ABSTRACT
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.
Subject(s)
Drosophila Proteins/genetics , Drosophila melanogaster/genetics , Gene Expression Regulation, Developmental , Molecular Chaperones/genetics , Spermatocytes/metabolism , Testis/metabolism , Animals , Cell Differentiation , Drosophila Proteins/metabolism , Drosophila melanogaster/growth & development , Drosophila melanogaster/metabolism , Male , Meiosis , Molecular Chaperones/metabolism , Protein Biosynthesis , Protein Subunits/genetics , Protein Subunits/metabolism , Ribosomes/genetics , Ribosomes/metabolism , Spermatocytes/growth & development , Spermatocytes/ultrastructure , Spermatogenesis/genetics , Testis/growth & developmentABSTRACT
The Piwi protein and its orthologs are considered as the key components of the piRNA machinery implicated in transcriptional silencing of transposons. Ðеre, we show that nuclear localization of the Piwi protein is required not only for transposon repression, but also for proper differentiation of germline stem cells (GSCs). piwi^(Nt) mutation that causes loss of nuclear Piwi and its retention in the cytoplasm leads to the accumulation of undifferentiated GSC-like cells. The analysis of piwi^(Nt) mutation in combination with a bam gene mutation blocking GSC differentiation shows that the loss of nuclear Piwi decreases GSC proliferation rate. This is accompanied by the accumulation of DNA double-strand breaks in GSCs that may be caused by transposition events. Here, for the first time a set of transposons repressed by Piwi in GSCs and surrounding niche cells has been identified. The present study together with our previous data show that nuclear and cytoplasmic Piwi can regulate different stages of the functioning of germinal cells: cytoplasmic Piwi is sufficient to maintain GSCs, while nuclear Piwi localization is necessary for their proper proliferation and differentiation.
ABSTRACT
PIWI proteins interacting with specific type of small RNAs (piRNAs) repress transposable elements in animals. Besides, they have been shown to participate in various cellular processes: in the regulation of heterochromatin formation including telomere structures, in the control of translation and the cell cycle, and in DNA rearrangements. PIWI proteins were first identified by their roles in the self-renewal of germline stem cells. PIWI protein functions are not limited to gonadogenesis, but the role in determining the fate of stem cells is their specific feature conserved throughout the evolution of animals. Molecular mechanisms underlying these processes are far from being understood. This review focuses on the role of PIWI proteins in the control of maintenance and proliferation of germinal stem cells and its relation to the known function of PIWI in transposon repression.
Subject(s)
Argonaute Proteins/genetics , Stem Cells/cytology , Animals , Argonaute Proteins/metabolism , Cell Differentiation , Cell Proliferation , DNA Transposable Elements , Heterochromatin/genetics , Heterochromatin/metabolism , RNA InterferenceABSTRACT
Complexes of Piwi proteins and Piwi-interacting RNAs (piRNAs) carry out the repression of transposable elements in animal gonads. The Piwi protein clade is represented in D. melanogaster by three members: Piwi, Aub and Ago3. Piwi protein functions in the nuclei of somatic and germinal ovarian cells, whereas Aub and Ago3 are cytoplasmic proteins of germinal cells. Aub and Ago3 interact with each other in the perinuclear nuage organelle to perform piRNA amplification via the ping-pong mechanism. Previously, derepression of several transposable elements as a result of mutations in the piRNA silencing system was shown. Here we quantify the increase in expression level of an enlarged number of retrotransposons due to the mutations in the piwi gene, nuage components coding aub, mael and spn-E genes and the RNA helicase armi gene mutation that impairs Piwi nuclear localization, but not the ping-pong cycle. We reveal that piwi, armi, aub, spn-E and mael genes participate together in the repression of several transposons (HMS-Beagle, Gate and HeT-A), whereas silencing of land G elements requires the same genes except piwi. We suggest that Armi has other functions besides the localizing of Piwi protein in the nuclei. Our data suggest also a role of cytoplasmic Aub, Spn-E and Mael nuage proteins in Piwi-mediated repression of Gate and HMS-Beagle transposons in the germline nuclei. As a whole, our results corroborate the idea that genome stabilization in the germline is realized by different silencing strategies specific for different transposable elements. At the same time, our data suggest the existence of yet unknown mechanisms of interplay between nuclear and cytoplasmic components of the piRNA machinery in the germline.
Subject(s)
Drosophila Proteins/metabolism , Drosophila melanogaster/genetics , Drosophila melanogaster/metabolism , Peptide Initiation Factors/metabolism , RNA, Small Interfering/genetics , Retroelements/genetics , Adenosine Triphosphatases/genetics , Adenosine Triphosphatases/metabolism , Animals , Argonaute Proteins , Drosophila Proteins/genetics , Female , Gene Silencing , Ovary/metabolism , Peptide Initiation Factors/genetics , RNA Helicases/genetics , RNA Helicases/metabolism , RNA, Small Interfering/metabolism , RNA-Induced Silencing Complex/genetics , RNA-Induced Silencing Complex/metabolismABSTRACT
Two main types of short RNAs, 21 to 25 nucleotides long, are involved in the negative regulation of gene expression in eukaryotes: microRNAs and small interfering RNAs (siRNAs) of the RNA interference system. MicroRNAs predominantly suppress the translation of mRNA targets, while siRNAs not only prevent mRNA translation and/or lead to mRNA degradation, but are also involved in the regulation of gene expression at the transcriptional level. In germ cells translational regulation of gene expression plays a significant role and its mechanism has been extensively studied in oogenesis of Drosophila@. The role of heterochromatization and chromatin compaction, which can repress the expression of mobile elements and other repeated elements of the genome, was studied to a lesser extent. Activation and transposition of mobile elements accompanied by mutations and chromosome rearrangements are especially dangerous in germline cells. It has been proposed that a specialized class of short RNAs, repeat associated siRNAs (rasiRNAs), can be involved in repression of the expression of mobile elements in Drosophila germ cells. Here we describe the findings on subcellular ribonucleoprotein structures characteristic of germ cells: perinuclear and polar granules containing proteins of the RNA interference and microRNA maturation system. Also, we present our own results revealing the role of genes of the RNA interference system in mobile element silencing in Drosophila.
Subject(s)
Gene Silencing/physiology , Germ Cells/metabolism , MicroRNAs/metabolism , Protein Biosynthesis/physiology , RNA Stability/physiology , RNA, Small Interfering/metabolism , Animals , Chromatin Assembly and Disassembly/physiology , Drosophila , Female , Germ Cells/cytology , Heterochromatin/metabolism , Interspersed Repetitive Sequences/physiology , MicroRNAs/genetics , RNA, Messenger/metabolism , RNA, Small Interfering/geneticsABSTRACT
The antiacidotic and cardioprotective effects of dehydro-L-ascorbic acid and fructose-1,6-diphosphate were compared in experiments of rats. It was found that the both compounds exhibit the antiacidotic effect on the model of metabolic acidosis in the isolated hypoxic heart, decrease the excess-lactate degree, increase ATP level in the myocardium and reduce the size of the necrosis area 4 hours after the modelling of myocardial infarction. The significance of the antiacidotic component in the mechanism of the cardioprotective action of the energy-supplying agents is concluded.
Subject(s)
Acidosis/prevention & control , Dehydroascorbic Acid/therapeutic use , Fructosediphosphates/therapeutic use , Heart/drug effects , Acidosis/metabolism , Acidosis/pathology , Adenosine Triphosphate/metabolism , Animals , Drug Evaluation, Preclinical , Glucose-6-Phosphate , Glucosephosphates/metabolism , In Vitro Techniques , Male , Myocardium/metabolism , Myocardium/pathology , Necrosis , Perfusion/methods , RatsABSTRACT
The cardioprotective effects of fructose-1,6-diphosphate (FDP) were investigated in infarcted rats and in conscious rabbits with myocardial ischemia. The influence of FDP on metabolic acidosis was studied in isolated hypoxic rat hearts. It was shown that FDP did not change the threshold of the initiation of ischemia in conscious rabbits, but decreased necrotic zone in infarcted rat hearts. After administration of FDP the myocardial contractility was prolonged significantly as compared with control under conditions of severe metabolic acidosis. However, FDP was not effective in hypoxic hearts with compensated metabolic acidosis. It was considered, that FDP influenced only ischemic myocytes with the changes in sarcolemmal permeability.
