Sirt6 regulates the proliferation of neural precursor cells and cortical neurogenesis in mice.

Sirt6, a member of the class III histone deacetylases (HDACs), functions in the regulation of genomic stability, DNA repair, cancer, metabolism and aging. Sirt6 deficiency is lethal, and newborn SIRT6-null cynomolgus monkeys show unfinished brain development. After the generation of a cortex-specific Sirt6 conditional knockout mouse model, we investigated the specific deletion of Sirt6 in NPCs at E10.5. This study found that Sirt6 deficiency causes excessive proliferation of neural precursor cells (NPCs) and retards differentiation. The results suggest that endogenous Sirt6 in NPCs regulates histone acetylation and limits stemness-related genes, including Notch1, in order to participate in NPC fate determination. These findings help elucidate Sirt6's role in brain development and in NPC fate determination while providing data on species generality and differentiation.

Comparison of the Spatiotemporal Expression Patterns of Three Cre Lines, Emx1IRES-Cre, D6-Cre and hGFAP-Cre, Commonly Used in Neocortical Development Research.

Emx1IRES-Cre, D6-Cre and hGFAP-Cre are commonly used to conditionally manipulate gene expression or lineage tracing because of their specificity in the dorsal telencephalon during early neurogenesis as previously described. However, the spatiotemporal differences in Cre recombinase activity would lead to divergent phenotypes. Here, we compared the patterns of Cre activity in the early embryos among the three lines by mating with reporter mice. The activities of Emx1IRES-Cre, D6-Cre and hGFAP-Cre were observed in the dorsal telencephalon, starting from approximately embryonic day 9.5, 11.5 and 12.5, respectively. Although all the three lines have activity in radial glial cells, Emx1IRES-Cre fully covers the dorsal and medial telencephalon, including the archicortex and cortical hem. D6-Cre is highly restricted to the dorsal telencephalon with anterior-low to posterior-high gradients, partially covers the hippocampus, and absent in the cortical hem. Moreover, both Emx1IRES-Cre and hGFAP-Cre exhibit Cre activity outside the dorsal neocortex. Meanwhile, we used the three Cre lines to mediate Dicer knockout and observed inconsistent phenotypes, including discrepancies in radial glial cell number, survival and neurogenesis in the neocortex and hippocampus. Together we proved differences in Cre activity can perturb the resultant phenotypes, which aid researchers in appropriate experimental design.

Zbed3 Is Indispensable for Wnt Signaling Regulation of Cortical Layers Formation in Developing Brain.

Wnt/ß-catenin signaling plays multiple important roles during mammalian brain development, and it regulates the proliferation and differentiation of neural progenitors in a context-dependent manner and affects neocortex layer formation. However, the specific role of Wnt/ß-catenin in neuronal layer fate determination in the neocortex is still unclear. Here, we report that Zbed3, which is a positive regulator of Wnt/ß-catenin signaling, colocalizes with ß-catenin at the endfeet of radial glia in the ventricular zone of embryo mouse neocortex. Overexpression and knockdown of Zbed3 increased and decreased the activity of Wnt/ß-catenin signaling in the neocortex, respectively. Interestingly, knockdown of Zbed3 in vivo could significantly shift neuronal fates from deep layers to upper layers but is not required for the proliferation and differentiation of neural progenitors. Overexpression of Zbed3 led to increased generation of deep-layer neurons without impairing cell cycle exit of neural progenitors. More importantly, knockdown of Zbed3 could effectively block the effects of the ectopic expression of stabilized ß-catenin on neocortex layer formation. Hence, our results demonstrate that Zbed3 is indispensable for Wnt/ß-catenin signaling regulating neuronal layer fates in the developing brain.