Expression trapping: Identification of novel genes expressed in hematopoietic and endothelial lineages by gene trapping in ES cells

We have developed a large-scale, expression-based gene trap strategy to per form genome-wide functional analysis of the murine hematopoietic and vascul ar systems. Using two different gene trap vectors, we have isolated embryon ic stem (ES) cell clones containing lacZ reporter gene insertions in genes expressed in blood island and vascular cells, muscle, stromal cells, and un known cell types. Of 79 clones demonstrating specific expression patterns, 49% and 16% were preferentially expressed in blood islands and/or the vascu lature, respectively. The majority of ES clones that expressed lacZ in bloo d islands also expressed lacZ upon differentiation into hematopoietic cells on OP9 stromal layers. Importantly, the in vivo expression of the lacZ fus ion products accurately recapitulated the observed in vitro expression patt erns. Expression and sequence analysis of representative clones suggest tha t this approach will be useful for identifying and mutating novel genes exp ressed in the developing hematopoietic and vascular systems. (C) 1998 by Th e American Society of Hematology.