Mutations in genes encoding chromatin-remodelling proteins, such as the ATRX gene, underlie a number of genetic disorders including X-linked mental retardation syndromes; however knowledge of the role of these proteins in CNS development is limited. In Drosophila, ISWI is essential for development, the protein functions as the ATP-hydrolysing component in several chromatin-remodelling complexes. The two mammalian ISWI orthologs, SNF2H and SNF2L are differentially expressed, suggesting that they possess distinct developmental roles. Prevalent expression of SNF2H occurs during neuroprogenitor proliferation while SNF2L transcripts are increased in maturing neurons. It is well known that an appropriate balance between neuroprogenitor proliferation and neuronal differentiation during the embryonic stages is critical to regulate the size of the developing neocortex. Here, I have analyzed mice ablated for Snf2l chromatin remodelling activity to determine its role in cortical development. The loss of active Snf2l resulted in a 1.4-fold increase in the ratio between brain weight and body weight. This was accompanied by a concomitant increase in cell number in the cerebral cortical strata ranging from 1.3- to 1.6-fold (in embryonic and adult tissues). This increase did not coincide with an observable change in the frequency of apoptotic events. Pulse-labelling experiments with BrdU resulted in similar proportions of labelled cells within the periventricular zone of embryonic (E15.5) cortices from wildtype and mutant mice. We observed a 3-fold increase in mitotic cells by phospho-histone H3 staining. BrdU birthdating and BrdU/Ki67 double-labelling experiments revealed that there was a 3-fold increase in the number of progenitors that re-entered the cell cycle and a concomitant decrease in cell cycle exit. Gene expression analysis of Snf2l-mutants revealed a perturbation in the expression patterns of many genes, including genes encoding neurogenic factors and cell cycle regulators. One such gene identified was Foxg1. Foxg1 is regulated by Snf2l, and limiting Foxg1 mitigated the brain phenotype. Our results suggest loss of Snf2l alters the timing between cell cycle exit and differentiation leading to increased cell numbers in the developing neocortex.
| Identifer | oai:union.ndltd.org:uottawa.ca/oai:ruor.uottawa.ca:10393/29982 |
| Date | January 2010 |
| Creators | Yip, Darren John |
| Publisher | University of Ottawa (Canada) |
| Source Sets | Université d’Ottawa |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | 218 p. |
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