Reduction of background problems in nonradioactive northern and Southern blot analyses enables higher sensitivity than 32P-based hybridizations

Characterization, chromosomal mapping, and expression of different polyubiquitin genes in tissues from control and heat-shocked maize seedlings

Polyubiquitin transcripts accumulate in plant and animal cells following a heat shock. Most species have a few to several polyubiquitin genes; within a species, the genes may differ in nucleotide (nt) sequence and (or) the number of 228-nt repeats encoding the ubiquitin monomer. This study examines three maize (inbred Oh43) polyubiquitin genes. Two of the genes, MubG9 and MubG5, possess five repeats; the third, MubG1 possesses seven repeats. Sequence analyses of the genomic clones, MubG9 and MubG1 and a cDNA clone, MubG5, reveal that they differ primarily from each other in their nt sequences 5' and 3' to their open reading frames. MubG1 contains a 1004-base pair (bp) intron in its 5' untranslated region. Using gene-specific probes, we show that the amount of polyribosome-associated mRNA transcripts from MubG9 isolated from 2- and 5-day old plumules and radicles is unchanged by heat shock. While the amount of transcript from MubG1 and MubG5 on the polyribosomes in plumules and radicles of 2-day-old seedlings is also unchanged by heat shock, the levels of these transcripts are elevated considerably in similar tissues from heat-shocked 5-day-old seedlings. Similar or identical gene-specific probes were employed to map the genes using the recombinant inbred method. MubG9 maps to chromosome 4L position 186; MubG1 maps to 5L104 and MubG5 to 4L188. The opportunity to use gene-specific probes extends the evidence for distinct modulation (time and tissue) of polyubiquitin gene expression in maize and provides the basis for locus assignment within the genome.

TGF-beta induced transdifferentiation of mammary epithelial cells to mesenchymal cells: involvement of type I receptors

The secreted polypeptide transforming growth factor-beta (TGF-beta) exerts its multiple activities through type I and II cell surface receptors. In epithelial cells, activation of the TGF-beta signal transduction pathways leads to inhibition of cell proliferation and an increase in extracellular matrix production. TGF-beta is widely expressed during development and its biological activity has been implicated in epithelial-mesenchymal interactions, e.g., in branching morphogenesis of the lung, kidney, and mammary gland, and in inductive events between mammary epithelium and stroma. In the present study, we investigated the effects of TGF-beta on mouse mammary epithelial cells in vitro. TGF-beta reversibly induced an alteration in the differentiation of normal mammary epithelial NMuMG cells from epithelial to fibroblastic phenotype. The change in cell morphology correlated with (a) decreased expression of the epithelial markers E-cadherin, ZO-1, and desmoplakin I and II; (b) increased expression of mesenchymal markers, such as fibronectin; and (c) a fibroblast-like reorganization of actin fibers. This phenotypic differentiation displays the hallmarks of an epithelial to mesenchymal transdifferentiation event. Since NMuMG cells make high levels of the type I TGF-beta receptor Tsk7L, yet lack expression of the ALK-5/R4 type I receptor which has been reported to mediate TGF-beta responsiveness, we evaluated the role of the Tsk7L receptor in TGF-beta-mediated transdifferentiation. We generated NMuMG cells that stably overexpress a truncated Tsk7L type I receptor that lacks most of the cytoplasmic kinase domain, thus function as a dominant negative mutant. These transfected cells no longer underwent epithelial to mesenchymal morphological change upon exposure to TGF-beta, yet still displayed some TGF-beta-mediated responses. We conclude that TGF-beta has the ability to modulate E-cadherin expression and induce a reversible epithelial to mesenchymal transdifferentiation in epithelial cells. Unlike other transdifferentiating growth factors, such as bFGF and HGF, these changes are accompanied by growth inhibition. Our results also implicate the Tsk7L type I receptor as mediating the TGF-beta-induced epithelial to mesenchymal transition.

The ‘prespore-like cells’ of Dictyostelium have ceased to express a prespore gene: analysis using short-lived beta-galactosidases as reporters

In transgenic strains of Dictyostelium discoideum that express beta-galactosidase under the control of a prespore-specific promoter, only early slugs show reporter confined to the prespore zone. As slugs migrate beta-galactosidase-positive cells accumulate in the prestalk zone; ultimately, there may be so many that the prestalk-prespore boundary is no longer distinguishable (Harwood, A., Early, A., Jermyn, K. and Williams, J. (1991) Differentiation 46, 7–13). It is not clear whether these ‘anomalous’ reporter-positive cells currently express prespore genes; another possibility is that they are ex-prespore cells that have transformed to prestalk and sorted to the prestalk zone (Sternfeld, J. (1993) Roux Archiv. Dev. Biol. 201, 354–363), while retaining their previously produced reporter. To test the activity of the prespore genes in these cells, we have made prespore reporter constructs whose products decay quickly; these are based on constructs used to investigate protein turnover in yeast (Bachmair, A., Finley, D. and Varshavsky, A. (1986) Science 234, 179–186). In strains bearing such constructs, beta-galactosidase-positive cells do not appear in the prestalk zone. The apparent deterioration of the prestalk/prespore pattern in older slugs is thus an artefact of reporter stability.

Structural organization of the Helicoverpa zea gene encoding the precursor protein for pheromone biosynthesis-activating neuropeptide and other neuropeptides

Sex pheromone biosynthesis in a number of moth species is induced by a conserved 33-amino acid amidated neuropeptide PBAN (pheromone biosynthesis-activating neuropeptide). We have isolated and characterized the Helicoverpa zea PBAN cDNA corresponding to a 766-nucleotide mRNA that is expressed in the subesophageal ganglion of adult moths. This mRNA is encoded on a transcription unit comprising 6 exons. The longest open reading frame of the cDNA encodes a 194-amino acid precursor protein that contains the PBAN peptide sequence. Proteolytic processing of this protein, which has structural features consistent with its being a preprohormone, is predicted to generate Hez-PBAN and four additional neuropeptides having a common C-terminal pentapeptide motif, Phe-Xaa-Pro-(Arg or Lys)-Leu (Xaa = Gly, Ser, or Thr), which is also found in insect pyrokinin and myotropin peptide families.

Generation of transgenic dairy cattle from transgene-analyzed and sexed embryos produced in vitro

We have generated a transgenic calf from in vitro produced bovine embryos which had undergone transgene analysis and sexing prior to the embryo transfer. Bovine oocytes were isolated from slaughter-house-derived ovaries, matured and fertilized in vitro and subsequently microinjected with a dam-methylated gene construct consisting of genomic sequences encoding human erythropoietin and governed by bovine alpha S1-casein regulatory sequences. After 6 to 7 days in culture, the embryos were biopsied and while the embryo remained in culture, the biopsy was subjected to transgene analysis and sexing. The transgene analysis was accomplished with a combined treatment of the embryo lysates with DpnI restriction endonuclease and Bal31 exonuclease followed by polymerase chain reaction (PCR). The transgene analysis was based on the fact that DpnI only cleaves its recognition sequence if the adenine in the sequence is methylated. Pregnancy was induced by the transfer of three viable female embryos with a distinct transgene signal to a hormonally synchronized heifer recipient. Amniotic fluid analysis performed two months after the embryo transfer confirmed the presence of the transgene. The calf born was found to be transgenic by PCR analysis from blood, ear and fetal membranes. The presence of the transgene was also confirmed by Southern blotting.

Reverse dot blot hybridization: a useful method for the direct identification of lactic acid bacteria in fermented food

A rapid method for a reliable and simultaneous identification of different lactic acid bacteria in fermented food has been developed. Various 16S and 23S rRNA-targeted, species-specific oligonucleotides were applied as capture probes in a non-radioactive reverse dot blot hybridization. A simple and fast DNA extraction method in combination with in vitro amplification of rRNA gene fragments enables the direct detection of typical starter organisms without any preceding enrichment or cultivation steps. Various lactic acid bacteria occurring in cheese, yogurt, sausages, sauerkraut and sourdough could be identified at the species level within 1 day.

The primary structure of two chlorosome proteins from Chloroflexus aurantiacus

The complete nucleotide sequence of two chlorosome proteins with apparent molecular weights of M(r) 18,000 and M(r) 11,000 from Chloroflexus aurantiacus have been determined. The two polypeptides were 145 and 97 amino acids long and possessed true molecular masses of 15,545 and 10,820 Da, respectively. Protein chemical sequencing was done in parallel to confirm the primary structure deduced from nucleotide sequencing. By Northern blot analysis of RNA isolated from phototrophically grown cells a transcript of 0.95 kb was detected which is the expected length for a mRNA encoding both genes.

Tenascin is a cytoadhesive extracellular matrix component of the human hematopoietic microenvironment

Tenascin is a large extracellular matrix (ECM) glycoprotein found in restricted tissue locations in the adult organism. It is copiously synthesized in regenerative organs or regenerating tissues and by certain tumors. We have analyzed the expression of tenascin in human long term bone marrow cultures as well as in cryostat sections of native bone marrow and found it strongly expressed by the stromal cells of the microenvironment. Two different protein subunits of 280 and 220 kD were detected by immunoblotting. These two forms are derived most likely from two different mRNA splice variants of 6 and 8 kb detected by Northern blotting. The in vivo analysis of cryostat sections showed a codistribution with other ECM molecules such as fibronectin and collagen type III in the microenvironment surrounding the maturing hematopoietic cells. Using two independent cell adhesion assays tenascin could be shown to function as a cytoadhesive molecule for hematopoietic cells. These data suggest a direct involvement of tenascin in the retention of hematopoietic progenitor cells in the stroma.