FEMALE PREDISPOSITION TO CRANIAL NEURAL-TUBE DEFECTS IS NOT BECAUSE OF A DIFFERENCE BETWEEN THE SEXES IN THE RATE OF EMBRYONIC GROWTH OR DEVELOPMENT DURING NEURULATION

The susceptibility of females to anencephaly is well established and h as been suggested to result from a slower rate of growth and developme nt of female embryos during cranial neurulation. We have tested this h ypothesis by measuring the rates of growth and development, both in ut ero and in vitro, of male and female embryos of the curly tail (ct) mu tant mouse strain, in which cranial neural tube defects occur primaril y in females. Embryonic growth was assessed by increase in protein con tent, while development progression was judged from increase in somite number and morphological score. Embryos were sexed by use of the poly merase chain reaction to amplify a DNA sequence specific to the Y chro mosome, and by sex chromatin analysis. We find that, during neurulatio n (between 8.5 and 10.5 days of gestation), males are advanced in grow th and development relative to their female litter mates, but that the rates of growth and development do not differ between the sexes durin g this period. We conclude that rate of embryonic growth and developme nt is unlikely to determine susceptibility to cranial neural tube defe cts. It seems more likely that male and female embryos differ in some specific aspect(s) of the neurulation process that increases the susce ptibility of females to development of anencephaly.