Otx2 and HNF3beta genetically interact in anterior patterning.

Patterning the developing nervous system in the mouse has been proposed to depend on two separate sources of signals, the anterior visceral endoderm (AVE) and the node or organizer. Mutation of the winged-helix gene HNF3beta leads to loss of the node and its derivatives, while mutation of the homeobox gene Otx2 results in loss of head structures, apparently at least partially because of defects in the AVE. To investigate the potential genetic interactions between the two signaling centers, we crossed Otx2+/- and HNF3beta+/- mice and found that very few Otx2+/-;HNF3beta+/- double heterozygous mutants survived to weaning.

The SH2 tyrosine phosphatase shp2 is required for mammalian limb development.

The tyrosine phosphatase Shp2 is recruited into tyrosine-kinase signalling pathways through binding of its two amino-terminal SH2 domains to specific phosphotyrosine motifs, concurrent with its re-localization and stimulation of phosphatase activity. Shp2 can potentiate signalling through the MAP-kinase pathway and is required during early mouse development for gastrulation. Chimaeric analysis can identify, by study of phenotypically normal embryos, tissues that tolerate mutant cells (and therefore do not require the mutated gene) or lack mutant cells (and presumably require the mutated gene during their developmental history).

Parental origin-specific expression of Mash2 is established at the time of implantation with its imprinting mechanism highly resistant to genome-wide demethylation.

The Mash2 gene encodes a basic helix-loop-helix transcription factor, which is highly expressed in diploid trophoblast cells of the postimplantation mouse embryo and is required for development of the spongiotrophoblast in order to form a functional placenta. Genomic imprinting of Mash2 has been previously reported; transcriptional inactivation of the paternal wild-type allele in heterozygotes carrying a maternal null allele results in a null-equivalent embryonic lethal phenotype. In order to study the Mash2 imprinting mechanism, we have created a new allele at this locus carrying a targeted insertion of an IRES (internal ribosome entry site)-lacZ cassette within the 3' untranslated region of the gene (referred to as "Mash2-lacZ").

Multiple developmental roles of VEGF suggested by a LacZ-tagged allele.

Vascular endothelial growth factor (VEGF) is an angiogenic factor and a potent stimulator of microvascular permeability. It is a mitogen specific for endothelial cells. The expression of VEGF and its two receptors, Flk-1 and Flt-1, is pivotal for the proper formation of blood vessels in embryogenesis as shown by gene-targeting experiments.

The transcription factor HNF3beta is required in visceral endoderm for normal primitive streak morphogenesis.

During early embryogenesis, the transcription factor HNF3beta is expressed in visceral and definitive endoderm, node, notochord and floorplate. A targeted mutation in the HNF3&bgr ; gene results in the lack of a definitive node and notochord. Furthermore, lack of HNF3beta results in failure of proper primitive streak elongation.