Mouse mutations disrupting somitogenesis and vertebral patterning

The mouse was one of the first model organisms used in genetic analysis, beginning in 1902 with the studies of inheritance carried out by William E. Castle, Director of the Bussey Institute at Harvard1. The first mutations identified derived from mouse fanciers, who primarily selected coat color variants or neurobehavioral triats. However, disruptions affecting the axial skeleton were also reported early in the century. For example, the classic brachyury (T) short tail mutant was identified in a laboratory stock by Dobrovolskaïa-Zavadskaïa in 1927 and was subsequently cloned and found to be a member of the T-box family of transcription factors, required for the formation and differentiation of paraxial mesoderm2. Spontaneous mutations causing vertebral defects, including undulated (Pax1 ^un ) and pudgy (Dll3 ^pu ), have also been cloned and found to encode genes involved in somite patterning3,4. More recently, advances in genetic technologies have greatly expanded the number of mouse mutations with somite defects. These approaches include use of homologous recombination in embryonic stem (ES) cell lines to generate "knock-out" and "knock-in" mice, transgenic insertion of dominant-negative alleles and chemical mutagenesis by agents such as N-ethyl-N-nitrosourea (ENU). Mouse mutant phenotypes and signaling pathways have been studied and characterized through analysis of double mutants. These genetic studies in the mouse have yielded a tremendous amount of information about the process of mammalian somitogenesis.