Phosphorylation of Ind by MAP kinase enhances Ind-dependent transcriptional repression

Abstract

The Drosophila neuroectoderm is initially subdivided into three longitudinal domains that give rise to columns of neuroblasts. This subdivision is coordinately accomplished by the action of the signaling pathways, Dorsal and Epidermal Growth Factor Receptor (EGFR), in conjunction with the homeodomain proteins, Ventral nervous system defective, Intermediate neuroblasts defective (Ind) and Muscle Segment Homeobox. We previously demonstrated that Ind expression is activated in response to the EGFR pathway. Here we show that EGF signaling subsequently mediates the direct phosphorylation of Ind by MAP kinase, which enhances the capacity of Ind to repress target genes, such as achaete. Specifically, we show that reduced EGF signaling results in diminished repression of achaete in the intermediate column, despite the presence of high levels of Ind protein. We also demonstrate that ectopic activation of MAP kinase results in the lateral expansion of the Ind expression domain with a corresponding reduction in achaete expression. This regulation is also dependent on the co-repressor, Dichaete. Our data indicate that EGF signaling, acting through MAP kinase, impinges on multiple aspects of Ind regulatory activity. While it has been often demonstrated that MAP kinase phosphorylation of transcriptional repressors attenuates their repressor activity, here we provide an example of phosphorylation enhancing repressor activity.

Neuronal Cell Fate Specification by the Convergence of Different Spatiotemporal Cues on a Common Terminal Selector Cascade

“…Guinea pig anti-Odd (1:500); guinea pig anti-Runt (both provided by M. Ruiz and D. Kosman). Rat a-Msh (1:500) (provided by Z. Paroush) [ 51 ].…”

Epidermal Growth Factor Pathway Signaling in Drosophila Embryogenesis: Tools for Understanding Cancer

“…EGF signaling has been shown to mediate the direct phosphorylation of ind through its downstream effector MAP kinase. Phosphorylation of ind results in repression of ind target genes, which allows EGF signaling to modify cell fate even in the presence of high levels of ind protein [ 56 ].…”

Intrinsic dorsoventral patterning and extrinsic EGFR signaling genes control glial cell development in the Drosophila nervous system

“…Since ind expression is activated by the EGFR signaling ligand, Spi, in the VNE to establish the identity of the intermediate column, it is plausible that glial phenotypes in spi and ind mutants are similar to each other. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 15 mediated repression of msh expression in the lateral column, EGFR signaling provides a consolidating extrinsic cue to make ind a repressor of some of the target genes in the intermediate column via MAPK-mediated phosphorylation (Moses et al, 2011). This interpretation is compatible with the results obtained by overexpression of Spi and Vn through Kr-and sca-Gal4 drivers, which show repressed Repo expression in the VNE due to the repressor activity of Ind, which in turn is activated by EGFR signaling (Fig.…”

“…4-6). Thismay be due to the repressor activity of ind, since activation of EGFR signaling induces phosphorylation of ind and vnd to consolidate their repressor activity(Uhler et al, 2007;Moses et al, 2011). In addition, since Egfr overexpression can cause expansion of vnd expression from the medial column to the lateral area(Zhao et al, 2007), the intermediate and lateral columns may have acquired the medial identity, such that the LG and various types of other glia originating from the VNE are not generated after…”