Regulation of neuroblast mitosis is determined by PACAP receptor isoform expression

Abstract

Although neurogenesis in the embryo proceeds in a region-or lineage-specific fashion coincident with neuropeptide expression, a regulatory role for G protein-coupled receptors (GPCR) remains undefined. Pituitary adenylate cyclase activating polypeptide (PACAP) stimulates sympathetic neuroblast proliferation, whereas the peptide inhibits embryonic cortical precursor mitosis. Here, by using ectopic expression strategies, we show that the opposing mitogenic effects of PACAP are determined by expression of PACAP receptor splice isoforms and differential coupling to the phospholipase C (PLC) pathway, as opposed to differences in cellular context. In embryonic day 14 (E14) cortical precursors transfected with the hop receptor variant, but not cells transfected with the short variant, PACAP activates the PLC pathway, increasing intracellular calcium and eliciting translocation of protein kinase C. Ectopic expression of the hop variant in cortical neuroblasts transforms the antimitotic effect of PACAP into a promitogenic signal. Furthermore, PACAP promitogenic effects required PLC pathway function indicated by antagonist U-73122 studies in hop-transfected cortical cells and native sympathetic neuroblasts. These observations highlight the critical role of lineage-specific expression of GPCR variants in determining mitogenic signaling in neural precursors.

Pituitary adenylate cyclase-activating polypeptide prevents the effects of ceramides on migration, neurite outgrowth, and cytoskeleton remodeling

“…PACAP and its receptors are actively expressed in the central nervous system during development, notably in the germinative neuroepithelia and migratory zones (9, 10), suggesting that PACAP could be involved in the regulation of neurogenesis and͞or cell differentiation (11). In agreement with this hypothesis, in vitro studies have shown that PACAP exerts growth cone attraction in cultured neural tube precursors from Xenopus laevis (12) and promotes survival and differentiation of rat cerebellar granule cells (13)(14)(15). In vivo, PACAP injection at the surface of the cerebellum of 8-day-old rats increases the number of granule neurons in the internal granule cell layer (16).…”

Direct cAMP Signaling through G-Protein-Coupled Receptors Mediates Growth Cone Attraction Induced by Pituitary Adenylate Cyclase-Activating Polypeptide

“…In particular, PAC1 splice variants activate a number of signaling cascades, including the activation of adenylate cyclase, phosphatidyl inositol turnover, and L-type Ca 2ϩ channels (Pisegna and Wank, 1993;Spengler et al, 1993;Chatterjee et al, 1996). For instance, PAC1 hop splice variant activation increases PI turnover, protein kinase C localization, and intracellular Ca 2ϩ mobilization, whereas PAC1 short activation only stimulates adenylate cyclase (Lu et al, 1998;DiCicco-Bloom et al, 2000;Nicot and DiCicco-Bloom, 2001). Our current data demonstrate that PACAP-induced growth cone attraction was independent of Ca 2ϩ , PLC, and PI3 kinase pathways, implying that PAC1 short , not PAC1 hop , likely mediates the turning.…”

“…Different splice variants of PAC1 receptors elicit different intracellular signaling cascades besides the cAMP pathway, including PLC, PI-3 kinases, and L-type Ca 2ϩ channels (Pisegna and Wank, 1993;Spengler et al, 1993;DiCicco-Bloom et al, 2000;Nicot and DiCicco-Bloom, 2001). To determine whether PACAP elicits Ca 2ϩ responses in cultured Xenopus spinal neurons, we used fura-2 ratiometric imaging to measure intracellular Ca 2ϩ concentrations ([Ca 2ϩ ] i ).…”

Stimulation of the ERK Pathway by GTP-loaded Rap1 Requires the Concomitant Activation of Ras, Protein Kinase C, and Protein Kinase A in Neuronal Cells

“…PACAP neurotrophic activity is mediated by the activation of Pac1, the PACAP-specific GPCR. Pac1 displays a complex pattern of alternative splicing that modulates its ligand binding and signaling properties (31)(32)(33)(34) resulting in the modulation of PACAP physiological effects (28,35). We and others (21,31) showed that Pac1 potently stimulated the AC and PLC activities as well as the ERK pathway that was implicated in its neurotrophic activity (23,36).…”

“…This neurotrophic activity was extended to the protection of cerebellar granule (22,23) and dorsal root ganglion neurons (24) from apoptosis, and of cortical (25) and hippocampal (26) neurons from ischemia-induced cell death. PACAP was also shown to control the proliferation and differentiation of cortical (27)(28)(29) and cerebellar neuroblasts (30). PACAP neurotrophic activity is mediated by the activation of Pac1, the PACAP-specific GPCR.…”