Physical localization of the mesoderm development (mesd) functional region

The mesoderm development (mesd) functional interval is essential for primitive streak formation and mesoderm induction. Mesd is defined by overlapping albino (c) deletions on chromosome 7. We have constructed a bacterial artificial chromosome (BAC) contig that spans the mesd functional region. BAC end-sequence identifies three segments that recognize novel expressed sequences. Localization of the proximal breakpoints from Del(7)Tyr(c-3YPSd) and Del(7)Tyr(c-112K) within the contig defines a deletion interval of 310-350 kb that is essential for mesd function. Importantly, using BAC transgene rescue, we define a 75-kb mesd critical region containing at least one expressed sequence.