Distinct variant DNA-binding sites determine cell-specific autoregulated expression of the Drosophila POU domain transcription factor drifter in midline glia or trachea.

Transcriptional regulators utilizing the POU domain DNA-binding motif have been shown to form multi-protein complexes dependent on the POU domain itself and its flexible recognition of various octamer sequence elements. We have identified two variant POU domain recognition elements DFRE1 and DFRE2, which are found within a 514-bp autoregulatory enhancer of the Drosophila melanogaster POU domain gene drifter (dfr). Both elements are capable of binding bacterially produced full-length DFR protein with high affinity, although they differ in the 5'-to-3' orientation of POU-specific and POU homeodomain subelements. When placed in dfr loss-of-function genetic backgrounds, all expression of dfr-lacZ fusion genes under control of the autoregulatory enhancer is dependent on DFR activity levels. However, the complete enhancer sequence directs beta-galactosidase expression in only a subset of cells which normally express the endogenous DFR protein, including the middle pair of midline glias of the ventral nerve cord, the oenocyte clusters, and all tracheal cells. In addition, DFRE1 and DFRE2 exhibit separable tissue-specific functions when independently disrupted or deleted. Disruption of DFRE1 function specifically abolishes beta-galactosidase expression in the middle pair of midline glias. Deletion of DFRE causes a specific loss of tracheal expression, leaving oenocyte and midline glia expression intact. These results suggest that dfr cell-specific autoregulation is determined by the context of DFR POU domain binding within the enhancer, which is possibly mediated by the formation of recognition element-specific heteromultimeric complexes containing additional tissue-specific factors.

TWO NEW SPECIES OF ISOSOMA

Isosoma Allynii, n. s.Female.—Average length .10 of an inch. Color of body and antennæ uniform black, the first with a slight greenish lustre. Head about .025 of an inch wide, about two thirds as long; the antennæ a little enlarged at the ends, hairy, microscopic hairs moderately scattered over the head and thorax. Thorax, as well as head, punctured; wings hyaline, dotted over with microscopic hairs, the thorax in its widest part about the width of the head. Abdomen gradually tapering from near the base, the ovipositor slightly exserted. The color of the legs vary slightly; in five specimens the anterior and posterior legs have the femurs fuscous except at the ends; the tibiæ with basal half fuscous, the rest yellow; the terminal joint of tarsi fuscous, the rest yellow; the middle pair of legs are yellow throughout except the terminal tarsi. Two specimens have all the femurs fuscous, yellow at the ends. One specimen has all the femurs pale red, and the tibiæ fuscous, but this is probably a change from yellow by the poison bottle used in killing. One is marked like the first five, with the yellow replaced by pale red; another is like the first five, except that the middle tibiæ are a little clouded at base.