Cell and cubitus interruptus dominant: two segment polarity genes on the fourth chromosome in Drosophila.

The cubitus interruptus Dominant 4-O [ciD] locus is a member of a class of genes required for the proper formation of the repeating segmental pattern of the embryo. We have found a second locus on the fourth chromosome, Cell (Ce), which is also required for proper segmentation. Mutations in Ce cause the elimination of the posterior half and anterior margin of each segment. The complementation pattern of ciD and Ce alleles is complicated; certain alleles complement fully while others do not. We have isolated a series of translocations which have breakpoints within the ciD gene. These mutations also disrupt Ce2 function, indicating that ciD and Ce2 are intimately associated. We have also studied the maternal contribution of the wild-type gene product of the ciD and Ce genes by pole cell transplants. These experiments suggest that there is no maternal contribution of the ciD+ and Ce+ gene products, and that they are not required for oogenesis. Thus, it appears that the ciD and Ce loci may represent a gene complex that is activated during zygotic development and is required for the proper formation of segments.