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Biomedical subjects

J F Martin

Publications and source records attributed to J F Martin.

At least 37 records · Page 2Linked to original sources
PubMed2000

Assembling a functional tympanic membrane: signals from the external acoustic meatus coordinate development of the malleal manubrium.

In terrestrial mammals, hearing starts with the perception of acoustic pressure by the tympanic membrane. Vibrations in this membrane are then transduced into the inner ear by the ossicle chain of the middle ear, composed of the malleus, incus and stapes. The proper connection of the ossicle chain with the tympanic membrane, provided by the insertion of the manubrium of the malleus into the eardrum, is essential for the functionality of the hearing apparatus. We describe here the mechanisms regulating the development of the manubrium and its integration into the tympanic membrane. We show that the external acoustic meatus (EAM), which eventually forms the outer epithelium of the tympanic membrane, plays an essential role in this developmental process. Histological and expression analyses indicate that the manubrium develops close to the EAM with a similar temporal sequence. In addition, when the middle ear ossicles are allowed to develop in vitro under conditions that do not support further EAM development, the manubrium develops only up to the stage of its induction at the time of explantation. Moreover, genetically or teratogenically derived alterations in the EAM also have an effect on manubrial development. Finally, we show that the EAM is the source of two quite opposite activities, one that induces chondrogenesis and another that represses it. The combination of these two activities results in the proper positioning of the manubrium.

Animals↗
PubMed2000

Alpha-aminoadipyl-cysteinyl-valine synthetases in beta-lactam producing organisms. From Abraham's discoveries to novel concepts of non-ribosomal peptide synthesis.

The tripeptide delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine (ACV) was discovered by ARNSTEIN and MORRIS in Penicillium chrysogenum and ABRAHAM and coworkers in Acremonium chrysogenum. Other analogous tripeptides and tetrapeptides were later reported in these and other beta-lactam producing fungi and actinomycetes. The ACV tripeptide is synthesized by a large non-ribosomal peptide synthetase named ACV synthetase encoded by the 11 kb pchAB gene. This gene has been cloned from the DNA of four different filamentous fungi and two actinomycetes. Detailed analysis of the multifunctional ACV synthetases reveals that they consist of three repeated modules (initially named domains) involved in activation of the corresponding amino acids L-alpha-aminoadipic acid, L-cysteine and L-valine. Each module consists of functional domains for amino acid activation (A), condensation (C) and thiolation (T). In addition the last module of the ACV synthetase contains an epimerization domain (E) involved in conversion of the L-valine to its D-isomer when the tripeptide is still enzyme linked. There are seven epimerization motifs conserved in the third module of all ACV synthetases. In addition, there is an integrated thioesterase domain in the C-terminal region of the ACV synthetases that appears to be involved in the selective release of the tripeptide with the correct LLD configuration. The structure of the ACV synthetase is similar to that of other modular non-ribosomal peptide synthetases of bacterial and fungal origin. This molecular knowledge opens the way for engineering novel tripeptide synthetases that may result in new bioactive compounds.

Actinomycetales↗
PubMed2000

Identification of a prx1 limb enhancer.

Mice with a loss of function of prx1, a paired-related homeobox gene formerly called Mhox, showed craniofacial defects, limb shortening, and incompletely penetrant spina bifida. To investigate the mechanisms that regulate prx1 expression, we analyzed a 2.4-kb prx1 genomic flanking region in transgenic mice. This region of the prx1 gene contains an enhancer element that directs expression of a LacZ reporter gene in limb bud mesenchyme and a subset of craniofacial mesenchyme. Deletional analysis in transgenic founders identified a necessary 530-bp core element. Comparison of this core element with human Prx1 sequence showed two highly conserved cassettes that also contained a prx recognition element. Moreover, transgene expression was diminished in posterior handplate of prx1; prx2 double mutant mice. Our data reveal that the prx1 limb enhancer is proximally located within the prx1 gene and suggest that prx1 may have an autoregulatory function in limb mesenchyme.

Animals↗
PubMed1999

Function of Rieger syndrome gene in left-right asymmetry and craniofacial development.

Rieger syndrome, an autosomal dominant disorder, includes ocular, craniofacial and umbilical abnormalities. The pitx2 homeobox gene, which is mutated in Rieger syndrome, has been proposed to be the effector molecule interpreting left-right axial information from the early embryonic trunk to each organ. Here we have used gene targeting in mice to generate a loss-of-function allele that would be predicted to result in organ randomization or isomerization. Although pitx2-/- embryos had abnormal cardiac morphogenesis, mutant hearts looped in the normal direction. Pitx2-/- embryos had correctly oriented, but arrested, embryonic rotation and right pulmonary isomerism. They also had defective development of the mandibular and maxillary facial prominences, regression of the stomodeum and arrested tooth development. Fgf8 expression was absent, and Bmp4 expression was expanded in the branchial-arch ectoderm. These data reveal a critical role for pitx2 in left-right asymmetry but indicate that pitx2 may function at an intermediate step in cardiac morphogenesis and embryonic rotation.

Abnormalities, Multiple↗
PubMed1999

Molecular characterization of the Acremonium chrysogenum cefG gene product: the native deacetylcephalosporin C acetyltransferase is not processed into subunits.

Constructions starting at each of the three in-frame ATG codons of the Acremonium chrysogenum cefG gene (Met1, Met46 and Met60) were expressed in Escherichia coli, obtaining proteins of 49, 44 and 43 kDa, respectively. All three proteins showed deacetylcephalosporin C (DAC) acetyltransferase activity. The native A. chrysogenum DAC acetyltransferase was purified to electrophoretic homogeneity by immunoaffinity chromatography. It showed a molecular mass of 50 kDa by filtration in calibrated Sephadex G-75 SF or Superose 12 (FPLC) columns. The N-terminal end of the pure DAC acetyltransferase was Met-Leu-Pro-Ser-Ala-Gln-Val-Ala-Arg-Leu, which matched perfectly the deduced amino acid sequence starting at Met1. The putative alpha- and beta-subunits of DAC acetyltransferase were also obtained in E. coli but showed no enzymic activity either separately or in combination. Immunoblotting (Western) analysis revealed that the 50 kDa DAC acetyltransferase showed high protein levels in A. chrysogenum cultures at 72 and 96 h and decreased sharply thereafter, but in all cases no detectable processing of the enzyme into subunits was found. Three different A. chrysogenum strains (including the wild-type Brotzu strain and two high-cephalosporin-producing mutants) showed the same unprocessed 50 kDa DAC acetyltransferase. The non-producer mutant ATCC 20371 showed no DAC acetyltransferase protein band but formed a normal transcript of 1.4 kb.

Acetyltransferases↗
PubMed1999

Paired-related homeobox genes cooperate in handplate and hindlimb zeugopod morphogenesis.

The closely related homeobox genes prx-1 and prx-2 are expressed in lateral plate and limb bud mesoderm, but targeted inactivation of these genes failed to demonstrate a limb phenotype. Here we report that mice carrying compound mutations in prx-1 and prx-2 have severe limb deformities. In the forelimb autopod, pre- and postaxial polydactyly were found most commonly, but also syndactyly, oligodactyly, and abnormal digit placement affecting posterior elements were observed. In the hindlimb, preaxial polydactyly with variable expressivity was seen in all cases. Extreme distal digit duplications were seen in both the fore- and hindlimbs. prx-1; prx-2 double-mutant mice also displayed extreme shortening and impaired ossification of the hindlimb zeugopods. Integrity of the forelimb apical ectodermal ridge was abnormal as determined by expression of FGF8 and BMP4. Expression of msx-1 and msx-2, markers for BMP signaling pathways, was absent in regions of the posterior handplates, while expression of Shh and patched was unaffected. The mutant phenotypes were dosage dependent, since prx-1 -/-; prx-2 +/- mice also displayed severe limb abnormalities. These data suggest that prx-1 and prx-2 cooperatively regulate handplate and hindlimb zeugopod morphogenesis through BMP-mediated signaling pathways.

Animals↗
PubMed1999

Variations in human masseter and temporalis muscle activity related to food texture during free and side-imposed mastication.

Adjustments of mastication to food texture have been examined in various studies, but the notion of food texture is often ill defined and usually assessed in terms of hardness. The goal of this study was to examine the pattern of activity in masseter and temporalis muscles during mastication of different food samples with known textural properties and to determine the interindividual variability. Electromyograms were recorded from the right and left masseter and temporalis muscles in 36 young adults during 'free-style' and side-imposed mastication. Five different types of food with known rheological properties were used. Both temporalis and masseter activity increased with increased stress at maximum strain of the chewed samples. A power function optimally described the relation between muscle work per chew and the mechanical measurements of food; this confirmed that the masticatory process is adjusted to accommodate to food texture. Temporalis muscle activity was more influenced by food texture than was masseter muscle activity. Less muscle work was needed to prepare the food bolus for swallowing during free-style mastication. However, 25% of the participants showed no differences between unilateral side-imposed mastication and 'free-style', suggesting that they might have greater chewing efficiency on one side.

Adult↗
PubMed1999

Induction of myocardial nitric oxide synthase by Coxsackie B3 virus in mice.

BACKGROUND: Inducible nitric oxide synthase (iNOS) expression is regulated by cytokines. This study investigated whether Coxsackie group B virus (CVB) myocarditis resulted in an environment suitable for induction of NOS in the murine heart. MATERIALS AND METHODS: Myocardium was removed from mice infected with CVB3 and from controls. Histology, reverse transcriptase polymerase reaction (RT-PCR) for murine iNOS, NOS enzyme activity and immunohistochemistry were assessed. RESULTS: Histology revealed severe myocarditis 7 days after infection with CVB3 but not in controls. RT-PCR using primers for murine iNOS detected iNOS mRNA in infected mice but not in controls. Calcium-independent NOS activity increased by day 5 after infection with a peak at day 7. Calcium-dependent NOS activity was present throughout, with a trend to lower levels during peak calcium-independent activity. Immunohistochemistry revealed iNOS to be localized to inflammatory cells rather than to myocytes. CONCLUSION: This study demonstrates the development of calcium-independent NOS activity and de novo gene transcription for iNOS in the murine myocardium in response to CVB3 infection. The nitric oxide produced at such high output may act at times as part of the immune defence as an antiviral agent and may be toxic to host tissue.

Animals↗
PubMed1999

Endogenous mediators and thrombophilia.

Platelets are one of the most important components of primary haemostasis. Since they lack a nucleus, their functional characteristics are determined at the time of production. The role of platelets in thrombosis is further modified by the interaction with vascular mediators that are endogenously produced in response to a variety of stimuli. This chapter discusses the factors that influence platelet production, the interaction with endogenous mediators, and the potential therapeutic benefits achieved by modifying this interaction in the clinical setting.

Animals↗
PubMed1999

Thaumatin production in Aspergillus awamori by use of expression cassettes with strong fungal promoters and high gene dosage.

Four expression cassettes containing strong fungal promoters, a signal sequence for protein translocation, a KEX protease cleavage site, and a synthetic gene (tha) encoding the sweet protein thaumatin II were used to overexpress this protein in Aspergillus awamori lpr66, a PepA protease-deficient strain. The best expression results were obtained with the gdhA promoter of A. awamori or with the gpdA promoter of Aspergillus nidulans. There was good correlation of tha gene dosage, transcript levels, and thaumatin secretion. The thaumatin gene was expressed as a transcript of the expected size in each construction (1.9 or 1.4 kb), and the transcript levels and thaumatin production rate decayed at the end of the growth phase, except in the double transformant TB2b1-44-GD5, in which secretion of thaumatin continued until 96 h. The recombinant thaumatin secreted by a high-production transformant was purified to homogeneity, giving one major component and two minor components. In all cases, cleavage of the fused protein occurred at the KEX recognition sequence. This work provides new expression systems in A. awamori that result in very high levels of thaumatin production.

Actins↗
PubMed1999

Organization of the gene cluster for biosynthesis of penicillin in Penicillium nalgiovense and antibiotic production in cured dry sausages.

Several fungal isolates obtained from two cured meat products from Spain were identified as Penicillium nalgiovense by their morphological features and by DNA fingerprinting. All P. nalgiovense isolates showed antibiotic activity in agar diffusion assays, and their penicillin production in liquid complex medium ranged from 6 to 38 microgram. ml-1. We constructed a restriction map of the penicillin gene cluster of P. nalgiovense and found that the organization of the penicillin biosynthetic genes (pcbAB, pcbC, and penDE) is the same as in Penicillium chrysogenum and Aspergillus nidulans. The pcbAB gene is located in an orientation opposite that of the pcbC and penDE genes in all three species. Significant amounts of penicillin were found in situ in the casing and the outer layer of salami meat during early stages of the curing process, coinciding with fungal colonization, but no penicillin was detected in the cured salami. The antibiotic produced in situ was sensitive to penicillinase.

Blotting, Southern↗
PubMed1999

Inducing effect of diamines on transcription of the cephamycin C genes from the lat and pcbAB promoters in Nocardia lactamdurans.

The diamines putrescine, cadaverine, and diaminopropane stimulate cephamycin biosynthesis in Nocardia lactamdurans, in shake flasks and fermentors, without altering cell growth. Intracellular levels of the P7 protein (a component of the methoxylation system involved in cephamycin biosynthesis) were increased by diaminopropane, as shown by immunoblotting studies. Lysine-6-aminotransferase and piperideine-6-carboxylate dehydrogenase activities involved in biosynthesis of the alpha-aminoadipic acid precursor were also greatly stimulated. The diamine stimulatory effect is exerted at the transcriptional level, as shown by low-resolution S1 protection studies. The transcript corresponding to the pcbAB gene and to a lesser extent also the lat transcript were significantly increased in diaminopropane-supplemented cultures, whereas transcription from the cefD promoter was not affected. Coupling of the lat and pcbAB promoters to the reporter xylE gene showed that expression from the lat and pcbAB promoters was increased by addition of diaminopropane in Streptomyces lividans. Intracellular accumulation of diamines in Nocardia may be a signal to trigger antibiotic production.

Cadaverine↗
PubMed1999

A role for changes in platelet production in the cause of acute coronary syndromes.

Platelets are heterogeneous with respect to their size, density, and reactivity. Large platelets are more active hemostatically, and platelet volume has been found to be increased both in patients with unstable angina and with myocardial infarction. Furthermore, platelet volume is a predictor of a further ischemic event and death when measured after myocardial infarction. Platelets which are anucleate cells with no DNA are derived from their precursor, the megakaryocyte. Therefore, it is suggested that changes in platelet size are determined at thrombopoiesis in the megakaryocyte and that those changes might precede acute cardiac events. Understanding of the signaling system that controls platelet production may also further elucidate the cascade of events leading to acute vascular occlusion in some patients.

Acute Disease↗
PubMed1999

prx-1 functions cooperatively with another paired-related homeobox gene, prx-2, to maintain cell fates within the craniofacial mesenchyme.

The paired-related homeobox gene, prx-1, is expressed in the postmigratory cranial mesenchyme of all facial prominences and is required for the formation of proximal first arch derivatives. We introduced lacZ into the prx-1 locus to study the developmental fate of cells destined to express prx-1 in the prx-1 mutant background. lacZ was normally expressed in prx-1(neo); prx-1(lacZ )mutant craniofacial mesenchyme up until 11.5 d.p.c. At later time points, lacZ expression was lost from structures that are defective in the prx-1(neo) mutant mice. A related gene, prx-2, demonstrated overlapping expression with prx-1. To test the idea that prx-1 and prx-2 perform redundant functions, we generated prx-1(neo;)prx-2 compound mutant mice. Double mutant mice had novel phenotypes in which the rostral aspect of the mandible was defective, the mandibular incisor arrested as a single, bud-stage tooth germ and Meckel's cartilage was absent. Expression of two markers for tooth development, pax9 and patched, were downregulated. Using a transgene that marks a subset of prx-1-expressing cells in the craniofacial mesenchyme, we showed that cells within the hyoid arch take on the properties of the first branchial arch. These data suggest that prx-1 and prx-2 coordinately regulate gene expression in cells that contribute to the distal aspects of the mandibular arch mesenchyme and that prx-1 and prx-2 play a role in the maintenance of cell fate within the craniofacial mesenchyme.

Alleles↗
PubMed1999

Lumbar sympathectomy as isolated technique for the treatment of lower limbs chronic ischemia.

BACKGROUND: Lumbar sympathectomy (LS) is often the only alternative treatment that can be considered as a means of improving the distal circulation to such extent that major amputation is prevented. To make a retrospective study in order to know the current value of LS as isolated technique for the treatment of severe ischemia of lower limbs in the absence of the possibility for vascular reconstruction. METHODS: Between 1987 and 1992, 100 LS were performed in 93 patients (82 males and 11 females) aged 64.5+/-11.1 yrs. 63% were older than 70 years. Indication was invalidant claudication/rest pain (grade II, 57%) or trophic lesion (grade III, 43%) in patients where previous reconstructive surgery failed (18%), was not possible to do (23%) or refused revascularization (20%), or with poor surgical risk (39%). Preoperative evaluation included Doppler measures, ankle/brachial index (ABI) and arteriography in every case. Surgical sympathectomy was performed in all patients. Success was considered if rest pain was absent or trophic lesions have healed at six months, comparing results in patients diabetics and non-diabetics with ABI higher or lower 0.3. RESULTS: Postoperative stage was 6.4+/-2.3 days. Morbidity was 4% and mortality was 7% in the 30-day postoperative period, related with patients older than 70 years. Long-term mortality was 9%, for a global nortality of 16%. 12 patients needed inflow surgery after LS. There was success in 58.5% of grade II and 61.7% of grade III patients at six months, with significative difference (p=0.049) if ABI was >0.3. In diabetics with ABI >0.3, trophic lesions have worse prognostic than ABI <0.3. Pre- and postoperative ABI were correlated (R2=0.65), and the increasing of 0.1 in preoperative ABI had a positive prognostic value over lesion healing. Patency of superficial femoral artery (SFA) has correlated significantly (p=0.000021) with successful outcome after LS. CONCLUSIONS: LS could be a technique that moderately improves the ischemic limb in patients who refuse major surgery or where arterial reconstruction is not indicated. Preoperative ABI has prognostic value in postoperative outcome, with clinical improvement if it is >0.3. Diabetes has not been a negative predictive factor in our series. Patency of superficial femoral artery is related to successful outcome of the patients.

Adult↗