Control of Neural Daughter Cell Proliferation by Multi-level Notch/Su(H)/E(spl)-HLH Signaling

Abstract

The Notch pathway controls proliferation during development and in adulthood, and is frequently affected in many disorders. However, the genetic sensitivity and multi-layered transcriptional properties of the Notch pathway has made its molecular decoding challenging. Here, we address the complexity of Notch signaling with respect to proliferation, using the developing Drosophila CNS as model. We find that a Notch/Su(H)/E(spl)-HLH cascade specifically controls daughter, but not progenitor proliferation. Additionally, we find that different E(spl)-HLH genes are required in different neuroblast lineages. The Notch/Su(H)/E(spl)-HLH cascade alters daughter proliferation by regulating four key cell cycle factors: Cyclin E, String/Cdc25, E2f and Dacapo (mammalian p21CIP1/p27KIP1/p57Kip2). ChIP and DamID analysis of Su(H) and E(spl)-HLH indicates direct transcriptional regulation of the cell cycle genes, and of the Notch pathway itself. These results point to a multi-level signaling model and may help shed light on the dichotomous proliferative role of Notch signaling in many other systems.

sequoia controls the type I>0 daughter proliferation switch in the developing Drosophila nervous system

“…We analyzed mutants in the kuz gene, which encodes an ADAM metalloprotease crucial for cleavage of the Notch receptor (Pan and Rubin, 1997;Sotillos et al, 1997), that have been demonstrated to reduce Notch signaling without affecting NB selection (Ulvklo et al, 2012;Bivik et al, 2016). However, we did not observe any apparent reduction in Seq protein levels in kuz mutants (Fig.…”

“…These regulators exert their roles by regulating the key cell cycle genes (Baumgardt et al, 2014). In addition, the canonical Notch pathway was also found to be important for the type I>0 switch, via regulation of all four key cell cycle genes (Ulvklo et al, 2012;Bivik et al, 2015Bivik et al, , 2016. Notch signaling is initially off in NBs -a prerequisite for establishment of NB cell identity in the neuroectoderm -but is gradually activated during lineage progression (Ulvklo et al, 2012;Bivik et al, 2016).…”

“…In addition, the canonical Notch pathway was also found to be important for the type I>0 switch, via regulation of all four key cell cycle genes (Ulvklo et al, 2012;Bivik et al, 2015Bivik et al, , 2016. Notch signaling is initially off in NBs -a prerequisite for establishment of NB cell identity in the neuroectoderm -but is gradually activated during lineage progression (Ulvklo et al, 2012;Bivik et al, 2016). The selective activation of Notch signaling in the latter stages of lineage progression is not, however, mediated by cas, grh or Antp (Ulvklo et al, 2012;Baumgardt et al, 2014;Bivik et al, 2016).…”

“…Notch signaling is initially off in NBs -a prerequisite for establishment of NB cell identity in the neuroectoderm -but is gradually activated during lineage progression (Ulvklo et al, 2012;Bivik et al, 2016). The selective activation of Notch signaling in the latter stages of lineage progression is not, however, mediated by cas, grh or Antp (Ulvklo et al, 2012;Baumgardt et al, 2014;Bivik et al, 2016). Hence, it is unclear what controls the late temporal onset of Notch signaling in NBs to thereby ensure precise type I>0 switches.…”

“…We analyzed the expression of the Notch target gene and key effector E(spl)m8-HLH (Jennings et al, 1994;Bang et al, 1995;Lecourtois and Schweisguth, 1995) using an E(spl)m8-HLH-GFP reporter transgene that is known to be dependent upon Notch signaling in VNC NBs (Ulvklo et al, 2012;Bivik et al, 2016). In controls at St14, GFP expression was apparent in many, but not all NBs in the VNC (Fig.…”