ISOLATED MAXILLARY BENDING IN CL FR STRAIN MICE - OBSERVATION OF CRANIOFACIAL DEFORMITY AND INHERITANCE PATTERN/

Objective: The CL/Fr mouse, known as a strain with spontaneous cleft l ip and/or palate (CL/P), has been used as an animal model to investiga te etiology in CL/P. Method: We examined a facial asymmetry mutant dis covered in a CL/Fr mouse colony that was not associated with CL/P and was shown to be inheritable in subsequent generations. Facial asymmetr y became apparent with postnatal growth, whereas it was not detectable at birth, and was termed ''maxillary bending'' (MB) based on the char acteristic bending of the maxilla. Results: As a result of selective b reeding, an 'MB line,' in which MB was observed in 21.68% (67/309) in addition to CL/P in 17.80% (55/309) of the offspring, was developed in the CL/Fr colony. In mating experiments between the MB line and C57BL /6J, all F1 progeny showed the normal phenotype, MB was observed in 0. 72% (1/139) of the F2 generation, and the backcross generation showed segregation of MB in 6.25% (22/352) and CL/P in 1.42% (5/352). These i nstances suggested the occurrence of an additional mutation in the CL/ Fr mouse genome controlled by an autosomal recessive gene with low pen etrance. However, since the CL/Fr mouse primarily has a developmental deficiency in the maxilla, the possibility that CL/P and MB share comm on etiologic factors cannot be completely ruled out. Conclusion: The m axillary bending retains significance, as this mutant can serve as an animal model of abnormal facial growth. Elucidation of the etiologic r elationship between MB and CL/P may provide clues to clarifying the de ficiency in first branchial arch in the mouse.