Biomedical subjects

Carlos Merino

Publications and source records attributed to Carlos Merino.

9 recordsLinked to original sources

PubMed2005

The 4.1 protein coracle mediates subunit-selective anchoring of Drosophila glutamate receptors to the postsynaptic actin cytoskeleton.

Glutamatergic Drosophila neuromuscular junctions contain two spatially, biophysically, and pharmacologically distinct subtypes of postsynaptic glutamate receptor (GluR). These receptor subtypes appear to be molecularly identical except that A receptors contain the subunit GluRIIA (but not GluRIIB), and B receptors contain the subunit GluRIIB (but not GluRIIA). A- and B-type receptors are coexpressed in the same cells, in which they form homotypic clusters. During development, A- and B-type receptors can be differentially regulated. The mechanisms that allow differential segregation and regulation of A- and B-type receptors are unknown. Presumably, A- and B-type receptors are differentially anchored to the membrane cytoskeleton, but essentially nothing is known about how Drosophila glutamate receptors are localized or anchored. We identified coracle, a homolog of mammalian brain 4.1 proteins, in yeast two-hybrid and genetic screens for proteins that interact with and localize Drosophila glutamate receptors. Coracle interacts with the C terminus of GluRIIA but not GluRIIB. To test whether coracle is required for glutamate receptor localization, we immunocytochemically and electrophysiologically examined receptors in coracle mutants. In coracle mutants, synaptic A-type receptors are lost, but there is no detectable change in B-type receptor function or localization. Pharmacological disruption of postsynaptic actin phenocopies the coracle mutants, suggesting that A-type receptors are anchored to the actin cytoskeleton via coracle, whereas B-type receptors are anchored at the synapse by another (yet unknown) mechanism.

Actin Cytoskeleton↗

PubMed2005

Glutamate receptor dynamics organizing synapse formation in vivo.

Insight into how glutamatergic synapses form in vivo is important for understanding developmental and experience-triggered changes of excitatory circuits. Here, we imaged postsynaptic densities (PSDs) expressing a functional, GFP-tagged glutamate receptor subunit (GluR-IIA(GFP)) at neuromuscular junctions of Drosophila melanogaster larvae for several days in vivo. New PSDs, associated with functional and structural presynaptic markers, formed independently of existing synapses and grew continuously until reaching a stable size within hours. Both in vivo photoactivation and photobleaching experiments showed that extrasynaptic receptors derived from diffuse, cell-wide pools preferentially entered growing PSDs. After entering PSDs, receptors were largely immobilized. In comparison, other postsynaptic proteins tested (PSD-95, NCAM and PAK homologs) exchanged faster and with no apparent preference for growing synapses. We show here that new glutamatergic synapses form de novo and not by partitioning processes from existing synapses, suggesting that the site-specific entry of particular glutamate receptor complexes directly controls the assembly of individual PSDs.

Animals↗

PubMed2005

Prospective evaluation of aortic valve replacement in young adults and middle-aged patients: mechanical prosthesis versus pulmonary autograft.

BACKGROUND AND AIM OF THE STUDY: The best option for aortic valve replacement (AVR) in young adults and middle-aged patients remains controversial. A longitudinal comparison between the Ross procedure (RP) and mechanical prosthesis (MP) was conducted in this group of patients. METHODS: Between January 1997 and January 2003, 125 consecutive patients (age range: 20-50 years) were submitted for AVR; 62 patients (mean age 37.73+/-7.28 years) were included in the MP group, and 63 (mean age 35.33+/-7.63 years) in the RP group. Gender, etiology, NYHA functional class and other preoperative data were comparable between the two groups. RESULTS: The operative mortality was four (6.5%) in the MP group, and one (1.6%) in the RP group (p = NS). The postoperative complication rate was similar in both groups. Two RO patients required early autograft replacement due to severe regurgitation. There were no late deaths during the follow up period. In the MP group, three patients (4.8%) suffered major bleeding, three (4.8%) were diagnosed with prosthetic endocarditis (one required reoperation), and three (4.8%) suffered valve- or coumarin-related thromboembolic complications. All RP patients were free from bleeding, thromboembolic, or infectious complications, but three suffered severe pulmonary homograft stenosis (one re-replacement, one Palmaz stent, and one under clinical surveillance). The combined freedom from death or major complications was 64.72+/-4.3% in the MP group, and 87.92+/-9.65% in the RP group (p = 0.068). CONCLUSION: Intraoperative and early postoperative morbidity and mortality rates were similar among RP and MP patients, despite a steep learning curve during the early RP cases. Although the follow up was limited, and homograft-related morbidity was seen in the RP group, the overall five-year major complication rate supported use of the pulmonary autograft for AVR in patients aged between 20 and 50 years.

Adult↗

PubMed2004

RNA polymerase II 140wimp mutant and mutations in the TFIIH subunit XPB differentially affect homeotic gene expression in Drosophila.

Mutations in the XPB and XPD helicases of the DNA repair/transcription factor TFIIH are involved in several human genetic disorders. An unanswered problem concerning the complexity of the phenotype-genotype relationship is why mutations in individual subunits of TFIIH produce specific phenotypes and not many others. In order to investigate this question we tested whether mutations in the Drosophila XPB homolog, haywire (hay), would modify homeotic derepression phenotypes. In this work, we report that mutations in hay and in the 140-kDa subunit of the RNA polymerase II (RpII140wimp) act as dominant modifiers of the derepression phenotypes of the Sex combs reduced (Scr) and Ultrabithorax (Ubx) genes. The hay mutations only weakly suppress the Scr derepression phenotype caused by the Antp(Scx) mutation but not by Polycomb. In contrast, the RpII140wimp mutation strongly suppresses both Scr derepression phenotypes. In addition, the RpII140wimp also generates phenotypes indicative of loss of Ubx function. On the other hand, all the derepression homeotic phenotypes are sensitive to the generalized reduction of transcription levels when the flies are grown with actinomycin D. We also show that different promoter control regions have differential sensitivity to different hay alleles. All these results support that although TFIIH is a basal transcription factor, mutations in the subunit encoded by hay have specific effects in the transcription of some genes.

Animals↗

PubMed2003

The transcriptional complexity of the TFIIH complex.

Mutations in some subunits of the basal DNA repair and transcription factor II H (TFIIH) are involved in several human genetic disorders. Transcription factor II H interacts with a variety of factors during transcription, including nuclear receptors, tissue-specific transcription factors, chromatin remodeling complexes and RNA, suggesting that, in addition to its essential role in transcription initiation, it also participates as a regulatory factor. Interpretation of the phenotypes produced by mutations in TFIIH is complicated by the recent finding that TFIIH plays a role in RNA polymerase I (RNA Pol I)-mediated transcription. In vitro reconstituted systems and genetic analysis suggest two possible explanations for the transcriptional phenotypes of TFIIH mutations that are not mutually excluding. The first is that different sets of genes require different levels of transcription to maintain a wild-type phenotype. The second suggests that mutations in TFIIH produce specific phenotypes arising from differential interactions of this complex with different transcription regulatory factors.

Animals↗

PubMed2003

Mitral homograft in the tricuspid position, aortic homograft and mitral plasty in a drug addict with multiple valve endocarditis.

The case is reported of multiple valve surgery using as little prosthetic material as possible in a drug addict with recurrent right and left bacterial endocarditis. The patient underwent aortic valve replacement with a cryopreserved aortic homograft, mitral repair and tricuspid valve replacement with a mitral homograft, using a modified technique. The indications and surgical options for tricuspid valve endocarditis in this patient group are discussed, with particular focus on technical aspects of using mitral homografts in the tricuspid position.

Adult↗

PubMed2002

Molecular characterization and developmental expression of the TFIIH factor p62 gene from Drosophila melanogaster: effects on the UV light sensitivity of a p62 mutant fly.

TFIIH is a multiprotein complex that has a central role in the RNA pol II mediated transcription, in DNA repair and in the control of the cell cycle. Mutations in some components of TFIIH are associated with three hereditary human syndromes: xeroderma pigmentosum (XP), Cockayne syndrome (CS) and trichothiodystrophy (TTD). The p62 protein is a structural component of the TFIIH core and no syndromes have been identified up to date by mutations in this human gene. In this work we report the molecular and genetic characterization of the Drosophila melanogaster p62 gene (Dmp62). The Dmp62 gene product shows high identity with its human and mouse homologues. Using computer analysis we identified several common motifs in the p62 proteins from different organisms, suggesting that these motifs could be involved in possible protein-protein interactions within the TFIIH complex or with other transcription and DNA repair factors. The Dmp62 transcript is expressed at similar levels throughout development, although there is a significant increase of the transcript level during the late embryogenesis and in the adult male. The analysis of a Drosophila line with a P-element enhancer trap insertion at the Dmp62 5'-UTR that directs the lac-Z expression from the Dmp62 promoter, showed a high level of expression in the gut, the testis and the pericardial cells. A P-element that disrupts the Dmp62 gene (Dmp62mut) produces early embryo lethality in homozygous flies. Heterozygous Dmp62mut larvae are more sensitive to UV light irradiation, and those individuals that are able to develop into adults have severe abdominal cuticular damage after UV light irradiation.

Amino Acid Sequence↗

PubMed2002

DNA repair and transcriptional effects of mutations in TFIIH in Drosophila development.

Mutations in XPB and XPD TFIIH helicases have been related with three hereditary human disorders: xeroderma pigmentosum, Cockayne syndrome, and trichothiodystrophy. The dual role of TFIIH in DNA repair and transcription makes it difficult to discern which of the mutant TFIIH phenotypes is due to defects in any of these different processes. We used haywire (hay), the Drosophila XPB homolog, to dissect this problem. Our results show that when hay dosage is affected, the fly shows defects in structures that require high levels of transcription. We found a genetic interaction between hay and cdk7, and we propose that some of these phenotypes are due to transcriptional deficiencies. We also found more apoptotic cells in imaginal discs and in the CNS of hay mutant flies than in wild-type flies. Because this abnormal level of apoptosis was not detected in cdk7 flies, this phenotype could be related to defects in DNA repair. In addition the apoptosis induced by p53 Drosophila homolog (Dmp53) is suppressed in heterozygous hay flies.

Alleles↗

PubMedDate not supplied

The Ross procedure.

BACKGROUND: The search for the ideal substitute for the aortic valve led Donald Ross to develop the pulmonary autograft concept in 1967. A historical, technical, and scientific review of this surgical option is presented together with our clinical experience. MATERIALS AND METHODS: The literature is reviewed to identify the advantages and pitfalls of the Ross procedure over the last decades. We also present our clinical experience with 92 patients operated between 1997 and May 2003. RESULTS: Of the total, 70.65% (n = 65) were males, mean age was 29.32 +/- 11.9 years, with 20 patients under 16 and 6 patients under 10 years. Twenty-five patients (27.17%) had 31 previous interventions. There were 41 associated procedures in 34 patients. Perioperative mortality was 2.17% (two patients). Eight patients required reexploration for bleeding, one required an aortocoronary bypass, and one a permanent pacemaker. Follow-up was 97% with 2.71 patients/year (average 32.55 +/- 19.01 months). Two patients required autograft replacement, one suffered a 44-mm dilatation of the autograft, and one 13-year-old girl developed autograft endocarditis. Six patients suffered severe homograft stenosis (>50 mmHg), two were treated percutaneously, and one required replacement. Combined freedom from reintervention is 93.56 +/- 2.81% at 5 years. CONCLUSIONS: The Ross procedure is a mature concept with thousands of patients operated worldwide and a cumulative experience of over 30 years. Although we believe that it is the procedure of choice in the pediatric population, women in child-bearing age, and substantial subgroups of adult patients, efforts must continue to minimize the incidence of auto- and homograft failure in the long term.

Adolescent↗