GENE-EXPRESSION OF BONE-MATRIX PROTEINS AND ENDOTHELIN RECEPTORS IN ENDOTHELIN-1-DEFICIENT MICE REVEALED BY IN-SITU HYBRIDIZATION

Endothelin-1 (ET-1) was first found as a vasoconstrictor protein excre ted by vascular endothelial cells, but recently ET-1 has been consider ed to have widespread functions that include regulation of osteochondr ogenic metabolism, We analyzed sections of head regions in ET-1 knocko ut mice that are known to have abnormalities in pharyngeal arch-derive d tissues and found that there was severe hypoplasia in facial bones, The hypoplasia suggests that the matrix mineralization system of facia l bones is disrupted in ET-1(-/-)homozygous mice, To elucidate,whether osteogenic cells in facial bones are the targets for ET-1 and whether expression of bone matrix genes are modulated by ET-1, we examined ge ne expression of ET-1 receptors, ETA and ETB, and that of the bone mat rix proteins, osteonectin (ON) and osteopontin (OF), both in the head regions of ET-1(+/-)heterozygous and ET-1(-/-)homozygous mice by means of in situ hybridization, Different patterns of expression between ET A and ETB mRNAs,were observed in both groups, In 18.5 days post coitus fetuses, ETA mRNA was most strongly expressed in osteogenic cells alo ng craniofacial bones, but ETB mRNA was most strongly expressed in tru nks of trigeminal nerve, This finding suggests that ET-1 may modulate osteogenic cells through ETA receptor but not through ETB receptor, Th e expression patterns of ETA, OF, and ON mRNAs were distinct between t he two groups, In the lower jaw of ET-1(+/-)heterozygous mice, the ETA , ON, and OP mRNA positive cells were scattered in the inner and outer regions of the thick bone matrix, but in ET-1(-/-)homozygous mice, ce lls containing those mRNAs were located close to each other at the sur face of thin bone matrix, However, cellular expression of ON and OP mR NAs in osteogenic cells of ET-1(-/-)homozygous mice was not suppressed as compared with ET-1(+/-)heterozygous mice, We conclude that ET-1 ma y regulate proliferation and migration of osteogenic cells in the maxi llofacial region, rather than modulating the expression level of ON an d OP mRNAs.