The zebrafish nlz gene has a rostral expression limit at the presumptive rhombomere (r) 3/r4 boundary during gastrula stages, and its expression progressively expands rostrally to encompass both r3 and r2 by segmentation stages, suggesting a role for nlz in hindbrain development. We find that Nlz is a nuclear protein that associates with the corepressor Groucho, suggesting that Nlz acts to repress transcription. Consistent with a role as a repressor, misexpression of nlz causes a loss of gene expression in the rostral hindbrain, likely due to ectopic nlz acting prematurely in this domain, and this repression is accompanied by a partial expansion in the expression domains of r4-specific genes. To interfere with endogenous nlz function, we generated a form of nlz that lacks the Groucho binding site and demonstrate that this construct has a dominant negative effect. We find that interfering with endogenous Nlz function promotes the expansion of r5 and, to a lesser extent, r3 gene expression into r4, leading to a reduction in the size of r4. We conclude that Nlz is a transcriptional repressor that controls segmental gene expression in the hindbrain. Lastly, we identify additional nlz-related genes, suggesting that Nlz belongs to a family of zinc-finger proteins.

C2H2 zinc finger proteins make up one of the largest protein families in eukaryotic organisms. Recent study in several different systems has identified a set of novel zinc finger proteins that appear to form a distinct subfamily that we have named the NET family. Members of the NET family (Noc, Nlz, Elbow, and Tlp-1) share two protein motifs--a buttonhead box and an Sp motif--with zinc finger proteins from the Sp family. However, the NET family is uniquely characterized by a single atypical C2H2 zinc finger, in contrast to the Sp family that contains three tandem C2H2 fingers. Here, we review current information about the biochemical function and in vivo role for members of this subfamily. In general, NET family proteins are required during embryonic development. They appear to act by regulating transcription, most likely as repressors, although they are unlikely to bind DNA directly. In the future, it will be important to directly test if NET family proteins control transcription of specific target genes, perhaps via interactions with DNA-binding transcription factors, as well as to further explore their function in vivo.

In this study, we first cloned nlz2, a second zebrafish member of the nlz-related zinc-finger gene family. nlz2 was expressed together with nlz1 in a broad posterior domain during gastrula stages as well as at the midbrain-hindbrain boundary and in the hindbrain caudal to rhombomere 4 during segmentation. nlz2 was also expressed in regions distinct from nlz1, notably in the forebrain, midbrain, and trunk. Misexpression of nlz2 in zebrafish embryos disrupted gene expression in the rostral hindbrain, similar to the effect of misexpressing nlz1. We next compared the nlz1 and nlz2 sequences to identify and characterize domains conserved within this family. We found a C-terminal domain required for nuclear localization and two conserved domains (the Sp motif and a putative C 2 H 2 zinc finger) required for nlz1 function. We also demonstrate that Nlz1 self-associated via its C terminus, interacted with Nlz2, and bound to histone deacetylases. Last, we found two forms of Nlz1 generated from alternative translation initiation sites in vivo. These forms have distinct activities, apparently depending on the function of the N-terminal Sp motif. Our data demonstrate that nlz2 functions similarly to nlz1 and define conserved domains essential for nuclear localization, self-association, and corepressor binding in this novel family of zinc-finger genes.nlz (herein referred to as nlz1) was recently identified as a member of a novel subfamily of zinc-finger genes (1, 2). We have demonstrated that nlz1 functions to control segmental gene expression in the zebrafish hindbrain and likely represses transcription by recruiting the corepressor Groucho (3). Sequence similarities between members of this zinc-finger subfamily suggest that their functions are evolutionarily conserved and that the nlz-related genes nocA, elbow, and tlp-1 regulate embryonic development in Drosophila (4, 5) and Caenorhabditis elegans (6). Homozygous elbow and nocA mutants exhibit defects in tracheal development, particularly stalled and aberrant migration of the dorsal branch and lateral trunks of the trachea (5). Conversely, misexpression of elbow in the trachea results in the repression of genes expressed in the visceral branch and dorsal trunk, whereas the number of cells forming the dorsal branch increases (5). Homozygous nocA mutants also display brain abnormalities such as protrusion of the embryonic supraesophageal ganglion and a reduction of ocelli (4). Mutations in tlp-1 affect specification of asymmetric cell fates and cell fusion, resulting in abnormal tail morphogenesis in C. elegans (6). This family also includes two hypothetical proteins each in mouse and human, which have not yet been functionally characterized (1, 3, 5).The Nlz subfamily of zinc-finger proteins is related to the vertebrate Sp1-like family of transcription factors (3, 6), and members of both families are expressed in developing embryos. However, although nlz-related genes have restricted expression patterns, sp1-related genes are more ubiquitously expressed. Sp1-like proteins ...

In FriedreichÕs ataxia, reduction of the mitochondria protein frataxin results in the accumulation of iron and reactive oxygen species, which leads to oxidative damage, neurodegeneration and a diminished lifespan. Recent studies propose that frataxin might play a role in the antioxidative process. Here we show that overexpression of Drosophila frataxin in the mitochondria of female transgenic animals increases antioxidant capability, resistance to oxidative stress insults, and longevity. This suggests that Drosophila frataxin may function to protect the mitochondria from oxidative stresses and the ensuing cellular damage.