Role of Cxcl12a on habenular axon projection in Danio rerio

Abstract

The habenula is a forebrain region that is responsible for many emotional responses. The habenular axons project posteriorly to the interpeduncular nucleus (IPN), a region in midbrain. Correct projection of these habenular axons depend on chemokine signaling. Components of this signaling pathway include chemokine ligand, Cxcl12a, and chemokine receptor, Cxcr4b. Cxcr4b is made in the habenula, while Cxcl12a is made along the path of the habenular axons. Loss of either Cxcl12a or Cxcr4b results in abnormal anterior growth of habenular axons. However, the exact function of Cxcl12a as a directional cue at the habenula is not known. To explore this, overexpression of cxcl12a is being performed. Overexpression of cxcl12a is induced by heat shock in larvae carrying a transgenic line that produces GFP in the habenula and its axons. Heat shock is performed at 33 hours post fertilization (hpf), several hours prior to initial axon outgrowth. However, there have been challenges confirming overexpression of cxcl12a at this time point. Once overexpression is confirmed we will examine the habenular axons at 5 days post fertilization (dpf). We hypothesize that the overexpression of cxcl12a in larval zebrafish will cause a disruption in the growth of the axons of the habenula, implying that Cxcl12a is an attractant in habenular axon guidance. If no habenular axon disruption is noted, this implies that 33 hpf is not the correct window for chemokine signaling at the habenula or that excess Cxcl12a is insufficient in disrupting habenular axon pathfinding.