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J Ngai

Publications and source records attributed to J Ngai.

10 recordsLinked to original sources
PubMed1992

Molecular cloning and single-channel properties of the cyclic nucleotide-gated channel from catfish olfactory neurons.

We have cloned a functional cDNA encoding the cyclic nucleotide-gated channel selectively expressed in catfish olfactory sensory neurons. The cyclic nucleotide-gated channels share sequence and structural features with the family of voltage-gated ion channels. This homology is most evident in transmembrane region S4, the putative voltage sensor domain, and the H5 domain, thought to form the channel pore. We have characterized the single-channel properties of the cloned catfish channel and compared these properties with the channel in native catfish olfactory sensory neurons. The channel is activated equally well by cAMP and cGMP, shows only a slight voltage dependence of gating, and exhibits a pH- and voltage-dependent subconductance state similar to that observed for the voltage-gated L-type calcium channel.

Amino Acid Sequence↗
PubMed1990

Localization of newly synthesized vimentin subunits reveals a novel mechanism of intermediate filament assembly.

We have assessed the mechanism of intermediate filament assembly by assaying the sites of incorporation of chicken vimentin subunits expressed under the control of an inducible promoter in transfected mouse fibroblasts. The localization of newly synthesized vimentin was determined by immunofluorescence and immunoelectron microscopy at short time periods of induced synthesis, using antibodies specific for chicken vimentin. Under conditions where neither the soluble subunit pools nor the steady-state distribution of endogenous filaments are affected, newly synthesized vimentin incorporates into the vimentin filament network at numerous and discrete sites throughout the cell. Over time, the pattern of newly assembled vimentin converts to a continuous array coincident with preexisting vimentin filaments. These results are consistent with a novel mechanism of intermediate filament assembly, whereby growth of intermediate filaments occurs by topographically restricted and localized subunit addition, necessitating a transient disruption of filament integrity.

Animals↗
PubMed1987

Regulated expression of multiple chicken erythroid membrane skeletal protein 4.1 variants is governed by differential RNA processing and translational control.

Protein 4.1 is an extrinsic membrane protein that facilitates the interaction of spectrin and actin in the erythroid membrane skeleton and exists as several structurally related polypeptides in chickens. The ratio of protein 4.1 variants is developmentally regulated during terminal differentiation of chicken erythroid and lenticular cells. To examine the mechanisms by which multiple chicken protein 4.1 variants are differentially expressed, we have isolated cDNA clones specific for chicken erythroid protein 4.1. We show that a single protein 4.1 gene gives rise to multiple 6.6-kilobase mRNAs by differential RNA processing. Furthermore, the ratios of protein 4.1 mRNAs change during chicken embryonic erythropoiesis. We observe a quantitative difference in variant ratios when protein 4.1 is synthesized in vivo or in a rabbit reticulocyte lysate in vitro. Our results show that the expression of multiple protein 4.1 polypeptides is regulated at the levels of translation and RNA processing.

Amino Acid Sequence↗
PubMed1987

Expression of transfected vimentin genes in differentiating murine erythroleukemia cells reveals divergent cis-acting regulation of avian and mammalian vimentin sequences.

We studied the expression of transfected chicken and hamster vimentin genes in murine erythroleukemia (MEL) cells. MEL cells normally repress the levels of endogenous mouse vimentin mRNA during inducermediated differentiation, resulting in a subsequent loss of vimentin filaments. Expression of vimentin in differentiating MEL cells reflects the disappearance of vimentin filaments during mammalian erythropoiesis in vivo. In contrast, chicken erythroid cells express high levels of vimentin mRNA and vimentin filaments during terminal differentiation. We demonstrate here that chicken vimentin mRNA levels increase significantly in differentiating transfected MEL cells, whereas similarly transfected hamster vimentin genes are negatively regulated. In conjunction with in vitro nuclear run-on transcription experiments, these results suggest that the difference in vimentin expression in avian and mammalian erythropoiesis is due to a divergence of cis-linked vimentin sequences that are responsible for transcriptional and posttranscriptional regulation of vimentin gene expression. Transfected chicken vimentin genes produce functional vimentin protein and stable vimentin filaments during MEL cell differentiation, further demonstrating that the accumulation of vimentin filaments is determined by the abundance of newly synthesized vimentin.

Animals↗
PubMed1986

Spinal configuration during lifting.

The change in spinal configuration of the cervical, thoracic, and lumbar regions in relation to an amount of weight lifted was determined using videophotogrammetry. Fifteen healthy male subjects, 20-38 years of age, with no previous history of back pain participated in the study. The subjects lifted a crate containing 0, 10, and 20 kg weights using the straight-legs, bent-over-back method of lifting. The results showed that cervical and thoracic spinal segment configurations were not significantly influenced by the amount of weight lifted and that the mobility of the lumbar spinal segment was significantly decreased with increasing load (p = .03).

Adult↗
PubMed1985

Tissue-specific expression of distinct spectrin and ankyrin transcripts in erythroid and nonerythroid cells.

cDNA probes for three components of the erythroid membrane skeleton, alpha spectrin, beta spectrin, and ankyrin, were obtained by using monospecific antibodies to screen a lambda gt11 expression vector library containing cDNA prepared from chicken erythroid poly(A)+ RNA. Each cDNA appears to hybridize to one gene type in the chicken genome. Qualitatively distinct RNA species in myogenic and erythroid cells are detected for beta spectrin and ankyrin, while alpha spectrin exists as a single species of transcript in all tissues examined. This tissue-specific expression of RNAs is regulated quantitatively during myogenesis in vitro, since all three accumulate only upon myoblast fusion. Furthermore, RNAs for two of the three genes do not accumulate to detectable levels in chicken embryo fibroblasts, demonstrating that their accumulation can be noncoordinate. These observations suggest that independent gene regulation and tissue-specific production of heterogeneous transcripts from the beta spectrin and ankyrin genes underlie the formation of distinct membrane skeletons in erythroid and muscle cells.

Animals↗
PubMed1984

Differentiation of murine erythroleukemia cells results in the rapid repression of vimentin gene expression.

We show that vimentin filaments are present in undifferentiated Friend murine erythroleukemia cells, but are lost progressively to undetectable levels by 96 h of dimethyl sulfoxide-mediated differentiation. The amount of newly synthesized cytoskeletal vimentin is decreased dramatically by 24 h of induction, and is paralleled by a rapid loss of vimentin mRNA (approximately 25-fold reduction at 96 h). Hence, disappearance of vimentin filaments in these cells appears to be regulated at the level of vimentin mRNA abundance. On the other hand, the levels of actin synthesis and actin mRNA remain essentially unchanged. The kinetics of vimentin mRNA reduction during dimethyl sulfoxide-mediated differentiation, and the levels of vimentin mRNA observed in the presence of hexamethylene-bisacetamide or hemin as inducers suggest that the cessation of vimentin expression precedes, but may be associated with commitment to terminal differentiation. Our results demonstrate the dynamic regulation of vimentin expression in mammalian erythropoiesis.

Acetamides↗
PubMed1983

Tissue-specific expression of two mRNA species transcribed from a single vimentin gene.

We have isolated chicken cDNA and genomic clones for the intermediate filament subunit vimentin and show that the gene for this protein, which exists in a single copy in the haploid chicken genome, is transcribed into two mature mRNA species with approximate lengths of 2.0 and 2.3 kb. We have found cell-specific regulation in the expression of these two mRNAs; whereas both mRNA species are present in muscle cells, fibroblasts, spinal cord and lens, erythroid cells from 10- and 15-day-old chicken embryos express predominantly the lower molecular weight RNA. The difference between these two mRNAs is due to different lengths of their 3' untranslated regions, suggesting that the cell-specific regulation of their expression occurs either by specific termination of transcription or by differential post-transcriptional processing of the 3' untranslated region. Additionally, a remarkable induction (40- to 50-fold) in the abundance of the vimentin mRNA is observed in erythroid cells as chicken development proceeds from 4 to 15 days, which suggests that the level of expression of vimentin during erythroid development is regulated at the transcriptional level.

Animals↗