Expression of reporters containing 2 or 6 kb of sequences upstream of the gene was not observed in the embryonic gut lineage. It has been shown that cell- or tissue-specific cis-regulatory elements of the Drosophila string/cdc25 gene, a developmentally controlled cell cycle regulator, extend over a 30 kb interval. Thus, it is conceivable that the spatiotemporal expression of cki-1
is also controlled by an extended stretch of cis-regulatory elements. The 20 kb region upstream of the cki-1
gene does not contain any predicted protein coding sequences and it is possible that a cis-acting element required for embryonic gut expression may reside 6kb upstream of the gene. Indeed, we found that when a cki-1
reporter gene was co-transformed with two cosmids containing ~30 kb of sequence upstream of the gene, the resultant extrachromosomal array, which is presumably generated by homologous recombination of the introduced DNA, expresses GFP in the gut cells at around the comma stage. However, the level of expression is too low and variable to identify in which gut cells GFP is expressed. Moreover, the cosmid T05A6, which contains about 11 kb upstream sequence of the cki-1
gene, can rescue the gut hyperplasia in mnDf100 embryos.