EXPRESSION OF THE NOVEL BASIC HELIX-LOOP-HELIX GENE EHAND IN NEURAL CREST DERIVATIVES AND EXTRAEMBRYONIC MEMBRANES DURING MOUSE DEVELOPMENT

We employed the yeast two-hybrid technique to screen a mouse embryo cD NA library for novel tissue-specific Class B basic helix-loop-helix (b HLH) transcription factors, which heterodimerize with the ubiquitously expressed Class A bHLH protein E12. From this screen, we cloned a nov el bHLH protein, which we named eHAND. Its low sequence identity with other bHLH family members and unique expression pattern during develop ment suggest that eHAND defines a new subclass of Class B bHLH protein s. eHAND was expressed at high levels in trophoblast cells and extraem bryonic membranes throughout development. The first site of eHAND expr ession in embryos was the heart, where it was expressed at high levels between 8.5 and 10.5 days post coitum (d.p.c.), after which transcrip t levels declined abruptly. By 13.5 d.p.c., eHAND expression in the he art was localized to regions of valve formation, Expression in other r egions of the embryo was confined to tissues with a substantial neural crest component, eHAND was expressed in the first branchial arch and its derivatives, in the sympathoadrenal lineage, and in the enteric sy stem. The expression pattern of eHAND during development is distinct f rom that of other bHLH genes and suggests that it has a role in format ion of extraembryonic tissues, heart, and neural crest derivatives. (C ) 1995 Academic Press, Inc.