On the effects of the modularity of gene regulatory networks on phenotypic variability and its association with robustness.

Biological adaptations depend on natural selection sorting out those individuals that exhibit characters fit to their environment. Selection, in turn, depends on the phenotypic variation present in a population. Thus, evolutionary outcomes depend, to a certain extent, on the kind of variation that organisms can produce through random genetic perturbation, that is, their phenotypic variability. Moreover, the properties of developmental mechanisms that produce the organisms affect their phenotypic variability. Two of these properties are modularity and robustness. Modularity is the degree to which interactions occur mostly within groups of the system's elements and scarcely between elements in different groups. Robustness is the propensity of a system to endure perturbations while preserving its phenotype. In this paper, we used a model of gene regulatory networks (GRNs) to study the relationship between modularity and robustness in developmental processes and how modularity affects the variation that random genetic mutations produce in the expression patterns of GRNs. Our results show that modularity and robustness are correlated in multifunctional GRNs and that selection for one of these properties affects the other as well. We contend that these observations may help to understand why modularity and robustness are widespread in biological systems. Additionally, we found that modular networks tend to produce new expression patterns with subtle changes localized in the expression of a few groups of genes. This effect in the phenotypic variability of modular GRNs may bear important consequences for adaptive evolution: it may help to adjust the expression of one group of genes at a time, with few alterations on other previously evolved expression patterns.

[Pyogenic liver abscess. Study of 20 patients treated with percutaneous drainage]. / Abscesos hepáticos piógenos. Estudio de 20 pacientes tratados mediante drenaje percutáneo.

We conducted a descriptive study of pyogenous hepatic abscesses (PHA) and their treatment with percutaneous drainage and antibiotherapy in the general hospital of Galdácano between 1989 and 1992. We assessed prevalence, clinical characteristics, responses to treatment, evolution and complications. We studied 20 PHAs in adults confirmed through puncture guided with echography and/or computerized tomography. We considered as causal germs those isolated in the abscess and/or hemocultures. All the patients were treated with catheter drainage and antibiotics. After discharge, follow-up and regular TC controls were performed at least for 6 months. The average age of the patients was 56 +/- 3 years and the men/women rate was 2.5:1. The most frequent origin of the infection was cholecystitis/cholangitis in 50% of patients and hydatidic cysts in 20%. Twelve patients had isolated abscess and 8 patients, multiple abscesses. The diagnostic sensitivity was 95% for the echography and 100% for CAT. The most frequent germs were E. Coli, Streptococcus, K. pneumoniae and Salmonella spp. In three cases, it was not possible to bacteriologically identified the germ. After drainage, the abscesses disappeared in 16 patients. The average duration of percutaneous drainage was 10 days. Three patients required surgery after drainage due to complications or incomplete drainage; two other patients required extirpation of hydatidic cysts. The mortality rate was 10%, although it was not related to PHA. We did not observe any differences between isolated or multiple abscesses with regard to prognosis. The drainage guided by echography and/or CT, associated to antibiotic therapy, is a successful technique for the treatment of PHAs in most patients.(ABSTRACT TRUNCATED AT 250 WORDS)