Analysis of differential gene expression in the aging brain: the case study of Col4a1, Col25a1, and Id3 and their involvement in the adult neurogenesis of the short-lived teleost Nothobranchius furzeri

Adult neurogenesis is a highly dynamic process, decreasing exponentially with aging in many vertebrate species. In mammalian brain, it is restricted to the subventricular and subgranular zones, while in teleost fish it occurs in approximately sixteen regions distributed along the entire rostro-caudal brain axis. Among teleost fish, Nothobranchius furzeri is a well-established model for aging studies, due to its very short lifespan together with anatomical and physiological aging features. In vertebrates, Col4a1 is mainly located in brain ventricular areas, is involved in axonal growth and guidance, and participates in nerve repair; Col25a1 is specifically expressed in neurons and encodes for a protein named collagenous Alzheimer amyloid plaque component (CLAC), which binds to Alzheimer plaques reducing Aβ growth. Id3 is another gene required for embryonic neurogenesis and angiogenesis, and it persists in adult brain, where it regulates adult neural stem cells maintenance and function. Quantitative and qualitative analysis of Col4a1, Col25a1 and Id3 was assessed in N. furzeri young (5 weeks post hatching (wph)) and old (27 wph) brains, showing all the three genes are upregulated during aging and are expressed in recognizable neurogenic areas. Furthermore, double labeling of fluorescence in situ hybridization (FISH), for genes' mRNAs, and immunofluorescence (IF), for PCNA, confirms that Col4a1, Col25a1 and Id3 are expressed in numerous PCNA containing cells, confirming that their expression in nerogenic areas is related to cells proliferation and / or differentiation. The phenotype of Col4a1, Col25a1 and Id3 expressing cells was assessed by FISH/IF double labeling with neural markers S100, DCX, and HuC/D. Our data confirm that, as for other vertebrates, also in N. furzeri Col4a1, Col25a1 and Id3 are involved in adult neurogenesis. Furthermore, they colocalize mainly with DCX and HuC/D expressing cells, suggesting that they are involved in proliferation and differentiation of neural cells more than radial glial ones. These data lay the foundations to further studies on the pathways regulating Col4a1, Col25a1 and Id3, to better understand their specific role in neural proliferation and differentiation pathways and identifying possible interactors.