Deletion analysis of the tumorous-head (tuh-3) gene in Drosophila melanogaster.

In the presence of the naturally occurring maternal-effect alleles tuh-1h or tuh-1g, the tuh-3 mutant gene can cause the tumorous-head trait or the sac-testis trait. The tuh-3 gene functions as a semidominant in the presence of the tuh-1h maternal effect. Eye-antennal structures are replaced by posterior abdominal tergites and genital structures. If tuh-1h is replaced by its naturally occurring allele tuh-1g, tuh-3 functions as a recessive hypomorph and the defect switches from anterior to posterior structures, with a male genital-disc defect appearing with variable penetrance. Function and regulation of tuh-3+ may better be understood in light of the cytological localization of tuh-3 either adjacent to or as part of the bithorax complex. The tuh-3+ gene product appears to be essential for normal development, at least in the posterior end of the embryo.