Impaired Olfactory Bulb Neurogenesis In Conditional Mutant Mice Of The Transcription Factor Sp8

Olfactory bulb (OB) acts as the primary olfaction processing center, which contains several distinct subtypes of inhibitory interneurons. These specific interneuron subtypes arise from molecular defined LGE/SVZ progenitor pools, which process is regulated by both intrinsic mechanisms and extrinsic environment. Previous work in our lab has shown that PV+ interneurons in the EPL of rat OB are also generated from the SVZ, but the specific regulating mechanism remains unclear.The transcription factor Sp8, a new member of the Sp1 zinc-finger protein family, plays essential roles in limb morphogenesis and development of the central nervous system. In the present study, using immunohistochemical staining, we found that nearly all the PV+ interneuorns in the EPL of mouse OB co-express Sp8. Our fate mapping data show that Dlx5/6-expressing progenitors contribute to PV+ interneurons in the OB. Genetic ablation of Sp8 in Dlx5/6 lineage by cre/loxp based recombination resulted in complete loss of Sp8 expression in the OB, indicating that Dlx5/6 lineage contributes to nearly all the PV+ EPL interneurons. Compared to controls, the density of PV+/Sp8+ interneurons was reduced by 80% in the EPL of conditional mutant mice OB, and we did not observe any increase in other interneuron subtypes in the EPL.In addition, we explored the function of Sp8 in newly born OB interneurons after birth. Utilizing shRNA mediated gene knockdown and Ad-cre based recombination, we successfully depleted the expression of Sp8 in newborn OB interneurons. In these cells, however, we did not observe any significant phenotypes compared to controls. In order to find the downstream signaling molecules of Sp8, we performed whole genome expression profile analysis in the OBs of conditional mutant mice and wild type controls, using Agilent gene expression array. Compared to controls, we identified 68 and 23 genes that have two fold up/down-regulation in the OB of conditional knockout mice, respectively.Collectively, in the present study, we show for the first time that Dlx5/6-expressing progenitors contribute to nearly all the PV+ interneurons in the EPL of mice OB and Sp8 is required for the normal production of these PV+ interneurons. These data expand our understanding of molecular regulation of OB interneuron production.