Structural basis for CRISPR RNA-guided DNA recognition by Cascade

The CRISPR (clustered regularly interspaced short palindromic repeats) immune system in prokaryotes uses small guide RNAs to neutralize invading viruses and plasmids. In Escherichia coli, immunity depends on a ribonucleoprotein complex called Cascade. Here we present the composition and low-resolution structure of Cascade and show how it recognizes double-stranded DNA (dsDNA) targets in a sequence-specific manner. Cascade is a 405-kDa complex comprising five functionally essential CRISPR-associated (Cas) proteins (CasA1B2C6D1E1) and a 61-nucleotide CRISPR RNA (crRNA) with 5′-hydroxyl and 2′,3′-cyclic phosphate termini. The crRNA guides Cascade to dsDNA target sequences by forming base pairs with the complementary DNA strand while displacing the noncomplementary strand to form an R-loop. Cascade recognizes target DNA without consuming ATP, which suggests that continuous invader DNA surveillance takes place without energy investment. The structure of Cascade shows an unusual seahorse shape that undergoes conformational changes when it binds target DNA.

Sex Reversal in Zebrafish fancl Mutants Is Caused by Tp53-Mediated Germ Cell Apoptosis

The molecular genetic mechanisms of sex determination are not known for most vertebrates, including zebrafish. We identified a mutation in the zebrafish fancl gene that causes homozygous mutants to develop as fertile males due to female-to-male sex reversal. Fancl is a member of the Fanconi Anemia/BRCA DNA repair pathway. Experiments showed that zebrafish fancl was expressed in developing germ cells in bipotential gonads at the critical time of sexual fate determination. Caspase-3 immunoassays revealed increased germ cell apoptosis in fancl mutants that compromised oocyte survival. In the absence of oocytes surviving through meiosis, somatic cells of mutant gonads did not maintain expression of the ovary gene cyp19a1a and did not down-regulate expression of the early testis gene amh; consequently, gonads masculinized and became testes. Remarkably, results showed that the introduction of a tp53 (p53) mutation into fancl mutants rescued the sex-reversal phenotype by reducing germ cell apoptosis and, thus, allowed fancl mutants to become fertile females. Our results show that Fancl function is not essential for spermatogonia and oogonia to become sperm or mature oocytes, but instead suggest that Fancl function is involved in the survival of developing oocytes through meiosis. This work reveals that Tp53-mediated germ cell apoptosis induces sex reversal after the mutation of a DNA–repair pathway gene by compromising the survival of oocytes and suggests the existence of an oocyte-derived signal that biases gonad fate towards the female developmental pathway and thereby controls zebrafish sex determination

Malnutrition as a risk factor for the development of pressure ulcers Desnutrición como factor de riesgo para el desarrollo de las úlceras por presión Desnutrição como fator de risco para o desenvolvimento de úlceras por pressão

Malnutrition - as a fundamental aspect both in genesis as in healing of pressure ulcers - is the object of this update paper. Countless studies point out that malnutrition, immune function alterations, hypoalbuminemia, low hemoglobin levels, as well as low diet intake, as responsible for an increase in the risk of developing these lesions. Therefore, it is essential to include the assessment of the nutrition status - monitoring of the calorie-protein intake and the difficulties to use the nutrients - in the prevention and treatment protocols of this type of chronic wound.<br>La desnutrición - como aspecto fundamental en la génesis y cicatrización de las úlceras por presión (UP) - es el tema de esta atualización. Muchos estudios destacan la desnutrición, los cambios del funcionamiento imunológico, la hipoalbuminemia, los bajos niveles de hemoglobina así como la baja aceptación alimentaria como los responsables del aumento del riesgo para el desarrollo de las UP. En conclusión, es fundamental incluir la evaluación del estado nutricional en los protocolos de prevención y tratamiento de las UP. Esa evaluación debe incluir medidas objetivas, seguimiento de la ingestión calórica y protéica y además de las dificultades para el aprovechamiento de los nutrientes.<br>A desnutrição - como aspecto fundamental tanto na gênese como na cicatrização das úlceras por pressão - é objeto deste artigo de atualização. Inúmeros estudos salientam a desnutrição, alterações da função imune, hipoalbuminemia, níveis baixos de hemoglobina bem como a baixa aceitação dietética como responsáveis por aumentar o risco para o desenvolvimento dessas lesões. É, portanto, fundamental incluir a avaliação do estado nutricional - monitorização da ingestão calórico-protéica e das dificuldades para o aproveitamento dos nutrientes nos protocolos de prevenção e tratamento desse tipo de ferida crônica

Cost effectiveness of nutrition support in the prevention of pressure ulcer in hospitals

Background/objectives: This study estimates the economic outcomes of a nutrition intervention to at-risk patients compared with standard care in the prevention of pressure ulcer. Subjects/methods: Statistical models were developed to predict 'cases of pressure ulcer avoided', 'number of bed days gained' and 'change to economic costs' in public hospitals in 2002-2003 in Queensland, Australia. Input parameters were specified and appropriate probability distributions fitted for: number of discharges per annum; incidence rate for pressure ulcer; independent effect of pressure ulcer on length of stay; cost of a bed day; change in risk in developing a pressure ulcer associated with nutrition support; annual cost of the provision of a nutrition support intervention for at-risk patients. A total of 1000 random re-samples were made and the results expressed as output probability distributions. Results: The model predicts a mean 2896 (s.d. 632) cases of pressure ulcer avoided; 12 397 (s.d. 4491) bed days released and corresponding mean economic cost saving of euros 2 869 526 (s.d. 2 078 715) with a nutrition support intervention, compared with standard care. Conclusion: Nutrition intervention is predicted to be a cost-effective approach in the prevention of pressure ulcer in at-risk patients