The cluster represses receptor tyrosine kinase signaling to determine cell fates in the eye.

Photoreceptors in the crystalline eye are recruited by receptor tyrosine kinase (RTK)/Ras signaling mediated by Epidermal growth factor receptor (EGFR) and the Sevenless (Sev) receptor. Analyses of an allelic deletion series of the locus, along with a panel of modified genomic rescue transgenes, show that eye patterning depends on both miRNAs. Transcriptional reporter and activity sensor transgenes reveal expression and function of miR-279/996 in non-neural cells of the developing eye.

miRNA suppression of a Notch repressor directs non-neuronal fate in mechanosensory organs.

Although there is abundant evidence that individual microRNA (miRNA) loci repress large cohorts of targets, large-scale knockout studies suggest that most miRNAs are phenotypically dispensable. Here, we identify a rare case of developmental cell specification that is highly dependent on miRNA control of an individual target. We observe that binary cell fate choice in the peripheral sensory organ lineage is controlled by the non-neuronally expressed cluster, with a majority of notum sensory organs exhibiting transformation of sheath cells into ectopic neurons.

Multiple In Vivo Biological Processes Are Mediated by Functionally Redundant Activities of Drosophila mir-279 and mir-996.

While most miRNA knockouts exhibit only subtle defects, a handful of miRNAs are profoundly required for development or physiology. A particularly compelling locus is Drosophila mir-279, which was reported as essential to restrict the emergence of CO2-sensing neurons, to maintain circadian rhythm, and to regulate ovarian border cells. The mir-996 locus is located near mir-279 and bears a similar seed, but they otherwise have distinct, conserved, non-seed sequences, suggesting their evolutionary maintenance for separate functions.

Differential activity of Drosophila Hox genes induces myosin expression and can maintain compartment boundaries.

Compartments are units of cell lineage that subdivide territories with different developmental potential. In Drosophila, the wing and haltere discs are subdivided into anterior and posterior (A/P) compartments, which require the activity of Hedgehog, and into dorsal and ventral (D/V) compartments, needing Notch signaling. There is enrichment in actomyosin proteins at the compartment boundaries, suggesting a role for these proteins in their maintenance.

Integration of RNA processing and expression level control modulates the function of the Drosophila Hox gene Ultrabithorax during adult development.

Although most metazoan genes undergo alternative splicing, the functional relevance of the majority of alternative splicing products is still unknown. Here we explore this problem in the Drosophila Hox gene Ultrabithorax (Ubx). Ubx produces a family of six protein isoforms through alternative splicing.

Function and specificity of Hox genes.

The Hox genes specify different structures along the anteroposterior axis of bilaterians. They code for transcription factors including a conserved domain, the homeodomain, that binds DNA. The specificity of Hox function is determined by each gene controlling the expression of different groups of downstream genes.

The ultrabithorax Hox gene of Drosophila controls haltere size by regulating the Dpp pathway.

The halteres and wings of Drosophila are homologous thoracic appendages, which share common positional information provided by signaling pathways. The activity in the haltere discs of the Ultrabithorax (Ubx) Hox gene establishes the differences between these structures, their different size being an obvious one. We show here that Ubx regulates the activity of the Decapentaplegic (Dpp) signaling pathway at different levels, and that this regulation is instrumental in establishing the size difference.