that Sox6 is an important regulatory molecule that plays a role in the development of the central nervous system [8–11], cartilage [6,12,13], and muscle [14,15]. A Sox6-null mutant mouse (p100H) has previously been identified in our laboratory [14]. Mice homozygous for p100H show delayed growth, develop myopathy and arterioventricular heart block, and die within 2 wk after birth [1