Type IV Collagen Controls the Axogenesis of Cerebellar Granule Cells by Regulating Basement Membrane Integrity in Zebrafish.

Miki Takeuchi,Shingo Yamaguchi,Tetsuya Higashiyama,Yoshikatsu Sato,Takashi Shimizu,Kisa Kakiguchi,Masahiko Hibi,Shigenobu Yonemura,Cecilia Moens

doi:10.1371/journal.pgen.1005587

Abstract

Granule cells (GCs) are the major glutamatergic neurons in the cerebellum, and GC axon formation is an initial step in establishing functional cerebellar circuits. In the zebrafish cerebellum, GCs can be classified into rostromedial and caudolateral groups, according to the locations of their somata in the corresponding cerebellar lobes. The axons of the GCs in the caudolateral lobes terminate on crest cells in the dorsal hindbrain, as well as forming en passant synapses with Purkinje cells in the cerebellum. In the zebrafish mutant shiomaneki, the caudolateral GCs extend aberrant axons. Positional cloning revealed that the shiomaneki (sio) gene locus encodes Col4a6, a subunit of type IV collagen, which, in a complex with Col4a5, is a basement membrane (BM) component. Both col4a5 and col4a6 mutants displayed similar abnormalities in the axogenesis of GCs and retinal ganglion cells (RGCs). Although type IV collagen is reported to control axon targeting by regulating the concentration gradient of an axonal guidance molecule Slit, Slit overexpression did not affect the GC axons. The structure of the BM surrounding the tectum and dorsal hindbrain was disorganized in the col4a5 and col4a6 mutants. Moreover, the abnormal axogenesis of the caudolateral GCs and the RGCs was coupled with aberrant BM structures in the type IV collagen mutants. The regrowth of GC axons after experimental ablation revealed that the original and newly formed axons displayed similar branching and extension abnormalities in the col4a6 mutants. These results collectively suggest that type IV collagen controls GC axon formation by regulating the integrity of the BM, which provides axons with the correct path to their targets.

Highlights

The cerebellum is involved in various brain functions, including motor coordination and motor learning [1,2,3]
The cerebellum is involved in motor coordination and motor learning
We found that mutants of both col4a5 and col4a6 showed similar axonal abnormalities in both the granule cells and the retinal ganglion cells, and that the basement membrane structure surrounding the central nervous system was disrupted in these mutants

Summary

Introduction

The cerebellum is involved in various brain functions, including motor coordination and motor learning [1,2,3]. The GCs in the rostromedial lobes, the valvula cerebelli (Va) and corpus cerebelli (CCe), form a layer that is deep to the molecular layer These GCs are derived from neuronal progenitors located in the rostral part of the rhombic lip, which migrate ventrally. The GCs in the caudolateral lobes, the eminentia granularis (EG) and lobus caudalis cerebelli (LCa), are derived from neuronal progenitors in the caudal and lateral parts of the rhombic lip, and their somata lie superficial to the molecular layer. They send their axons to PCs in the cerebellum, and extend them caudally to the dendrites of crest cells, which are Purkinje-like cells, in the dorsal hindbrain. The mechanisms responsible for the formation of these two distinct GC circuits remain unknown

Methods

Results

Conclusion