Cadherin mRNAs during rat embryo development in vivo and in vitro

Whole rat embryo cultures are being used in increasing numbers of laboratories to study the mechanisms by which teratogens disturb development. The development of early somite stage embryos in vitro is very similar morphologically to that in vivo, yet few biochemical comparisons have been made. The purpose of this study was to determine the steady‐state mRNA concentrations of a family of Ca²⁺ ‐dependent cell adhesion molecules, the cadherins, during rat embryonic development in vivo and in vitro. Embryos and yolk sacs were collected on days 10, 11, and 12 of gestation (in vivo); they were also obtained from day 10 embryos after growth in culture for 24 hr (day 11 in vitro) or 45 hr (day 12 in vitro). Total RNAs isolated from embryos and yolk sacs were studied by Northern blot analysis using specific cDNA probes for three cadherins, E‐cadherin, N‐cadherin, and P‐cadherin. Although E‐cadherin mRNA was detected in embryos, it was present at much higher concentrations in yolk sacs. In addition, multiple species of E‐cadherin mRNA ranging from 3.0 to 13 kb were detected. Interestingly, the concentration of the major 4.5‐kb E‐cadherin mRNA species in yolk sac after 45 hr in culture was increased 2.8‐fold over that on day 12 of gestation in vivo. Second, two species (4.3 and 3.5 kb) of N‐cadherin mRNA were detected, almost exclusively in embryos. In yolk sac, N‐cadherin mRNA was detected only after 45 hr in culture. Third, P‐cadherin mRNA was detected as a single 3.5‐kb species, mainly in embryos. Pcadherin mRNA concentrations in yolk sac after 45 hr in culture were 5.6‐fold higher than in vivo. Thus, these results demonstrate that there is a differential distribution of cadherin mRNAs in rat embryos and yolk sacs. Further, there appear to be multiple species of mRNAs for E‐cadherin and N‐cadherin. Finally, while whole embryo culture in vitro did not significantly alter the steady‐state concentrations of cadherin mRNAs in the embryo, these concentrations were dramatically increased in the yolk sac.