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At least 19 recordsLinked to original sources
PubMed1978

Developmental regulation in cotton seed germination: polyadenylation of stored messenger RNA.

Evidence that RNA preexisting in the cotyledons of mature cotton seed (stored mRNA) is polyadenylated during the first day of germination is presented, based on three different experimental data sets. First, actinomycin D is found to inhibit 32PO4 incorporation into mRNA-poly(A) by 62%, into mRNA by 70%, but into poly(A) only 30%. Second, far more 32PO4 and [2-3H]adenosine are incorporated into the poly(A) portion of mRNA-poly(A) than into the mRNA portion as would be expected from their relative sizes and base composition. This underlabeling of the mRNA moiety is enhanced when cotyledons are germinated in actinomycin D. However, an expected distribution of the isotopes between the mRNA and poly(A) moieties is found in cotyledons labeled later in germination. Third, spectral measurements of the absolute amount of mRNA-poly(A) accumulated during the first day of germination in cotyledons germinated in actinomycin D are larger than would be expected from the 70% inhibition of mRNA labeling caused by the drug. The three sets of data suggest that over 50% of the total mass of mRNA polyadenylated during early germination exists in the mature seed. Its complexity, however, has not been measured. These data may explain the sensitivity of much of germination enzyme synthesis to inhibition by 3'dAdo during early germination and its insensitivity to actinomycin D during this period.

Adenosine Monophosphate↗
PubMed1985

Identification of a 60-kDa phosphoprotein that binds stored messenger RNA of Xenopus oocytes.

Rapidly labelled, polyadenylated RNA is contained in three distinct fractions isolated from homogenized amphibian oocytes: (a) in ribonucleoprotein particles that are associated with a fibrillar matrix, the complexes sedimenting at greater than 1500S; (b) in ribonucleoprotein particles that sediment at 20-120S and have the characteristics of stored (maternal) messenger ribonucleoprotein (mRNP) and (c) in polyribosomes that sediment at 120-360S. We have compared the RNA and protein components of the first two of these RNP fractions. The polyadenylated RNA extracted from the two RNP fractions differs in that the RNA from fibril-associated RNP contains a much higher content of repeat sequences than does the RNA from mRNP. In other words, the RNA from fibril-associated RNP is largely unprocessed and may constitute a premessenger state, which for convenience is referred to as premessenger RNP (pre-mRNP). RNA-binding experiments demonstrate that the polypeptide most tightly bound in pre-mRNP is a 54-kDa component (p54), whereas the polypeptide most tightly bound in mRNP is a 60-kDa component (p60). Antibodies raised against p60 are used to show that this polypeptide is a common major component of pre-mRNP and mRNP and that it is also located in oocyte nuclei. However the state of p60 is modified between the premessenger and stored message levels: the polypeptide in mRNP is heavily phosphorylated whereas the equivalent polypeptide in pre-mRNP is completely unphosphorylated. The relative roles of the presence of repeat sequences and phosphorylation of mRNA-associated protein in blocking translation are discussed.

Animals↗
PubMed1989

Multiple modifications in the phosphoproteins bound to stored messenger RNA in Xenopus oocytes.

Messenger RNA molecules accumulated in amphibian oocytes are stabilized and blocked from translation through association with a defined set of phosphoproteins. Phosphoproteins of 60 kDa and 56 kDa (pp60 and pp56) isolated from messenger ribonucleoprotein particles of Xenopus laevis oocytes can be bound in vitro to mRNA sequences. After phospholabelling in vitro, both pp60 and pp56 show a range of ionic forms, which resolve on two-dimensional gel electrophoresis as a series of pairs with identical charge. The similarities between pp60 and pp56 in their ionic properties suggest a common protein primary structure. This suggestion gains further support from proteinase digestion analysis of pp60 and pp56: practically identical size patterns of phospholabelled fragments are generated using a range of different proteinases. However, in spite of their structural similarities, pp60 and pp56 are recognised as antigenically distinct from each other by using polyclonal antibodies. It is concluded from these, and other, observations that pp60 and pp56 are members of a family of structurally similar polypeptides which are subjected to multiple secondary modifications. Of these modifications, phosphorylation appears to be instrumental in establishing tight binding to mRNA, while antigenicity appears to be determined by some other modification. The role of microheterogeneity in the structure of RNA-binding proteins is discussed in relation to the differential activation of mRNA sequences for translation during early development.

Animals↗
PubMed1979

Sub-cellular distribution of the cytoplasmic myosin heavy chain mRNA during myogenesis.

In the light of earlier work [1] which demonstrated the presence of a large number of myosin heavy chain (MHC) transcripts in chick myoblasts prior to cell fusion and the burst of MHC synthesis it was of great interest to determine the subcellular localization of the still inactive transcripts. It has been determined in differentiating muscle cells in culture. Two populations of cells were examined -- monucleated myoblasts just prior to cell fusion and myotubes where at least 80% of the cells were fused. Utilizing a myosin complementary DNA (cDNA) probe [2] it is observed that just prior to cell fusion, when the "burst" of myosin synthesis has not yet occurred, the vast majority of cytoplasmic myosin mRNA transcripts are found in a stored messenger RNA protein complex with a minimal amount found in the heavy polysome fraction. In differentiated myotube cultures, when myosin synthesis is progressing at a high rate, the reverse is found, i.e, the amount of stored myosin messenger RNA (mRNA) is minimal while the largest amount of myosin mRNA transcripts are localized in the polysome fraction. The number of total cytoplasmic myosin transcripts is found to decrease after cell fusion at a time when myosin synthesis is maximal suggesting that the efficiency of translation of myosin mRNA increases during terminal differentiation.

Animals↗
PubMed1973

Maternal histone messenger RNA: detection by molecular hybridization.

A competition-hybridization assay has been developed for the majority of sequences present in embryonically synthesized histone messenger RNA. The assay permits the first direct demonstration of specific "maternal" messengers in unfertilized sea-urchin eggs. The molecular size of histone messenger RNA stored in the egg appears to be the same as that of histone messenger RNA synthesized by the embryo. Maternal histone messenger RNA is found in the soluble phase of egg homogenates, in the form of ribonucleoprotein particles, unassociated with ribosomes.

Animals↗
PubMed2026

Maternal redd1 mRNA decline triggers mTORC1 activation during the blastula-gastrula transition in zebrafish embryos.

During early metazoan development, maternal mRNAs and proteins stored in the egg sustain initial cellular functions. After the blastula stage, developmental control shifts to zygotic gene expression, and maternal transcripts are progressively degraded. Although mTORC1 is a central regulator of global mRNA translation and cell growth, its role in controlling maternal mRNA translation prior to gastrulation remains poorly understood. In zebrafish embryos, the mTORC1 inhibitor redd1 is abundantly expressed after fertilization but decreases following the maternal-to-zygotic transition (MZT), inversely correlating with mTORC1 activity. Overexpression of redd1 suppresses mTORC1, impairs gastrulation, and reduces translation of 5'TOP mRNAs and key regulatory genes, underscoring the necessity of relieving mTORC1 inhibition after the blastula stage. To investigate redd1 translation under conditions of low mTORC1 activity, we injected reporter mRNAs containing its 5' and 3' UTRs. The 3'UTR promoted polyadenylation and enhanced translation, while both UTRs enabled efficient reporter expression despite mTORC1 suppression, indicating that redd1 mRNA is translated independently of canonical mTORC1 pathways. Similarly, maternal mRNAs such as nanog, myca, pou5f3, and ccnb1, as well as the early zygotic transcript dharma, are translated through mTORC1-independent mechanisms. Together, these findings reveal a transient phase of mTORC1 suppression in early zebrafish embryos and demonstrate that select maternal and zygotic mRNAs bypass this regulation to ensure proper developmental progression.

Animals↗
PubMed2006

Regulation of sexual development of Plasmodium by translational repression.

Translational repression of messenger RNAs (mRNAs) plays an important role in sexual differentiation and gametogenesis in multicellular eukaryotes. Translational repression and mRNA turnover were shown to influence stage-specific gene expression in the protozoan Plasmodium. The DDX6-class RNA helicase, DOZI (development of zygote inhibited), is found in a complex with mRNA species in cytoplasmic bodies of female, blood-stage gametocytes. These translationally repressed complexes are normally stored for translation after fertilization. Genetic disruption of pbdozi inhibits the formation of the ribonucleoprotein complexes, and instead, at least 370 transcripts are diverted to a degradation pathway.

Animals↗
PubMed1982

Molecular biology of the sea urchin embryo.

Research on the early development of the sea urchin offers new insights into the process of embryogenesis. Maternal messenger RNA stored in the unfertilized egg supports most of the protein synthesis in the early embryo, but the structure of maternal transcripts suggests that additional functions are also possible. The overall developmental patterns of transcription and protein synthesis are known, and current measurements describe the expression of specific genes, including the histone genes, the ribosomal genes, and the actin genes. Possible mechanisms of developmental commitment are explored for regions of the early embryo that give rise to specified cell lineages, such as the micromere-mesenchyme cell lineage.

Actins↗
PubMed1981

Is Haploid gene expression possible for sperm antigens?

The development of spermatozoon (sperm) from a spermatid involves a complex process of differentiation during which a variety of new gene products appear. It has been generally assumed that no genetic transcription occurs after meiosis and, if this were so, that all the new sperm proteins would have to to be transcribed from stored messenger RNA. However, the biochemical evidence suggests that there is no abrupt change in the rate of RNA synthesis during meiosis and that qualitative changes in RNA synthesis, to the extent that they are known, favor the likelihood of continuing messenger RNA synthesis. Experimental analyses of distorted transmission ratios of t-alleles and unbalanced chromosomal states in makes also suggest that genes are expressed in haploid nuclei after meiosis. It is probable that spermatozoa are functionally equivalent in most respects because of intercellular bridges that create a continuous cytoplasm between developing spermatozoa, facilitating an exchange of most postmeiotic gene products. Plasma membrane proteins which are potential antigens might not be shared across the intercellular bridges but the evidence to date for haploid expression of sperm antigens is poor.

Alleles↗
PubMed2006

Elongation of the Kcnq1ot1 transcript is required for genomic imprinting of neighboring genes.

The imprinted gene cluster at the telomeric end of mouse chromosome 7 contains a differentially methylated CpG island, KvDMR, that is required for the imprinting of multiple genes, including the genes encoding the maternally expressed placental-specific transcription factor ASCL2, the cyclin-dependent kinase CDKN1C, and the potassium channel KCNQ1. The KvDMR, which maps within intron 10 of Kcnq1, contains the promoter for a paternally expressed, noncoding, antisense transcript, Kcnq1ot1. A 244-base-pair deletion of the promoter on the paternal allele leads to the derepression of all silent genes tested. To distinguish between the loss of silencing as the consequence of the absence of transcription or the transcript itself, we prematurely truncated the Kcnq1ot1 transcript by inserting a transcriptional stop signal downstream of the promoter. We show that the lack of a full-length Kcnq1ot1 transcript on the paternal chromosome leads to the expression of genes that are normally paternally repressed. Finally, we demonstrate that five highly conserved repeats residing at the 5' end of the Kcnq1ot1 transcript are not required for imprinting at this locus.

Animals↗
PubMed2001

Onset of zygotic transcription and maternal transcript legacy in the rabbit embryo.

Onset of zygotic transcription is progressive from the one-cell stage onward in the rabbit embryo. Maternal transcripts remain fairly stable until the 8-16 cell stage when major transcriptional activation of the zygotic genome takes place. To understand the mechanisms of the maternal-to-zygotic transition in the genetic information governing development, we asked whether a progressive synthesis of zygotic transcripts takes over the maternal molecules, or whether the synthesis of zygotic transcripts is very abrupt and independent of the persistence of the maternal counterparts. To answer this question, we set up mRNA differential display experiments comparing the mRNA content of rabbit embryos at different stages during the preimplantation period. We isolated eight zygotic transcripts whose synthesis is abruptly turned on at the 8-16 cell stage. These transcripts are involved in general cellular metabolism and their maternal counterparts are still present up to the four-cell and even the 8-16 cell stage. This identification of early zygotic transcripts suggests that global long range modifications of chromatin structure result in a rapid increase in transcription rates during the major transcriptional activation of the zygotic genome.

3' Untranslated Regions↗
PubMed2001

Expression of axolotl DAZL RNA, a marker of germ plasm: widespread maternal RNA and onset of expression in germ cells approaching the gonad.

How germ cell specification occurs remains a fundamental question in embryogenesis. The embryos of several model organisms contain germ cell determinants (germ plasm) that segregate to germ cell precursors. In other animals, including mice, germ cells form in response to regulative mechanisms during development. To investigate germ cell determination in urodeles, where germ plasm has never been conclusively identified, we cloned a DAZ-like sequence from axolotls, Axdazl. Axdazl is homologous to Xdazl, a component of Xenopus germ plasm found in the vegetal pole of oocytes and eggs. Axdazl RNA is not localized in axolotl oocytes, and, furthermore, these oocytes do not contain the mitochondrial cloud that localizes Xdazl and other germ plasm components in Xenopus. Maternal Axdazl RNA is inherited in the animal cap and equatorial region of early embryos. At gastrula, neurula, and tailbud stages, Axdazl RNA is widely distributed. Axdazl first shows cell-specific expression in primordial germ cells (PGCs) approaching the gonad at stage 40, when nuage (germ plasm) appears in PGCs. These results suggest that, in axolotls, germ plasm components are insufficient to specify germ cells.

Ambystoma↗
PubMed2007

SMAUG is a major regulator of maternal mRNA destabilization in Drosophila and its translation is activated by the PAN GU kinase.

In animals, egg activation triggers a cascade of posttranscriptional events that act on maternally synthesized RNAs. We show that, in Drosophila, the PAN GU (PNG) kinase sits near the top of this cascade, triggering translation of SMAUG (SMG), a multifunctional posttranscriptional regulator conserved from yeast to humans. Although PNG is required for cytoplasmic polyadenylation of smg mRNA, it regulates translation via mechanisms that are independent of its effects on the poly(A) tail. Analyses of mutants suggest that PNG relieves translational repression by PUMILIO (PUM) and one or more additional factors, which act in parallel through the smg mRNA's 3' untranslated region (UTR). Microarray-based gene expression profiling shows that SMG is a major regulator of maternal transcript destabilization. SMG-dependent mRNAs are enriched for gene ontology annotations for function in the cell cycle, suggesting a possible causal relationship between failure to eliminate these transcripts and the cell cycle defects in smg mutants.

3' Untranslated Regions↗
PubMed2005

The mitochondrial ribosome-specific MrpL55 protein is essential in Drosophila and dynamically required during development.

We report on the essential Drosophila mRpL55 gene conserved exclusively in metazoans. Null mRpL55 mutants did not grow after hatching, moved slowly and died as first instar larvae. MrpL55 is similar to mammalian MRPL55, a protein that, in a large-scale mass spectrometry study, has been found as a mitoribosome-specific large subunit protein. We showed that MrpL55 was localised to the mitochondrion in S2 cells and tissues and was enriched in cells with a higher protein synthesis activity. The MrpL55 protein contains a KOW-like motif present in proteins with a role in transcriptional anti-termination and regulation of translation. Modulation of mRpL55 expression level is critical for development. Somatic clonal analysis showed that MrpL55 was not required in larval eye imaginal discs but required in pupal discs apparently during the second mitotic wave. Therefore, our results showed that the MrpL55 protein acts dynamically in the cell during development. We propose that MrpL55 is involved in Drosophila mitochondrial biogenesis and G2/M phase cell cycle progression.

Amino Acid Motifs↗
PubMed2001

The DEAD box helicase, Dhh1p, functions in mRNA decapping and interacts with both the decapping and deadenylase complexes.

A major pathway of mRNA turnover in eukaryotic cells initiates with deadenylation, leading to mRNA decapping and subsequent 5' to 3' exonuclease digestion. We show that a highly conserved member of the DEAD box family of helicases, Dhh1p, stimulates mRNA decapping in yeast. In dhh1delta mutants, mRNAs accumulate as deadenylated, capped species. Dhh1p's effects on decapping only occur on normal messages as nonsense-mediated decay still occurs in dhh1delta mutants. The role of Dhh1p in decapping appears to be direct, as Dhh1p physically interacts with several proteins involved in mRNA decapping including the decapping enzyme Dcp1p, as well as Lsm1p and Pat1p/Mrt1p, which function to enhance the decapping rate. Additional observations suggest Dhh1p functions to coordinate distinct steps in mRNA function and decay. Dhh1p also associates with Pop2p, a subunit of the mRNA deadenylase. In addition, genetic phenotypes suggest that Dhh1p also has a second biological function. Interestingly, Dhh1p homologs in others species function in maternal mRNA storage. This provides a novel link between the mechanisms of decapping and maternal mRNA translational repression.

Amino Acid Sequence↗
PubMed2000

Dynamic shuttling of TIA-1 accompanies the recruitment of mRNA to mammalian stress granules.

Mammalian stress granules (SGs) harbor untranslated mRNAs that accumulate in cells exposed to environmental stress. Drugs that stabilize polysomes (emetine) inhibit the assembly of SGs, whereas drugs that destabilize polysomes (puromycin) promote the assembly of SGs. Moreover, emetine dissolves preformed SGs as it promotes the assembly of polysomes, suggesting that these mRNP species (i.e., SGs and polysomes) exist in equilibrium. We used green flourescent protein-tagged SG-associated RNA-binding proteins (specifically, TIA-1 and poly[A] binding protein [PABP-I]) to monitor SG assembly, disassembly, and turnover in live cells. Fluorescence recovery after photobleaching shows that both TIA-1 and PABP-I rapidly and continuously shuttle in and out of SGs, indicating that the assembly of SGs is a highly dynamic process. This unexpected result leads us to propose that mammalian SGs are sites at which untranslated mRNAs are sorted and processed for either reinitiation, degradation, or packaging into stable nonpolysomal mRNP complexes. A truncation mutant of TIA-1 (TIA-1DeltaRRM), which acts as a transdominant inhibitor of SG assembly, promotes the expression of cotransfected reporter genes in COS transfectants, suggesting that this process of mRNA triage might, directly or indirectly, influence protein expression.

Animals↗