title: Progressive and inhibitory cell cycle proteins act simultaneously to regulate neurotrophin-mediated proliferation and maturation of neuronal precursors.
abstract: Neuronal stem cell expansion and differentiation is a process involving stages of proliferation and maturation governed by the sequential and combinatorial exposure of cells to extrinsic factors. The olfactory epithelium is an excellent model to investigate regulation of this process, as it undergoes neuronal replacement post-natally. We have shown that the neurotrophins NGF and BDNF sequentially promote proliferation of developing olfactory sensory neuronal precursors, although their kinetics of proliferation and cell fate outcomes differ. Interestingly, CNP inhibits this neurotrophin-induced proliferation and promotes the maturation of these precursors to their next developmental stage. Here, we investigate the mechanisms behind these actions. Both NGF and BDNF increase the expression of cyclin D1 and cyclin-dependent kinase 4 (cdk4), with temporal expression patterns that parallel the proliferation kinetics of their cellular targets. The timing of cyclin D1 expression reflects differences in the need for transcription and translation in early and late stage precursors. CNP inhibits neurotrophin-induced cyclin D1 expression, and induces the expression of different profiles of inhibitory cell cycle proteins, which are neurotrophin-specific and correlate with the attainment of different maturational cell fates. Inhibition of protein degradation reverses the effects of neurotrophins and CNP on cyclin D1 and inhibitor expression levels, respectively. These results suggest a model for cell cycle regulation that involves the simultaneous expression of progressive and inhibitory cell cycle regulatory proteins in response to both proliferation and differentiation agents, followed by selective degradation of these proteins, providing a mechanism for rapid and exquisite control of the cell cycle.
authors.affiliation: Department of Neuroscience, The Johns Hopkins University School of Medicine, Baltimore, Maryland, USA.
authors.forename: P Jeanette
authors.initials: PJ
authors.lastname: Simpson
authors.forename: Cheil
authors.initials: C
authors.lastname: Moon
authors.forename: Amy M
authors.initials: AM
authors.lastname: Kleman
authors.forename: Erin
authors.initials: E
authors.lastname: Connolly
authors.forename: Gabriele V
authors.initials: GV
authors.lastname: Ronnett
mesh_terms: D000818:Animals; D019208:Brain-Derived Neurotrophic Factor / Q000037:antagonists & inhibitors / Q000235:genetics / Q000494:pharmacology*; D018797:Cell Cycle Proteins / Q000378:metabolism*; D002454:Cell Differentiation; D049109:Cell Proliferation / Q000187:drug effects; D002478:Cells, Cultured; D019938:Cyclin D1 / Q000378:metabolism; D051358:Cyclin-Dependent Kinase 4 / Q000378:metabolism; D003513:Cycloheximide / Q000494:pharmacology; D020935:MAP Kinase Signaling System; D020098:Natriuretic Peptide, C-Type / Q000494:pharmacology*; D020932:Nerve Growth Factor / Q000037:antagonists & inhibitors / Q000235:genetics / Q000494:pharmacology*; D018034:Olfactory Receptor Neurons / Q000166:cytology / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism; D061988:Proteasome Inhibitors; D051381:Rats; D013234:Stem Cells / Q000166:cytology / Q000378:metabolism*
chemical_list: D019208:Brain-Derived Neurotrophic Factor; D018797:Cell Cycle Proteins; D061988:Proteasome Inhibitors; D020098:Natriuretic Peptide, C-Type; D019938:Cyclin D1; D020932:Nerve Growth Factor; D003513:Cycloheximide; D051358:Cyclin-Dependent Kinase 4; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease