Chromosome assignment of human brain expressed sequence tags (ESTs) by analyzing fluorescently labeled PCR products from hybrid cell panels

Microtubule-associated protein 1B, a growth-associated and phosphorylated scaffold protein

Microtubule-associated protein 1B, MAP1B, is one of the major growth associated and cytoskeletal proteins in neuronal and glial cells. It is present as a full length protein or may be fragmented into a heavy chain and a light chain. It is essential to stabilize microtubules during the elongation of dendrites and neurites and is involved in the dynamics of morphological structures such as microtubules, microfilaments and growth cones. MAP1B function is modulated by phosphorylation and influences microtubule stability, microfilaments and growth cone motility. Considering its large size, several interactions with a variety of other proteins have been reported and there is increasing evidence that MAP1B plays a crucial role in the stability of the cytoskeleton and may have other cellular functions. Here we review molecular and functional aspects of this protein, evoke its role as a scaffold protein and have a look at several pathologies where the protein may be involved.

Linkage mapping of the Bra, Brb and Brg genes for rat protein phosphatase 2A 55 kDa B-regulatory subunit isotypes

We previously identified the rat Bra, Brb and Brg genes, which encode alpha, beta and gamma isotypes of the 55 kDa B-regulatory subunit of protein phosphatase 2A. Polymerase chain reaction-single strand conformation polymorphism analysis in the present study identified polymorphisms in Bra, Brb and Brg between the ACI and BUF, ZI and TM, and BN and WTC strains, respectively. Linkage analysis using mapping panels composed of F2 or back-crosses of these strains allowed Bra, Brb and Brg to be assigned to chromosomes 15, 18 and 14, respectively. Furthermore, it was revealed that Bra is located close to the Rb1 locus. Using polymorphism in Bra, loss of heterozygosity (LOH) was analyzed for rat mammary tumors induced in (SD x F344) F1 female rats by a food-borne carcinogen, 2-amino-1-methyl-6-phenylimidazo[4,5-b]pyridine, and a typical mammary carcinogen, 7,12-dimethylbenz[a]anthracene. No LOH was detected at the Bra locus.

"Spot 14" protein: a metabolic integrator in normal and neoplastic cells

"Spot 14" (S14) was originally identified as a mRNA from rat liver that responded rapidly to thyroid hormone, and has now been shown to play a key role in the tissue-specific regulation of lipid metabolism. In addition to its responsiveness to thyroid hormone, S14 gene transcription is controlled by dietary substrates, such as glucose and polyunsaturated fatty acids, and by fuel-related hormones including insulin and glucagon. The S14 protein forms homodimers via a carboxyl-terminal "zipper" domain. The protein is located primarily in the cell nucleus, and its expression in liver is limited to the perivenous portion of the hepatic lobule, the site of fatty acid synthesis. S14 protein is critical for the induction of key enzymes involved in the switching of hepatic metabolism from the fasted to the fed state. S14 antisense oligonucleotides inhibit both the intracellular production of lipids and their export as very low-density lipoprotein (VLDL) particles. S14 acts at the level of transcription to regulate expression of genes encoding key metabolic enzymes, including those required for long-chain fatty acid synthesis. The human S14 gene is located at 11q13.5, a region that is amplified in a subset of aggressive breast cancers. S14 mRNA is expressed in most breast cancer-derived cell lines, and the protein is found in the nuclei of two thirds of human breast cancer specimens, but not in normal nonlactating mammary glands. S14 expression in breast tumors is highly concordant with overabundance of a key lipogenic enzyme. This indicates the association of S14 with enhanced tumor lipogenesis, an established marker of poor prognosis. In addition to the utility of S14 as a model system for elucidation of the mechanism of thyroid hormone action, studies of its regulation and function have provided insights into tissue-specific metabolic control by hormones and dietary substrates in both normal and neoplastic tissues.

Cloning and expression of human liver rhodanese cDNA

cDNA for the human rhodanese (thiosulfate; cyanide sulfurtransferase, EC 2.8.1.1) was cloned from a human fetal liver cDNA library. Sequencing of the cDNA revealed an open reading frame that encodes a 297-residue polypeptide with a calculated mass of 33,427 daltons. When the rhodanese cDNA was transiently expressed in Escherichia coli and Cos7 cells, the rhodanese activity increased 40-fold and 150-fold, respectively. Sequence homology analysis showed that the human rhodanese is 89.6% identical to bovine, 90.2% identical to rat, 91.2% identical to mouse and Chinese hamster, and 71.4% similar to avian counterparts, respectively, and that rhodanese was highly conserved across evolution.

Regional assignment of human ESTs by whole-genome radiation hybrid mapping

The UK HGMP Resource Centre's collection of human partial cDNA sequences (ESTs) have been examined for suitability for mapping by PCR on a panel of somatic cell hybrids. The chromosomal assignments of 92 ESTs were determined with a monochromosomal hybrid panel, and a subset of 45 were linked to genetic markers with a panel of whole-genome radiation hybrids (WG-RHs). These results demonstrate the potential of WG-RHs to construct a transcript map of the human genome.

Analysis of gene expression by tissue and developmental stage

High-throughput sequencing of cDNAs from multiple tissue- and stage-specific libraries is an efficient method for characterizing gene expression by tissue and developmental stage. When combined with functional information derived from the systematic study of transcription factors, signal transducers, and other regulatory molecules in model systems, data from expressed sequence tag projects provide an increasingly detailed picture of gene expression and its regulation. Understanding this picture will require the development of highly sophisticated databases to organize and correlate these data.

Diversity in the regulatory B-subunits of protein phosphatase 2A: identification of a novel isoform highly expressed in brain

The physiological role of type 2A protein phosphatases (PP2A) is dependent upon the association of the catalytic subunit with a variety of regulatory subunits. In order to understand the function of PP2A, we have undertaken purification of the holoenzymes and molecular cloning of the regulatory subunits. Two trimeric forms containing distinct B-subunits, PP2A0 and PP2A1, have been purified from rabbit skeletal muscle. The B-subunits associated with PP2A0 and PP2A1 migrated on sodium dodecyl sulfate-polyacrylamide gel electrophoresis with slightly different mobility, approximately 52.5 and approximately 51.5 kDa, respectively and showed distinct immunological properties. The B' form of B-subunit associated with PP2A0 was recognized by antibodies against the B-subunit present in bovine heart PP2A but not by antibodies specific to the B subunit isoforms of rabbit PP2A1. Cloning of cDNAs encoding the B subunit of PP2A1 resulted in the isolation of a cDNA highly homologous to, but distinct from, the B alpha subunit isoform. The deduced amino acid sequence of this novel isoform, which was designated B gamma, encoded a protein which was 81% and 87% identical to the B alpha and B beta isoforms, respectively. Northern blot analysis indicated that the B gamma isoform is highly expressed in rabbit brain as a transcript of 3.9 kb. Analysis of B-subunit expression by Western blot indicated a general parallel with the message levels. In conclusion, our data reveal even greater complexity of PP2A trimeric holoenzymes due to the identification of a novel B regulatory subunit isoform of PP2A1 and a distinct B' subunit associated with PP2A0.