THE DROSOPHILA ZYGOTIC LETHAL GENE SHUTTLE CRAFT IS REQUIRED MATERNALLY FOR PROPER EMBRYONIC-DEVELOPMENT

The Drosophila gene shuttle craft (stc) is expressed zygotically in th e embryonic central nervous system (CNS) where it is required to maint ain the proper morphology of motoneuronal axon nerve routes following their migration from the ventral cord. Here, we report that a prominen t maternal source of STC protein is also present throughout both oogen esis and embryogenesis. To determine whether this maternal component i s required in the ovary and/or embryo, we used the Drosophila autosoma l dominant female sterile technique to generate germ-line clones that lacked the ste maternal function. Our results demonstrate that a mater nally derived source of STC protein is required during embryogenesis b ut not oogenesis. In contrast to the zygotic phenotype, the primary de fect in embryos derived from ste germline clones affects segmentation by causing disruptions and deletions in distinct thoracic (T1-T3) and abdominal (A4-A8) segments. These localized defects are responsible fo r additional phenotypes observed later in development which include ga ps in the ventral nerve cord and deletions of denticle belts in the cu ticle. An additional phenotype occurring in all other neuromeric segme nts consists of the misguided migration of motoneuronal axons as they project out of the ventral nerve cord. Thus, the ste zygotic function is required later in development and cannot correct the segmentation a nd subsequent CNS abnormalities associated with loss of its earlier ac ting maternally derived activity.