Genetic regulation of adult hippocampal neurogenesis: A Systems genetics approach using BXD recombinant inbred mouse strains

Adult hippocampal neurogenesis is regulated at various levels and by various factors. Genetic influence is an important key determinant of adult neurogenesis and exerts its effects at all levels. In vivo studies have suggested that adult hippocampal neurogenesis is highly variable and heritable among different laboratory strains of mice. To dissect the genetic effect from other contributing factors, it is necessary to study adult neurogenesis under highly controlled environment conditions. We extracted adult hippocampal precursor cells (AHPCs) from 20 strains of the BXD set of recombinant inbred mice, cultured them and studied the effect of genetic background on neurogenesis. The BXD panel consists of mouse lines derived from an intercross between inbred parentals C57BL/6J and DBA/2J. Both of the parentals are fully sequenced and all the strains are well characterized in terms of genotypic and phenotypic characteristics. This allows us to use advanced genetic techniques to identify novel genomic loci and gene-gene interactions important in adult neurogenesis. Comparison of the AHPCs from 20 BXD strains, with respect to cell proliferation and neuronal and astrocytic differentiation in vitro, revealed a large variation for these traits across the strains. Proliferation, as measured by BrdU incorporation, showed over two- fold differences between the extremes. Similar differences were observed for neurogenic (4-fold) and astrogenic differentiation (2-fold). These three traits all showed strong heritability values indicating that the differences were mainly attributed to the genetic component. QTL mapping, with these phenotypic data, revealed that there was no major contribution from single loci controlling these traits. Instead, we found many loci with smaller effects associated with these traits. Gene expression profiling using RNA samples from proliferating cultures of the 20 BXD mice strains yielded two cis eQTL candidates that directly regulated proliferation, LRP6