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PubMed2004

Ryanodine receptor regulation by intramolecular interaction between cytoplasmic and transmembrane domains.

Ryanodine receptors (RyR) function as Ca(2+) channels that regulate Ca(2+) release from intracellular stores to control a diverse array of cellular processes. The massive cytoplasmic domain of RyR is believed to be responsible for regulating channel function. We investigated interaction between the transmembrane Ca(2+)-releasing pore and a panel of cytoplasmic domains of the human cardiac RyR in living cells. Expression of eGFP-tagged RyR constructs encoding distinct transmembrane topological models profoundly altered intracellular Ca(2+) handling and was refractory to modulation by ryanodine, FKBP12.6 and caffeine. The impact of coexpressing dsRed-tagged cytoplasmic domains of RyR2 on intracellular Ca(2+) phenotype was assessed using confocal microscopy coupled with parallel determination of in situ protein: protein interaction using fluorescence resonance energy transfer (FRET). Dynamic interactions between RyR cytoplasmic and transmembrane domains were mediated by amino acids 3722-4610 (Interacting or "I"-domain) which critically modulated intracellular Ca(2+) handling and restored RyR sensitivity to caffeine activation. These results provide compelling evidence that specific interaction between cytoplasmic and transmembrane domains is an important mechanism in the intrinsic modulation of RyR Ca(2+) release channels.

Animals↗
PubMed2000

Defective nuclear localization of p53 protein in a Chinese hamster cell line is associated with the formation of stable cytoplasmic protein multimers in cells with gene amplification.

Many p53 functions require p53 transport into the nucleus. Mutant p53 also generally accumulates in the nucleus of transformed or neoplastic cells. However, examples of cytoplasmic accumulation of wild-type or mutant p53 have also been reported. Various explanations have been provided for defective nuclear localization. Here we propose a novel example of cytoplasmic p53 localization which occurs in cells showing gene amplification and appears to be due to the formation of stable p53 multimers. We studied a methotrexate-resistant Chinese hamster cell line (MTX M) carrying amplified dihydrofolate reductase genes and derived from a cell line with p53 nuclear accumulation. MTX M showed cytoplasmic p53 localization and, on immunoblots, several extra bands in the high molecular weight region, besides the expected 53 kDa band. p53 localization and the appearance of high molecular weight bands appeared to be correlated with the degree of DNA amplification. However, amplification of dihydrofolate reductase itself was not involved. Changing the p53 phosphorylation status quantitatively influenced the formation of high molecular weight bands. Cell fusion experiments demonstrated that p53 cytoplasmic localization in MTX M is a dominant phenotype. This result suggests that the defect causing lack of nuclear localization in this cell line does not reside in the nucleus. In the cytoplasm of MTX M and of wild-type/MTX M heterodikaryons p53 gives rise to protein complexes that are unable to re-enter the nucleus. The formation of such protein complexes is dependent on the amplification of an unknown gene product.

3T3 Cells↗
PubMed1999

Apoptosis inhibitory activity of cytoplasmic p21(Cip1/WAF1) in monocytic differentiation.

p21(Cip1/WAF1) inhibits cell-cycle progression by binding to G1 cyclin/CDK complexes and proliferating cell nuclear antigen (PCNA) through its N- and C-terminal domains, respectively. The cell-cycle inhibitory activity of p21(Cip1/WAF1) is correlated with its nuclear localization. Here, we report a novel cytoplasmic localization of p21(Cip1/WAF1) in peripheral blood monocytes (PBMs) and in U937 cells undergoing monocytic differentiation by in vitro treatment with vitamin D3 or ectopic expression of p21(Cip1/WAF1), and analyze the biological consequences of this cytoplasmic expression. U937 cells which exhibit nuclear p21(Cip1/WAF1) demonstrated G1 cell-cycle arrest and subsequently differentiated into monocytes. The latter event was associated with a cytoplasmic expression of nuclear p21(Cip1/WAF1), concomitantly with a resistance to various apoptogenic stimuli. Biochemical analysis showed that cytoplasmic p21(Cip1/WAF1) forms a complex with the apoptosis signal-regulating kinase 1 (ASK1) and inhibits stress-activated MAP kinase cascade. Expression of a deletion mutant of p21(Cip1/WAF1) lacking the nuclear localization signal (DeltaNLS-p21) did not induce cell cycle arrest nor monocytic differentiation, but led to an apoptosis-resistant phenotype, mediated by binding to and inhibition of the stress-activated ASK1 activity. Thus, cytoplasmic p21(Cip1/WAF1) itself acted as an inhibitor of apoptosis. Our findings highlight the different functional roles of p21(Cip1/WAF1), which are determined by its intracellular distribution and are dependent on the stage of differentiation.

Amino Acid Sequence↗
PubMed2001

The Y14 protein communicates to the cytoplasm the position of exon-exon junctions.

We recently described an RNA-binding protein, Y14, that binds preferentially to spliced mRNAs and persists in the cytoplasm. Y14 is part of a multi-protein complex that also contains the mRNA export factor TAP. This suggests that splicing imprints the mRNA with a unique set of proteins that communicate the history of the transcript to the cytoplasm. Here, using microinjection of pre-mRNAs into Xenopus oocyte nuclei followed by immunoprecipitation of RNase-fragmented mRNAs from the cytoplasm, we show that Y14 is stably bound to sequences immediately upstream of exon-exon junctions. This feature appears to be unique to Y14. Using monoclonal antibodies that we produced against Aly/REF, another component recently reported to be an mRNA export factor, we show that Aly/REF is associated with spliced mRNAs in the nucleus but is not detectable on mRNAs in the cytoplasm. Thus, we propose that the splicing- dependent binding of Y14 provides a position-specific molecular memory that communicates to the cytoplasm the location of exon and intron boundaries. This novel mechanism may play an important role in post-splicing events.

Active Transport, Cell Nucleus↗
PubMed1990

Cytoplasmically inherited reproductive incompatibility in Tribolium flour beetles: the rate of spread and effect on population size.

This paper reports on the effects of a cytoplasmically inherited reproductive incompatibility in different genetic strains of the flour beetle, Tribolium confusum. We measured the rate of spread and the effect of host population size using different initial frequencies of infection with a cytoplasmic factor that mediates reproductive incompatibility. There were two experiments, in one the infected and uninfected lines were from the same genetic strain, b-Yugoslavia. In the other, the infected line was from the "high cannibalism" bIV strain and the uninfected line from the "low cannibalism" bI strain. We estimate that the fitness ratio of infected to uninfected in b-Yugoslavia is 0.63 and the observed rate of spread for this strain corresponds to a model of cytoplasmic inheritance that takes into account the productivity differences between the infected and cured lines. In the bI-bIV experiment, because the uninfected and infected lines are from different genetic strains, we cannot partition the effects of the cytoplasmic factor from other factors. The rate of spread in the bI-bIV experiment is faster in males and slower in females than predicted from a model of cytoplasmic inheritance. In both experiments, productivity varies with initial infection frequency; however, the relationship is not explained by a simple model that predicts lower population size at intermediate infection frequencies.

Animals↗
PubMed1992

Comparative effects of pollen and seed migration on the cytonuclear structure of plant populations. II. Paternal cytoplasmic inheritance.

We continue our study of the effects of pollen and seed migration on the cytonuclear structure of mixed-mating plant populations by analyzing two deterministic continent-island models under the critical assumption of paternal cytoplasmic inheritance. The major results of this study that contrast with our previous conclusions based on maternal cytoplasmic inheritance are (i) pollen gene flow can significantly affect the cytonuclear structure of the island population, and in particular can help to generate cytonuclear disequilibria that greatly exceed the magnitude of those that would be produced by seed migration or mixed mating alone; (ii) with simultaneous pollen and seed migration, nonzero cytonuclear disequilibria will be maintained not only when there is disequilibrium in the immigrant pollen or seeds, but also through a variety of intermigrant admixture effects when the two pools of immigrants differ appropriately in their cytonuclear compositions; (iii) either immigrant pollen or immigrant seeds can generate disequilibria de novo in populations with initially random cytonuclear associations, but pollen migration alone generally produces lower levels of disequilibrium than does comparable seed migration, especially at high levels of self-fertilization when the overall fraction of immigrant pollen is low; (iv) the equilibrium state of the island population will be influenced by the rate of pollen gene flow whenever there is either allelic disequilibrium in the immigrant pollen or simultaneous seed migration coupled with different cytoplasmic or nuclear allele frequencies in immigrant pollen and seeds or nonzero allelic disequilibrium in either immigrant pool. The estimation of pollen migration should therefore be facilitated with paternal cytoplasmic inheritance relative to the case of maternal cytoplasmic inheritance. These basic conclusions hold whether the population is censused as seeds or as adults, but with simultaneous pollen and seed migration, the relationship between census time and the ability to detect nonrandom cytonuclear associations is complex. When migration is through pollen alone, however, the cytonuclear structure of the island population is independent of the life stage censused.

Alleles↗
PubMed1996

Cytoplasmic dynein function is essential in Drosophila melanogaster.

The microtubule motor cytoplasmic dynein has been implicated in a variety of intracellular transport processes. We previously identified and characterized the Drosophila gene Dhc64C, which encodes a cytoplasmic dynein heavy chain. To investigate the function of the cytoplasmic dynein motor, we initiated a mutational analysis of the Dhc64C dynein gene. A small deletion that removes the chromosomal region containing the heavy chain gene was used to isolate EMS-induced lethal mutations that define at least eight essential genes in the region. Germline transformation with a Dhc64C transgene rescued 16 mutant alleles in the single complementation group that identifies the dynein heavy chain gene. All 16 alleles were hemizygous lethal, which demonstrates that the cytoplasmic dynein heavy chain gene Dhc64C is essential for Drosophila development. Furthermore, our failure to recover somatic clones of cells homozygous for a Dhc64C mutation indicates that cytoplasmic dynein function is required for cell viability in several Drosophila tissues. The intragenic complementation of dynein alleles reveals multiple mutant phenotypes including male and/or female sterility, bristle defects, and defects in eye development.

Alleles↗
PubMed2000

The effects of pollen and seed migration on nuclear-dicytoplasmic systems. II. A new method for estimating plant gene flow from joint nuclear-cytoplasmic data.

A new maximum-likelihood method is developed for estimating unidirectional pollen and seed flow in mixed-mating plant populations from counts of joint nuclear-cytoplasmic genotypes. Data may include multiple unlinked nuclear markers with a single maternally or paternally inherited cytoplasmic marker, or with two cytoplasmic markers inherited through opposite parents, as in many conifer species. Migration rate estimates are based on fitting the equilibrium genotype frequencies under continent-island models of plant gene flow to the data. Detailed analysis of their equilibrium structures indicates when each of the three nuclear-cytoplasmic systems allows gene flow estimation and shows that, in general, it is easier to estimate seed than pollen migration. Three-locus nuclear-dicytoplasmic data only increase the conditions allowing seed migration estimates; however, the additional dicytonuclear disequilibria allow more accurate estimates of both forms of gene flow. Estimates and their confidence limits for simulated data sets confirm that two-locus data with paternal cytoplasmic inheritance provide better estimates than those with maternal inheritance, while three-locus dicytonuclear data with three modes of inheritance generally provide the most reliable estimates for both types of gene flow. Similar results are obtained for hybrid zones receiving pollen and seed flow from two source populations. An estimation program is available upon request.

Cell Nucleus↗
PubMed2002

Complex glycosylation of Skp1 in Dictyostelium: implications for the modification of other eukaryotic cytoplasmic and nuclear proteins.

Recently, complex O-glycosylation of the cytoplasmic/nuclear protein Skp1 has been characterized in the eukaryotic microorganism Dictyostelium. Skp1's glycosylation is mediated by the sequential action of a prolyl hydroxylase and five conventional sugar nucleotide-dependent glycosyltransferase activities that reside in the cytoplasm rather than the secretory compartment. The Skp1-HyPro GlcNAcTransferase, which adds the first sugar, appears to be related to a lineage of enzymes that originated in the prokaryotic cytoplasm and initiates mucin-type O-linked glycosylation in the lumen of the eukaryotic Golgi apparatus. GlcNAc is extended by a bifunctional glycosyltransferase that mediates the ordered addition of beta1,3-linked Gal and alpha1,2-linked Fuc. The architecture of this enzyme resembles that of certain two-domain prokaryotic glycosyltransferases. The catalytic domains are related to those of a large family of prokaryotic and eukaryotic, cytoplasmic, membrane-bound, inverting glycosyltransferases that modify glycolipids and polysaccharides prior to their translocation across membranes toward the secretory pathway or the cell exterior. The existence of these enzymes in the eukaryotic cytoplasm away from membranes and their ability to modify protein acceptors expose a new set of cytoplasmic and nuclear proteins to potential prolyl hydroxylation and complex O-linked glycosylation.

Amino Acid Sequence↗
PubMed2001

CRB1 has a cytoplasmic domain that is functionally conserved between human and Drosophila.

Mutations in the human Crumbs homologue 1 (CRB1) gene cause severe retinal dystrophies, ranging from retinitis pigmentosa to Leber congenital amaurosis. The CRB1 gene is expressed specifically in human retina and brain and encodes a protein homologous to the Drosophila Crumbs protein. In crumbs mutant embryos apico-basal polarity of epithelial cells is lost, leading to widespread epidermal cell death. The small cytoplasmic domain of Crumbs organizes an intracellular protein scaffold that defines the assembly of a continuous zonula adherens. The crumbs mutant phenotype can be partially rescued by expression of just the membrane-bound cytoplasmic domain, and overexpression of this domain in a wild-type background results in a multilayered epidermis. A striking difference between CRB1 and Crumbs was that the latter contains a transmembrane region and a 37 amino acid cytoplasmic domain. Here we describe an alternative splice variant of human CRB1 that encodes a cytoplasmic domain 72% similar to that of Drosophila Crumbs. Two intracellular subdomains that are necessary for function in Drosophila are absolutely conserved. Rescuing and overexpression studies in Drosophila show that the cytoplasmic domains are functionally related between these distant species. This suggests that CRB1 organizes an intracellular protein scaffold in the human retina. Human homologues of proteins binding to Crumbs may be part of this complex and represent candidate genes for retinal dystrophies.

Alternative Splicing↗
PubMed1999

Effect of varicocelectomy on the abnormal retention of residual cytoplasm by human spermatozoa.

Abnormal retention of cytoplasmic residues by human spermatozoa is associated with the generation of reactive oxygen species (ROS) in semen and defective sperm function. We have examined the effect of varicocelectomy on the retention of residual cytoplasm by human spermatozoa. Clinical reports of 43 men who underwent microsurgical varicocelectomy at our institution during a 1 year period beginning July 1996 were reviewed. Standard semen parameters (concentration, motility and morphology) and residual cytoplasm retention (monitored by Papanicolaou stain) were assessed before and 6 months after varicocelectomy. The percentage of spermatozoa with residual cytoplasm decreased significantly following varicocelectomy compared to pre-operatively (25.8 versus 18.1% respectively). The percentages of motile spermatozoa and normal forms increased significantly (P = 0.0003, P = 0.005 respectively) following varicocelectomy (22.6 versus 32.9% and 46.4 versus 54.4% respectively). Our data suggest that varicocelectomy can improve the disposal of residual sperm cytoplasm by the testis and/or epididymis in infertile men with varicocele. These data also suggest that varicocelectomy reduces the potential for ROS generation by human spermatozoa in these men.

Adult↗
PubMedDate not supplied

Cytoplasmic transfer in assisted reproduction.

This report details the use of cytoplasmic transfer in human oocytes. The introduction of a small amount of ooplasm from a donor oocyte or zygote may alter the function of oocytes, with probable deficiencies. Cytoplasmic transfer from fertile donor oocytes or zygotes into compromised oocytes from patients with recurrent implantation failure after assisted reproduction has now led to the birth of nearly 30 healthy babies worldwide. Transfer of small amounts of cytoplasm probably involves mRNAs, proteins and mitochondria, as well as other factors and organelles. Even though the use of cytoplasmic transfer has been employed in several IVF clinics--and pregnancies have resulted--it is not known definitively whether the physiology of the early embryo is affected. This review outlines the experimental cytoplasmic transfer techniques and postulates the future impact in assisted reproduction.

Animals↗
PubMed2004

Importance of class II transactivator leucine-rich repeats for dominant-negative function and nucleo-cytoplasmic transport.

Class II transactivator (CIITA), the master regulator of MHC class II (MHC-II) gene transcription, shows a complex behavior in terms of self-association, nucleo-cytoplasmic transport and MHC-II gene transactivation. Here, we analyzed the mechanisms of dominant-negative function and nucleo-cytoplasmic transport of CIITA with emphasis on the role of the C-terminal leucine-rich-repeat (LRR) region in these processes. First, we determined nucleo-cytoplasmic transport of endogenous CIITA and thus validated results obtained with epitope-tagged CIITA constructs. LRR mutations in potential protein-protein contact positions lead to either completely blocked or reduced nuclear import, but can also give rise to increased nuclear export. Surprisingly, N-terminally truncated CIITA mutants show dominant-negative inhibition of wild-type CIITA, whether they are located in the nucleus or in the cytoplasm. Integrity of the LRR is necessary for the dominant-negative function of both types of mutants. LRR mutations are dominant over the effect of an exogenously added N-terminal nuclear localization signal (NLS) leading to cytoplasmic localization. Taken together, our results show that the LRR regulate the function of one or several NLS within CIITA, and control both nuclear import and export. Self-association is not affected in these mutants; we therefore suggest that interaction of the LRR with an unknown protein partner may be necessary for import and transactivation function of CIITA.

Active Transport, Cell Nucleus↗
PubMed1996

Formyltetrahydrofolates associated with mitochondria have longer polyglutamate chains than the methyltetrahydrofolates associated with cytoplasm in rat brain.

The subcellular distribution of folate coenzymes in the brain is unknown. Brain folate concentrations are low and hence require a sensitive assay to determine the subcellular distribution. Rat brain was fractionated by differential centrifugation into cytoplasmic, mitochondrial and crude synaptosomal fractions. The compositions of the folate pools in these subcellular fractions were determined by differential conversion of one-carbon forms enzymatically to 5,10-methylenetetrahydrofolate (5,10CH2H4PteGlu(n)) followed by reaction of the 5,10CH2H4PteGlu(n) with thymidylate synthetase and [3H]fluorodeoxyuridylate to form ternary complexes, which were then separated as a function of polyglutamate chain length by isoelectric focusing, visualized by fluorography and quantified by densitometry. The distribution of the pteridine derivatives in brain was very similar to the distribution of these derivatives in liver. Cytoplasm contained primarily 5-methyltetrahydropteroylpolyglutamates with smaller amounts of unsubstituted tetrahydropteroylpolyglutamates, whereas mitochondria contained approximately equal concentrations of unsubstituted and formyl-substituted tetrahydropteroylpolyglutamates. The subcellular distribution of polyglutamate derivatives in brain, however, was different from that in liver. In the brain, the mitochondrial folates exhibited longer polyglutamate chains than did the cytoplasmic folates, a pattern opposite to that in the liver. Whereas the brain cytoplasmic pteroylpolyglutamates were primarily penta and hexa glutamates, the brain mitochondrial pteroylpolyglutamates were primarily hexa and hepta glutamates. The brain also contained small but measurable levels of oxidized folates, which were seen in crude synaptosomal fractions but not in cytoplasmic or mitochondrial fractions.

Animals↗
PubMed1994

AU-A, an RNA-binding activity distinct from hnRNP A1, is selective for AUUUA repeats and shuttles between the nucleus and the cytoplasm.

The 3'-untranslated regions of many labile transcripts contain AU-rich sequences that serve as cis determinants of mRNA stability and translational efficiency. Using a photocrosslinking technique, our laboratory has previously defined three cytoplasmic RNA-binding activities specific for the AUUUA multimers found in the 3'-untranslated regions of lymphokine mRNAs. One of these activities, AU-A, has an apparent molecular mass of 34 kDa, is constitutively expressed in both primary T cells and the Jurkat T cell leukemia line, and binds to a variety of U-rich RNA sequences. Previous studies had shown that AU-A is more prevalent in the nucleus than the cytoplasm, raising the possibility that AU-A is really a nuclear RNA-binding activity that is found in cytoplasmic extracts because of nuclear leakage during cell fractionation. We now show that AU-A shuttles between the cytoplasm and the nucleus. Our results indicate that AU-A is a candidate protein component of ribonucleoprotein complexes that participate in nucleocytoplasmic transport of mRNA and cytoplasmic mRNA metabolism. The properties of AU-A activity are similar to those of heterogeneous nuclear ribonucleoprotein A1 (hnRNP A1). However, using monoclonal antibodies to hnRNP A1 and protease digestion patterns, we show that AU-A activity and hnRNP A1 protein are distinct. These studies have also allowed us to define a fourth RNA-binding activity of apparent molecular mass 41 kDa with specificity for AUUUA multimers. This activity is restricted to the nucleus and contains the hnRNP C protein.

Base Sequence↗
PubMed2005

tRNA-linked molecular beacons for imaging mRNAs in the cytoplasm of living cells.

When oligonucleotide probes are microinjected into cells to image the distribution of RNAs, they are rapidly sequestered into the nucleus. As a result, it is difficult to detect mRNAs in the cytoplasm of living cells. We were able to overcome this process by attaching tRNA transcripts to the probes. We show that when fluorescently labeled tRNAs, tRNAs with extensions at their 5' end, or chimeric molecules in which a molecular beacon possessing a 2'-O-methylribonucleotide backbone is linked to a tRNA, are injected into the nucleus of HeLa cells, they are exported into the cytoplasm. When these constructs are introduced into the cytoplasm, they remain cytoplasmic. These constructs allow the distribution of both the general mRNA population and specific mRNAs to be imaged in living cells. This strategy should also be useful for enhancing the efficacy of antisense oligonucleotides by keeping them in the cytoplasm. Our observations show that the fidelity of the tRNA export system is relaxed for unnatural tRNA variants when they are introduced into the nucleus in large amounts.

Active Transport, Cell Nucleus↗
PubMed2002

Cytoplasmic localization of wild-type p53 in glioblastomas correlates with expression of vimentin and glial fibrillary acidic protein.

Cytoplasmic accumulation of wild-type p53 in tumor cells indicates that the tumor suppressor is inactive with regard to growth suppressive functions. Whether this occurs randomly during tumor development or characterizes a certain tumor cell subset is not known. Here we assayed primary glioblastomas for expression and subcellular localization of p53 and determined a correlation with expression of intermediate filament proteins characterizing glial cell development. Sixty-nine percent of the tumors were p53 positive in immunohistochemistry. A significant number of tumors (23%) accumulated wild-type p53 in the cytoplasm, which correlated with the presence of vimentin and glial fibrillary acidic protein, except for 1 case. Tumors with exclusive nuclear p53 contained none or only one of these intermediate filament proteins. In an alternative approach, tumors positive for glial fibrillary acidic protein were screened for expression of p53 and vimentin. Thirty-eight percent of these tumors showed cytoplasmic p53, and all of those also expressed vimentin. Tumors with only nuclear p53 were vimentin negative, except for 1 case. No mutation was detected in p53 exons 5 to 8 in tumors with cytoplasmic p53, suggesting that they express wild-type p53. The data indicate that a cytoplasmic accumulation of wild-type p53 in human primary glioblastomas correlates with a certain intermediate filament protein expression, suggesting that it identifies a certain subset of tumors.

Active Transport, Cell Nucleus↗
PubMed1989

Maturation at high frequency of germinal-vesicle-stage mouse oocytes after cryopreservation: alterations in cytoplasmic, nuclear, nucleolar and chromosomal structure and organization associated with vitrification.

After thawing and culture in vitro, greater than 90% of germinal-vesicle (GV)-stage mouse oocytes cryopreserved by vitrification, were capable of resuming meiosis and undergoing normal chromosomal and cytoplasmic maturation to metaphase II. This high frequency of development occurred against a background of profound alterations in the structure and organization of the cytoplasm, nucleus, nucleolus and chromatin during the dehydration stage of vitrification. Most, but not all, cytoplasmic and nuclear perturbations returned to a normal state during post-thaw culture. However, the results clearly demonstrate that vitrification is associated with chromosomal and cellular disorders that could adversely affect development after fertilization. Irreversible changes of potential developmental significance observed after vitrification at the GV stage include (i) premature chromosomal condensation, (ii) mixing of nucleoplasmic and cytoplasmic components prior to GV breakdown, and (iii) externalization of chromatin fragments into the cytoplasm after reformation of the oocyte nucleus, which shows the potential for the generation of fertilizable oocytes containing deleted segments of DNA.

Animals↗