摘要:

AbstractTenascin is a large glycoprotein which is expressed in a restricted pattern in the extracellular matrix (ECM) of vertebrate embryos. Tenascin interferes with cell‐fibronectin interactions in vitro, and may play a role in the control of cell migration and differentiation during development. InXenopus, tenascin immunoreactivity is first detected at the early tailbud stage in the ECM of the most anterior somite. Thereafter, it is distributed dorsally along neural crest cell migration pathways. In this paper, we report that tenascin mRNA is most abundant in dorsal mesoderm at the neurula stage and in somites at the early tailbud stage, indicating that the initial accumulation of tenascin in the ECM is due to secretion from paraxial mesoderm. To understand how tenascin expression in somitic mesoderm is controlled, we have expressedXbraand the myogenic factors XMyoD and XMyf5 in blastula animal cap tissue. The tenascin gene is activated by all three transcription factors. Interestingly, expression of tenascin mRNA, and accumulation of the protein in the ECM, can occur without formation of muscle. Our results suggest that tenascin regionalization in earlyXenopusembryos depends on tenascin RNA expression by somitic mesoderm, where it is likely to be activated by myogenic factors. © 1994 Wiley‐Liss,

ISSN:1058-8388    

DOI:10.1002/aja.1002000402

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

年代:1994

数据来源: WILEY

摘要:

AbstractPgk‐1 is an X‐linked gene encoding 3‐phosphoglycerate kinase, an enzyme necessary in every cell for glycolysis. The regulatory sequences of thePgk‐1 gene were used to drive the E. colilacZreporter gene and 2 strains of transgenic animals created with thisPgk‐lacZtransgene carried on autosomes. The levels of expression ofPgk‐1 varied from one adult tissue to another and the transgene was similarly regulated. However, in situ staining of the β‐galactosidase encoded by the transgene indicated extensive cell‐to‐cell variability in its level of expression. A reproducible subset of cells stained darkly for the transgene product. Some of these β‐galactosidase positive cells were rapidly proliferating while others appeared to be metabolically very active, suggesting that thePgk‐1 promoter is regulated so as to be more active in cells requiring high levels of glycolysis. AlthoughPgk‐1 is X‐linked and subject to X chromosome inactivation, the transgenes were not inactivated in either female somatic or male germ cells. Thus, thePgk‐1 promoter drives transgene expression in all tissues but the levels of expression are not uniform in each

ISSN:1058-8388    

DOI:10.1002/aja.1002000403

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

年代:1994

数据来源: WILEY

摘要:

AbstractWe present new evidence of the temporal and spatial expression of type II collagen in the embryonic chick heart during the very early stages of its development. In particular, we emphasize the distribution of its mRNA and protein during valve formation. Type II collagen as well as several other fibrillar collagens (types I, III, and V) are present in stage 18 endocardial cushion mesenchymal cells. At stage 23, α1(II) collagen transcripts and the cognate polypeptide co‐localize in the atrioventricular valves. As development proceeds, the relative abundance of α1(II) collagen transcripts decreases during the stages studied (stages 22 to 45; day 3.5 to day 19) as assayed by RNA blotting of extracts of whole hearts. Type II collagen protein was immunologically undetectable in stage 38 (day 12) hearts, although collagens I, III, and V persisted and localize in the valve regions, in the endothelial lining of the heart, and in the epicardium. In keeping with other observations of type II collagen expression in non‐chondrogenic regions of a variety of vertebrate embryos, the avian heart also exhibits transient type II collagen expression. © 1994 Wiley‐L

ISSN:1058-8388    

DOI:10.1002/aja.1002000404

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

年代:1994

数据来源: WILEY

摘要:

AbstractCadherins form a large family of membrane glycoproteins which mediate homophilic calcium‐dependent cell adhesion. They are thought to mediate the initial calcium‐dependent cell adhesion which precedes the plasma membrane fusion of skeletal myoblasts. Two cadherin subtypes are known to be expressed in mammalian skeletal myoblasts: muscle cadherin (M‐cadherin) and neural cadherin (N‐cadherin). In the present study we demonstrate that (1) the expression of M‐ and N‐cadherin is differentially regulated during myoblast differentiation in vitro, (2) the expression of M‐cadherin but not N‐cadherin is inhibited by 5‐bromo‐2′‐deoxyuridine (BUdR), an agent which selectively inhibits skeletal myoblast differentiation, and (3) fusion and differentiation‐competent rat L6myoblasts do not express detectable levels of N‐cadherin mRNA. In vivo, M‐cadherin mRNA was detectable exclusively in skeletal muscle. M‐cadherin mRNA levels peaked during the secondary myogenic wave in rat hindlimb muscle, becoming barely detectable in 1‐week‐old and adult rats. These observations indicate that M‐cadherin is unique in two ways: It is the first cadherin to be included in the family of skeletal muscle‐specific genes, and its shows peak leels of expression in developing skeletal muscle tissue. Taken together, these results suggest that M‐cadherin plays an important role in sk

ISSN:1058-8388    

DOI:10.1002/aja.1002000405

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe concept of the morphogenetic field has been used extensively in developmental biology. However, little is known about the mechanisms that partition these broad areas of tissue into the smaller areas which actually form the corresponding structures, and the remaining tissue. In the Mexican axolotl, the heart field forms as the anterior lateral plate mesoderm migrates over the underlying pharyngeal endoderm between stages 14 and 28. We have previously shown that both the mid‐ventral and lateral walls of the pharyngeal cavity have considerable inductive capacity at stage 14. If this inductive capability, and the competence of the mesoderm to respond, is retained between stages 14 and 28, a much broader area of mesoderm would be induced than actually participates in heart development. In this paper, we use explant cultures to establish that pharyngeal endoderm retains its inductive activity, and that both pre‐cardiac mesoderm and lateral plate mesoderm caudal to the pharyngeal cavity remain competent to respond to the induction throughout this period. We also map the specified region of the antero‐lateral mesoderm between stages 14 and 28 by placing carefully measured areas of mesoderm in culture without inductive endoderm. We found that the region capable of initiating a spontaneous beat approximately doubles in size during this period. Since the specified region is larger than the actual heart primordium, some mechanism must exist to partition “induced” mesoderm into heart‐forming and non‐heart‐forming areas. One possibility is a reaction‐diffusion mechanism involving local activation of the first mesodermal cells to contact the inductive endoderm, accompanied by production of a diffusible inhibitor that limits the extent of the heart‐forming region. ©

ISSN:1058-8388    

DOI:10.1002/aja.1002000406

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

年代:1994

数据来源: WILEY

摘要:

AbstractThe “elastic matrix” constitutes a specialized component of the extracellular matrix which confers resiliency to tissues and organs subjected to repeated deformations. The role of the elastic matrix in living organisms appears to be of key importance since diseases characterized by expression of defective inherited genes which encode components of the elastic matrix lead to premature death. While the elastic matrix of adult organs has received a great deal of attention, little is known about when it first appears in embryonic tissues or its possible role in developing organs. In the present study we have performed an immunohistochemical study of the distribution of elastin and three additional components often associated with elastic matrices in adult tissues (i.e., fibrillin, emilin, and type VI collagen) during the development of the chicken embryonic heart. The three‐dimensional arrangement of these components was established through the observation of wholemount specimens with scanning laser confocal microscopy. Our results revealed three different periods of heart development regarding the composition of the elastic matrix. Prior to stage 21 the embryonic heart lacks elastin but exhibits a matrix scaffold of fibrillin and emilin associated with the endocardium and the developing cardiac jelly. Between stages 22 and 29 the heart shows a transient elastic scaffold in the outflow tract which contains elastin, fibrillin, and emilin. Elastin‐positive fibrillar material is also observed during these stages in the base of the atrioventricular cushion adjacent to the myocardial wall. In addition, emilin‐positive material appears to be associated with the zones of formation of ventricular trabeculae. Collagen type VI was not detected during these early stages. From stage 30 to stage 40 a progressive modification of the pattern of distribution of elastin, fibrillin, emilin, and collagen type VI is observed in association with the formation of the definitive four‐chambered heart. The distribution of the elastic scaffold in the outflow tract appears to be rearranged and becomes restricted to the roots of the main arteries. Each of the components studied here is also deposited at increasing levels in the developing valvular apparatus including the valve leaflets and the chordae tendinea. The components are also present in the subendocardial space where they form aligned fibrillar tracts, an arrangement suggestive of a role in ventricular contractile function. The epicardium constitutes an additional region of elastic matrix deposition during these later stages and contains elastic, fibrillin, and collagen type VI. Finally, during the later stages the intramyocardial matrix (“myocardial interstitium”) is formed and characterized by an abundance of collagen type VI, emilin, and fibrillin but lacks elastin‐positive material. This study suggests that during cardiac development there is not a fixed composition of the so‐called “elastic matrix.” Rather, combinations of the different components of the elastic matrices appear to characterize the matrix associated with specific regions of the embryonic heart and may reflect the different tensile properties required in these regions during development. Possible roles for these specific elastic matrices during heart morphogenesis are discussed.

ISSN:1058-8388    

DOI:10.1002/aja.1002000407

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

年代:1994

数据来源: WILEY

摘要:

AbstractFatty acid binding proteins (FABP) constitute a family of small, cytosolic carriers of hydrophobic ligands. These proteins are thought to be important for lipid trafficking toward specific metabolic pathways, and are potentially important for the establishment of characteristic lipid compositions of neural tissue. In the embryonic chick retina and brain, FABP resembles the heart subtype, as determined by protein characterization and immunoblot studies. In this paper, the developmental expression and cellular localization of chick retinal FABP were examined. Results of immunoblot analysis suggest that FABP is maximally expressed around embryonic day 9 (E9) and declines thereafter. In adult retinas, FABP is barely detectable on a Western blot. Immunohistochemical staining of the retina shows light labeling on day E6 and a more intense staining throughout the retina on day E9. As the retina differentiates, labeling becomes increasingly localized. By day E18 subpopulations of ganglion cells and photoreceptor inner segments are stained, as are all photoreceptor cell bodies, most of the inner nuclear layer, and the nerve fiber layer. Staining is decreased in older retinas such that in adult animals, only light staining of the photoreceptor cell bodies is visible. The decrease in relative amount of FABP in the retina after day E9 suggests a role for FABP in the early stages of retinal differentiation. Localization in the retina is consistent with this hypothesis, as label becomes more restricted to those cells undergoing maturation at a particular developmental age. Thus, in young embryos (E6–E9), FABP immunolabeling is apparent throughout the retina, and transiently localizes at different ages (E12–E15) to plexiform and nuclear layers. Near hatching (E18–E21), the photoreceptors are in the final stages of maturation, and are the principal cells immunoreactive for FABP. In the adult retina, FABP lightly labels only the photoreceptor cells bodies; thus, we conclude that chick retinal FABP is not involved in outer segment membrane homeostasis. Instead, FABP may serve to sequester fatty acids needed for the period of neurite outgrowth which occurs as the retina ends its mitotic cycles and begins the process of synaptogenesis. © 1994 Wiley‐L

ISSN:1058-8388    

DOI:10.1002/aja.1002000408

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

年代:1994

数据来源: WILEY

摘要:

AbstractWe have examined the biological and biomechanical consequences of defective type II collagen production for fracture repair employing a genetically engineered mouse line Del1 which was generated by microinjection of a 39‐kb mouse proα1(II) collagen gene construct containing a deletion of exon 7 and intron 7 (Metsäranta et al. [1992] J. Cell Biol. 118:203–212). Standardized tibial fractures were produced in transgenic Del1 mice and their nontransgenic littermates were used as controls. The fracture callus tissues were analyzed at days 7, 9, 14, 28, and 42 using radiography, histomorphometry, biomechanical testing, and Northern analysis of mRNAs for several tissue‐specific matrix components. Deficient production of cartilage in Del1 mice resulted in reduced radiographic callus size, smaller cross‐sectional area, and impaired biomechanical properties when compared with fractures of nontransgenic control mice. The differences were most evident in 14‐day fracture calluses. Consequently mRNAs for cartilage‐specific type IX and X collagens and aggrecan were also reduced in Del1 calluses. Levels of type II collagen mRNAs were unaffected since the mutated transgene produced additional type II collagen mRNA molecules. Further abnormalities in the fracture repair process of Del1 mice were observed in callus remodeling. In the control animals a typical feature of external callus remodeling was reduction of callus size during endochondral ossification between days 14 and 28. Such reduction was not observed in the transgenic mice. Histological examination of fracture calluses suggested also a reduction in trabecular surface area, which was found to be even more pronounced in metaphyseal bone of Del1 mice. Despite these differences the biomechanical properties of the calluses in the two groups became similar by day 28 of fracture healing. The results thus suggest that reduced chondrogenesis due to the presence of mutated transgenes in Del1 mice not only causes a temporary impairment in biomechanical properties of healing fractures but also affects later stages of callus remodeling. © 1994 W

ISSN:1058-8388    

DOI:10.1002/aja.1002000409

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.1002000401

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

年代:1994

数据来源: WILEY