Expression of FGFR-4 mRNA in developing mouse tissues.

We have previously reported the isolation of human FGFR-4 cDNA encoding a receptor for aFGF and shown that the expression patterns of FGFR-1 through FGFR-4 mRNAs are overlapping, but distinct in human fetal tissues (Partanen et al., 1991). In order to define cells and tissues expressing FGFR-4 more accurately, we have cloned mouse FGFR-4 cDNA and used it in Northern and in situ hybridization of mouse embryonic tissues. Our results show that the 3.5 kb FGFR-4 mRNA is expressed in day 10 to full term embryos and newborn mice, with maximal expression levels during days 14-16 p.c. Adult mice express the FGFR-4 mRNA predominantly in the liver, kidney and lung. In in situ hybridization of 10-13 day p.c. mouse embryos, FGFR-4 mRNA is present primarily in tissues of mesodermal origin and in the developing lung and gut. Particularly the mesenchymal tissue in association with the first pharyngeal arch and along the prevertebrae (in developing myotomes) which will differentiate into muscle tissue express high amounts of FGFR-4 mRNA. In addition, the developing metanephros contains FGFR-4 transcripts. These results suggest that FGFR-4 may be particularly important for the differentiation of skeletal muscle and endodermally derived organs.