Mutant Huntingtin Affects Cortical Progenitor Cell Division and Development of the Mouse Neocortex

Abstract

A polyglutamine expansion in huntingtin (HTT) causes the specific death of adult neurons in Huntington's disease (HD). Most studies have thus focused on mutant HTT (mHTT) toxicity in adulthood, and its developmental effects have been largely overlooked. We found that mHTT caused mitotic spindle misorientation in cultured cells by altering the localization of dynein, NuMA, and the p150Glued subunit of dynactin to the spindle pole and cell cortex and of CLIP170 and p150Glued to microtubule plus-ends. mHTT also affected spindle orientation in dividing mouse cortical progenitors, altering the thickness of the developing cortex. The serine/threonine kinase Akt, which regulates HTT function, rescued the spindle misorientation caused by the mHTT, by serine 421 (S421) phosphorylation, in cultured cells and in mice. Thus, cortical development is affected in HD, and this early defect can be rescued by HTT phosphorylation at S421.

Selective expression of mutant huntingtin during development recapitulates characteristic features of Huntington’s disease

“…5D]. For units that we categorized as undergoing LTD, the ratio of extra spikes post-HFS/pre-HFS was comparable among all experimental mice [H (2,45) = 3.382, P = 0.184; Fig. 5E].…”

“…3A]. However, at 9 mo of age, both Q97 and Q97 CRE mice exhibited shorter latencies to fall compared with CTL mice [F (2,27) = 20.68, P < 0.0001; Fig. 3A].…”

“…Seven days postinjection, striatal lesions were quantified using Fluoro-Jade C (Millipore), a cell death marker. PBS-mediated lesions were similar across all experimental groups [F (2,11) = 0.245, P = 0.786], and were smaller than those lesions resulting from QA [t (8) ER yields highly efficient levels of mHtt excisional recombination in Q97 CRE mice. In contrast to striatal Q97 specimens, RT-PCR amplicons using primers that selectively detect the presence of mutant exon 1 of the Htt cDNA (Top) and Western blot analysis probed with the mAb 2166 anti-Htt antibody (∼350 kDa, Bottom) show no discernible bands in control and Q97 CRE striatal specimens (n per strain = 3).…”

“…To examine motor coordination, we measured the number of slips of the mice using the balance beam test. Compared with CTL mice, both 3-and 9-mo-old Q97 CRE and Q97 mice displayed higher numbers of slips [F (2,26) = 3.92, P = 0.032 and F (2,28) = 39.4, P < 0.0001, respectively; Fig. 3C].…”

“…Research initiatives in the field have traditionally focused on defining the biological processes mediating neuronal dysfunction and death during adult life. More recently, our studies and others have shown that the HD pathogenic mutation impairs the specification and maturation of striatal medium spiny neurons (MSNs), the primary target of HD neurodegeneration, and alters cortical progenitor cell divisions and neurogenesis by causing deregulation of mitotic spindle orientation (1,2). Although the role of these diverse developmental defects for HD pathogenesis remains undefined, they have the potential to impair the integrity of striatal and cortical neuronal homeostasis and function through multiple inductive interactions.…”