EVIDENCE FOR POSITIVE AND NEGATIVE REGULATION OF THE HOX-3.1 GENE

The region-specific patterns of expression of mouse homeobox genes are considered important for establishing the embryonic body plan. A 5-kilobase (kb) DNA fragment from the Hox-3.1 locus that is sufficient to confer region-specific expression to a β-galactosidase reporter gene in transgenic mouse embryos has been defined. The observed reporter gene expression pattern closely parallels endogenous Hox-3.1 expression in 8- to 9.5-day postcoitum (p.c.) embryos. At 10.5 days p.c. and later, the pattern of β-galactosidase activity diverges from the Hox-3.1 pattern, and an inappropriately high level of reporter gene expression is observed in posterior spinal ganglia. Inclusion of an additional 2 kb of upstream sequences is sufficient to suppress this aberrant expression in the developing spinal ganglia. Together, these results show that the control of early Hox-3.1 expression is complex, involving at least one positively acting and one negatively acting element.