Molecular cloning and expression of cardiac-specific myosin heavy chain gene sequences in chick embryo

The differential distribution of beta tubulin mRNAs in individual mammalian brain cells

It has been shown by in vitro translation of polyadenylated messenger RNAs (poly(A)+ mRNAs) that the mRNAs encoding both alpha and beta tubulin isotypes are present at much higher relative levels in the developing rat brain than they are in the adult, suggesting that the requirements for tubulin subunits vary with cell type and/or with the developmental stages of a particular cell type. The postnatally developing rat cerebellum, with its readily identifiable cell populations that perform the gamut of developmental tasks, is a suitable model for analyzing specific cellular mRNA distributions during development. In this report, by in situ hybridization techniques it is shown that, by comparison to total cellular poly(A)+ mRNA levels, there is relatively more of the total beta tubulin mRNAs in mitotically active external granule layer cells than in those in the internal granule layer. These results show that migration and differentiation of these granule cells is accompanied by a decrease in their beta tubulin mRNA levels relative to the levels in granule cells of the external granule cell layer. Furthermore, the relative levels of beta tubulin mRNA both in the prenatally formed Purkinje cells and the postnatally formed stellate cells are two to fourfold less than in the granule cells of the internal granule cell layer.

Co-ordinate control of gene expression. Muscle-specific 7 S RNA contains sequences homologous to 3'-untranslated regions of myosin genes and repetitive DNA

We have cloned and sequenced a complementary DNA copy (pSS48) of a novel muscle-specific, low molecular weight RNA, 7 S RNA, isolated from embryonic chick cardiac muscle cells. The hybridization pattern of plasmid pSS48 DNA to chick genomic DNA suggests that 7 S RNA is derived from the repetitive chick DNA with a repetition frequency of about 300 copies per haploid genome. Under low stringency, pSS48 DNA also hybridizes with high specificity to the single copy gene for chick myosin light chain (MLC) and to myosin heavy chain (MHC), and possibly to other co-ordinately expressed genes for chick muscle proteins. The sequence analysis of recombinant plasmids pSS48, pML10 and pMHC8, for 7 S RNA, MLC mRNA and MHC RNA, respectively, indicated that short nucleotide stretches homologous to 7 S RNA reside in the 3' untranslated regions of the respective genes. The 7 S RNA sequence appears to be highly specific for the chick muscle tissue, since RNA and DNA from several sources did not hybridize to pSS48 DNA. Furthermore, the 7 S RNA-like sequence(s) appears in chick blastodermal cells preferentially earlier than the onset of transcription of genes for major muscle proteins. These results, taken together, suggest a possible function for 7 S RNA in expression of muscle-specific genes during chick development.

Tissue specificity of 3'-untranslated sequence of myosin light chain gene: unexpected interspecies homology with repetitive DNA

Using the 3' noncoding and coding sequences of chick heart myosin light chain mRNA cloned into Escherichia coli as probes, it was observed that, while the coding sequence shared homology with myosin light-chain mRNAs from other sources, the 3' noncoding sequence was specific for chick heart muscle. This property was used to detect chick heart-specific myosin light-chain gene activity in chick blastoderms of very early developmental stages where cells of different muscle origins cannot be distinguished morphologically. However, in spite of the tissue-specific divergence of the 3' noncoding sequence of myosin light-chain gene, which is present in a single copy in the chick genome, a surprising homology with DNA from such a diverse source like Dictyostelium discoideum was noted. The sequence homologous to chick myosin light-chain DNA was apparently present in a high repetition frequency in the Dictyostelium genome.

Characterization of a human genomic DNA fragment coding for a myosin heavy chain

A DNA segment from the human genome with information for myosin heavy chain (MHC) was isolated from a human genomic DNA library cloned in lambda Charon 4A phages. The isolation was accomplished by a myosin cDNA probe obtained from rabbit heart muscle mRNA (Sinha et al. 1982). The selected human DNA clone, designated lambda gMHC1, contains a genomic DNA fragment of about 14 kilobase pairs. The transcriptional polarity of this DNA was determined. The 5'-end of the gene is missing from the cloned fragment. This human gene exhibits sequence homology to MHC DNA of rabbit and chicken, but not to an MHC sequence of nematode. The isolated gene fragment is a member of the human MHC multi-gene family, which is presumed to consist of probably more than ten separate sarcomeric MHC genes per haploid genome.

Sequence analysis of the cloned mRNA coding for glyceraldehyde-3-phosphate dehydrogenase from chicken heart muscle

Using a cloned cDNA (pGAP30) the nucleotide sequence for chicken glyceraldehyde-3-phosphate dehydrogenase mRNA has been determined. The cDNA insert contains 1051 nucleotides representing the amino acid coding sequence, with the exception of 49 NH2-terminal amino acids, and includes the entire 3'-noncoding region. Sequence information on the missing 5' terminus of the mRNA, not represented in the clone pGAP30, was obtained by extension of the cDNA using an 85-nucleotide-long internal fragment as a primer. Thus the sequence of 310 amino acids of chicken glyceraldehyde-3-phosphate dehydrogenase representing 93% of the complete primary structure could be derived. The coding portion exhibits non-random utilization of synonymous codons with a strong bias for codons with G or C at the third position. The non-coding region contains several octanucleotides which are repeated and shows a potentially stable stem-and-loop structure located towards the end of the mRNA. Hypothetical functional implications of the putative secondary structure are discussed.