Marzban, H. | bioRxiv Science

bioRxiv2017

Axons from the trigeminal ganglia are the earliest afferent projections to the mouse cerebellum

The first stage standard model for the development of afferent pathways to the cerebellum is that ingrowing axons target the embryonic Purkinje cells (E13-E16 in mice). Perinatally and early postnatal (E18-P15) the climbing fibers translocate to the Purkinje cell dendrites, and as the granular layer develops the mossy fibers translocate from the Purkinje cell somata and synapse with granule cell dendrites. In this report we describe a novel earlier stage in the development. Immunostaining for a neurofilament-associated antigen (NAA) reveals the early axon distributions with remarkable clarity. Axons from the trigeminal system enter the cerebellar primordium as early as embryo age (E)9. By using a combination of axon tract tracing, analysis of neurogenin1 null mice - which do not develop trigeminal ganglia - and mouse embryos maintained in vitro - we show that the first axons to innervate the cerebellar primordium are direct projections from the trigeminal ganglia. The data show that the early trigeminal projections are in situ before the Purkinje cells are born, and double immunostaining for NAA and markers of the different domains in the cerebellar primordium reveal that they first target the cerebellar nuclear neurons of the nuclear transitory zone (E9-E10), and only later (E10-E11) extend collateral branches to the Purkinje cell plate.

neuroscience↗

bioRxiv2017

Early Subset Of Cerebellar Nuclei Neurons Derived From Mesencephalon In Mice

Cerebellar nuclei (CN) neurons serve as the primary output of the cerebellum and originate from the cerebellar primordium at early stages of cerebellar development. These neurons are diverse, integrating information from the cerebellar cortex and relaying it to various brain regions. Employing various methodologies, we have characterized a specific subset of CN neurons that do not originate from the rhombic lip or ventricular zone of the cerebellar primordium. Embryos were collected at early stages of development and processed for immunohistochemistry (IHC), Western blotting, in situ hybridization (ISH), embryonic culture, DiI labeling, and flow cytometry analysis (FCM). Our findings indicate that a subset of CN neurons expressing -synuclein (SNCA), OTX2, MEIS2, and p75NTR (NGFR) are located in the rostroventral region of the nuclear transitory zone (NTZ). While CN neurons derived from the rhombic lip are positioned in the caudodorsal area of the NTZ in the cerebellar primordium. Utilizing Otx2-GFP and Atoh1-/- mice, we have determined that these cells do not originate from the germinal zone of the cerebellar primordium. These results suggest the existence of a novel extrinsic germinal zone for the cerebellar primordium, possibly the mesencephalon, from which early CN neurons originate. SIGNIFICANCE STATEMENTThe cerebellum contains a variety of distinct neuronal populations, each playing a significant role in its function within the brain. This research demonstrates that a particular subset of cerebellar nuclei neurons originates from a previously unrecognized germinal zone specific to the cerebellar primordium, independently of Atoh1s influence.

developmental biology↗