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Research has been conducted on the role of the Notch4 gene in the intercellular signaling mechanism. The generation of the Notch4-deficient mice by gene targeting is described.

The mouse Nkx3.1 (ital) homeobox gene has roles in prostate development and in cancer. This gene is the earliest known marker of prostate epithelium in embryogenesis and is expressed after that at all stages of prostate differentiation in vivo and in tissue recombinants. NKX3.1 (ital) may be a prostate-specific tumor suppressor gene. Loss a single allele may constitute a predisposition to carcinogenesis in the prostate.

The Slug gene encodes a zinc finger protein, homologous to the product of the Drosophila Snail gene, that is implicated in the generation and migration of both mesoderm and neural crest cells in several vertebrate species. We describe here the cloning and genetic analysis of the mouse Slug (Slugh) gene. Slugh encodes a 269-amino-acid protein that shares 92% amino acid identity with the product of the chicken Slug gene. We have characterized Slugh gene expression during early mouse embryogenesis by whole mount in situ hybridization of Slugh mRNA and through detection of [Beta]-galactosidase expression from an in-frame [Slugh.sup.1acZ] allele generated through homologous recombination. Slugh expression is first detected in extraembryonic mesoderm and is later detected in many mesodermal subsets, although it is not detected in the primitive streak. In contrast to many other vertebrates, the mouse Slug gene is not expressed in premigratory neural crest cells but is expressed in migratory neural crest cells. Analysis of a targeted null mutation that deleted all Slugh coding sequences revealed that Slugh is not required for mesoderm formation or for neural crest generation, migration, or development in mice. These results indicate that neither the expression pattern nor the biological function of the Slug gene is conserved among all vertebrates. These data also raise interesting questions about the regulation of neural crest generation, which is one of the distinguishing characteristics of the vertebrate subphylum.

Jagged2 gene and Notch signaling, which is a intercellular signaling mechanism, play an important part in the limb, thymic and craniofacial development of mice. Mutant mice without a domain of the Jagged2 protein had fatal defects in craniofacial morphogenesis. The mice also had fusion in the limbs and modified thymic morphology.

The Snail gene family encodes zinc finger-containing transcriptional repressor proteins. Three members of the Snail gene family have been described in mammals, encoded by the Snai1, Snai2, and Snai3 genes. The function of the Snai1 and Snai2 genes have been studied extensively during both vertebrate embryogenesis and tumor progression and metastasis, and play critically important roles during these processes. However, little is known about the function of the Snai3 gene and protein. We describe here generation and analysis of Snai3 conditional and null mutant mice. We also generated an EYFP-tagged Snai3 null allele that accurately reflects endogenous Snai3 gene expression, with the highest levels of expression detected in thymus and skeletal muscle. Snai3 null mutant homozygous mice are viable and fertile, and exhibit no obvious phenotypic defects. These results demonstrate that Snai3 gene function is not essential for embryogenesis in mice. [ABSTRACT FROM AUTHOR]

The Notch signaling pathway is an evolutionarily conserved intercellular signaling mechanism essential for embryonic development in mammals. Mutations in the human JAGGED1 (JAG1) gene, which encodes a ligand for the Notch family of transmembrane receptors, cause the autosomal dominant disorder Alagille syndrome. We have examined the in vivo role of the mouse Jag1 gene by creating a null allele through gene targeting. Mice homozygous for the Jag1 mutation die from hemorrhage early during embryogenesis, exhibiting defects in remodeling of the embryonic and yolk sac vasculature. We mapped the Jag1 gene to mouse chromosome 2, in the vicinity of the Coloboma (Cm) deletion. Molecular and complementation analyses revealed that the Jag1 gene is functionally deleted in the Cm mutant allele. Mice heterozygous for the null Jag1 allele exhibit an eye dysmorphology similar to that of Cm[sup /+] heterozygotes, but do not exhibit other phenotypes characteristic of Cm[sup /+] mice or of humans with Alagille syndrome. These results establish the phenotype of Cm[sup /+] mice as a contiguous gene deletion syndrome and demonstrate that Jag1 is essential for remodeling of the embryonic vasculature. [ABSTRACT FROM AUTHOR]

Objective: Bone morphogenetic protein-9 (BMP9)/activin-like kinase-1 and delta-like 4 (DLL4)/Notch promote endothelial quiescence, and we aim to understand mechanistic interactions between the 2 pathways. We identify new targets that contribute to endothelial quiescence and test whether loss of Dll4(+/-) in adult vasculature alters BMP signaling., Approach and Results: Human endothelial cells respond synergistically to BMP9 and DLL4 stimulation, showing complete quiescence and induction of HEY1 and HEY2. Canonical BMP9 signaling via activin-like kinase-1-Smad1/5/9 was disrupted by inhibition of Notch signaling, even in the absence of exogenous DLL4. Similarly, DLL4 activity was suppressed when the basal activin-like kinase-1-Smad1/5/9 pathway was inhibited, showing that these pathways are interdependent. BMP9/DLL4 required induction of P27(KIP1) for quiescence, although multiple factors are involved. To understand these mechanisms, we used proteomics data to identify upregulation of thrombospondin-1, which contributes to the quiescence phenotype. To test whether Dll4 regulates BMP/Smad pathways and endothelial cell phenotype in vivo, we characterized the vasculature of Dll4(+/-) mice, analyzing endothelial cells in the lung, heart, and aorta. Together with changes in endothelial structure and vascular morphogenesis, we found that loss of Dll4 was associated with a significant upregulation of pSmad1/5/9 signaling in lung endothelial cells. Because steady-state endothelial cell proliferation rates were not different in the Dll4(+/-) mice, we propose that the upregulation of pSmad1/5/9 signaling compensates to maintain endothelial cell quiescence in these mice., Conclusions: DLL4/Notch and BMP9/activin-like kinase-1 signaling rely on each other's pathways for full activity. This represents an important mechanism of cross talk that enhances endothelial quiescence and sensitively coordinates cellular responsiveness to soluble and cell-tethered ligands., (© 2015 American Heart Association, Inc.)