The Drosophila zygotic lethal gene shuttle craft is required maternally for proper embryonic development

The Drosophila gene shuttle craft (stc) is expressed zygotically in the embryonic central nervous system (CNS) where it is required to maintain the proper morphology of motoneuronal axon nerve routes following their migration from the ventral cord. Here, we report that a prominent maternal source of STC protein is also present throughout both oogenesis and embryogenesis. To determine whether this maternal component is required in the ovary and/or embryo, we used the Drosophila autosomal dominant female sterile technique to generate germ-line clones that lacked the stc maternal function. Our results demonstrate that a maternally derived source of STC protein is required during embryogenesis but not oogenesis. In contrast to the zygotic phenotype, the primary defect in embryos derived from stc germ-line clones affects segmentation by causing disruptions and deletions in distinct thoracic (T1-T3) and abdominal (A4-A8) segments. These localized defects are responsible for additional phenotypes observed later in development which include gaps in the ventral nerve cord and deletions of denticle belts in the cuticle. An additional phenotype occurring in all other neuromeric segments consists of the misguided migration of motoneuronal axons as they project out of the ventral nerve cord. Thus, the stc zygotic function is required later in development and cannot correct the segmentation and subsequent CNS abnormalities associated with loss of its earlier acting maternally derived activity.