Proto-oncogene of int-3, a mouse Notch homologue, is expressed in endothelial cells during early embryogenesis.
BACKGROUND
Notch and its homologues are key regulatory receptors of the cell fate decision in various developmental processes. The int-3 oncogene was originally identified as a frequent target in Mouse Mammary Tumour Virus (MMTV)-induced mammary tumours and has been regarded as a Notch homologue, based on its similarity to the intracellular domain of Notch. Studies with int-3 transgenic mice have suggested that the int-3 transgene affects the differentiation capacity of stem cells and leads to neoplastic proliferation in epithelial cells. However, the exact nature and the in vivo expression pattern of the int-3 proto-oncogene are unknown. The function of gene products in embryogenesis is also not clear.


RESULTS
We isolated cDNA clones corresponding to the proto-oncogene of int-3 and analysed its overall structure. The predicted amino acid sequence of the int-3 proto-oncogene contains the conserved motif found in Notch family receptors. Therefore, we name Notch-4 for the int-3 proto-oncogene. However, Notch-4 has fewer EGF repeats and shows less similarity to Notch, compared with other mammalian Notch homologues. In embryogenesis, the expression of Notch-4 was detected in endothelial cells of blood vessels forming tissues such as the dorsal aorta, intersegmental vessels, yolk sac vessels, cephalic vessels, heart, vessels in branchial arches, and capillary plexuses. In these tissues, Notch-4 expression coincided with flk-1, the major regulatory gene of vasculogenesis and angiogenesis. We also found that Notch-4 expression was up-regulated in vitro during the differentiation of endothelial cells from embryonic stem cells (ES cells).


CONCLUSIONS
The endothelial cell specific expression pattern of Notch-4, as well as its structural similarity of Notch, suggest that Notch-4 is an endothelial cell specific homologue of Notch and it may play a crucial role in vasculogenesis and angiogenesis.
Shirayoshi
Y
Y
Mammalian Development Laboratory, National Institute of Genetics, Mishima, Japan. yshirayo@lab.nig.ac.jp
Yuasa
Y
Y
Suzuki
T
T
Sugaya
K
K
Kawase
E
E
Ikemura
T
T
Nakatsuji
N
N
D000595:Amino Acid Sequence; D000818:Animals; D003001:Cloning, Molecular; D018076:DNA, Complementary; D005314:Embryonic and Fetal Development / Q000235:genetics*; D018507:Gene Expression Regulation, Developmental; D008565:Membrane Proteins / Q000235:genetics*; D051379:Mice; D008813:Mice, Inbred ICR; D008822:Mice, Transgenic; D008969:Molecular Sequence Data; D011518:Proto-Oncogene Proteins / Q000235:genetics*; D011519:Proto-Oncogenes; D020794:Receptor Protein-Tyrosine Kinases / Q000235:genetics; D000074562:Receptor, Notch4; D011956:Receptors, Cell Surface; D017978:Receptors, Growth Factor / Q000235:genetics; D051880:Receptors, Notch; D040262:Receptors, Vascular Endothelial Growth Factor
D018076:DNA, Complementary; D008565:Membrane Proteins; D011518:Proto-Oncogene Proteins; D000074562:Receptor, Notch4; D011956:Receptors, Cell Surface; D017978:Receptors, Growth Factor; D051880:Receptors, Notch; C073572:Notch4 protein, mouse; D020794:Receptor Protein-Tyrosine Kinases; D040262:Receptors, Vascular Endothelial Growth Factor