differentiation, and responsiveness of these cells. For example, mesenchyme from the distal anterior region of the wing bud exhibited lower intrinsic chondrogenic capacity and greater responsiveness to serum than other regions. Patterns of in vitro chondrogenesis also suggest that, at the stages examined, distal wing‐bud mesenchyme may be less homogeneous than has been believed. A case is made for the suitability of serum‐free medium for future in vitro studies of chick limb‐bud mesenchyme. The results are considered in relation to the process of limb development and regional expression of pattern‐related gene

ISSN:1058-8388    

DOI:10.1002/aja.1002000105

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

年代:1994

数据来源: WILEY

摘要:

AbstractWe studied the differentiation of elastin‐producing fetal bovine chondrocytes to understand the regulatory processes associated with induction of elastin expression. Analysis of auricular elastic cartilage development in vivo indicated that differentiation of the prechondrogenic blastema to an elastogenic phenotype was preceded and accompanied by condensation of the mesenchymal cells. In addition, induction of elastin production was temporally and spatially linked to expression of type II collagen and proteoglycans. We assessed the influence of cell density on the induction of tropoelastin expression in pre‐elastogenic cells from developing ear buds. Tropoelastin expression was induced in prechondrogenic mesenchymal cells only if the cells were maintained at a high cellular density. In addition, high density culture upregulated tropoelastin expression in fully differentiated chondrocytes. Together these data suggest that high cell density facilitates cell:cell interactions that affect cell proliferation and influence tropoelastin expression. © 1994 Wiley‐Lis

ISSN:1058-8388    

DOI:10.1002/aja.1002000106

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

年代:1994

数据来源: WILEY

摘要:

AbstractSkeletal myogenesis in the chick embryo first occurs in the somite. Somites are transient, paired mesodermal structures adjacent to the neural tube. Somites form from the segmental plate mesenchyme at approximately 90‐min intervals. We identify somitic myogenic cells by using confocal microscopy to detect the muscle specific intermediate filament protein, desmin, in whole mount chick embryo preparations. The appearance of desmin in somitic cells does not occur at a constant interval after the somite has formed. The rate of chick somitic myogenic onset, as evidenced by detection of desmin, is approximately 1.5 times faster than the rate of somitogenesis (Borman and Yorde [1994] J. Histochem. Cytochem. 42:265–272). Somitic myogenesis does not appear to be directly linked to somitogenesis but instead may be regulated by some influence external to the somite. Here we have specifically addressed the issue of whether an impermeable barrier placed between the neuraxis and the somites can prevent the onset of somitic myogenesis. When tantalum foil barriers are placed medial to the caudalmost 3–5 somites of embryos having up to 20 somites total (stage 13), the predominant result is an inhibition of myogenic cells lateral to the barrier. Conversely, when the tantalum foil is placed medial to the caudal somites of an embryo having 21 somites (stage 14) or more, desmin is detected lateral to the barrier in most cases. There is a temporal influence originating in the neuraxis which plays a role in the onset of somitic myogenesis. Although the nature of this interaction between the neuraxis and the somites is not yet clear, we have defined a precise temporal location within the developing embryo at which this tissue interaction is taking place. © 1994 Wiley‐L

ISSN:1058-8388    

DOI:10.1002/aja.1002000107

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe developing neural retina expresses a set of extracellular proteases including plasminogen activator and gelatinases. Since neurites of retina cells cultured on fluorescent gelatin digest the substrate in their paths, we have suggested that the proteases are used by the tips of growing fibers to allow them to migrate within the mass of the tissue in vivo. In order to obtain further information about relationships between extracellular proteases and fiber growth, we have examined the effects of the specific inhibitors HS‐LFA (HS‐Leu‐Phenylala‐Ala, enantiomeric forms 1 and 2), bathophenanthroline sulfonate (BPS), phenylmethyl sulfonyl fluoride (PMSF), and relevant controls on the activity of retinal growth cones in vitro monitored by time lapse video microscopy. Of the inhibitors tested, only the two enantiomeric forms of HS‐LFA caused a reproducible cessation of both spike extensiion and filopodial processes at the growth cone ruffling, while control media had no effect. In some cases, the growth cone swelled and exhibited small protrusions. The behavior of growth cones was in sharp distinction to that of the cytoplasm of neural cells, and membrane ruffling of flat cells, which continued in activity throughout. Growth cone activity returned after several hours in the presence of the agent. BPS was toxic at concentrations above 2.5 mM. Below that, it had no effect. L‐cysteine, PMSF, and control media had no effect. The relevance of these results to the possible role of proteases in fiber outgrowth from retinal cells is discussed. © 1994 Wil

ISSN:1058-8388    

DOI:10.1002/aja.1002000108

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

年代:1994

数据来源: WILEY

ISSN:1058-8388    

DOI:10.1002/aja.1002000101

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

年代:1994

数据来源: WILEY