Netrin1 is required for neural and glial precursor migrations into the olfactory bulb

Netrin1 (NTN1) deficiency in mouse brain causes defects in axon guidance and cell migration during embryonic development. Here we show that NTN1 is required for olfactory bulb (OB) development at late embryogenesis and at early postnatal stages to facilitate the accumulation of proper numbers of granular and glomerular neuron subtypes and oligodendrocytes into the OB. In addition to the analysis of Ntn1−/− mice we made tissue and neurosphere cultures to clarify the role of NTN1 in the anterior forebrain. We propose that a subset of neural progenitors/precursors requires NTN1 to efficiently enter the rostral migratory stream to migrate into the OB. The analysis of postnatal Ntn1−/− OBs revealed a reduction of specific types of interneurons which have been shown to originate from particular subregions of the lateral ventricle walls. Based on Ntn1 expression in ventral parts of the ventricle walls, we observed a decrease in the mainly ventrally derived type II interneurons that express calcium-binding proteins calretinin and calbindin. Instead, no change in the numbers of dorsally derived tyrosine hydroxylase expressing interneurons was detected. In addition to the specific reduction of type II interneurons, our results indicate that NTN1 is required for oligodendroglial migration into the OB. Furthermore, we characterised the Ntn1 expressing subpopulation of neurosphere-forming cells from embryonic and adult brain as multipotent and self-renewing. However, NTN1 is dispensable for the proliferation of neurosphere forming progenitor cells and for their differentiation.

Research highlights
► Netrin1 is required for OB development.
► Specific interneuron subtypes are reduced in Netrin1−/− OBs.
► New knowledge on how oligodendrocytes populate the OB.
► Netrin1 acts cell-autonomously or at short-distance.
► Netrin1 expressing neural progenitor cells are multipotent in vivo and in vitro.