Roles of the nlz zinc finger protein in zebrafish development

Our laboratory studies anteroposterior axis formation in the zebrafish embryo. A subtractive hybridization-based cloning approach has identified the nlz (nocA like zinc finger) gene, which is first expressed in the blastoderm margin and then in a broad dorsoposterior domain that extends from the rhombomere (r) 3/r4 boundary to the caudal end of the embryo. During somitogenesis, expression becomes restricted to the hindbrain where it progressively expands anteriorly to encompass both r3 and r2, while expression caudal to r4 is reduced. Ectopic expression of nlz in zebrafish embryos leads to a reduction in r3 gene expression (krox20, ephA4) that is at least partially replaced by the expansion of r4 gene expression (hoxb1a, ephrinB2a). To elucidate functional domains within nlz, a series of deletions within the nlz construct have indicated that the C2H2 zinc finger and an unidentified domain conserved among the Sp1 family of transcription factors are important for the r3/r4 phenotype and the C-terminus is required for nuclear localization. Defects in cellular movements of convergence were exhibited either with the injection of nlz constructs with N-terminal deletions or with a VP16 activation domain fused to full-length nlz. This phenotype is reminiscent of the expression of soluble Eph receptor tyrosine kinases and their ephrin ligands. We hypothesize that nlz is involved in the coordination of cell migration and the proper formation of r3 and r4 through the regulation of Eph and ephrin signaling.