Gene expression data from wild-type (WT) and ribbon (rib) mutant Drosophila mid through late stage embryos

Transcription factors, which regulate the spatiotemporal patterns of gene expression during organogenesis, often regulate multiple aspects of tissue morphogenesis, including cell-type specification, cell proliferation, cell death, cell polarity, cell shape, cell arrangement and cell migration. In this work, we describe a distinct role for Ribbon (Rib) in controlling cell shape changes during elongation of the Drosophila salivary gland (SG). Notably, the morphogenetic changes in rib mutants occurred without effects on general SG cell attributes such as specification, proliferation and apoptosis. Moreover, the abnormal cell/organ shape in rib mutants occurred without compromising epithelial-specific morphological attributes such as apicobasal polarity and junctional integrity. To identify the genes regulated by Rib that control cell and organ shape, we performed ChIP-seq analysis in embryos driving rib expression specifically in the SGs. To learn if the Rib binding sites identified in the ChIP-seq analysis were linked to changes in gene expression through transcriptional activation, repression, or both, we performed microarray analysis comparing RNA samples from age-matched wild-type and rib null embryos. From the superposed ChIP-seq and microarray gene expression data, we identified 60 genomic sites of bound Rib most likely to regulate SG-specific gene expression. We confirmed several of the identified Rib targets by qRT-pCR and/or in situ hybridization. Our results indicate that Rib regulates cell shape change in the Drosophila salivary gland via a diverse array of targets through both transcriptional activation and repression. Furthermore, our results suggest that a critical component of the SG morphogenetic gene network involving Rib is its autoregulation.

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Loganathan R, Lee JS, Wells MB, Grevengoed E, Slattery M, Andrew DJ