Purkinje cell expression of the mouse aldolase C gene in transgenic mice is directed by an upstream regulatory element

We have sought to understand the regulation of the expression pattern of aldolase C (Zebrin II) in cerebellar Purkinje cells. Normally, aldolase C is expressed in a series of sagittal stripes of Purkinje cells interrupted by stripes of little or no expression. Genomic aldolase C:LacZ fusion genes with 1.8 kb of sequence 5′ to the transcription start site drive CNS expression of LacZ only in astrocytes and cells of the pia mater. If the 5′ portion of the transgene is extended to a full 5.0 kb, expression is reliably observed in Purkinje cells, yet none of the astrocyte expression is lost. We broke the additional 3.0 kb into 1.0 kb fragments and tested each for Purkinje cell enhancer activity when appended to the original 1.8 kb construct. We show that the 886 bp region from nucleotide -2796 to -3682 (relative to the start of transcription) contains virtually all of the Purkinje cell enhancer activity. However, neither the full 5.0 kb nor the 886 bp region directed a striped expression pattern, as is seen for the endogenous gene. Taken together, our study localizes a Purkinje cell enhancer to a small 5′ region of the aldolase C gene and illustrates that the element(s) responsible for the normal anatomically complex pattern of aldolase C expression are separate from those conferring cell-type specificity. The relationship of these findings to previous work in other laboratories is discussed.