Chapter 7 Retinal axon divergence in the optic chiasm: growth cone behaviors and signalling cells

Abstract

Publisher Summary The chapter describes the behavior of retinal ganglion cell axon growth cones within the chiasm and the resident cells in this region. Subsequently, it also discusses the potential mechanisms by which ventrotemporal or uncrossed axons diverge from crossing axons. In the optic chiasm, the trajectories of retinal axons during divergence to ipsi- and contralateral targets, the tempo of growth and behaviors of retinal axon growth cones during the process of divergence, and the resident cells that might direct divergence have been characterized. The process of divergence is a multi-step progression, most likely involving several classes of molecular directives, including the retardation of growth of all axons in the midline zone, specific and/or differential inhibition and permission to transgress the midline, and refasciculation with axons of different retinal origin. With the culture systems based on the living slices or dissociated cells of the chiasm midline, it should now be possible to investigate and to identify the cellular and molecular mechanisms that direct retinal axon divergence. In addition, an analysis of patterns of gene expression and of the retinal axon patterning in the albino should elucidate the specification of retinal ganglion cells underlying the responses to cues in the optic chiasm.