Cerebellum (2010) 9:537–547 DOI 10.1007/s12311-010-0190-9 c- and N-myc Regulate Neural Precursor Cell Fate, Cell Cycle, and Metabolism to Direct Cerebellar Development Alice Wey & Veronica Martinez Cerdeno & David Pleasure & Paul S. Knoepfler Published online: 25 July 2010 # The Author(s) 2010. This article is published with open access at Springerlink.com Abstract Separate murine knockout (KO) of either c- or N- myc genes in neural stem and precursor cells (NSC) driven by nestin-cre causes microcephaly. The cerebellum is particularly affected in the N-myc KO, leading to a strong reduction in cerebellar granule neural progenitors (CGNP) and mature granule neurons. In humans, mutation of N-myc also causes microcephaly in Feingold Syndrome. We created a double KO (DKO) of c- and N-myc using nestin-cre, which strongly impairs brain growth, particu- larly that of the cerebellum. Granule neurons were almost absent from the Myc DKO cerebellum, and other cell types were relatively overrepresented, including astroglia, oligodendrocytes, and Purkinje neurons. These findings are indicative of a profound disruption of cell fate of cerebellar stem and precursors. DKO Purkinje neurons were strikingly lacking in normal arborization. Inhibitory neurons were ectopic and exhibited very abnormal GAD67 staining patterns. Also consistent with altered cell fate, the adult DKO cerebellum still retained a residual external germinal layer (EGL). CGNP in the DKO EGL were almost uniformly NeuN and p27KIP1 positive as well as negative for Math1 and BrdU at the peak of normal cerebellar proliferation at P6. The presence of Electronic supplementary material The online version of this article (doi:10.1007/s12311-010-0190-9) contains supplementary material, which is available to authorized users. A. Wey : V. M. Cerdeno : D. Pleasure : P. S. Knoepfler (*) Institute of Pediatric Regenerative Medicine, University of California Davis School of Medicine, Sacramento, CA 95817, USA e-mail: knoepfler@ucdavis.edu A. Wey : V. M. Cerdeno : D. Pleasure : P. S. Knoepfler Department of Cell Biology and Human Anatomy, Shriners Hospital for Children Northern California, Sacramento, CA 95817, USA some mitotic CGNP in the absence of S phase cells suggests a possible arrest in M phase. CGNP and NSC metabolism also was affected by loss of Myc as DKO cells exhibited weak nucleolin staining. Together these findings indicate that c- and N-Myc direct cerebellar development by maintaining CGNP and NSC populations through inhibiting differentiation as well as directing rapid cell cycling and active cellular metabolism. Keywords Cerebellum . Myc . Neural stem cells . Transcription . Differentiation Introduction Myc is most well known for its role in tumorigenesis when overexpressed including medulloblastomagenesis [1–6], but at physiological levels myc genes are important regulators of many aspects of normal cellular biological behavior including cellular metabolism and cell cycling (Reviewed in [7]). Myc genes encode atypical members of the basic- helix-loop-helix zipper transcription factor superfamily, which can activate and repress the transcription of specific genes. In addition in some cells including cerebellar granule neural progenitors (CGNP), they can act more globally on chromatin to maintain euchromatic domains associated with specific histone modifications such as acetylation of lysine 9 and methylation of lysine 4 of histone H3, as well as others including modifications of histone H4 [8–13]. While the vast majority of Myc studies have been conducted in tumor cells, there is growing evidence of key roles for myc genes at endogenous levels in both somatic and embryonic stem cells. Constitutive knockout (KO) of c- or N-myc causes embryonic lethality around midgestation [14, 15]. Conditional disruption of N-myc in neural stem