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L Etkin

Publications and source records attributed to L Etkin.

5 recordsLinked to original sources
PubMed1991

The cloning and characterization of a maternally expressed novel zinc finger nuclear phosphoprotein (xnf7) in Xenopus laevis.

We report the cloning of a cDNA (xnf7) coding for a maternally expressed Xenopus protein that becomes highly enriched in nuclei of the central nervous system during later development and in nuclei of adult brain. The protein also shows stage-specific nuclear/cytoplasmic partitioning and phosphorylation that may be related to its function. In addition, it binds to double-stranded DNA in vitro. The conceptual protein produced by the xnf7 clone contains several acidic domains, a novel zinc finger domain, three putative p34cdc2 protein kinase phosphorylation sites, and a bipartite basic nuclear localization signal. The xnf7 mRNA was detected as a maternal transcript that decreased in abundance during development through the gastrula stage. It was reexpressed at the neural stage in mesoderm and neural tissues, and its reexpression was not dependent upon the normal juxtaposition of the mesoderm and ectoderm that occurs during neural induction as demonstrated by high titer in exogastrulae. In situ hybridization showed enrichment of the mRNA in the neural tube and a small amount in the mesoderm at the late neurula stage. Xnf7 is normally phosphorylated during oocyte maturation. The bacterially expressed xnf7 protein was phosphorylated in vitro by purified maturation-promoting factor at a threonine in a small N-terminal domain containing one of the p34cdc2 protein kinase phosphorylation sites, but not by several other protein kinases. The structural domains present in the protein and its localization in nuclei suggest that the xnf7 gene product performs an important nuclear function during early development, perhaps as a transcription factor or a structural component of chromatin.

Amino Acid Sequence↗
PubMed1989

xlgv7: a maternal gene product localized in nuclei of the central nervous system in Xenopus laevis.

The Xenopus oocyte nucleus (GV) is a storehouse for a large number of proteins that are used during early development. We have cloned and characterized a cDNA coding for a maternal gene product that is localized in the GV and then becomes highly enriched in the nuclei of the central nervous system (CNS) of tadpoles and adult frogs. This cDNA (xlgv7) is 2.1 kb and hybridizes to a 2.4-kb RNA species on Northern blots. Southern blots of genomic DNA suggest that this gene is a member of a multigene family. The cDNA sequence reveals a long open reading frame (ORF) of 1773 nucleotides, with a putative nuclear targeting signal (Glu Arg Arg Lys Lys Lys Thr) at the extreme carboxyl terminus and an internal histidine (His)-rich region with a repeated conserved amino acid sequence between His pairs. The significance of this region is unclear, but the protein is a DNA-binding protein, and it is possible that this region is involved in this function. The xlgv7 protein also possesses a putative nucleotide-binding consensus sequence that is similar to the bacterial RecA and RecB and yeast RAD proteins. Protein xlgv7 exists as several isotypes that exhibit developmental and cell-specific changes during development. Northern blot analysis of the abundance of the xlgv7 mRNA shows an accumulation following neural induction at stages 15-16. There is a transient expression of the mRNA in the gut of tadpoles. In the adult, the mRNA is highly enriched in the brain and is absent or in very low abundance in other tissues. Immunohistochemical analysis of the protein shows that the protein is localized in the nuclei of the brain cells. We conclude that the xlgv7 gene product is a maternal protein that may serve several important functions, one of which may be in the development and maintanance of the CNS.

Amino Acid Sequence↗
PubMed1989

The maternal store of the xlgv7 mRNA in full-grown oocytes is not required for normal development in Xenopus.

We have attempted to analyze the function of a maternal mRNA xlgv7 which is distributed as an animal-vegetal gradient in stage 6 oocytes using a combination of antisense oligodeoxynucleotide injection into oocytes followed by in vitro maturation and fertilization. Injection of 20 ng of the antisense oligodeoxynucleotide resulted in the destruction of the xlgv7 mRNA to undetectable levels. Upon maturation and fertilization the resulting embryos develop with no specific defects suggesting that the maternal store of xlgv7 in stage 6 oocytes is not required and that the embryo can develop solely with the maternal store of the xlgv7 protein. Also, these results demonstrate the feasibility of this approach in destroying a specific maternal RNA and assaying its effect on development.

Animals↗
PubMed1988

Differential stimulation of sea urchin early and late H2B histone gene expression by a gastrula nuclear extract after injection into Xenopus laevis oocytes.

Sea urchin early histone genes are active in preblastula embryos; late histone genes are maximally expressed during subsequent stages of embryogenesis. We used the Xenopus laevis oocyte to assay for trans-acting factors involved in this differential regulation. Sea urchin nuclear proteins were prepared by extracting gastrula-stage chromatin successively with 0.45, 1, and 2 M NaCl. We injected three fractions into oocytes along with plasmids bearing sea urchin early and late H2b histone genes. While neither the 0 to 0.45 M nor the 1 to 2 M salt fraction affected H2b gene expression, the 0.45 to 1 M salt fraction stimulated early and late H2b mRNA levels significantly. Late H2b gene expression was stimulated preferentially when the early and late genes were coinjected into the same oocytes. This extract did not stimulate the accumulation of transcripts of injected herpesvirus thymidine kinase genes or of the sea urchin Spec 1 gene, suggesting that the stimulatory activity is not a general transcription factor. We localized the DNA sequence required for the stimulatory effect to a region of the late H2b gene located between -43 and +62 relative to the transcription start site. A component of the 0.45 to 1 M salt wash fraction specifically bound to the 105-base-pair late gene DNA sequence and to the corresponding early gene fragment. The abundance of this binding activity decreased on a per genome basis during early development of the sea urchin.

Animals↗