A genetic hierarchy establishes mitogenic signalling and mitotic competence in the renal tubules ofDrosophila

Abstract

Cell proliferation in the developing renal tubules of Drosophila is strikingly patterned, occurring in two phases to generate a consistent number of tubule cells. The later phase of cell division is promoted by EGF receptor signalling from a specialised subset of tubule cells, the tip cells, which express the protease Rhomboid and are thus able to secrete the EGF ligand, Spitz. We show that the response to EGF signalling, and in consequence cell division, is patterned by the specification of a second cell type in the tubules. These cells are primed to respond to EGF signalling by the transcription of two pathway effectors, PointedP2, which is phosphorylated on pathway activation, and Seven up. While expression of pointedP2 is induced by Wingless signalling, seven up is initiated in a subset of the PointedP2 cells through the activity of the proneural genes. We demonstrate that both signalling and responsive cells are set aside in each tubule primordium from a proneural gene-expressing cluster of cells, in a two-step process. First, a proneural cluster develops within the domain of Wingless-activated, pointedP2-expressing cells to initiate the co-expression of seven up. Second, lateral inhibition, mediated by the neurogenic genes, acts within this cluster of cells to segregate the tip cell precursor, in which proneural gene expression strengthens to initiate rhomboid expression. As a consequence, when the precursor cell divides, both daughters secrete Spitz and become signalling cells. Establishing domains of cells competent to transduce the EGF signal and divide ensures a rapid and reliable response to mitogenic signalling in the tubules and also imposes a limit on the extent of cell division, thus preventing tubule hyperplasia.

Early patterning followed by tissue growth establishes proximo-distal identity in Drosophila Malpighian tubules

“…We therefore analysed embryos mutant for the as-c genes ( Df(1)sc-B57 ) which fail to develop the tip/sibling-cells (Hoch et al, 1994; Sudarsan et al, 2002). In mutant embryos, the MpTs still expressed distal transcription factors (Fig.…”

“…The emergence of the tip/sibling-cells as a signalling centre could then orchestrate the morphological changes underlying tubule elongation, in a way which results in their surrounding cells coming to have a distal position in the final tubule. The EGF signal which emanates from the tip/sibling-cells drives cell proliferation (Baumann and Skaer, 1993; Kerber et al, 1998; Sudarsan et al, 2002), as well as defining planar cell polarity in surrounding cells to orchestrate their intercalation and the convergent extension of the distal MpT (Saxena et al, 2014), so orchestrating the morphological changes which propel the tip/sibling-cells, and their neighbouring cells with distal identity, to finally reside at the distal end of the extended MpT. Together these processes could convert an already established asymmetry in the gut, into a P-D axis in the MpTs which grow out perpendicular to the gut axis.…”

“…We then used genetic approaches to manipulate EGF and Wg signalling. We drove expression of constitutively active EGFR (UAS-λtop) or dominant negative EGFR (UAS-EGFR-DN) in the developing tubules using CtB-Gal4 which expresses in all MpT cells from the stage when they bud from the gut (Sudarsan et al, 2002). If EGF signalling is required to induce distal identity it would be expected that the constitutively active form would induce expression of distal markers throughout the MpT, whilst distal marker expression would be abolished by the dominant negative form.…”

“…Wg is expressed in the hindgut, as well as the MpT primordium from the start of tubule development (Skaer and Martinez Arias, 1992), and is required for expression of Achaete in the proneural cluster. Wg is also required for expression of Seven up and PointedP2 (Sudarsan et al, 2002; Wan et al, 2000), two distal transcription factors considered to play roles in promoting cell proliferation (Kerber et al, 1998; Sudarsan et al, 2002).…”

Piezo buffers mechanical stress via modulation of intracellular Ca2+ handling in the Drosophila heart

“…Inhibition of Piezo was achieved by crossing Piezo-Gal4 (above) or Tin-Gal4, P{tinC-Gal4.Δ4} to P{UAS-GsMTx4-FL, P{UAS-GsMTx4-AP or P{UAS-GsMTx4-SR 52 . Hypertensive flies were generated by inducing renal failure by crossing CtB-Gal4 82 to UAS-λtop 4.4 (gift from Trudi Schüpbach). Experiments on hypertensive flies were carried out at 10 days to allow the haemolymph pressure to build in the body cavity (Fig.…”