Commissural projection from the vestibular nucleus in rat embryos: role of chondroitin sulfates

Abstract

To determine if chondroitin sulfates (CS) contribute restrictive guidance in commissural projections from the vestibular nucleus, we treated embryos (E12.5-14.5, Sprague-Dawley rats) with chondroitinase ABC or vehicle via the fourth ventricle for 24 hrs in culture and then tracked projections following DiI injection into the vestibular nucleus on one side. After 1 day in vitro (DIV), control treatment resulted in projections that were similar to those that developed in vivo. The projections remained fasciculated as they approached the midline (E12.5+1DIV), crossed the floor plate (E13.5+1DIV), and reached the contralateral nucleus (E14.5+1DIV). In enzyme- treated embryos, unfasciculated projections diverted from the course of the fasciculated pioneer-projections. To determine if the restrictive guidance is due to modulations in sulfation of chondroitins, we determined the mRNA expression profiles of chondroitin sulfotransferases in the hindbrains of E11.5-E16.5 embryos. Semi-quantitative RT-PCR indicated increasing expression as from E11.5 and by E13.5-14.5, peaking of the 6-sulfotransferase mRNA, leveled basal expression of the 4-sulfotransferase-1 mRNA and progressively rising 4-sulfotransferase-2 mRNA were observed. The results highlight roles of CS in fostering axonal fasciculation and limiting stray outgrowth and suggest involvement of chondroitin sulfotransferases in modulating these roles during development of vestibular commissures.