EXPRESSION OF THE HELIX-LOOP-HELIX GENE ID3 DURING MURINE EMBRYONIC-DEVELOPMENT

The family of dominant-negative helix-loop-helix (dnHLH) transcription al modulators consists of four mammalian genes known to date: Id1, Id2 , Id3 (Id3 was formerly designated HLH462 or HEIR1 or HLH1R21), and Id 4. We have performed a detailed study of Id3 expression in mouse embry os in order to gain insight into the possible developmental control fu nctions of this gene and to compare its expression to that of other ma mmalian dnHLH genes. Employing RNA in situ hybridization on sectioned mouse embryos of gestational stages E9.5-17.5 and neonatal head, we ge nerally detected a high abundance of transcripts at early stages that gradually declined at most sites toward E15.5. Expression of Id3 in em bryos was detected in brain, spinal cord, olfactory system, branchial arches, limbs, sclerotome, endocardiac cushions, the outer lining of t he gut, lung, retina, the collecting system of the kidney, and in toot h anlagen. Although the abundance of mRNA decreased toward later stage s in most tissues, it remained high in teeth and kidney. This expressi on pattern suggests that Id3 functions both in undifferentiated tissue s and in organs which are in the process of differentiation. When comp ared to the expression of other dnHLH genes, it becomes obvious that t he pattern of Id3 mainly coincides with that of Id1. This may reflect a partial redundancy in gene function. Furthermore, previous experimen ts suggested a mutually exclusive expression of the proto-oncogene N-m yc an Id3. The results of the present study confirm these data. (C) 19 95 Wiley-Liss, Inc.