Retinoic acid upregulates beta(1)-integrin in vascular smooth muscle cells and alters adhesion to fibronectin.

Retinoic acid has an established physiological role in differentiation, development, and cellular growth. This study investigated the action of all-trans retinoic acid (ATRA) on vascular integrins, cell-surface receptors that control growth and remodeling of blood vessels. The beta(1)-integrin subunit mRNA and protein was induced after treatment with ATRA in two different rat vascular smooth muscle cell lines. To relate this result to the in vivo state, the aortas from adult rats fed with therapeutic doses of ATRA were examined for beta(1)-integrin protein. A significant upregulation of the integrin subunit was observed in vivo. To assess if this increase contributed to physiological changes in cellular function, cells treated with ATRA were tested for alterations in adhesion to extracellular matrix proteins. The cells exposed to the retinoid were seen to adhere more strongly to fibronectin, via the beta(1)-integrin. These results showed that modulation of vascular integrins by ATRA in adult rats contributes to functional changes that can cause remodeling of blood vessels.

1 alpha,25-dihydroxyvitamin D3 up-regulates expression of the osteoclast integrin alpha v beta 3.

Osteoclast precursors selectively attach to bone and differentiate into multinucleated cells that function to remodel and resorb it. We have shown previously that attachment of osteoclasts to bone and subsequent resorption are mediated by the integrin alpha v beta 3. 1 alpha,25-Dihydroxyvitamin D3 (1,25-(OH)2D3) enhances osteoclast precursor differentiation in vivo by mechanisms that are still not clearly understood but entail enhanced attachment of cells to bone. This observation raises the possibility that at least one component of vitamin D-induced osteoclast precursor differentiation involves modulation of integrin expression. To test if the steroid modulates the osteoclast integrin alpha v beta 3 (the vitronectin receptor), we examined the effects of 1,25-(OH)2D3 on transcription of the alpha v gene as well as surface expression and function of alpha v beta 3, in chicken osteoclast precursors. Treatment of the cells with 1,25-(OH)2D3 led to a progressive dose-dependent increase in steady state alpha v mRNA levels with enhanced expression evident within 24 h. The effect was receptor-mediated as indicated by the effects of other vitamin D analogs. The increase in alpha v mRNA levels did not reflect decreased message degradation but, as demonstrated by nuclear run-on experiments, was due to accelerated rates of transcription. Most importantly, induction of alpha v mRNA by 1,25-(OH)2D3 was mirrored by higher levels of expression of alpha v beta 3 on the cell surface, as well enhanced attachment to its substrate, vitronectin.

Drosophila nonsense suppressors: functional analysis in Saccharomyces cerevisiae, Drosophila tissue culture cells and Drosophila melanogaster.

Amber (UAG) and opal (UGA) nonsense suppressors were constructed by oligonucleotide site-directed mutagenesis of two Drosophila melanogaster leucine-tRNA genes and tested in yeast, Drosophila tissue culture cells and transformed flies. Suppression of a variety of amber and opal alleles occurs in yeast. In Drosophila tissue culture cells, the mutant tRNAs suppress hsp70:Adh (alcohol dehydrogenase) amber and opal alleles as well as an hsp70:beta-gal (beta-galactosidase) amber allele. The mutant tRNAs were also introduced into the Drosophila genome by P element-mediated transformation. No measurable suppression was seen in histochemical assays for Adhn4 (amber), AdhnB (opal), or an amber allele of beta-galactosidase. Low levels of suppression (approximately 0.1-0.5% of wild type) were detected using an hsp70:cat (chloramphenicol acetyltransferase) amber mutation. Dominant male sterility was consistently associated with the presence of the amber suppressors.

Excision of the Drosophila transposable element mariner: identification and characterization of the Mos factor.

Genetic and molecular evidence presented in this paper demonstrate that the Mos factor for inherited mosaicism is a special copy of the transposable element mariner. Mosaicism observed in the presence of the Mos (Mosaic) factor results from a high frequency of excision of the mariner element from an insertion site near the white-eye gene in Drosophila mauritiana. The Mos factor promotes the excision of mariner elements from genomic insertion sites other than the site in wpch, and it also promotes its own loss from the genome. Putative transpositions of Mos to new genomic sites have also been observed. A copy of mariner present at a particular site in a Mos strain has been shown to be missing in derived strains in which the Mos factor has been lost, and in strains with putative transpositions. We propose that this copy of mariner is identical to the Mos factor.

Molecular structure of a somatically unstable transposable element in Drosophila.

A transposable element has been isolated from an unstable white mutation in Drosophila mauritiana, a sibling species of Drosophila melanogaster. The unstable white-peach (wpch) allele exhibits a spectrum of germ-line and somatic mutability more similar to insertion mutations in maize and in the nematode Caenorhabditis elegans than has been reported for insertion mutations in Drosophila. The inserted element mariner is 1286 nucleotides long and has terminal inverted repeats. The element contains a single open reading frame encoding 346 amino acids. A duplication of 2 base pairs of white sequence is present at the insertion site. Mariner is present in approximately 20 copies in the D. mauritiana genome, is present from 0 to 7 copies in other members of the sibling species group, and is apparently absent from the genome of D. melanogaster.