DISSECTING THE ROLE OF N-MYC IN DEVELOPMENT USING A SINGLE TARGETING VECTOR TO GENERATE A SERIES OF ALLELES

The N-myc proto-oncogene is expressed in many organs of the mouse embr yo, suggesting that it has multiple functions. A null mutation leads t o mid-gestation lethality [1-4], obscuring the later roles of the gene in organogenesis. We have generated a multi-purpose gene alteration b y combining the potential for homologous and site-specific recombinati on in a single targeting vector, and using the selectable marker for n eomycin-resistance, neo, to downregulate gene activity. This allowed u s to create a series of alleles that led to different levels of N-myc expression. The phenotypes revealed a spectrum of developmental proble ms. The hypomorphic allele produced can be repaired in situ by Cre-rec ombinase-mediated DNA excision. We show here for the first time the us e of a single targeting vector to generate an allelic series. This, an d the possibility of subsequent lineage-specific or conditional allele repair in situ, represent new genome modification strategies that can be used to investigate multiple functions of a single gene, (C) Curre nt Biology Ltd ISSN 0960-9822.