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MLR COMPASS-like complexes are highly conserved histone modifiers and enhancer regulators recruited by multiple transcription factors during differentiation and development, including lineage-determining factors, nuclear receptors, and developmental signaling pathway effectors. While the essential functions of MLR complexes during differentiation-associated transcriptional reprogramming has been well-explored, roles that these complexes play during reprogramming events in terminally differentiated cells remain understudied. We determined that the Drosophila MLR complex is required in fat body adipocytes for proper regulation of the triglyceride depletion rate during non-feeding periods, including metamorphosis and adult starvation. Transcriptome analysis revealed that the complex plays a critical role in controlling stress-related reprogramming in these cells, suggesting that the metabolic phenotypes are indirect effects of dysregulated stress transcription. Furthermore, our evidence suggests that the complex interacts with Foxo and Relish (Nf-κb) pathways and is required for proper expression of their targets. This investigation further elucidates the necessary functions of MLR complexes in regulating transcriptional reprogramming in terminally differentiated cells as well as suggests novel binding partners. Apparent roles for these complexes in the proper regulation of stress-induced transcription implies new mechanisms involved in cancer and other human diseases associated with MLR subunit mutation.

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The conserved MLR COMPASS-like complexes are histone modifiers that are recruited by a variety of transcription factors to enhancer regions where they act as necessary epigenetic tools for enhancer establishment and function. A critical in vivo target of the Drosophila MLR complex is the bantam miRNA that regulates cell survival and functions in feedback regulation of cellular signaling pathways during development. We determine that loss of Drosophila MLR complex function in developing wing and eye imaginal discs results in growth and patterning defects that are sensitive to bantam levels. Consistent with an essential regulatory role in modulating bantam transcription, the MLR complex binds to tissue-specific bantam enhancers and contributes to fine-tuning expression levels during larval tissue development. In wing imaginal discs, the MLR complex attenuates bantam enhancer activity by negatively regulating expression; whereas, in differentiating eye discs, the complex exerts either positive or negative regulatory activity on bantam transcription depending on cell fate. Furthermore, while the MLR complex is not required to control bantam levels in undifferentiated eye cells anterior to the morphogenetic furrow, it serves to prepare critical enhancer control of bantam transcription for later regulation upon differentiation. Our investigation into the transcriptional regulation of a single target in a developmental context has provided novel insights as to how the MLR complex contributes to the precise timing of gene expression, and how the complex functions to help orchestrate the regulatory output of conserved signaling pathways during animal development.3