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Biomedical subjects

A Laroche

Publications and source records attributed to A Laroche.

34 records · Page 2Linked to original sources
PubMed1995

The two alleles of the hapP gene in Physarum polycephalum code for different proteins.

Many mRNAs show cell-type specific expression in the acellular slime mold Physarum polycephalum. The most abundant plasmodial-specific mRNA (hapP) encodes a small hydrophobic protein of 187 amino acids that contains a potential signal peptide. Southern hybridizations using the hapP cDNA showed that the hapP gene is a single copy gene with two alleles, hapP1 and hapP2. The alleles have restriction enzyme polymorphisms. The nucleotide sequence of the coding region of the hapP1 allele was obtained from a genomic clone, and the nucleotide sequence of the hapP2 allele was obtained from a cDNA clone. The hapP1 and hapP2 alleles code for proteins that are 9.6% different in amino acid sequence. All differences are found in the central region of the protein. The nucleotide sequences of the first and last exons, which contain coding and non-coding regions, are identical. PCR amplification of cDNAs (RT-PCR) showed that both alleles are expressed in the same cell.

Alleles↗
PubMed1993

Two developmentally regulated mRNAs encoding actin-binding proteins in Physarum polycephalum.

A cDNA library from amoebae of Physarum polycephalum was screened by differential hybridization. Two clones contained inserts for mRNAs present in amoebae and absent in plasmodia. The LAV3-4 cDNA encodes a 402 aa protein (ABP-46) that shows sequence similarity to the actin binding site in the N-terminal region of the alpha-actinin family. The LAV3-5 cDNA is 76% identical to the Dictyostelium actin bundling protein, which cross-links and stabilizes actin filaments in amoebal filopodia.

Actinin↗
PubMed1993

Reproducibility of random amplified polymorphic DNA (RAPD) analysis among laboratories.

Random amplified polymorphic DNA (RAPD) analysis appears to offer a cost- and time-effective alternative to restriction fragment-length polymorphism (RFLP) analysis. However, concerns about the ability to compare RAPD results from one laboratory to another have not been addressed effectively. DNA fragments that were amplified by five primers and shown to be reproducibly polymorphic between two oat cultivars (within the Ottawa laboratory) were tested in six other laboratories in North America. Four of the six participants amplified very few or no fragments using the Ottawa protocol. These same participants were able to generate a considerable number of amplified fragments by using their own protocols. The reproducibility of results among laboratories was affected by two factors. First, different laboratories amplified different size ranges of DNA fragments, and, consequently, small and large polymorphic fragments were not always reproduced. Second, although reproducible results were obtained with four of the primers, reproducible results were not obtained with the fifth primer, using the same reaction conditions. It is suggested that if the overall temperature profiles (especially the annealing temperature) inside the tubes are identical among the laboratories, then RAPD fragments are likely to be reproducible.

Base Sequence↗
PubMed1991

An unusual actin-encoding gene in Physarum polycephalum.

Actin is one of the most conserved proteins in eukaryotic organisms. In the present work, we cloned and determined the nucleotide sequence of an unusual actin-encoding gene, ardD, from the slime mold, Physarum polycephalum. The ardD gene encodes an ArdD protein containing 367 amino acids (aa) instead of the 375-376 aa found in a typical actin. The nine missing aa are accounted for by deletions of three aa in the first exon, five in the fifth exon and one in the sixth exon. These deletions in the coding sequence were observed in a polymerase chain reaction (PCR)-generated cDNA fragment, which excludes the possibility of a cloning artifact. In addition, ArdD contains numerous aa substitutions distributed throughout the protein. The ArdD aa sequence was compared with published actin sequences. The most identity is seen with the P. polycephalum ArdA, ArdB and ArdC (84%) and Acanthamoeba (82%) actins, while the least identity is found with Tetrahymena actin (67%). The expression of the ardD gene is developmentally regulated. The highest levels of ardD mRNA were found in spherules, less was seen in plasmodia and no detectable transcripts were observed in amoebae. The PCR amplification of an ardD cDNA from spherules confirmed the presence of mRNA in this developmental stage. The aa deletions and substitutions in the predicted ArdD aa sequence make it one of the most distinctive actins known.

Actins↗
PubMed1990

Cell-specific expression of a profilin gene family.

Profilin is a ubiquitous eukaryotic protein that inhibits actin polymerization. We cloned and sequenced the two profilin genes from the acellular slime mold Physarum polycephalum. The genes, proA and proP, each contain two introns. Primer extension experiments showed two possible transcription start sites in the profilin A gene and one start site in the profilin P gene. The profilin A mRNA has two polyadenylation sites, which yield mRNAs of about 600 and 500 nucleotides. The profilin P mRNA has a single polyadenylation site. The protein sequences were deduced from cDNA nucleotide sequencing. The profilin A and profilin P proteins contain 125 amino acids and are 66% identical in sequence. They show sequence similarity to Acanthamoeba (approximately 54%), yeast (approximately 46%), mouse (approximately 22%), calf (approximately 21%), and human (approximately 21%) profilins. The presence of the profilin A and profilin P mRNAs was studied throughout the life cycle. Profilin A mRNA was found in amebas, encysted amebas, and mature spores. The profilin P mRNA was present in plasmodia and spherulating plasmodia. Most cell types of P. polycephalum contain either the amebal or the plasmodial profilin mRNA, and no cell contains both mRNAs. This is the first evidence for developmental regulation of profilin isoforms.

Amino Acid Sequence↗
PubMed1989

Developmentally regulated late mRNAs in the encystment of Physarum polycephalum plasmodia.

Physarum polycephalum plasmodia survive adverse conditions by transforming into encysted cells called spherules. In this work we analysed the developmentally regulated mRNAs from the late stages of spherulation. A cDNA library was constructed and four abundant mRNAs were identified. One of the mRNAs was present in trace amounts in early spherules, while the other three were found only in late spherules. A cDNA clone for one of the late spherulation specific mRNAs was sequenced. It codes for a 332-amino-acid protein that did not show significant similarities with any known protein. Since the mRNA for this protein accumulates during spherulation, the protein was called spherulin 4. This protein has many features of a plasma membrane protein; it contains a signal peptide and a long hydrophobic region, which could serve as a transmembrane anchor. Another interesting feature is the presence of seven consecutive glycine residues in the N-terminal region. This is even more remarkable since the protein is not rich in glycine.

Amino Acid Sequence↗
PubMed1989

Low Temperature-Induced Decrease in trans-Delta-Hexadecenoic Acid Content Is Correlated with Freezing Tolerance in Cereals.

The effect of growth at 5 degrees C on the trans-Delta(3)-hexadecenoic acid content of phosphatidyl(d)glycerol was examined in a total of eight cultivars of rye (Secale cereale L.) and what (Triticum aestivum L.) of varying freezing tolerance. In these monocots, low temperature growth caused decreases in the trans-Delta(3)-hexadecenoic acid content of between 0 and 74% with concomitant increases in the palmitic acid content of phosphatidyl(d)glycerol. These trends were observed for whole leaf extracts as well as isolated thylakoids. The low growth temperature-induced decrease in the trans-Delta(3)-hexadecenoic acid content was shown to be a linear function (r(2) = 0.954) of freezing tolerance in these cultivars. Of the six cold tolerant dicotyledonous species examined, only Brassica and Arabidopsis thaliana L. cv Columbia exhibited a 42% and 65% decrease, respectively, in trans-Delta(3)-hexadecenoic acid content. Thus, the relationship between the change in trans-Delta(3)-hexadecenoic acid content of phosphatidyl(d)glycerol and freezing tolerance cannot be considered a general one for all cold tolerant plant species. However, species which exhibited a low growth temperature-induced decrease in trans-Delta(3)-hexadecenoic acid also exhibited a concomitant shift in the in vitro organization of the light harvesting complex II from a predominantly oligomeric form to the monomeric form. We conclude that the proposed role of phosphatidyl(d)glycerol in modulating the organization of light harvesting complex II as a function of growth temperature manifests itself to varying degrees in different plant species. A possible physiological role for this phenomenon with respect to low temperature acclimation and freezing tolerance in cereals is discussed.

Journal Article↗
PubMed1987

Isolation and in vitro translation of polysomes from mature rye leaves.

Cytoplasmic polysomes have been prepared from mature leaves of winter rye (Secale cereale L. cv Puma). This is the first time a method has been developed for isolation of highly polymerized polysomes from mature leaves. The degree of intactness of isolated plant polysomes has been determined by two independent but complementary methods: size class distribution by sucrose gradient centrifugation and in vitro translation. The polymerization of isolated polysomes was estimated by the ratio of the proportion of large polysomes to the proportion of small polysomes obtained from the profiles. Our results show that the composition of the optimal polysome isolation buffer for mature rye leaves is different from that reported for young tobacco and pea leaves. Polysomes were translated in vitro with the S-105 wheat germ fraction. The degree of polysome polymerization has a significant effect on their in vitro translation since both the incorporation of amino acid and the presence of high molecular weight polypeptides are proportional to the large polysomes/small polysomes ratio. This study emphasizes the need to evaluate isolation conditions carefully before proceeding with polysome studies in any particular tissue or in tissues under different physiological status.

Journal Article↗
PubMed1987

Polysomes from winter rye seedlings grown at low temperature : I. Size class distribution, composition, and stability.

We have studied the influence of growth at low temperature on size class distribution, stability and composition of leaf cytoplasmic polysomes from rye seedlings (Secale cereale, cv Puma) grown at 5 degrees C and at 20 degrees C. Leaves of seedlings grown at 5 degrees C contain 2.7 times more cytoplasmic polysomes (expressed on a DNA basis) and the polysome size class distribution is skewed toward larger polysomes. These changes were more pronounced in the free polysome fraction than in the membrane-bound fraction. The melting point of the total ribosome fraction from cold-grown leaves was decreased by 3.7 degrees C. Electrophoresis did not reveal any difference in the rRNA or in core-ribosomal proteins (KCl nondissociable) following growth at low temperature. Some differences were noted in peripheral ribosomal proteins. This study is the first to examine the effect of growth at low and high temperatures on polysome metabolism using plants of similar developmental stage. Polysome quantity, polymerization, melting point and peripheral ribosomal proteins in rye seedlings are modified during growth at low temperature.

Journal Article↗
PubMed1980

ADP-ribosylation of rye histones.

Chromatin from etiolated rye seedlings synthesized protein-bound, acid-insoluble material from [3H]NAD, presumably poly(ADP-ribose). [3H]ADP-ribosylated histone fractions were isolated from crude chromatin and characterized by gel electrophoresis and exclusion chromatography. It was found that histone H2B was the main acceptor, that H2A and H1 were modified to a lesser extent, and that H3 and H4 were only slightly modified. The average chain length on purified histones was 2.5 units of polymer.

Chromatography, Gel↗
PubMedDate not supplied

[Macular imaging with optical coherence tomography].

PURPOSE: Optical Coherence Tomography (OCT) is a novel noninvasive and noncontact imaging technique providing cross-sectional representations of the eye structures. OCT is analogous to Ultrasound B-scan, except that it analyzes the reflection of a 850 nm light wave. The aim of this study was to assess the potential of ocular coherence tomography for diagnosing and monitoring macular diseases. METHODS: Cross-sectional images were performed with the Zeiss-Humphrey OCT. Over one year period, we examined approximately 300 patients with idiopathic full thickness macular hole, lamellar hole, cystoid macular edema, choroidal new vessels, epiretinal membrane, diabetic maculopathy, and central serous chorioretinopathy. RESULTS: OCT can provide new information concerning the posterior pole diseases mentioned above. OCT can also be useful in thickness measurements. CONCLUSION: OCT allows tomographic analysis of macular diseases. The information obtained is different from that obtained by histologic study which is sometimes hard to interprete. OCT is mostly useful in studying internal layers of the retina. Further applications may be developed.

Choroid Diseases↗