NOVEL MOUSE REPETITIVE ELEMENT STRUCTURES IN AN EMBRYONAL CARCINOMA MUTANT-CELL LINE

A mutant embryonal carcinoma (EC) cell line, NR1-6, has been isolated subsequent to infection with a retroviral insert containing a neomycin resistance cassette (Neo(r)) (1). This variant cell line has only a s ingle insertion site, but is unique in its morphology, tumorigenicity, and differentiative potential (2). In order to understand the exact n ature of the mutational event, we have sequenced the regions immediate ly flanking the insertion site (encompassing over 18 kb). Searches for homology in GenBank using the GCG and Blast programs have revealed ho mology to only a few small conserved regions (4 B1 repetitive elements approximately 150 bp long and a CA/GT dinucleotide repeat). Interesti ngly, B1 repetitive elements have been reported to play a role in germ cell differentiation. One of these elements is immediately 5' upstrea m of the insertion site and it appears as if the retroviral insertion may be responsible for activating or repressing the expression of this element. The CA/GT repeat has not yet been mapped within the mouse ge nome. Thus, we have identified a novel mouse locus which apparently re gulates a number of cellular phenotypes.