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Homothorax and Extradenticle alter the transcription factor network in Drosophila ommatidia at the dorsal rim of the retina.

ABSTRACT: A narrow band of ommatidia in the dorsal periphery of the Drosophila retina called the dorsal rim area (DRA) act as detectors for polarized light. The transcription factor Homothorax (Hth) is expressed in DRA inner photoreceptors R7 and R8 and is both necessary and sufficient to induce the DRA fate, including specialized morphology and unique Rhodopsin expression. Hth expression is the result of Wingless (Wg) pathway activity at the eye margins and restriction to the dorsal eye by the selector genes of the Iroquois complex (Iro-C). However, how the DRA is limited to exactly one or two ommatidial rows is not known. Although several factors regulating the Drosophila retinal mosaic are expressed in DRA ommatidia, the role of Hth in this transcriptional network is uncharacterized. Here we show that Hth functions together with its co-factor Extradenticle (Exd) to repress the R8-specific factor Senseless (Sens) in DRA R8 cells, allowing expression of an ultraviolet-sensitive R7 Rhodopsin (Rh3). Furthermore, Hth/Exd act in concert with the transcriptional activators Orthodenticle (Otd) and Spalt (Sal), to activate expression of Rh3 in the DRA. The resulting monochromatic coupling of Rh3 between R7 and R8 in DRA ommatidia is important for comparing celestial e-vector orientation rather than wavelengths. Finally, we show that Hth expression expands to many ommatidial rows in regulatory mutants of optomotorblind (omb), a transcription factor transducing Wg signaling at the dorsal and ventral eye poles. Therefore, locally restricted recruitment of the DRA-specific factor Hth alters the transcriptional network that regulates Rhodopsin expression across ommatidia.

SUBMITTER: Wernet MF

PROVIDER: S-EPMC3912834 | biostudies-other | 2014 Feb

REPOSITORIES: biostudies-other

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Homothorax and Extradenticle alter the transcription factor network in Drosophila ommatidia at the dorsal rim of the retina.

Wernet Mathias F MF Desplan Claude C

Development (Cambridge, England) 20140201 4

A narrow band of ommatidia in the dorsal periphery of the Drosophila retina called the dorsal rim area (DRA) act as detectors for polarized light. The transcription factor Homothorax (Hth) is expressed in DRA inner photoreceptors R7 and R8 and is both necessary and sufficient to induce the DRA fate, including specialized morphology and unique Rhodopsin expression. Hth expression is the result of Wingless (Wg) pathway activity at the eye margins and restriction to the dorsal eye by the selector g ...[more]

PMID: 24496628

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Project description:The proper balance of excitatory and inhibitory neurons is crucial to normal processing of somatosensory information in the dorsal spinal cord. Two neural basic helix-loop-helix transcription factors, Ascl1 and Ptf1a, are essential for generating the correct number and sub-type of neurons in multiple regions of the nervous system. In the dorsal spinal cord, Ascl1 and Ptf1a have contrasting functions in specifying inhibitory versus excitatory neurons. To understand how Ascl1 and Ptf1a function in these processes, we identified their direct transcriptional targets genome-wide in the embryonic mouse neural tube using ChIP-Seq and RNA-Seq. We show that Ascl1 and Ptf1a regulate the specification of excitatory and inhibitory neurons in the dorsal spinal cord through direct regulation of distinct homeodomain transcription factors known for their function in neuronal sub-type specification. Besides their roles in regulating these homeodomain factors, Ascl1 and Ptf1a each function differently during neuronal development with Ascl1 directly regulating genes with roles in several steps of the neurogenic program including, Notch signaling, neuronal differentiation, axon guidance, and synapse formation. In contrast, Ptf1a directly regulates genes encoding components of the neurotransmitter machinery in inhibitory neurons, and other later aspects of neural development distinct from those regulated by Ascl1. Moreover, Ptf1a represses the excitatory neuronal fate by directly repressing several targets of Ascl1. Examination of the Ascl1 and Ptf1a bound sequences shows they are enriched for a common E-Box with a GC core and with additional motifs used by Sox, Rfx, Pou, and Homeodomain factors. Ptf1a bound sequences are uniquely enriched in an E-Box with a GA/TC core and in the binding motif for its co-factor Rbpj, providing two keys to specificity of Ptf1a binding. The direct transcriptional targets identified for Ascl1 and Ptf1a provide a molecular understanding for how they function in neuronal development, particularly as key regulators of homeodomain transcription factors required for neuronal sub-type specification.

Dataset Information

Homothorax and Extradenticle alter the transcription factor network in Drosophila ommatidia at the dorsal rim of the retina.

Publications

Homothorax and Extradenticle alter the transcription factor network in Drosophila ommatidia at the dorsal rim of the retina.

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