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PubMed1991

H beta 58, an insertional mutation affecting early postimplantation development of the mouse embryo.

The generation and analysis of insertional mutations affecting mouse embryogenesis provides a powerful method to identify new genes that function in early development. In this paper, we describe an insertional mutation that interferes with postimplantation mouse development beginning at the time of gastrulation. Embryos homozygous for the H beta 58 transgenic insertion developed normally through the early postimplantation, egg cylinder stage (day 6.5 of development). At the primitive streak stage (day 7.5), however, they began to display characteristic abnormalities, including a retardation in the growth of the embryonic ectoderm (the earliest identifiable defect), and in some cases abnormalities of the amnion and chorion. Homozygotes continued to develop for 2-3 more days, reaching the size of a normal 8.5 day embryo, and formed tissues representative of all three germ layers, including several differentiated cell types. The site of insertion was mapped, by a combination of cytogenetic and genetic methods, to chromosome 10, and it appeared to define a new genetic locus. The inserted transgene provided a probe to clone and characterize the mutant locus, as well as the corresponding wild-type locus. In addition to an insertion of 10-20 copies of the transgene, the mutant locus contained a deletion of 2-3 kb of DNA found at the wild-type locus, and possibly an insertion of mouse repetitive DNA. However, genomic sequences on both sides of the insertion site remained co-linear in the wild-type and mutant genomes, and no chromosomal abnormalities could be detected. Five single copy DNA probes spanning the insertion site were tested for their ability to hybridize to RNA from 8.5 day embryos; one of the probes (located within the region deleted from the mutant chromosome) hybridized to a 2.7 kb mRNA encoded at the H beta 58 locus, thus identifying a gene whose disruption appears to be responsible for the mutant phenotype.

Animals↗
PubMed1991

A chicken caudal homologue, CHox-cad, is expressed in the epiblast with posterior localization and in the early endodermal lineage.

CHox-cad is a chicken homeobox gene whose homeodomain is homologous to the Drosophila caudal and the murine Cdx1 genes. Based on sequence analysis of a 2.5 kb CHox-cad cDNA clone, we deduced that the primary translation product consists of 248 amino acids. Comparison between the cDNA and genomic clones revealed the presence of an intron within the CHox-cad homeodomain between amino acids 44 and 45. The onset of CHox-cad transcription correlates temporarily with the beginning of gastrulation. During primitive streak stages CHox-cad exhibits a caudally localized pattern of expression restricted to the epiblast and the primitive streak. At these stages, CHox-cad transcripts can also be detected in the definitive endoderm cells. Later in embryogenesis CHox-cad is expressed in the epithelial lining of the embryonic gut and yolk sac. After four days of chicken development, no CHox-cad transcripts could be detected. The early CHox-cad posterior expression in the germ layer undergoing gastrulation and its continuous expression in the early endodermal lineage raise the possibility of CHox-cad involvement in the establishment of the definitive endoderm.

Amino Acid Sequence↗
PubMed1992

Spatial and temporal patterns of distribution of the gap junction protein connexin43 during mouse gastrulation and organogenesis.

Connexin43 (Cx43) is a member of the family of channel-forming proteins that make up the gap junction and are believed to provide pathways for cell-cell exchange of developmental signals. We have used immunofluorescence and confocal microscopy to characterize the patterns of distribution of Cx43 in postimplantation mouse embryos representing stages of development extending through gastrulation and the major period of organogenesis [through 13.5 days post coitum (dpc)]. We find that Cx43 is expressed early after implantation by the undifferentiated, pluripotent cells of the primitive embryonic ectoderm from which all tissues of the fetus are believed to be derived. As cells become committed to particular developmental pathways, there is a progressive restriction of Cx43 to specific areas and organ systems. The patterns are complex and not limited by germ layer of origin, although there is a clear preference for expression in ectodermal and, to a lesser extent, mesodermal derivatives. Expression in lens, retina, kidney, brain, pineal and pituitary glands is initiated early in organogenesis. In heart, the first clear signal for Cx43 appears in the ventricle at about 10 dpc and is only subsequently detected in the atrium at about 13-13.5 dpc. Particularly intriguing with regard to functional implications is the high level expression observed at sites of inductive interaction; the eye lens and optic cup, the infundibulum and the apical ectodermal ridge of the limb bud.

Animals↗
PubMed1992

Fgf-4 expression during gastrulation, myogenesis, limb and tooth development in the mouse.

Fgf-4, initially isolated as a transforming gene from human tumors, is a member of the Fibroblast Growth Factor (FGF) family. It has previously been shown by northern blot hybridization analysis to be expressed in teratocarcinoma and embryonic stem cells, suggesting that it plays a role in embryonic development. We have carried out an RNA in situ hybridization analysis of Fgf-4 expression in the developing mouse embryo, from fertilization through the 14th day of gestation (E14.5). Our results show that Fgf-4 RNA is first detected at the late blastocyst stage in cells that give rise to all of the embryonic lineages (inner cell mass cells). During the early stages of gastrulation, expression becomes restricted to the primitive streak where mesoderm and definitive endoderm are formed. Expression continues in the distal (rostral) two-thirds of the streak through approx. E10, and then is detected in the tail bud, which replaces the streak as the primary source of mesoderm. Additional sites of expression are found after the three primary germ layers are established and organogenesis begins. Fgf-4 RNA is detected transiently in the branchial arch units, the somitic myotome, the apical ectodermal ridge of the developing limb bud and the tooth bud, suggesting that the gene has multiple roles during embryogenesis. These results are compared with the expression patterns of other FGF genes. Taken together, the data suggest that individual members of the gene family are expressed sequentially in developmental pathways such as mesoderm formation and myogenesis, and play a role in specific epithelial-mesenchymal interactions.

Animals↗
PubMed1992

Prenatal expression of the growth hormone (GH) receptor/binding protein in the rat: a role for GH in embryonic and fetal development?

Although fetal growth is generally considered to be independent of pituitary growth hormone (GH), it is possible that pituitary GH plays a modulatory role in organ development or that a GH-like substance of non pituitary origin may influence fetal growth through the GH receptor. Accordingly, we have used immunohistochemistry, northern blot analysis, the reverse transcriptase-polymerase chain reaction and solution hybridization to study the ontogeny of the GH receptor/binding protein (BP) from the 12-day-old embryo (E12) to the E18 rat fetus. GH receptor/BP immunoreactivity was observed in all major organ systems of the E18 rat fetus and was not preferentially associated with any germ layer derivative. A general increase in GH receptor/BP immunoreactivity was evident from E12 to E18, with a marked increase occurring between E16 and E18. Hemangioblastic tissue was, however, strongly or intensely immunoreactive at all stages of development, as was the placenta. Most noteworthy of the other tissues expressing GH receptor/BP immunoreactivity by day 18 were skeletal and smooth muscle, chondroprogenitor cells, epithelial lining cells, neuronal ganglia, ependymal cells and the adrenal cortex. In the placenta, the most prominent immunoreactivity was associated with decidual cells. Total RNA was isolated from E12 to E18 rat fetuses and adult rat liver. Northern hybridization with a 35S-labelled rat GH receptor cRNA probe revealed that 3.9 kb and 1.2 kb transcripts complementary to the rat GH receptor riboprobe are present from at least E16. The existence of GH receptor mRNA at E12 and E14 was demonstrated by the polymerase chain reaction.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1992

Expression pattern of Motch, a mouse homolog of Drosophila Notch, suggests an important role in early postimplantation mouse development.

The Notch gene of Drosophila encodes a large transmembrane protein involved in cell-cell interactions and cell fate decisions in the Drosophila embryo. To determine if a gene homologous to Drosophila Notch plays a role in early mouse development, we screened a mouse embryo cDNA library with probes from the Xenopus Notch homolog, Xotch. A partial cDNA clone encoding the mouse Notch homolog, which we have termed Motch, was used to analyze expression of the Motch gene. Motch transcripts were detected in a wide variety of adult tissues, which included derivatives of all three germ layers. Differentiation of P19 embryonal carcinoma cells into neuronal cell types resulted in increased expression of Motch RNA. In the postimplantation mouse embryo Motch transcripts were first detected in mesoderm at 7.5 days post coitum (dpc). By 8.5 dpc, transcript levels were highest in presomitic mesoderm, mesenchyme and endothelial cells, while much lower levels were detected in neuroepithelium. In contrast, at 9.5 dpc, neuroepithelium was a major site of Motch expression. Transcripts were also abundant in cell types derived from neural crest. These data suggest that the Motch gene plays multiple roles in patterning and differentiation of the early postimplantation mouse embryo.

Amino Acid Sequence↗
PubMed1992

The function of the neurogenic genes during epithelial development in the Drosophila embryo.

The complex embryonic phenotype of the six neurogenic mutations Notch, mastermind, big brain, Delta, Enhancer of split and neuralized was analyzed by using different antibodies and PlacZ markers, which allowed us to label most of the known embryonic tissues. Our results demonstrate that all of the neurogenic mutants show abnormalities in many different organs derived from all three germ layers. Defects caused by the neurogenic mutations in ectodermally derived tissues fell into two categories. First, all cell types that delaminate from the ectoderm (neuroblasts, sensory neurons, peripheral glia cells and oenocytes) are increased in number. Secondly, ectodermal tissues that in the wild type form epithelial structures lose their epithelial phenotype and dissociate (optic lobe, stomatogastric nervous system) or show significant differentiative abnormalities (trachea, Malpighian tubules and salivary gland). Abnormalities in tissues derived from the mesoderm were observed in all six neurogenic mutations. Most importantly, somatic myoblasts do not fuse and/or form an aberrant muscle pattern. Cardioblasts (which form the embryonic heart) are increased in number and show differentiative abnormalities; other mesodermal cell types (fat body, pericardial cells) are significantly decreased. The development of the endoderm (midgut rudiments) is disrupted in most of the neurogenic mutations (Notch, Delta, Enhancer of split and neuralized) during at least two stages. Defects occur as early as during gastrulation when the invaginating midgut rudiments prematurely lose their epithelial characteristics. Later, the transition of the midgut rudiments to form the midgut epithelium does not occur. In addition, the number of adult midgut precursor cells that segregate from the midgut rudiments is strongly increased. We propose that, at least in the ectodermally and endodermally derived tissues, neurogenic gene function is primarily involved in interactions among cells that need to acquire or to maintain an epithelial phenotype.

Animals↗
PubMed1992

Pintallavis, a gene expressed in the organizer and midline cells of frog embryos: involvement in the development of the neural axis.

We have identified a novel frog gene, Pintallavis (the Catalan for lipstick), that is related to the fly fork head and rat HNF-3 genes. Pintallavis is expressed in the organizer region of gastrula embryos as a direct zygotic response to dorsal mesodermal induction. Subsequently, Pintallavis is expressed in axial midline cells of all three germ layers. In axial mesoderm expression is graded with highest levels posteriorly. Midline neural plate cells that give rise to the floor plate transiently express Pintallavis, apparently in response to induction by the notochord. Overexpression of Pintallavis perturbs the development of the neural axis, suppressing the differentiation of anterior and dorsal neural cell types but causing an expansion of the posterior neural tube. Our results suggest that Pintallavis functions in the induction and patterning of the neural axis.

Amino Acid Sequence↗
PubMed1993

Implications of dynamic patterns of Delta and Notch expression for cellular interactions during Drosophila development.

Delta and Notch function are required for cell fate specification in numerous tissues during embryonic and postembryonic Drosophila development. Delta is expressed by all members of interacting cell populations within which fates are being specified and is subsequently down-regulated as cells stably adopt particular fates. Multiphasic expression in the derivatives of many germ layers implies successive requirements for Delta function in a number of tissues. At the cellular level, Delta and Notch expression are generally coincident within developing tissues. At the subcellular level, Delta and Notch are localized in apparent endocytic vesicles during down-regulation from the surfaces of interacting cells, implying an interaction consistent with their proposed roles as signal and receptor in cellular interactions during development.

Animals↗
PubMed1993

The formation and maintenance of the definitive endoderm lineage in the mouse: involvement of HNF3/forkhead proteins.

Little is known about genes that govern the development of the definitive endoderm in mammals; this germ layer gives rise to the intestinal epithelium and various other cell types, such as hepatocytes, derived from the gut. The discovery that the rat hepatocyte transcription factor HNF3 is similar to the Drosophila forkhead gene, which plays a critical role in gut development in the fly, led us to isolate genes containing the HNF3/forkhead (HFH) domain that are expressed in mouse endoderm development. We recovered mouse HNF3 beta from an embryo cDNA library and found that the gene is first expressed in the anterior portion of the primitive streak at the onset of gastrulation, in a region where definitive endoderm first arises. Its expression persists in axial structures derived from the mouse equivalent of Hensen's node, namely definitive endoderm and notochord, and in the ventral region of the developing neural tube. Expression of the highly related gene, HNF3 alpha, appears to initiate later than HNF3 beta and is first seen in midline endoderm cells. Expression subsequently appears in notochord, ventral neural tube, and gut endoderm in patterns similar to HNF3 beta. Microscale DNA binding assays show that HNF3 proteins are detectable in the midgut at 9.5 days p.c. At later stages HNF3 mRNAs and protein are expressed strongly in endoderm-derived tissues such as the liver. HNF3 is also the only known hepatocyte-enriched transcription factor present in a highly de-differentiated liver cell line that retains the capacity to redifferentiate to the hepatic phenotype. Taken together, these studies suggest that HNF3 alpha and HNF3 beta are involved in both the initiation and maintenance of the endodermal lineage. We also discovered a novel HFH-containing gene, HFH-E5.1, that is expressed transiently in posterior ectoderm and mesoderm at the primitive streak stage, and later predominantly in the neural tube. HFH-E5.1 is highly similar in structure and expression profile to the Drosophila HFH gene FD4, suggesting that HFH family members have different, evolutionarily conserved roles in development.

Amino Acid Sequence↗
PubMed1995

wingless is required for the formation of a subset of muscle founder cells during Drosophila embryogenesis.

The final pattern of the Drosophila larval body wall muscles depends critically on the prior segregation of muscle founder cells. We would like to understand the underlying molecular mechanisms which ensure the precise allocation and placement of these muscle founder cells. We have begun our analysis by examining the role of the segment polarity genes, known to be involved in the patterning of the ectoderm. Mutations in only one member of this class, wingless (wg), lead to the complete loss of a subset of muscle founder cells characterised by the expression of S59. Using the GAL4-targetted expression system, we find that Wingless, a secreted glycoprotein and well characterized signalling molecule, acts directly on the mesoderm to ensure the formation of S59-expressing founder cells. Moreover, we present evidence that Wg can signal across germ layers and that, in the wild-type embryo, Wg from the ectoderm could constitute an inductive signal for the initiation of the development of a subset of somatic muscles.

Animals↗
PubMed1995

The somatic-visceral subdivision of the embryonic mesoderm is initiated by dorsal gradient thresholds in Drosophila.

The maternal dorsal regulatory gradient initiates the differentiation of the mesoderm, neuroectoderm and dorsal ectoderm in the early Drosophila embryo. Two primary dorsal target genes, snail (sna) and decapentaplegic (dpp), define the limits of the presumptive mesoderm and dorsal ectoderm, respectively. Normally, the sna expression pattern encompasses 18-20 cells in ventral and ventrolateral regions. Here we show that narrowing the sna pattern results in fewer invaginated cells. As a result, the mesoderm fails to extend into lateral regions so that fewer cells come into contact with dpp-expressing regions of the dorsal ectoderm. This leads to a substantial reduction in visceral and cardiac tissues, consistent with recent studies suggesting that dpp induces lateral mesoderm. These results also suggest that the dorsal regulatory gradient defines the limits of inductive interactions between germ layers after gastrulation. We discuss the parallels between the subdivision of the mesoderm and dorsal ectoderm.

Animals↗
PubMed1995

Dynamics of thin filopodia during sea urchin gastrulation.

At gastrulation in the sea urchin embryo, a dramatic rearrangement of cells establishes the three germ layers of the organism. Experiments have revealed a number of cell interactions at this stage that transfer patterning information from cell to cell. Of particular significance, primary mesenchyme cells, which are responsible for production of the embryonic skeleton, have been shown to obtain extensive positional information from the embryonic ectoderm. In the present study, high resolution Nomarski imaging reveals the presence of very thin filopodia (02-0.4 micron in diameter) extending from primary mesenchyme cells as well as from ectodermal and secondary mesenchyme cells. These thin filopodia sometimes extend to more than 80 microns in length and show average growth and retraction rates of nearly 10 microns/minute. The filopodia are highly dynamic, rapidly changing from extension to resorption; frequently, the resorption changes to resumption of assembly. The behavior, location and timing of active thin filopodial movements does not correlate with cell locomotion; instead, there is a strong correlation suggesting their involvement in cell-cell interactions associated with signaling and patterning at gastrulation. Nickel-treatment, which is known to create a patterning defect in skeletogenesis due to alterations in the ectoderm, alters the normal position-dependent differences in the thin filopodia. The effect is present in recombinant embryos in which the ectoderm alone was treated with nickel, and is absent in recombinant embryos in which only the primary mesenchyme cells were treated, suggesting that the filopodial length is substratum dependent rather than being primary mesenchyme cell autonomous. The thin filopodia provide a means by which cells can contact others several cell diameters away, suggesting that some of the signaling previously thought to be mediated by diffusible signals may instead by the result of direct receptor-ligand interactions between cell membranes.

Animals↗
PubMed1996

A fate map of the vegetal plate of the sea urchin (Lytechinus variegatus) mesenchyme blastula.

Previous lineage tracing experiments have shown that the vegetal blastomers of cleavage stage embryos give rise to all the mesoderm and endoderm of the sea urchin larva. In these studies, vegetal blastomers were labeled no later than the sixth cleavage division (60-64 cell stage). In an earlier study we showed that single cells in the vegetal plate of the blastula stage Lytechinus variegatus embryo could be labeled in situ with the fluorescent, lipophilic dye, DiI(C18), and that cells labeled in the central region of the vegetal plate of the mesenchyme blastula primarily gave rise to homogeneous clones consisting of a single secondary mesenchyme cell (SMC) type (Ruffins and Ettensohn (1993) Dev. Biol. 160, 285-288). Our clonal labeling showed that a detailed fate map could be generated using the DiI(C18) labeling technique. Such a fate map could provide information about the spatial relationships between the precursors of specific mesodermal and endodermal cell types and information concerning the movements of these cells during gastrulation and later embryogenesis. We have used this method to construct the first detailed fate map of the vegetal plate of the sea urchin embryo. Ours is a latitudinal map; mapping from the plate center, where the mesodermal precursors reside, through the region which contains the endodermal precursors and across the ectodermal boundary. We found that the precursors of certain SMC types are segregated in the mesenchyme blastula stage vegetal plate and that prospective germ layers reside within specific boundaries. To determine whether the vegetal plate is radially symmetrical with respect to mesodermal cell fates, single blastomeres of four cell stage embryos were injected with lysyl-rhodamine dextran (LRD). The resulting ectodermal labeling patterns were classified and correlated with the SMC types labeled. This analysis indicates that the dorsal and ventral blastomers do not contribute equally to SMC derivatives in L. variegatus.

Animals↗
PubMed1996

Autonomous and nonautonomous Notch functions for embryonic muscle and epidermis development in Drosophila.

The Notch (N) gene encodes a cell signaling protein that mediates neuronal and epidermal determination in Drosophila embryos. N also regulates several aspects of myogenic development; embryos lacking N function have too many muscle founder cells and fail to properly differentiate somatic muscle. To identify cell-autonomous requirements for Notch function during muscle development, we expressed a Notch minigene in the mesoderm, but not in the ectoderm, of amorphic N-embryos. In these embryos, muscle founder hypertrophy is rescued, indicating that Notch is autonomously required by mesoderm cells to regulate the proper number of muscle founders. However, somatic muscle differentiation is only partially normalized, suggesting that Notch is also required in the ectoderm for proper muscle development. Additionally, mesodermal expression of Notch partially rescues epidermal development in overlying neurogenic ectoderm. This is unexpected, since previous studies suggest that Notch is autonomously required by proneural ectoderm cells for epidermal development. Mesodermal expression of a truncated Notch protein lacking the extracellular domain does not rescue ventral epidermis, suggesting that the extra-cellular domain of Notch can non-autonomously rescue epidermal development across germ layers.

Animals↗
PubMed1996

TGF-beta signals and a pattern in Xenopus laevis endodermal development.

We have analyzed two gene products expressed in the early endoderm of Xenopus laevis: Xlhbox-8, a pancreas-specific transcription factor and intestinal fatty acid binding protein (IFABP), a marker of small intestinal epithelium. Expression of the pancreas marker relies on cell signaling mediated by both the TGF-beta and FGF classes of secreted peptide growth factors, whereas, expression of the more posterior small intestinal marker does not. Endodermal explants devoid of mesoderm express both markers in a regionalized manner. Cortical rotation is required for the expression of the more anterior marker, Xlhbox-8, but not for the small intestinal marker, IFABP. These findings suggest that endodermal patterning is dependent, in part, on the same events and signals known to play important roles in mesodermal development. Furthermore, inhibition of TGF-beta signaling in the endoderm leads to ectopic expression of both mesodermal and ectodermal markers, suggesting the TGF-beta signaling may play a general role in the segregation of the three embryonic germ layers.

Animals↗
PubMed1997

Establishment of the axis in chordates: facts and speculations.

A master plan for the early development of all chordates is proposed. The radial symmetry of the chordate ovum is changed at or after fertilization into a bilateral symmetry by an external signal. Until now two alternative triggers, sperm entry and gravity, have been demonstrated. It is suggested that a correlation exists between the amount of yolk stored in the egg and the mechanism used for axialization. The speed at which axialization of the embryo proper takes place depends on the translocation speed of maternal determinants from the vegetal pole towards the future dorsoposterior side of the embryo. On arrival at their destination, the activated determinants form, in all chordates, an induction center homologous to the amphibian 'Nieuwkoop center', which induces the formation of 'Spemann's organizer'. On the basis of the above general scenario, a revision is proposed of the staging of some embryonic types, as well as of the identification of germ layer and the spaces between them.

Amnion↗
PubMed1997

Developmental potency of the murine allantois.

The murine allantois is the future umbilical component of the placenta. The base of the allantois is also thought to contain the future germ line. We have examined the fate and developmental potency of cells within the murine allantois during gastrulation. lacZ-expressing headfold-stage allantoises (approximately 8.0 days postcoitum; dpc) were subdivided into three proximodistal regions and transplanted into three sites in synchronous non-transgenic host embryos: the primitive streak at the level of prospective paraxial mesoderm, the primitive streak at the level of lateral plate mesoderm, and the base of the allantois. After 23 hours in culture, operated conceptuses were examined histologically for contribution of donor allantoic cells to the conceptus. None of the allantoic regions contributed to paraxial mesoderm when placed into the fetus, but all three colonized the endothelium and adjacent mesenchyme of the dorsal aorta. The mid-region was most efficient at colonizing endothelium, whereas the base was the only allantoic region to exhibit relative pluripotency, colonizing several derivatives of all three primary germ layers. Differences in the state of differentiation along the proximodistal axis of the allantois were further borne out when the three allantoic regions were placed into the base of the allantois of host conceptuses. Striking differences were observed in final position along the proximodistal axis of the host allantois. Most grafted cells translocated distally from the base; however, basal donor allantoic cells translocated typically only as far as the host's mid-region, whereas donor allantoic tip cells typically returned to the tip, often colonizing the chorioallantoic fusion junction. Together, our data reveal that the headfold-stage allantois may contain a proximodistal gradient of differentiation, and raise intriguing questions about how this gradient was established and the role it plays in umbilical vasculogenesis.

Allantois↗