N-ETHYL-N-NITROSOUREA-INDUCED PRENATALLY LETHAL MUTATIONS DEFINE AT LEAST 2 COMPLEMENTATION GROUPS WITHIN THE EMBRYONIC ECTODERM DEVELOPMENT (EED) LOCUS IN MOUSE CHROMOSOME-7

Two loci [1(7)5Rn and 1(7)6Rn] defined by N-ethyl-N-nitrosourea (ENU)- induced, prenatally lethal mutations were mapped by means of trans com plementation crosses to mice carrying lethal deletions of the albino ( c) locus in Chromosome (Chr) 7. Both loci were found to map to the sub region of the Mod-2-sh-1 interval that contains the eed (embryonic ect oderm development) locus. eed has been defined by the inability of emb ryos homozygous for certain c deletions to develop beyond the early st ages of gastrulation. Evidence for at least two loci necessary for nor mal prenatal development, rather than one locus, that map within the e ed interval came from the observation that two prenatally lethal mutat ions, 3354SB [1(7)5Rn 3354SB] and 4234SB [1(7)6Rn 4234SB], could compl ement each other in trans, but could not each be complemented individu ally by c deletions known to include the eed locus. A somewhat leaky a llele of 1(7)5Rn [1(7)5Rn1989SB] was also recovered, in which hemizygo tes are often stillborn and homozygotes exhibit variable fitness and s urvival. The mapping of the loci defined by these mutations is likely to be useful for genetic, molecular, and phenotypic characterization o f the eed region, and mutations at either locus (or both loci) may con tribute to the eed phenotype.