Interaction between splotch (Sp) and curly tail (ct) mouse mutants in the embryonic development of neural tube defects.

The mouse mutations splotch (Sp) and curly tail (ct) both produce spinal neural tube defects with closely similar morphology, but achieve this by different embryonic mechanisms. To determine whether the mutants may interact during development, we constructed mice carrying both mutations. Double heterozygotes exhibited tail defects in 10% of cases, although the single heterozygotes do not express this phenotype. Backcrosses of double heterozygotes to ct/ct produced offspring with an elevated incidence of neural tube defects, both spina bifida and tail defects, compared with a control backcross in which Sp was not involved. Use of the deletion allele Sp2H permitted embryos carrying a splotch mutation to be recognised by polymerase chain reaction assay. This experiment showed that only embryos carrying Sp2H develop spina bifida in the backcross with ct/ct, suggesting that the genotype Sp2H/+, ct/ct is usually lethal around the time of birth as a result of severe disturbance of neurulation. The interaction between Sp and ct was investigated further by examining embryos in the backcross for developmental markers of the Sp/Sp and ct/ct genotypes. Sp/Sp embryos characteristically lack neural crest derivatives, such as dorsal root ganglia, and die on day 13 of gestation. Double mutant embryos from the backcross did not exhibit either of these characteristics suggesting that homozygosity for ct does not cause Sp/+ embryos to develop as if they were of genotype Sp/Sp. The angle of ventral curvature of the posterior neuropore region is enhanced in affected ct/ct embryos whereas it was found to be reduced in Sp/Sp embryos compared with their normal littermates.(ABSTRACT TRUNCATED AT 250 WORDS)