oa Analysis of cortical development in Lis1-GFP mice

The Lis1 gene encodes a non-catalytic sub-unit of the platelet-activating factor acetyl hydrolase enzyme (PAFAH1B1). Increased PAFAH1B1 dosage in humans causes mild brain structural abnormalities, moderate to severe developmental delay and failure to thrive. To investigate the effects of Lis1 over expression on cortical development, we analyzed the brains of Lis1-GFP mice with 30% over expression in the Lis1 gene.

Cortical width was thinner for Lis1-GFP mice than for wild type at embryonic day 14.5 (E14.5), post-natal day 1 (P1) and P6 but appeared to be similar at P120. Analysis of cell proliferation at E14.5 showed a reduction in rates of proliferation at the ventricular zone (VZ) of Lis1-GFP mice compared to wild type. As a result, less Pax6-positive cells of the VZ were seen at P1 in the Lis1-GFP mice. Immunostaining for pyramidal neuron marker Brn2 showed cellular disorganization within the upper cortical layers (layers II and III) of P1 mice, while other layers (I, IV, V and VI) appeared to form properly. Analysis of cortical plate formation and laminar structure via BrdU birth-dating at P1 and P21 showed successful radial migration of neurons born at the VZ at ∼E12.5 and ∼E14.5 to their final destined layer. Disorganization of layers II and III was also seen in BrdU birth-dating analysis, and that supported our Brn2 findings. The number and density of mature neurons was assessed in the cerebral cortex of adult Lis1-GFP mice (P120). Numbers and densities were similar in all cortical layers between Lis1-GFP mice and wild type, except for layers II and III which showed significant reduction in neuronal count. Quantification of GABAergic interneurons within the six cortical layers of P120 mice revealed no significant difference between wild type and Lis1-GFP mice.

Collectively, our results show that Lis1 over expression in the Lis1-GFP mice results in decreased proliferation rates of neuronal progenitors at the VZ pre-natally. Subsequently, this may interfere with the proper formation of upper cortical layers (layers II and III) in young and adult Lis1-GFP mice.