Biomedical subjects

T Pieler

Publications and source records attributed to T Pieler.

At least 37 records · Page 2Linked to original sources

PubMed1998

Kzf1 - a novel KRAB zinc finger protein encoding gene expressed during rat spermatogenesis.

Two novel KRAB (Krüppel associated box) type zinc finger protein encoding cDNAs, named Kzf1 and Kzf2 (Kzf for KRAB zinc finger), were identified by screening of a rat embryonic brain cDNA library with a human ZNF91 KRAB probe. Kzf1 and Kzf2 encode proteins with an amino-terminal KRAB domain and a carboxy-terminal zinc finger cluster containing 9 and 13 zinc finger units, respectively. While Kzf2 appears to be ubiquitously expressed, Kzf1 is preferentially expressed in the testis. Within the testis, Kzf1 mRNA is restricted to germ cells. The Kzf1 protein exhibits DNA binding activity and its KRAB domain can function as a repressor module in transcription. Using somatic cell hybrid analysis, the Kzf1 gene was mapped to chromosome 6.

Amino Acid Sequence↗

PubMed1998

Xiro3 encodes a Xenopus homolog of the Drosophila Iroquois genes and functions in neural specification.

We have identified in Xenopus and in the mouse two highly related genes, Xiro3 and Irx3 respectively, that encode a Drosophila Iroquois-related homeobox transcription factor. Xiro3 in Xenopus and Irx3 in the mouse are expressed early in the prospective neural plate in a subset of neural precursor cells. In Xenopus, injection of Xiro3 mRNA expands the neural tube and induces ectopic neural tissue in the epidermis, based on the ectopic expression of early neural markers such as Xsox3. In contrast, the differentiation of the early forming primary neurons, as revealed by the expression of the neuronal marker N-tubulin, is prevented by Xiro3 expression. Activation of Xiro3 expression itself requires the combination of a neural inducing (noggin) and a posteriorizing signal (basic fibroblast growth factor). These results suggest that Xiro3 activation constitutes one of the earliest steps in the development of the neural plate and that it functions in the specification of a neural precursor state.

Amino Acid Sequence↗

PubMed1998

The Xenopus homologue of the Drosophila gene tailless has a function in early eye development.

Genetic circuits responsible for the development of photoreceptive organs appear to be evolutionarily conserved. Here, the Xenopus homologue Xtll of the Drosophila gene tailless (tll), which we find to be expressed during early eye development, is characterized with respect to its relationship to vertebrate regulators of eye morphogenesis, such as Pax6 and Rx. Expression of all three genes is first detected in the area corresponding to the eye anlagen within the open neural plate in partially overlapping, but not identical, patterns. During the evagination of the optic vesicle, Xtll expression is most prominent in the optic stalk, as well as in the distal tip of the forming vesicle. In tadpole-stage embryos, Xtll gene transcription is most prominent in the ciliary margin of the optic cup. Inhibition of Xtll function in Xenopus embryos interferes specifically with the evagination of the eye vesicle and, in consequence, Xpax6 gene expression is severely reduced in such manipulated embryos. These findings suggest that Xtll serves an important regulatory function in the earliest phases of vertebrate eye development.

Aging↗

PubMed1998

Vax1 is a novel homeobox-containing gene expressed in the developing anterior ventral forebrain.

The vertebrate forebrain is formed at the rostral end of the neural plate under the regulation of local and specific signals emanating from both the endomesoderm and neuroectoderm. The development of the rostral and ventral forebrain in particular was difficult to study, mainly because no specific markers are available to date. Here, we report the identification of Vax1, a novel homeobox-containing gene identified in mouse, Xenopus and human. It is closely related to members of the Not and Emx gene families, all of which are required for the formation of structures where they are expressed. In mouse and Xenopus, Vax1 expression first occurs in the rostral neural plate, in the medial anterior neural ridge and adjacent ectoderm. Later, at midgestation in the mouse and tadpole stage in Xenopus, the expression remains confined in the derivatives of this territory which differentiate into rostromedial olfactory placode, optic nerve and disc, and anterior ventral forebrain. Together, these observations suggest that Vax1 could have an early evolutionary origin and could participate in the specification and formation of the rostral and ventral forebrain in vertebrates. Comparison of the limits of the expression territory of Vax1 with that of Dlx1, Pax6 and Emx1 indicates that the corticostriatal ridge is a complex structure with distinct identifiable genetic compartments. Besides, the study of Vax1 expression in Pax6-deficient homozygous brains indicates that its regulation is independent of Pax6, although the expression patterns of these two genes appear complementary in wild-type animals. Vax1 chromosomal location is mapped at the distal end of the mouse chromosome 19, linked with that of Emx2. These two genes may have arisen by tandem duplication. The Vax1 gene is thus an interesting new tool to study the rostral ventral forebrain patterning, morphogenesis and evolution as well as the terminal differentiation of the forebrain in mouse and Xenopus.

Amino Acid Sequence↗

PubMed1997

Nucleocytoplasmic transport of 5S ribosomal RNA.

Nucleocytoplasmic transport of 5S ribosomal RNA in Xenopus oocytes occurs in the context of small, non-ribosomal RNPs. The complex with the zinc finger protein TFIIIA (7S RNP) is exported from the nucleus and stored in the cytoplasm, whereas the complex with the ribosomal protein L5 (5S RNP) shuttles between the nucleus and the cytoplasm. Nuclear import- and export-signals appear to reside within the protein moiety of these RNPs. Import of TFIIIA is inhibited by RNA binding, whereas nuclear transfer of L5 is not influenced by RNA binding. We propose that the export capacity of both, TFIIIA and L5, is regulated by the interaction with 5S ribosomal RNA.

Journal Article↗

PubMed1997

Transcription regulation and alternative splicing of an early zygotic gene encoding two structurally distinct zinc finger proteins in Xenopus laevis.

We describe the structural organization of a gene, termed XFDL 141/156, that is transiently activated during early Xenopus development. XFDL 141/156 is first transcribed at the midblastula transition (MBT) and during early gastrulation events. A roughly 200 nucleotide fragment immediately 5' to the transcription start site is sufficient for transient, early zygotic activation of gene expression. The primary transcript is subject to alternative splicing. Corresponding cDNAs encode two structurally related but completely distinct C2H2-type zinc finger proteins of unknown biological function.

Alternative Splicing↗

PubMed1997

A role for Xenopus Gli-type zinc finger proteins in the early embryonic patterning of mesoderm and neuroectoderm.

Gli-type zinc finger proteins play important regulatory roles in vertebrate and invertebrate embryogenesis. In Xenopus, the Gli-type proteins XGli-3 and XGli-4 are first expressed in earliest stages of mesoderm and neural development. Transient transfection assays reveal that XGli-3 and XGli-4 can function as transcription repressors. Counteracting the Gli-protein repressor activity by ectopic expression of a fusion protein that contains the Gli-zinc finger cluster connected to the E1A activator domain in Xenopus embryos results in specific morphological alterations in the developing somites and in the central nervous system. Altered expression characteristics for a broad set of molecular markers highlighting specific aspects of mesodermal and neural differentiation demonstrate an important role for Gli-type zinc finger proteins in the early mesodermal and neural patterning of Xenopus embryos.

Amino Acid Sequence↗

PubMed1996

X-MyT1, a Xenopus C2HC-type zinc finger protein with a regulatory function in neuronal differentiation.

X-MyT1 is a C2HC-type zinc finger protein that we find to be involved in the primary selection of neuronal precursor cells in Xenopus. Expression of this gene is positively regulated by the bHLH protein X-NGNR-1 and negatively regulated by the Notch/Delta signal transduction pathway. X-MyT1 is able to promote ectopic neuronal differentiation and to confer insensitivity to lateral inhibition, but only in cooperation with bHLH transcription factors. Inhibition of X-MyT1 function inhibits normal neurogenesis as well as ectopic neurogenesis caused by overexpression of X-NGNR-1. On the basis of these findings, we suggest that X-MyT1 is a novel, essential element in the cascade of events that allows cells to escape lateral inhibition and to enter the pathway that leads to terminal neuronal differentiation.

Age Factors↗

PubMed1996

Cytoplasmic retention and nuclear import of 5S ribosomal RNA containing RNPs.

Nuclear export of newly transcribed 5S ribosomal RNA in Xenopus oocytes occurs in the context of either a complex with the ribosomal protein L5 (5S RNP) or with the transcription factor IIIA (7S RNP). Here we examine nuclear import of 5S RNA, L5 and TFIIIA. The 5S RNP shuttles between nucleus and cytoplasm and only 5S RNA variants which can bind to L5 gain access to the nucleus. The 7S RNP is retained in the cytoplasm. Only TFIIIA which is not bound to 5S RNA is imported into the nucleus. As a novel mechanism for cytoplasmic retention, we propose that RNA binding masks a nuclear localization sequence in TFIIIA. In contrast to the nuclear import of L5, import of TFIIIA is sensitive towards the nuclear localization sequence (NLS) competitor p(lys)-BSA, suggesting that these two proteins make use of different import pathways.

Amino Acid Sequence↗

PubMed1996

Xenopus poly(A) binding protein: functional domains in RNA binding and protein-protein interaction.

Subsets of the four RNA binding domains (RBD 1 to 4) in the Xenopus poly-adenylate binding protein (PABP) have distinct affinities and specificities for RNA. RBDs 1 plus 2 exhibit RNA affinity and selectivity equal to the wild-type (WT) protein. RBDs 3 plus 4 have distinct selectivity and about ten-fold reduced affinity for A23, and the isolated RBDs 2 or 3 or 4 exhibit about 100-fold reduced affinity for A23 in comparison to WT. For the full-length protein, independent RNA contacts have been mapped by UV crosslinking with RBDs 1/2 and RBDs 3/4. The carboxy-terminal, non-RBD portion of the protein does not contribute to RNA affinity or selectivity, but confers homodimerization activity on PABP. RBDs 3 and 4 cooperate with the C terminus to gain poly(A) organizing activity, i.e. the ability to form an RNP with multiple, regularly spaced copies of PABP on a poly(A) substrate.

Animals↗

PubMed1996

Xenopus Xsal-1, a vertebrate homolog of the region specific homeotic gene spalt of Drosophila.

We have isolated an amphibian homolog of the homeotic gene spalt of Drosophila. Like its Drosophila counterpart the Xenopus Xsal-1 gene encodes a protein that contains three widely separated sets of sequence related double zinc finger motifs of the CC/HH-type as well as a single CC/HH zinc finger. The Xenopus gene encodes a fourth double zinc finger and a single CC/HC zinc finger motif that have no counterpart in the fly protein. Alternative splicing of Xsal-1 transcripts gives rise to RNAs coding for either four, three or two double zinc fingers, respectively. The main expression domains of Xsal-1 in early development are confined to distinct regions along the lateral axon tracts within the midbrain, hindbrain, and spinal cord. Outside the central nervous system Xsal-1 is expressed in the facio-acoustic ganglion and in the developing limb buds. The pattern of expression suggests that Xsal-1 might be under control of signals emanating from the notochord and/or the floor plate and that it might function in neuronal cell specification.

Alternative Splicing↗

PubMed1996

Nucleoskeleton and nucleo-cytoplasmic transport in oocytes and early development of Xenopus laevis.

We use amphibian oocytes and eggs as favorite biological systems to study various cell biological phenomena. We have analyzed the role of the zinc finger protein TFIIIA and ribosomal protein L5 in nucleo-cytoplasmic transfer of 5S ribosomal RNA and report on the structural requirements of the 5S RNA for the interaction with TFIIIA. Furthermore, we have used the oocyte/egg system to analyze the kinetics of the posttranslational isoprenylation of oocyte nuclear lamin B3 and its fate during egg maturation. We demonstrate, that isoprenylation of newly synthesized lamins takes place in the oocyte cytoplasm before uptake into the nucleus and show, that the isoprene modifications alone are not sufficient to maintain stable association of lamins with nuclear envelope derived membranes in eggs. Finally, initial results of the identification of cis-acting sequence elements, involved in translational repression of lamin mRNAs in oocytes, are reported.

Animals↗

PubMed1996

Zinc finger proteins in early Xenopus development.

The C2H2-type zinc finger motif defines a large super family of specific DNA and specific RNA binding proteins. Individual members of this protein family have been demonstrated to carry important regulatory functions in embryogenesis. We have isolated a large collection of C2H2-type zinc finger proteins from Xenopus laevis. Some of these proteins are highly conserved in evolution and found to be differentially expressed during embryonic development of the central nervous system. We also summarize our recent findings on the biochemical characterization of RNA and DNA binding activities in vitro for other Xenopus zinc finger proteins, which fall into structurally defined, distinct subfamilies.

Amino Acid Sequence↗

PubMed1994

Sequence-specific recognition of a repetitive DNA element by a C2H2 zinc-finger protein in Xenopus.

XFG 20-1 is one of several hundred C2H2-type zinc finger proteins of unknown biological function in Xenopus. Affinity selection of genomic DNA fragments identifies a 54-bp consensus sequence with high affinity for the XFG 20-1 protein. This sequence is part of a conserved inverted repeat in REM-1, a 0.5-kb repetitive, dispersed genomic DNA element. This finding indicates a possible link between the non-conserved nature of a large subgroup of DNA-binding C2H2 zinc finger proteins and the non-conserved nature of putative genomic target sequences. The 19 zinc finger modules of XFG 20-1 are organized in three structurally distinct groups. Of these, only the first and third ones are required and are sufficient for high-affinity DNA binding. The finding that removal of five internal zinc finger units does not alter the DNase I protection pattern of the complex formed is indicative of a high degree of structural flexibility for linear arrays of zinc fingers, which we imagine to adopt a more rigid structure only upon interaction with their nucleic acid partner molecules.

Amino Acid Sequence↗

PubMed1994

The FAR domain defines a new Xenopus laevis zinc finger protein subfamily with specific RNA homopolymer binding activity.

The zinc finger motif defines a large superfamily of nucleic acid binding proteins. Conserved amino acid sequence elements associated with structurally variant zinc finger clusters define subfamilies of zinc finger proteins (ZFPs). The FAR domain (Finger Associated Repeats) is a novel type of repeat element found at the amino-terminus in a subfamily of Xenopus laevis ZFPs. Northern blot analyses of three different members of the FAR subfamily (XFO 6, XFO 9-3 and XFG 68) revealed that each of these genes is transcribed during oogenesis, embryogenesis and in all investigated tissues of adult animals thereby indicating a ubiquitous distribution of transcripts. All FAR-ZFPs tested so far have specific RNA homopolymer binding activity; they associate preferentially with poly(U). The FAR repeats possess limited primary sequence homology with a sequence in the nucleolar shuttling protein NO38, within a region that contains a casein kinase II phosphorylation site.

Amino Acid Sequence↗

PubMed1994

Perspectives on zinc finger protein function and evolution--an update.

Complexity is one of the hallmarks that applies to C2H2 type zinc finger proteins (ZFPs). Structurally distinct clusters of zinc finger modules define an extremely large superfamily of nucleic acid binding proteins with several hundred, perhaps thousands of different members in vertebrates. Recent discoveries have provided new insights into the biochemistry of RNA and DNA recognition, into ZFP evolution and genomic organization, and also into basic aspects of their biological function. However, as much as we have learned, other fundamental questions about ZFP function remain highly enigmatic. This essay is meant to define what we personally feel are important questions, rather than trying to provide a comprehensive, encyclopaedic review.

Amino Acid Sequence↗

PubMed1994

Functional aspects of B-Myb in early Xenopus development.

The gene encoding Xenopus B-Myb (XB-Myb), a protein structurally related to the nuclear protooncogene product c-Myb, is expressed in early Xenopus embryogenesis. We report on developmental alterations in the nucleocytoplasmic distribution and phosphorylation of XB-Myb in Xenopus oocytes and embryos, as well as on a negative regulatory role of the carboxyl terminus in sequence specific DNA binding. In growing oocytes and early embryonic stages the protein is primarily located in the nucleus; in the full-grown oocyte, however, it remains sequestered in the cytoplasmic compartment. Upon meiotic maturation of the oocyte, XB-Myb becomes hyperphosphorylated. Oocyte/egg isolates of XB-Myb are inhibited in their specific DNA binding activity; truncation of the carboxyl terminal region relieves this block in nucleic acid recognition. Furthermore, we have used overexpression of XB-Myb in Xenopus embryos by means of mRNA injection as an assay for gene function in vivo. Overexpression of full-length XB-Myb, not of the carboxyl terminal deletion mutant, results in an altered morphology of lateral plate mesoderm.

Animals↗

PubMed1993

Evidence for a clustered genomic organization of FAX-zinc finger protein encoding transcription units in Xenopus laevis.

Finger associated box-zinc finger proteins (FAX-ZFPs) constitute a subfamily of the many C2H2 type ZFPs in Xenopus laevis. FAX is a highly conserved protein domain connected to variable zinc finger clusters. Three different FAX-ZFPs encoding genomic fragments were isolated and subjected to a detailed structural characterization. All three exhibit a common, highly conserved exon/intron organization, with the variant zinc finger clusters organized in a single exon for each gene analysed. Two of the three genomic fragments contain a second FAX-ZFP encoding (partial) transcription unit each. Further evidence for a clustered organization of FAX-ZFP transcription units is provided by Southern blot analysis of large genomic restriction fragments separated by transverse field gel electrophoresis, and by in situ hybridization on intact chromosomes. Comparative sequence analysis of the genes isolated reveals an exceptional degree of DNA sequence conservation in both exon and intron regions in one part of the FAX encoding region, suggesting that recent gene conversion has led to the combination of these sequence elements with DNA segments including regions encoding variant zinc finger clusters. Overexpression of the FAX domain by itself or of a full-length FAX-ZFP in X. laevis embryos by means of mRNA injection does not interfere with the normal developmental program, suggesting general and not cell specific/regulatory functions for X. laevis FAX-ZFPs.

Amino Acid Sequence↗