N-myc is essential during neurogenesis for the rapid expansion of progenitor cell populations and the inhibition of neuronal differentiation

Abstract

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 ␤TUBIII 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.

The N-myc Oncogene: Maximizing its Targets, Regulation, and Therapeutic Potential

“…N-myc drives proliferation of granule neuron precursors derived from neuronal progenitor cells of the developing forebrain and hindbrain (10). Constitutive deletion of N-myc is embryonic lethal (6,9), whereas conditional inactivation in neuronal progenitor cells leads to ataxia, behavioral abnormalities, and tremors that correlate with an overall 2-fold decrease in brain mass that disproportionately affects the cerebellum and the cerebral cortex, both of which show signs of disorganization.…”

The Proto-Oncogene Myc Is Essential for Mammary Stem Cell Function

“…Cryosections were thawed at room temperature for 30 minutes, fixed for 15 minutes in 2% formaldehyde, 0.2% glutaraldehyde, 0.02% Nonidet P40 in PBS, washed with PBS, and incubated with the X-gal staining solution (0.025% X-gal, 3 mM K 3 Fe(CN) 6 , 3 mM K 4 Fe(CN) 6 , 1.5 mM MgCl 2 , 15 mM NaCl, 40 mM Hepes, and pH 8) overnight at 30 C. The sections were then postfixed with 4% formaldehyde and counterstained with nuclear Fast Red. X-gal staining of colonies was performed as for cryosections after fixation in 2% formaldehyde and 0.2% glutaraldehyde at 4 C for 4 minutes.…”

“…Several studies implicate Myc in the regulation of selfrenewal and differentiation of hematopoietic stem cells [3] and the maintenance of stem/progenitor cell function in the epidermis and intestine [4,5]. The related factor N-Myc plays an important role in the regulation of neural stem/progenitor cells [6].…”

Ink4c is dispensable for tumor suppression in Myc-induced B-cell lymphomagenesis

“…Ink4c expression is sustained in Em-Myc lymphomas Myc suppresses the expression of several CKIs, including p27 Kip1 , p21 Cip1 , p15 Ink4b and p18 Ink4c (Seoane et al, , 2002Staller et al, 2001;Yang et al, 2001;Herold et al, 2002;Knoepfler et al, 2002;Wu et al, 2003). To investigate potential links between Myc and p18 Ink4c , we initially used Affymetrix gene chip microarray analysis and compared the expression of Ink4c to that of other Ink4 family members, CKIs, Cdk4 and Cdk6 in B220 þ splenocytes isolated from wild-type and precancerous Em-Myc transgenic littermates ( Figure 1a).…”

“…Myc overexpression accelerates cell cycle progression (Roussel et al, 1991), and this occurs through their induction of D-type cyclins (Bouchard et al, 1999) and their partner Cdk4 (Hermeking et al, 2000), as well as by repressing p21 Cip1 (Herold et al, 2002;Seoane et al, 2002;Wu et al, 2003), p27 Kip1 (Yang et al, 2001), p15 Ink4b Staller et al, 2001) and p18 Ink4c (Knoepfler et al, 2002). However, in normal cells this proliferative response is counterbalanced by Myc's ability to provoke apoptosis (Askew et al, 1991;Evan et al, 1992;Eischen et al, 1999;Pelengaris et al, 2002;Nilsson and Cleveland, 2003).…”