The labial (lab) gene of Drosophila melanogaster is necessary for the proper development of the embryonic (larval) and adult head. We have identified the lab transcription unit within the proximal portion of the Antennapedia Complex (ANT-C) by mapping the molecular lesions associated with chromosomally rearranged lab alleles. We present its molecular structure, nucleotide sequence, and temporal pattern of expression. In addition, using antibodies generated against a fusion protein, we show that in the embryo the lab protein is distributed in neural and epidermal cells of the procephalic lobe; in a discrete loop of the midgut; and in specific progenitor sensory cells of the clypeolabrum, thoracic segments, and tail region. The regions of lab expression in the developing cephalon represent nonsegmented domains that are anterior to and largely nonoverlapping with the domains of expression of the Deformed (Dfd) and proboscipedia (pb) genes, two other homeotic loci of the ANT-C that also function to direct the development of head structures. Furthermore, lab head expression is associated with the complex cellular movements of head involution, a process that not only is defective in labembryos, but the failure of which appears to be largely responsible for the defects observed in mutant embryos.Finally, we suggest that lab head expression provides a molecular marker for an intercalary segment, an ancestral segment that has become morphologically indistinct during the evolution of the insect head.

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We have found that the early response of axotomized rat retinal ganglion cells is characterized by the differential regulation of a number of fast axonally transported proteins. The abundance of 23 radiolabeled fast transported proteins was analyzed at 2 and 5 days after axotomy using two-dimensional gel electrophoresis. Corresponding changes in retinal GAP-43 mRNA were measured using northern analysis. Within 2 days of injury, >40% of the transported proteins analyzed, including GAP-43, showed increased labeling above control levels. Approximately 13% of transported proteins decreased below control levels, whereas the remainder did not change. Five days after axotomy, only GAP-43 and another fast transported protein, C3, continued to sustain measurable increased labeling above control levels; all previously elevated proteins appeared to have been down-regulated by this time, which corresponds to the onset of cell death. These differential changes were accompanied by parallel increases in GAP-43 mRNA. These results suggest that the molecular changes within rat retinal ganglion cells are differentially regulated within two stages subsequent to damage, initial regenerative growth followed by cell death.