Zebra danio, Brain-Growth, Anterior commissure, Axonal transport, Astroglia, Diencephalon, Axon guidance
In the developing embryonic brain, axons are guided across the midline by contact attractants and repellants to form commissures. The postoptic commissure (POC) of the diencephalon is the first forming commissure in the zebrafish brain. During pathfinding, these POC axons closely contact a population of glial fibrillary acidic protein (Gfap) positive astroglia covering the midline. We hypothesize that diencephalic astroglia prefigure POC formation by serving as an instructive growth substrate to support axonal growth across the midline. To determine the necessity of Gfap+ astroglia in POC formation, we generated a gfap:nfsB-mCherry transgenic line to chemically induce Gfap+ cell ablation in a temporally controlled manner. Preliminary drug treatments in 10mM Metronidazole caused apoptosis of Gfap+ cells with associated axon scaffold errors by 52h of development. Our findings suggest astroglia may help maintain axonal pathways. We are currently testing if early ablation disrupts initial pathfinding. Unfortunately, little is known about the cellular and molecular identities of the Gfap+ astroglia. Using forebrain targeted transplantation of gfap:eGfp and olig2:eGfp transgenic cells into wild type embryos, we have identified four distinct astroglial populations surrounding POC axons: short and long radial glia, mesenchymal-like glial cells positioned on the posterior side of the commissure, and an Olig2+ mesenchymal cell positioned on the anterior side of the commissure. Furthermore, we have distinguished three molecularly distinct diencephalic sub-domains through zebrafish radial fiber (Zrf) 1-4 antibody labeling. Additionally, we are characterizing our glial morphologies based on differential Zrf immunoreactivity. Our current results support a model in which distinct populations of diencephalic astroglia play important roles in the guidance and maintenance of axonal pathways during development of the central nervous system.
Bashiruddin, Sarah Lubna, "Defining the cellular and molecular identities of diencephalic astroglia associated with postoptic commissure formation during Zebrafish forebrain development" (2010). Honors Project, Smith College, Northampton, MA.
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