Notch4^tm1Grid

This allele carries a deletion of 1.0 kb of sequence containing exons 21 and 22, which encode part of the extracellular domain of the protein. Subsequent analysis presented in J:212472 revealed that this allele is not null as it overexpresses a truncated transcript encoding most of the extracellular domain of the receptor, including all 29 EGF-like repeats and the Lin12-Notch repeats LNR-A and LNR-B followed by 10 amino acids. The predicted protein lacks the third LNR repeat (LNR-C), heterodimerisation domain, transmembrane domain, and the intracellular domain. Northern blot analysis using a probe upstream of the targeting site containing exons 1 to 5 indicated that Notch4 transcripts are overexpressed 2.6-fold in homozygous and 1.7-fold in heterozygous neonatal lung tissue. Whole-mount immunofluorescence detected strong NOTCH4 reactivity in the developing arteries of P5 homozygous mutant retinas, with heterozygous retinas showing intermediate expression. Importantly, the truncated receptor retains the capacity to inhibit NOTCH1 signaling when expressed in cis, raising the possibility that reported phenotypes may not be due to loss of NOTCH4 function. (J:62571, J:212472)