C2H2 Zinc Finger Domain Research Articles

Identification of a novel gene, DZIP ( DAZ-interacting protein), that encodes a protein that interacts with DAZ (deleted in azoospermia) and is expressed in embryonic stem cells and germ cells

Evidence from diverse organisms, including humans, suggests that the DAZ ( Deleted in AZoospermia) gene and a closely related homolog, DAZL ( DAZ-like), are required early in germ cell development to maintain initial germ cell populations. Here we report the identification and characterization of the DZIP ( DAZ-Interacting Protein) gene, which encodes at least three different protein isoforms that contain a C2H2 zinc-finger domain. The DZIP gene is expressed predominantly in human embryonic stem cells and fetal and adult germ cells; moreover, two DZIP protein isoforms colocalize with DAZ and/or DAZL proteins in these tissues. Finally, we provide evidence indicating that DZIP may associate with DAZ and its other cofactors in an RNA-binding protein complex that functions in both ES cells and germ cells.

Characterization of HRG22, a Human Homologue of the Putative Tumor Suppressor Gene HIC1

Database searches identified on chromosome 22q11.2, a region subject to translocations, an homologue of the HIC1 (hypermethylated in cancer) candidate tumor suppressor gene located at 17p13.3. This gene was termed HRG22 for HIC1-related gene on chromosome 22. We have characterized a new HRG22 upstream coding exon and defined the complete coding sequence of the human and zebrafish HRG22 genes. Alignment of the HRG22 and HIC1 proteins from various species revealed high sequence homology in their N-terminal BTB/POZ and five C-terminal C2H2 zinc finger domains and highlighted a conserved GLDLSKK/R peptide in their middle region. The full-length HRG22 and HIC1 proteins colocalize onto nuclear dots and share several functional properties since their BTB/POZ domains heterodimerize and are autonomous transcriptional repression domain insensitive to Trichostatin A, a histone deacetylase (HDAC) inhibitor. Thus, HIC1 and HRG22 define a subgroup of BTB/POZ domains unable to recruit repressing complexes containing an HDAC activity.

Sp5, a New Member of the Sp1 Family, Is Dynamically Expressed during Development and Genetically Interacts with Brachyury

We describe the identification, biochemical characterisation, and mutation of a novel mouse gene: Sp5. Sp5 encodes a protein having a C-terminal C2H2 zinc finger domain closely related to that of the transcription factor Sp1. In vitro, DNA binding studies show that it binds to the GC box, a DNA motif present in the promoter of a very large number of genes, including Brachyury, and recognised by members of the Sp1 family. However, outside of its DNA binding domain, Sp5 has little homology with any other member of the Sp1 family. In contrast to the ubiquitous expression of Sp1, Sp5 exhibits a remarkably dynamic pattern of expression throughout early development. This is suggestive of a role in numerous tissue patterning events, including gastrulation and axial elongation; differentiation and patterning of the neural tube, pharyngeal region, and somites; and formation of skeletal muscle in the body and limbs. Mice homozygous for a targeted mutation in Sp5 show no overt phenotype. However, the enhancement of the T/+ phenotype in compound mutant mice (Sp5lacZ/Sp5lacZ, T/+) indicates a genetic interaction betweenSp5 and Brachyury. These observations are consistent with a role for Sp5 in the coordination of changes in transcription required to generate pattern in the developing embryo.

Brakeless is required for lamina targeting of R1-R6 axons in the Drosophila visual system.

Photoreceptors in the Drosophila eye project their axons retinotopically to targets in the optic lobe of the brain. The axons of photoreceptor cells R1-R6 terminate in the first optic ganglion, the lamina, while R7 and R8 axons project through the lamina to terminate in distinct layers of the second ganglion, the medulla. Here we report the identification of the gene brakeless (bks) and show that its function is required in the developing eye specifically for the lamina targeting of R1-R6 axons. In mosaic animals lacking bks function in the eye, R1-R6 axons project through the lamina to terminate in the medulla. Other aspects of visual system development appear completely normal: photoreceptor and lamina cell fates are correctly specified, R7 axons correctly target the medulla, and both correctly targeted R7 axons and mistargeted R1-R6 axons maintain their retinotopic order with respect to both anteroposterior and dorsoventral axes. bks encodes two unusually hydrophilic nuclear protein isoforms, one of which contains a putative C(2)H(2) zinc finger domain. Transgenic expression of either Bks isoform is sufficient to restore the lamina targeting of R1-R6 axons in bks mosaics, but not to retarget R7 or R8 axons to the lamina. These data demonstrate the existence of a lamina-specific targeting mechanism for R1-R6 axons in the Drosophila visual system, and provide the first entry point in the molecular characterization of this process.

Cloning and expression of az2, a putative zinc finger transcription factor from Drosophila melanogaster.

A Drosophila gene (az2), mapping to a cluster of embryonic lethals at 43BC on the polytene chromosomes, has been sequenced and found to encode a predicted protein with six consecutive C2H2 zinc finger domains. The carboxy-terminus of az2 is related to a number of Drosophila and mammalian transcription factors. The 5' end of the gene is unrelated to genes in the databases. The gene is expressed in the adult female, in both the carcass and ovary, but is most abundant in the ovary. It is expressed in the nurse cells and transported to the oocyte.

New AUG initiation codons in a long 5' UTR create four dominant negative alleles of the Drosophila C2H2 zinc-finger gene ovo.

Promoters active in the germline produce OVO-A and OVO-B mRNAs encoding isoforms of a putative transcription factor. The isoforms have a common C2H2 zinc-finger domain but different N-termini that include potential effector domains. Single point mutations in three dominant-negative ovoD mutations result in new in-frame initiation codons in OVO-B mRNAs and amino acid substitutions within charged regions of OVO-A proteins. Three lines of evidence suggest that the dominant activity is due to the new initiation codons in OVO-B mRNAs and not the amino acid substitutions in OVO-A. First, we made a fourth ovoD allele by inserting a new in-frame AUG. This ovoD4 allele encodes a nearly full-length OVO-A isoform from OVO-B mRNAs. Second, engineered stop codons in ovoD1 downstream of the new AUG abolished dominant negative activity. Third, a substantial deletion of an OVO-A region encoding a highly charged amino acid domain fully rescued loss-of-function ovo alleles. These data suggest that ovoD mutations result in inappropriate expression of OVO-A in the female germline.

Zap1p, a metalloregulatory protein involved in zinc-responsive transcriptional regulation in Saccharomyces cerevisiae.

Zinc ion homeostasis in Saccharomyces cerevisiae is controlled primarily through the transcriptional regulation of zinc uptake systems in response to intracellular zinc levels. A high-affinity uptake system is encoded by the ZRT1 gene, and its expression is induced more than 30-fold in zinc-limited cells. A low-affinity transporter is encoded by the ZRT2 gene, and this system is also regulated by zinc. We used a genetic approach to isolate mutants whose ZRT1 expression is no longer repressed in zinc-replete cells, and a new gene, ZAP1, was identified. ZAP1 encodes a 93-kDa protein with sequence similarity to transcriptional activators; the C-terminal 174 amino acids contains five C2H2 zinc finger domains, and the N terminus (residues 1 to 706) has two potential acidic activation domains. The N-terminal region also contains 12% histidine and cysteine residues. The mutant allele isolated, ZAP1-1up, is semidominant and caused high-level expression of ZRT1 and ZRT2 in both zinc-limited and zinc-replete cells. This phenotype is the result of a mutation that substitutes a serine for a cysteine residue in the N-terminal region. A zap1 deletion mutant grew well on zinc-replete media but poorly on zinc-limiting media. This mutant had low-level ZRT1 and ZRT2 expression in zinc-limited as well as zinc-replete cells. These data indicate that Zap1p plays a central role in zinc ion homeostasis by regulating transcription of the zinc uptake system genes in response to zinc. Finally, we present evidence that Zap1p regulates transcription of its own promoter in response to zinc through a positive autoregulatory mechanism.

A Switch inBroad-ComplexZinc-Finger Isoform Expression Is Regulated Posttranscriptionally during the Metamorphosis ofDrosophilaImaginal Discs

TheBroad-Complex(BR-C) is a key member of the 20-hydroxyecdysone regulatory hierarchy that coordinates changes in gene expression duringDrosophilametamorphosis. The family of transcription factors encoded by theBR-Cshare a common amino-terminal domain which is fused by alternative splicing to one of four pairs of C2H2zinc-finger domains (Z1, Z2, Z3, and Z4). In this study, we examine the temporal expression of transcripts encoding eachBR-Czinc-finger isoform—including the newly discovered fourth zinc-finger domain—during the metamorphosis of imaginal discs which form the integumental structures of the adult head and thorax. We find that allBR-Czinc-finger RNA isoforms are induced as a primary response to 20-hydroxyecdysone. However, inducedBR-CRNA isoforms exhibit two divergent expression profiles. The Z2, Z3, and Z4 RNA isoforms accumulate to high levels at the beginning of the ecdysone response and abruptly disappear after several hours. In contrast, the Z1 RNA isoform continues to accumulate while the others decline, resulting in a switch in relative isoform levels. Using probes specific to different regions of theBR-C,we show that the switch inBR-CRNA isoform expression appears to be posttranscriptionally regulated, presumably by ecdysone-responsive factors. We propose that this switch results from a change in splice acceptor site choice. Finally, we present a model describing how this temporal switch in isoform expression could mediate changes inBR-Cfunction, from transcriptional activation to repression and vice versa, that are critical for coordinate downstream target gene expression.