N-myc is essential during neurogenesis for the rapid expansion of progenitor cell populations and the inhibition of neuronal differentiation.
To address the role of N-myc in neurogenesis and in nervous system tumors, it was conditionally disrupted in neuronal progenitor cells (NPCs) with a nestin-Cre transgene. Null mice display ataxia, behavioral abnormalities, and tremors that correlate with a twofold decrease in brain mass that disproportionately affects the cerebellum (sixfold reduced in mass) and the cerebral cortex, both of which show signs of disorganization. In control mice at E12.5, we observe a domain of high N-Myc protein expression in the rapidly proliferating cerebellar primordium. Targeted deletion of N-myc results in severely compromised proliferation as shown by a striking decrease in S phase and mitotic cells as well as in cells expressing the Myc target gene cyclin D2, whereas apoptosis is unaffected. Null progenitor cells also have comparatively high levels of the cdk inhibitors p27(Kip1) and p18(Ink4c), whereas p15(Ink4b), p21(Cip1), and p19(Ink4d) levels are unaffected. Many null progenitors also exhibit altered nuclear morphology and size. In addition, loss of N-myc disrupts neuronal differentiation as evidenced by ectopic staining of the neuron specific marker betaTUBIII in the cerebrum. Furthermore, in progenitor cell cultures derived from null embryonic brain, we observe a dramatic increase in neuronal differentiation compared with controls. Thus, N-myc is essential for normal neurogenesis, regulating NPC proliferation, differentiation, and nuclear size. Its effects on proliferation and differentiation appear due, at least in part, to down-regulation of a specific subset of cyclin-dependent kinase inhibitors.
Knoepfler
Paul S
PS
Division of Basic Sciences, Fred Hutchinson Cancer Research Center, Seattle, Washington 98109, USA.
Cheng
Pei Feng
PF
Eisenman
Robert N
RN
D000818:Animals; D017209:Apoptosis; D001259:Ataxia; D001522:Behavior, Animal; D002454:Cell Differentiation / Q000502:physiology; D002455:Cell Division; D002531:Cerebellum / Q000196:embryology* / Q000502:physiology; D056742:Cyclin D2; D018844:Cyclin-Dependent Kinases; D016213:Cyclins / Q000378:metabolism; D004247:DNA / Q000378:metabolism; D017931:DNA Primers / Q000737:chemistry; D005786:Gene Expression Regulation; D016259:Genes, myc / Q000502:physiology*; D007124:Immunoenzyme Techniques; D019426:Integrases / Q000378:metabolism; D051379:Mice; D018345:Mice, Knockout; D009024:Morphogenesis; D009474:Neurons / Q000502:physiology*; D012333:RNA, Messenger / Q000235:genetics; D020133:Reverse Transcriptase Polymerase Chain Reaction; D013234:Stem Cells / Q000502:physiology*; D014202:Tremor; D014764:Viral Proteins / Q000378:metabolism
C486196:Ccnd2 protein, mouse; D056742:Cyclin D2; D016213:Cyclins; D017931:DNA Primers; D012333:RNA, Messenger; D014764:Viral Proteins; D004247:DNA; D018844:Cyclin-Dependent Kinases; C045073:Cre recombinase; D019426:Integrases