Cephalic Hedgehog’s role in facilitating retinal axon recognition of the optic tectum target site during embryonic development in Xenopus laevis

Vertebrate hedgehog family proteins are integral for embryonic cell differentiation. The most well known gene in this class of morphogens is sonic hedgehog¸ shh. With regard to visual system development, the function of hedgehog gene homologues and the proteins they encode throughout retinal ganglion cell (RGC) extension is a topic of interest with many details yet to be elucidated. RGC axons create the exclusive link between eye and brain that facilitates visual perception, and has been well characterized in Xenopus. Xshh has most recently been characterized as a directional cue for RGC axon extension as well as potentially playing a role in successful recognition of the axon target, the optic tectum. I hypothesized that an additional Xenopus homologue cephalic hedgehog, Xchh facilitates RGC recognition of the target site, the optic tectum, and is therefore required for proper visual system wiring in the developing Xenopus embryo. Utilization of immunocytochemistry techniques were applied during tectal targeting stages 39-40 to visualize both Xchh expression with respect to axon extension into the midbrain where the optic tectum is located. The objective of this developing research is to determine precise expression patterns of Xchh as axons extend into the site of the optic tectum at stages 39-40 in Xenopus, as well as to determine if axons maintain their ability to recognize their target when Xchh expression is inhibited via introduction of Xchh morpholino. Immunofluorescence in stage 40 wildtype brain tissue illustrated that axons have in fact extended into the tectum and continue traveling along the optic tract. Additionally, morphologic analysis of like stage Xchh morpholino treated tissue revealed potential defects in neural tube closure, however, Xchh expression data for both samples proved inconclusive. Moreover, effective axon trajectory results could not be obtained in the morphant tissue, requiring further investigation for a definitive conclusion on Xchh’s influence on tectal targeting