RESUMO
During the process of spermatogenesis, the proliferation of spermatogonia (stem cell descendants) is replaced by their differentiation in growing spermatocytes responsible for the preparation to meiosis, which is accompanied by a cardinal change in transcriptional programs. We have demonstrated that, in drosophila, this process is accompanied by a splash of the expression of ß-subunit of nascent polypeptide-associated complex (NAC) associated by ribosomes. Nascent polypeptide-associated complex is known as a chaperone involved in co-translational protein folding. This is the first case of the detection of tissue-specific co-translational NAC cofactor in multicellular eukaryotes. It is proposed that spermatocyte specific NAC is involved in the modulation of the expression of the proteins that provide the functioning of subsequent stages of spermatogenesis.
Assuntos
Proteínas de Drosophila/genética , Drosophila melanogaster/genética , Regulação da Expressão Gênica no Desenvolvimento , Chaperonas Moleculares/genética , Espermatócitos/metabolismo , Testículo/metabolismo , Animais , Diferenciação Celular , Proteínas de Drosophila/metabolismo , Drosophila melanogaster/crescimento & desenvolvimento , Drosophila melanogaster/metabolismo , Masculino , Meiose , Chaperonas Moleculares/metabolismo , Biossíntese de Proteínas , Subunidades Proteicas/genética , Subunidades Proteicas/metabolismo , Ribossomos/genética , Ribossomos/metabolismo , Espermatócitos/crescimento & desenvolvimento , Espermatócitos/ultraestrutura , Espermatogênese/genética , Testículo/crescimento & desenvolvimentoRESUMO
The telomere is a nucleoprotein complex at the ends of linear chromosomes that protects them from fusion and degradation. The telomere consists of telomeric DNA, a protective protein complex and telomeric RNA. Biogenesis of telomeric transcripts in development is still far from being understood. Drosophila telomeres are elongated by a transposition of specialized telomeric retrotransposons that encode proteins. Using transgenic constructs encoding tagged telomeric protein, we found that transcripts of Drosophila telomeric element HeT-A bind Gag-HeT-A protein encoded by these transcripts. Maternal HeT-A transcripts and Gag-HeT-A form ribonucleoprotein granules around centrosomes, centers of microtubule organization, during blastoderm formation, upon disruption of telomere silencing during oogenesis. The specific localization of HeT-A RNA is dependent on microtubules since disruption of microtubules caused delocalization of HeT-A transcripts. This transgenic system is a valuable model for the study of telomeric RNA biogenesis.
Assuntos
Centrossomo/metabolismo , Proteínas de Drosophila/metabolismo , Embrião não Mamífero/metabolismo , Desenvolvimento Embrionário/fisiologia , Produtos do Gene gag/metabolismo , Retroelementos/fisiologia , Telômero/metabolismo , Animais , Proteínas de Drosophila/genética , Drosophila melanogaster , Feminino , Produtos do Gene gag/genética , Telômero/genéticaRESUMO
This review analyzes and summarizes a current knowledge about a role of RNA helicases in the development and maintenance of gametogenesis of eukaryotic organisms. Here we focused on three representatives of RNA helicase family containing the characteristic motifs in the amino acid sequence (DEAD-box) and carrying substantial and conservative functions in the germinal tissues of various species from drosophila to human. There are such proteins as Vasa/DDX4, BelIe/DDX3 and Spindle-E/TDRD9. They are involved in a wide range of activities that are associated with the regulation of transcription, splicing, nuclear export, and especially with the initiation of translation. The expression of genes required for the gametogenesis appears to be regulated mainly at the translational level. RNA helicases are involved in the formation of cytoplasmic RNP granules and in the implementation of gene RNA-silencing. "DEAD-box RNA helicases" that carry highly homologous central domain, which determines their basic biochemical activity in the ATP-dependent unwinding of short RNA duplexes, perform the essential and non-overlapping functions in the germinal tissues.
Assuntos
Núcleo Celular/enzimologia , RNA Helicases DEAD-box/metabolismo , Gametogênese/fisiologia , Regulação da Expressão Gênica/fisiologia , Biossíntese de Proteínas/fisiologia , Transporte Ativo do Núcleo Celular/fisiologia , Motivos de Aminoácidos , Animais , Núcleo Celular/genética , RNA Helicases DEAD-box/genética , Feminino , Humanos , Masculino , Splicing de RNA/fisiologia , Ribonucleoproteínas/genética , Ribonucleoproteínas/metabolismo , Transcrição Gênica/fisiologiaRESUMO
Novel site-specific H-N-H endonucleases F-TflI, F-TflII and F-TflIV were identified. These endonucleases are encoded by open reading frames localized in the bacteriophage T5 tRNA gene region. The endonuclease F-TflIV was shown to introduce double-strand break into pseudo palindromic 17 bp DNA sequence yielding 1 bp extensions with 3'-overhangs. In contrast to F-TflIV, endonucleases F-TflI and F-TflII cleave only one strand of their asymmetric divergent DNA substrates. Each of these endonucleases introduces interruptions into only the particular strand (template or coding). Amino acid sequences of the endonucleases under study are highly homologous in the H-N-H motif regions and C-terminal sequences, forming putative catalytic domain. Endonuclease F-TflIV N-terminal region is homologous to the amino acid sequences representing H-T-H recognition domain found in LuxR family transcription regulators. Putative recognition NUMOD4 motif characteristic for a number of H-N-H endonucleases was shown to be also present in the endonuclease F-TflI and F-TflII N-terminal sequences. Two-domain structure was proposed for endonucleases F-TflI, F-TflII and F-TflIV with N-terminal recognition domain and C-terminal catalytic domain. A hypothesis of evolutionary origin of these endonucleases as a result of catalytic and recognition domains recombination was suggested.
Assuntos
Bacteriófagos/genética , Enzimas de Restrição do DNA/metabolismo , Sequência de Aminoácidos , Sequência de Bases , Primers do DNA , Enzimas de Restrição do DNA/química , DNA Viral/genética , Dados de Sequência Molecular , RNA de Transferência/genética , Homologia de Sequência de Aminoácidos , Homologia de Sequência do Ácido NucleicoRESUMO
The Pseudomonas fluorescens 23F phosphonoacetate hydrolase gene (phnA) encodes a novel carbon-phosphorus bond cleavage enzyme whose expression is independent of the phosphate status of the cell. Analysis of the regions adjacent to the phosphonoacetate hydrolase structural gene (phnA) indicated the presence of five open reading frames (ORFs). These include one (phnR) whose putative product shows high levels of homology to the LysR family of positive transcriptional regulators. Its presence was shown to be necessary for induction of the hydrolase activity. 2-Phosphonopropionate was found to be an inducer (and poor substrate) for phosphonoacetate hydrolase. Unlike phosphonoacetate, which is also an inducer of phosphonoacetate hydrolase, entry of 2-phosphonopropionate into cells appeared to be dependent on the presence of a gene (phnB) that lies immediately downstream of phnA and whose putative product shows homology to the glycerol-3-phosphate transporter. RNA analysis revealed transcripts for the phnAB and phnR operons, which are transcribed divergently; the resulting mRNAs overlapped by 29 nucleotide bases at their 5' ends. Transcripts of phnAB were detected only in cells grown in the presence of phosphonoacetate, whereas transcripts of phnR were observed in cells grown under both induced and uninduced conditions. The expression of three additional genes found in the phnA region did not appear necessary for the degradation of phosphonoacetate and 2-phosphonopropionate by either Pseudomonas putida or Escherichia coli cells.
