摘要:

AbstractThree mouse homologues of theDrosophilahomeotic geneCaudal (Cad)have been described. They are currently designatedCdx‐1,Cdx‐2, andCdx‐4.Cdx‐1and2are both strongly expressed in the adult mid‐ and hindgut, whileCdx‐1and4have been shown to be activated in the embryonic primitive streak. Using a polyclonal antibody against a fusion protein containing the amino terminal 109 amino acids of murine Cdx‐2, we here describe the topographical location of the gene product from early cleavage to 12.5 days of embryonic development. Cdx‐2 expression begins at 3.5 days and is confined to the trophectoderm, being absent from the inner cell mass. Subsequently, staining is located in the extra‐embryonic ectoderm adjacent to the epiblast, but sparing the more superficially placed polar, as well as the mural trophoblastic cells. Continuing expression in the fetal membranes involves the chorion, the allantoic bud, and, at even later stages, the spongiotrophoblast. From 8.5 days, Cdx‐2 begins to be expressed in embryonic tissues, principally (unlike Cdx‐1) in the posterior part of the gut from its earliest formation, as well as in the tail bud and in the caudal part of the neural tube.Cdx‐2is, therefore, transcribed well before any other membrane of theCadhomologue group and of the relatedHox‐C group; its expression in the extra‐embryonic membranes and in the hindgut reflects the phylogenetic relationship between the cloaca and the chorio‐allantois and suggests the possibility that homeobox genes may be involved in placental development and/or patte

ISSN:1058-8388    

DOI:10.1002/aja.1002040302

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

年代:1995

数据来源: WILEY

摘要:

AbstractVascular endothelial growth factor (VEGF) is a candidate regulator of blood vessel growth during embryonic development and in tumors. To evaluate the role of VEGF receptor‐1/flt‐1 (VEGFR1/flt‐1) in the development of the vascular system, we have characterized the murine homolog of the human flt‐1 gene and have analyzed its expression pattern during mouse embryogenesis. Receptor binding studies using transfected COS cells revealed that the murine flt‐1 gene encodes a high affinity receptor for VEGF. The apparent Kdfor VEGF binding, as determined by Scatchard analysis, was 114 pM, demonstrating that VEGFR1/flt‐1 has a higher affinity to VEGF than VEGF receptor‐2/flk‐1 (VEGFR2/flk‐1). By in situ hybridization, VEGFR1/flt‐1 was detected in the yolk sac mesoderm already at the early stages of vascular development, while the receptor ligand was expressed in the entire endoderm of 7.5‐day mouse embryos. A comparison with VEGFR2/flk‐1 showed that the two receptors shared a common expression domain in the yolk sac mesoderm, but were expressed at different sites in the ectoplacental cone. The differential expression of the two VEGF receptors persisted in the developing placenta, where VEGFR1/flt‐1 mRNA was detected in the spongiotrophoblast layer, whereas VEGFR2/flk‐1 transcripts were present in the labyrinthine layer which is the site of VEGF expression. In the embryo proper, VEGFR1/flt‐1 mRNA was specifically localized in blood vessels and capillaries of the developing organs, closely resembling the pattern of VEGFR2/flk‐1 transcript distribution. In the developing brain, the expression of VEGF receptors in the perineural capillary plexus and in capillary sprouts which have invaded the neuroectoderm correlated with endothelial cell proliferation and brain angiogenesis. The data are consistent with the hypothesis that VEGF and its receptors have an important function both in the differentiation of the endothelial lineage and in the neovascularization of developing organs, and act in a paracrine

ISSN:1058-8388    

DOI:10.1002/aja.1002040303

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe α6β1 integrin is a receptor for laminins and is present from early stages of mouse embryogenesis. In the present study determined the temporal and spatial expression of the two cytoplasmic splice variants of the α6 integrin subunit, α6A and α6B, in the early‐ and midgestation mouse postimplantation embryo using RT‐PCR, in situ hybridization, and immunofluorescence. Our results show that α6B is present in the embryo at all stages studied and is expressed before α6A. α6A expression begins in 8.5 day p.c. embryos and is initially exclusively localized to the developing heart. In 8.5 (and 9.5) day p.c. embryos α6A mRNA and protein are present in a gradient in the myocardium of the heart tube from strongest expression in the sinus venosus and in the common atrial chamber to a weakening expression along the ventricle and bulbus cordis. In 10.5 day p.c. embryos this gradient is less evident and in 12.5 day p.c. embryos α6A mRNA and protein are present in comparable amounts between atria and ventricles. Neither α6A nor α6B is present in endocardial cushion tissue. By day 12.5 p.c. α6A expression is also present in the developing epidermis, dental primordia, lens, gonads, and in a few epithelia such as those of the digestive tract. α6B expression is always much more widespread than α6A expression. For example, only α6B is present in the myotome of the somites of 9.5 day p.c. embryos, in the developing central and peripheral nervous systems, and in the nephrogenic system at all stages studied, except after the differentiation of the gonads when α6A is also present. Furthermore, α6B is the only splice variant present on endothelial cells. We also examined the distribution of the β4 integrin subunit to determine whether the α6β4 integrin was present during these stages of development. β4 protein was absent in early postimplantation stages but was present in the epidermis and digestive tract of 12.5 day p.c. embryos. These results show a differential distribution of α6A and α6B during mouse development and thus strongly suggest a different function of these splice variants during embryogenesis. Our results point to a possible role for the α6Aβ1 integrin in the development of the myocardium of the developing heart, but not in the migration of endocardial cushion cells, while α6Bβ1 could be important in the developing nephrogenic and nervous

ISSN:1058-8388    

DOI:10.1002/aja.1002040304

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

年代:1995

数据来源: WILEY

摘要:

AbstractBy utilizing myosin immunostaining, we were able to identify early rat myocardium as a thin epithelial sheet and realized that its cohesive movement toward the midline leads to the straight heart tube formation. Localization study of fibronectin mRNA and protein was, therefore, carried out to investigate its tissue origin and possible roles in facilitating mesoderm migration and heart formation. Fibronectin mRNAs were first detected throughout the mesoderm during the early primitive streak stage, suggesting that the mesoderm is the source of fibronectin. By pre‐head fold (pre‐somite) and head fold (early somite) stages, the mesoderm became largely down‐regulated for fibronectin mRNAs, while it was also at these stages when myosin‐positive myocardium formed itself into the epithelium and was subsequently folding toward the midline. Thus, there appears to be little fibronectin synthesis during and directly relevant to early heart tube formation. Later, during the early straight heart tube stage (5 somite and older), endocardium became highly positive for fibronectin mRNAs, suggesting that the endocardium is the major source of fibronectin for the cardiac jelly. Based on the results, we present a map for the early mammalian heart in which the heart is a single crescentic band lying in front of the prechordal plate. We also suggest a process for heart tube formation based on the cohesive movement of the myocardial epithelium. During heart tube formation, fibronectin protein had been deposited previously by the mesoderm and was found uniformly in the ECM and not newly produced by any adjacent tissue. The data contradict the endodermal guidance of heart migration by fibronectin gradient and suggest, instead, a permissive role for the fibronectin substrate. © 1995 wiley

ISSN:1058-8388    

DOI:10.1002/aja.1002040305

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

年代:1995

数据来源: WILEY

摘要:

AbstractLittle is currently known regarding the ontogeny of smooth muscle tissues during normal mammalian development. The α‐smooth muscle and γ‐smooth muscle isoactins have been shown to be excellent molecular markers of smooth muscle cell phenotype. This study characterizes both the temporal and spatial patterns of α‐smooth muscle and γ‐smooth muscle isoactin expression in the developing mouse. In situ analysis was performed on serial sections of whole mouse embryos on embryonic day 9, 11, 13, 15, and 17 using α‐smooth muscle and γ‐smooth muscle isoactin‐specific riboprobes. Distinct temporal and spatial patterns of α‐smooth muscle and γ‐smooth muscle isoactin gene expression were observed in the developing gastrointestinal tract, urogenital tract, respiratory tract, and vascular system. Independent expression of the α‐smooth muscle isoactin was observed during the early stages of skeletal, cardiac, and smooth muscle myogenesis as well as in a novel subset of distinct organs including the postanal component of the hindgut, allantois, and primitive placenta. The results of this study indicate that distinct cellular phenotypes are involved in smooth muscle myogenesis and suggest that organ‐specific mechanisms might exist for the initiation of smooth muscle development in vivo. In addition, the pattern of independent α‐smooth muscle isoactin expression observed in this study provides novel information regarding the early stages of hindgut and placental development, and suggests that a common functional phenotype may be associated with the early stages of skeletal, cardiac, and smooth muscle m

ISSN:1058-8388    

DOI:10.1002/aja.1002040306

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

年代:1995

数据来源: WILEY

摘要:

AbstractOverexpression of either v‐ski, or the proto‐oncogene, c‐ski, in quail embryo fibroblasts induces the expression ofmyoDandmyogenin, converting the cells to myoblasts capable of differentiating into skeletal myotubes. In transgenic mice, overexpression ofskialso influences muscle development, but in this case it effects fully formed muscle, causing hypertrophy of fast skeletal muscle fibers. In attempts to determine whether endogenous mouse c‐skiplays a role in either early muscle cell determination or late muscle cell differentiation, we analyzed mRNA expression during muscle development in mouse embryos and during in vitro terminal differentiation of skeletal myoblasts. To generate probes for these studies we cloned coding and 3′ non‐coding regions of mouse c‐ski. In situ hybridization revealed low c‐skiexpression in somites, and only detected elevated levels of mRNA in skeletal muscle beginning at about 12.5 days of gestation. Northern analysis revealed a two‐fold increase in c‐skimRNA during terminal differentiation of skeletal muscle cell lines in vitro. Our results suggest that c‐skiplays a role in terminal differentiation of skeletal muscle cells not in the determination of cells to the myogenic lineage.

ISSN:1058-8388    

DOI:10.1002/aja.1002040307

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

年代:1995

数据来源: WILEY

摘要:

AbstractHindbrain segments, rhom‐bomeres, define distinct cellular and molecular domains which furnish the ground plan for important aspects of neural and cranial development. In this study, further evidence is presented that the interfaces between rhombomeres, rhombomere boundaries, contain both cells and extracellular matrix with specialised characteristics. Cells at rhombomere boundaries show temporally and spatially distinct expression patterns of developmentally important genes. Towards the end of the developmental period when rhombomeres are present, a fan‐shaped array of cells at rhom‐bomere boundaries, that constitute the ventricular ridge, shows decreased expression of two genes (Hoxb‐1andKrox‐20), which earlier in development were expressed in all cells of specific rhombomeres. In contrast, these boundary cells showincreasedexpression of another gene,Pax‐6, which earlier in development has a rhombomere‐specific expression pattern. A specialised identity for boundary cells is further suggested by increased labelling with an anti‐vimentin antibody at rhombomere boundaries, indicating that at least some boundary cells are radial glia or glial precursors. In addition to distinct cellular properties, the extracellular domain at rhombomere boundaries is also specialised. Chondroitin sulphate proteoglycan (CSPG) immunoreactivity is increased and, as revealed by immuno‐electron microscopy, localised to extracellular spaces. CSPG is also enriched in boundaries regenerated after ablation, or boundaries generated ectopically by rhombomere transplantation. We propose that rhombomere boundaries form their characteristic morphology at the interface between groups of cells with differing molecular characteristics, representing different cell states. A specialised band of cells then develops at the interface. Both the boundary cells and extracellular matrix have characteristics which could be important in later events of neural development such as axon guidance and cell migration. © 19

ISSN:1058-8388    

DOI:10.1002/aja.1002040308

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

年代:1995

数据来源: WILEY

摘要:

AbstractThe murine homologue of the Drosophilatwistgene has been shown to be essential for head mesenchyme formation and to act as an inhibitor of muscle differentiation. This paper presents a detailed analysis of M‐twist expression patterns from day 7 post coitum (p.c.) to day 18 p.c., indicating a more general function of the M‐twist gene. At day 7 p.c., M‐twist is expressed in the mesoderm outside the primitive streak. Later M‐twist message is predominantly found in the somites, the head mesenchyme, the branchial arches, the limbs, and in the mesenchyme underneath the epidermis. Beginning at day 8 p.c., M‐twist is mainly expressed in undifferentiated cells committed to muscle and cartilage development: this exspression is consistent with a suggested role of M‐twist in inhibiting overt muscle and cartilage differentiation. However, during organogenesis, M‐twistt is expressed in several areas of mesenchyme‐epithelia interactions, suggesting additional tissue specific functions. © 1995

ISSN:1058-8388    

DOI:10.1002/aja.1002040309

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

年代:1995

数据来源: WILEY

摘要:

AbstractMorphogenetic movements during neurulation cause a tissue to change shape within the plane of the epithelium (e.g., conversion of the oval neural plate into the narrow spinal plate and the wide brain plate), cause bending out of the plane of the epithelium (e.g., raise the neural folds and curl the neural plate into a tube), or contribute to both phenomena. In this study, pieces that contain neural plate alone, epidermis alone, or both tissues (with or without underlying tissues) are cut from chick embryos and allowed to develop for up to 24 hr. Examination of histological sections through such isolates allows analysis of the formation of neural folds. When the neural plate/epidermis transition zone is disrupted, neural folds do not form. Conversely, when the transition zone remains intact, neural folds form. Neural folds form even when most of the medial neural plate and lateral epidermis has been removed, leaving only the isolated transition zone. These data indicate that the transition zone is both necessary and sufficient for the formation of neural folds. The transition zone may play a number of roles in epithelial bending including organizing, focussing, and redirecting movements that are autonomous to the neural plate or epidermis. Time‐lapse video recording, and sequential photographs allowed the documentation of such movements. Neural plate isolates exhibit autonomous rostrocaudal lengthening and mediolateral narrowing. Isolated strips of epidermis exhibit autonomous movements which, unlike wound‐healing movements, are unidirectional (mediad), and region‐specific (beginning and reaching their greatest extent in the cranial region). Isolated pieces of neural plate or epidermis remain flat instead of bending, providing further evidence that the transition zone is necessary for the formation of neural folds. © 1995 wiley‐L

ISSN:1058-8388    

DOI:10.1002/aja.1002040310

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

年代:1995

数据来源: WILEY

摘要:

AbstractTheGrggene encodes a 197 amino acid protein homologous to the amino‐terminal domain of the product of thegrouchogene of theDrosophila Enhancer of splitcomplex. Analysis with a polyclonal antisera specific for the Grg protein revealed that Grg is a 25 kd nuclear protein that can participate in specific protein‐protein interactions. A null mutation of theGrggene was constructed by gene targeting. Mice homozygous for this mutation completed embryogenesis and were born, but exhibited varying degrees of postnatal growth deficiency. No dosage‐sensitive genetic interaction was detected between theNotch1andGrggenes in mice heterozygous for aNotch1mutant allele and homozygous for theGrgnull mutation. © 1995 wiley‐L

ISSN:1058-8388    

DOI:10.1002/aja.1002040311

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

年代:1995

数据来源: WILEY