THE EFFECT OF DAM STRAIN ON THE CRANIOFACIAL MORPHOGENESIS OF CL FR MOUSE FETUSES/

The embryo transfer technique and cephalometry were used to investigat e the effect of dam strain on intrauterine craniofacial growth and the severity of cleft lip and palate (CLP) in a CLP-susceptible CL/Fr str ain of embryos. The CL/Fr strain of embryos at early blastocyst stage was transferred to the same dam strain and to the CLP-resistant C57BL dam strain. On the 18th gestational day, each dam was laparotomized to take out the fetuses. The spontaneous incidence of CLP in the fetuses was checked and a cephalometric observation of the craniofacial compl ex of each fetus was done just after laparotomy. The dorsoventral cran iofacial size of the unaffected fetuses and the severity of CLP in the affected ones were compared between both dam strains. The following r esults were obtained: 1) The overall craniofacial sizes of the unaffec ted fetuses observed in the CL/Fr dam strain were significantly smalle r than those seen in the C578L dam strain. Those of the affected fetus es observed in the CL/Fr dam strain were smaller than those seen in th e C57BL dam strain, although the interstrain difference was not signif icant. 2) The dam strain had a highly significant effect on the cranio facial size of the unaffected fetuses, 3) The CLP frequency in the CL/ Fr dam strain was significantly higher than that in the C57BL dam stra in. 4) The severity of CLP in the affected fetuses observed in the CL/ Fr dam strain was significantly more serious than that seen in the C57 BL dam strain. These results indicated that the CLP-susceptible CL/Fr dam strain retarded the intrauterine craniofacial growth of the fetuse s and that the cleft condition in the affected fetuses observed in the CL/Fr dam strain was more seriously affected than that seen in the CL P-resistant C57BL dam strain. Thus, it can be concluded that the effec t of the dam strain played an important role in the craniofacial morph ogenesis of the CL/Fr strain of mouse fetuses that developed from the embryo transferred to the CL/Fr and C57BL dam strains along with the g enotype of embryos.