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Biomedical subjects

J Ngai

Publications and source records attributed to J Ngai.

24 records · Page 2Linked to original sources
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

Characterization and regulation in the expression of a gene coding for the intermediate filament protein desmin.

Using synthetic oligonucleotide probes, we have isolated chicken cDNA clones for the intermediate filament protein desmin. We show that the gene for this protein probably exists as a single copy in the haploid chicken genome and is transcribed into one mature mRNA species of approximately equal to 2.4 kilobases. Expression of this mRNA is tissue-specific, as it is present in high abundance in smooth and skeletal muscle but is absent from erythrocytes, spinal cord, and lens cells. A 10- to 20-fold increase in desmin mRNA is observed in myogenic cells upon fusion, which suggests that the level of expression of the desmin gene and the accumulation of desmin filaments during muscle differentiation is regulated at the transcriptional and/or posttranscriptional level but not at the translational level. Hybridization studies and nucleotide sequence comparison of the cDNAs specific for desmin and for other intermediate filament subunits reveal a region that is highly conserved (80%) among different members of the intermediate filament protein gene superfamily, with the exception of the chicken vimentin gene; this gene appears to be less homologous to the genes for the other chicken intermediate filament subunits than the mammalian vimentin gene is to the genes for other mammalian intermediate filament proteins and to the chicken desmin gene.

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↗