Glycerophosphodiester Phosphodiesterase GDE6 (gdpd4) belongs to the six transmembrane GDE protein family (GDE2, GDE3, and GDE6) a small family of enzymes that are expressed on the cell surface of neural cells. These proteins cleave within the GPI-anchor of GPI-anchored proteins, shedding them from the cell surface. GDE6 has been shown to be expressed by radial glia cells during neural patterning in the chick but its role is uncharacterized in the nervous system. GDE6 (gdpd4) has two homologs in the zebrafish gdpd4a and gdpd4b. In this project, we are investigating the role of gdpd4 in CNS development in zebrafish. To do this we examined the expression of gdpd4a and gdpd4b by whole-mount RNA in situ hybridization at different developmental stages in zebrafish. Both gdpd4a and gdpd4b are expressed in the forebrain, midbrain, hindbrain, and spinal cord at 24 and 48 hpf. While gdpd4b expression is restricted to earlier time points, gdpd4a continues to be expressed throughout the brain and spinal cord. By 5dpf, gdpd4a in zebrafish larvae is restricted to the brain. We concluded that gdpd4 is expressed during the early stages of brain development. We are using CRISPR/Cas9 to make gdpd4a and gdpd4b mutants to understand their function during neural development. We have identified a gdpd4a mutant with five-base pair insertion with a 30% germline mutation rate. Further analysis of homozygous gdpd4a mutants will allow us to examine its role during neural patterning.