Rafael Prieto

Isolation and characterization of two new negative regulatory mutants for nitrate assimilation inChlamydomonas reinhardtii obtained by insertional mutagenesis

Plasmid DNA carrying either the nitrate reductase (NR) gene or the argininosuccinate lyase gene as selectable markers and the correspondingChlamydomonas reinhardtii mutants as recipient strains have been used to isolate regulatory mutants for nitrate assimilation by insertional mutagenesis. Identification of putative regulatory mutants was based on their chlorate sensitivity in the presence of ammonium. Among 8975 transformants, two mutants, N1 and T1, were obtained. Genetic characterization of these mutants indicated that they carry recessive mutations at two different loci, namedNrg1 andNrg2. The mutation in N1 was shown to be linked to the plasmid insertion. Two copies of the nitrate reductase plasmid, one of them truncated, were inserted in the N1 genome in inverse orientation. In addition to the chlorate sensitivity phenotype in the presence of ammonium, these mutants expressed NR, nitrite reductase and nitrate transport activities in ammonium-nitrate media. Kinetic constants for ammonium (14C-methylammonium) transport, as well as enzymatic activities related to the ammonium-regulated metabolic pathway for xanthine utilization, were not affected in these strains. The data strongly suggest thatNrg1 andNrg2 are regulatory genes which specifically mediate the negative control exerted by ammonium on the nitrate assimilation pathway inC. reinhardtii.

Toxicity of and mutagenesis by chlorate are independent of nitrate reductase activity in Chlamydomonas reinhardtii

SummarySpontaneous chlorate-resistant (CR) mutants have been isolated from Chlamydomonas reinhardtii wildtype strains. Most of them, 244, were able to grow on nitrate minimal medium, but 23 were not. Genetic and in vivo complementation analyses of this latter group of mutants indicated that they were defective either at the regulatory locus nit-2, or at the nitrate reductase (NR) locus nit-1, or at very closely linked loci. Some of these nit-1 or nit-2 mutants were also defective in pathways not directly related to nitrate assimilation, such as those of amino acids and purines. Chlorate treatment of wild-type cells resulted in both a decrease in cell survival and an increase in mutant cells resistant to a number of different chemicals (chlorate, methylammonium, sulphanilamide, arsenate, and streptomycin). The toxic and mutagenic effects of chlorate in minimal medium were not found when cells were grown either in darkness or in the presence of ammonium, conditions under which nitrate uptake is drastically inhibited. Chlorate was also able to induce reversion of nit− mutants of C. reinhardtii, but failed to produce His+ revertants or Arar mutants in the BA-13 strain of Salmonella typhimurium. In contrast, chlorate treatment induced mutagenesis in strain E1F1 of the phototrophic bacterium Rhodobacter capsulatus. Genetic analyses of nitrate reductase-deficient CR mutants of C. reinhardtii revealed two types of CR, to low (1.5 mM) and high (15 mM) chlorate concentrations. These two traits were recessive in heterozygous diploids and segregated in genetic crosses independently of each other and of the nit-1 and nit-2 loci. Three her loci and four lcr loci mediating resistance to high (HC) and low (LC) concentrations of chlorate were identified. Mutations at the nit-2 locus, and deletions of a putative locus for nitrate transport were always epistatic to mutations responsible for resistance to either LC or HC. In both nit+ and nit− chlorate-sensitive (CS) strains, nitrate and nitrite gave protection from the toxic effect of chlorate. Our data indicate that in C. reinhardtii chlorate toxicity is primarily dependent on the nitrate transport system and independent of the existence of an active NR enzyme. At least seven loci unrelated to the nitrate assimilation pathway and mediating CR are thought to control indirectly the efficiency of the nitrate transporter for chlorate transport. In addition, chlorate appears to be a mutagen capable of inducing a wide range of mutations unrelated to the nitrate assimilation pathway.

Salt-Sensitive Mutants of Chlamydomonas reinhardtii Isolated after Insertional Tagging.

We describe the isolation of salt-sensitive Chlamydomonas reinhardtii mutants by insertional mutagenesis using the nitrate reductase (Nit1) gene. The plasmid pMN24, containing Nit1, was used for transformation of 305CW15 (nit1 cw15 mt+), and transformants were selected for complementation of the nit- phenotype. From 6875 nit+ colonies, four transformants (S4, S18, S46, and S66) were isolated that exhibited both Na+ and Li+ sensitivity (sod-), and another transformant (S33) was selected that exhibited sensitivity to Li+ but not Na+ (lit-) based on relative growth comparisons with the wild-type strain. S33, S46, and S66 were no more growth inhibited by sorbitol than was 305CW15. In comparison, S4 and S18 exhibited substantial growth inhibition in medium supplemented with sorbitol. Genetic analyses indicated that the salt-sensitive mutants were each defective in a single recessive gene. The mutant genes in S4 (sod1), S33 (lit1), and S66 (sod3) are linked to a functional copy of Nit1 and are presumably tagged with a pMN24 insertion.

Isolation, sequence and expression in Escherichia coli of the nitrite reductase gene from the filamentous, thermophilic cyanobacterium Phormidium laminosum

The nitrite reductase (NiR) gene (nirA) has been isolated and sequenced from the filamentous, thermophilic non-N2-fixing cyanobacterium Phormidium laminosum. Putative promoter-like and Shine-Dalgarno sequences appear at the 5′ end of the 1533 bp long nir-coding region. The deduced amino acid sequence of NiR from P. laminosum corresponds to a 56 kDa polypeptide, a size identical to the molecular mass previously determined for the pure enzyme, and shows a high identity with amino acid sequences from ferredoxin-dependent NiR. This cyanobacterial NiR gene has been efficiently expressed in Escherichia coli DH5α from the E. coli lac promoter and probably from the P. laminosum NiR promoter.

Priapismo de alto flujo en el contexto de una enfermedad oncológica sistémica

We present the case of a 21-year-old man with a 2-month history of high-flow priapism and no antecedents of direct perineal trauma. Relevant history included Raynauds disease without current treatment. Cavernous body gasometry was performed. Intracavernous phenylephrine injection was unsuccessful. Selective arteriography of the internal pudenda with selective unilateral embolization with autologous coagulation was unsuccessful due to early recanalization. The priapism was resolved by perfusion of 30 ml of phenylephrine at a concentration of 10 μg/ml. During follow-up, the patient developed bulbourethral-membranous stenosis and erectile dysfunction secondary to corpus cavernosum fibrosis. Tumoral disease was ruled out by imaging tests. Six months later, the patient was diagnosed with primary monophasic pulmonary sarcoma and subsequently with poorly differentiated oral epidermoid carcinoma. We highlight the poor outcome of priapism with corpus cavernosum fibrosis, even though this entity is not associated with changes due to acidosis or potential tissue injury. We also stress the temporal association of the development of two distinct, highly aggressive neoplastic processes, although prior studies showed no clinical or radiological evidence of malignancy that would warrant a diagnosis of paraneoplastic syndrome.

Relationship Between Erectile Dysfunction, Diabetes and Dyslipidemia in Hypertensive-Treated Men

PURPOSE PRESIDEN study is a large study to analyze the erectile dysfunction (ED) incidence in Spanish population. The present study is a pilot sub-analysis from PRESIDEN to determine if ED or plasma testosterone (TST) level in controlled hypertensive patients may be associated with comorbidities and/or plasma nitrite+nitrate and antioxidant capacity. MATERIALS AND METHODS Forty-four hypertensive individuals were aleatory selected from PRESIDEN study, matching by age (28 showing ED and 16 without ED). RESULT Diabetes was present in 28.57% of ED patients and in 18.75% of patients without ED. In patients with and without ED, increasing age showed tendency of higher frequency of an additional comorbidity (diabetes or dyslipemia) (P = .09). Apparently, plasma TST levels were lower in older ED patients compared to younger patients with and without ED, although it did not reach statistical significance (P = .69). Older ED patients also showed lower TST levels than older patients without ED, although it was not statistical significant (16.15 ± 2.84 vs 13.91± 2.77; P = .69). Dyslipidemia was showed by 52.17% with lower TST (? nmol/L) while 23.80% of patients with plasma TST levels > 15 nmol/L had dyslipidemia. The percentage of ED patients was similar between patients with low and high TST levels. CONCLUSION More ED hypertensive patients seem to show two comorbidities (diabetes and dyslipidemia) than hypertensivepatients without ED. Younger patients with ED tended to show more commonly diabetes than older ED patients. Plasma TST levels were not associated with more prevalence of ED but lower plasma TST levels showed tendency to higher prevalence of dyslipidemia.

Uso continuado de inhibidores de la PDE5 en el tratamiento de la disfunción eréctil: nuevas perspectivas y oportunidades

At present, there is debate regarding the continuous use of phosphodiesterase 5 inhibitors in the treatment of erectile dysfunction. Cumulative evidence supports the benefit, even at low doses, thatcontinuous treatment has on erectile function -even in difficult-to-treat patients-, and on the spontaneity and naturalness of sexual relationships. Safety and tolerability have also proven to be good. Beyond phosphodiesterase 5 inhibition, the effect of continuous treatment of erectile function appears to be based on improvement of endothelial function and oxygenation of the penile vascular bed as a result of the increased number of erections, hence playing down the importance of pharmacokinetics. Although evidence is still limited, this new scenario opens new paths for the treatment of erectile dysfunction patients in whom on-demand treatments are not effective or deemed appropriate, and would benefit the spontaneity of sexual life.