The goal of this proposal is to understand the function of the Drosophila segmentation gene tailless ( tll ). The mutant phenotype consists of characteristic defects or absence of structures of segmental origin located near the anterior and the posterior of the ectodermal region of the blastoderm. The remaining segments appear larger. Like the identified "gap" segmentation genes, tll mutants alter the ftz blastoderm striping pattern. Hence, tll acts early in development. However, it appears to serve a unique function, as there are no other zygotically active genes altering both poles of the embryo. While the development of a segment pattern in insects has been explained on the basis of a double gradient resulting from the action of two separate systems, it has not been predicted that the products of a single gene might be involved in establishing the two opposite poles. The objectives are to use molecular techniques to isolate the tll gene and to characterize its gene product. In situ hybridizations will be carried out to early embryos to determine whether the transcript is localized to the anterior and posterior regions altered in the mutants. The transcription unit will be defined and the transcription pattern determined. The gene will be sequenced, antibodies will be raised against fusion proteins, and the effect of mutations in other segmentation genes on expression of tll will be assessed. The experiments will provide insight into a unique gene which controls segmentation at the two ends of an organism, and so into the process of cell determination at the onset of development.
