A Notch-Independent Activity of Suppressor of Hairless Is Required for Normal Mechanoreceptor Physiology

Abstract

Suppressor of Hairless [Su(H)]/Lag-1/RBP-Jkappa/CBF1 is the only known transducing transcription factor for Notch receptor signaling. Here, we show that Su(H) has three distinct functions in the development of external mechanosensory organs in Drosophila: Notch-dependent transcriptional activation and a novel auto-repression function, both of which direct cell fate decisions, and a novel auto-activation function required for normal socket cell differentiation. This third phase of activity, the first known Notch-independent activation function for Su(H) in development, depends on a cell type-specific autoregulatory enhancer that is active throughout adult life and is required for proper mechanoreception. These results establish a direct link between a broadly deployed cell signaling pathway and an essential physiological function of the nervous system.

Notch signaling patternsDrosophilamesodermal segments by regulating the bHLH transcription factortwist

“…Differences between Notch and Su(H) phenotypes and gene regulation have previously been reported in a variety of invertebrate and vertebrate systems (Barolo et al, 2000b;Brennan et al, 1999;Furriols and Bray, 2000;Hsieh et al, 1996;Klein et al, 2000;Koelzer and Klein, 2003;Ligoxygakis et al, 1998;Morel and Schweisguth, 2000;Ordentlich et al, 1998;Rusconi and Corbin, 1998;Shawber et al, 1996). These results were explained by two non-exclusive models: (1) Fig.…”

“…1428twist was then subcloned as a Xba-BamHI fragment into the pH-Stinger transformation vector upstream of nuclear enhanced GFP (Barolo et al, 2000a). Sequence analysis, using MacVector, of 1428twist identified one site (TGTGGGAA) matching the YRTGDGAD consensus Su(H) binding sequence (Barolo et al, 2000b). Using site-directed mutagenesis (Promega, USA, Gene Editor), the conserved Su(H) binding site was mutated to TTCTATCC.…”

“…Nevertheless, since Notch exerted an effect on 1428twist, we utilized the promoter construct to further understand how Notch signaling regulates Twist expression. 1428twist contains only one site (TGTGGGAA) that matches the YRTGDGAD Su(H)-binding consensus sequence (Barolo et al, 2000b). Published gel shift experiments have shown that Su(H) binds oligonucleotides containing this GTGGGAA core sequence with high affinity (Morel and Schweisguth, 2000).…”

Three habits of highly effective signaling pathways: principles of transcriptional control by developmental cell signaling

“…." Nelson et al (1988) " Lecourtois and Schweisguth 1995;Kim et al 1996;Nellesen et al 1999;Barolo et al 2000;Lai et al 2000;Morel and Schweisguth 2000). Yet these genes are expressed in remarkably diverse and often nonoverlapping subsets of Notch-responsive cells throughout development, in both embryonic and postembryonic tissues, and no two expression patterns are identical, even when reporter genes that reflect only transcriptional responses are considered.…”

“…Thus, single-minded, which encodes a bHLH-PAS transcription factor, is activated by Notch signaling in two rows of cells in the ventrolateral ectoderm of the fly embryo that will adopt highly specialized midline neuronal and glial fates; single-minded function is essential for all steps of midline cell development (Nambu et al 1991). Su(H), in contrast, is (auto)activated by Notch signaling in only one cell type throughout development: the socket cells of external sensory bristles, where it is essential for the differentiation and physiological function of these organs (Barolo et al 2000). Despite the presence of eight high-affinity Su(H) binding sites in the Su(H) socket cell enhancer, Notch signaling does not activate Su(H) in midline cells; nor does it activate singleminded in socket cells, despite the presence of five highaffinity Su(H) sites in the single-minded midline regulatory region.…”