Predictive models of fish microhabitat selection in multiple sites accounting for abundance overdispersion

Microhabitat selection models are frequently used in rivers to evaluate anthropogenic effects on aquatic organisms. Fish models are generally developed from few rivers, with debatable statistical treatments for coping with overdispersed abundance distributions. Analyses of data from multiple rivers are needed to test their transferability and increase their relevance for stakeholders. Using 3,528 microhabitats sampled in nine French rivers during 129 surveys, we developed models for 35 specific size classes of 22 fish species. We used mixed‐effects generalized linear models (accounting for multiple surveys), involving B‐spline transformations (accounting for nonlinear responses) and assuming a negative binomial distribution (accounting for abundance overdispersion). We compared models of increasing complexity: no selection (M1), an “average” selection similar in all surveys (M2), two models with different selection across surveys (M3–M4). Of 132 univariate cases (specific size classes by habitat), 63% indicated selection for depth, 71% for velocity, 45% for substratum size and 13% for substratum heterogeneity. A total of 50 models were retained, involving 26/35 specific size classes. Model fits indicated low explained deviance (R²MF < 0.19) and higher rank correlations (ρ < 0.69) between observed and modelled values. However, Bayesian posterior predictive checks validated these results since excellent fits would generate R²MF lower than 0.59 and ρ lower than 0.78. We found high transferability among rivers and dates, because (a) M2 was the most appropriate in 26/50 cases; (b) the R²MF and ρ values by M2 was, respectively, 72% and 75% of that explained by the complex M4 and (c) independent river cross‐validations showed good transferability. Bivariate models for selected specific size classes improved univariate model fits (ρ from 0.30 to 0.38). Overall, using a nonlinear mixed‐effect approach, our results confirmed the relevance of “average” models based on several rivers for developing helpful e‐flow tools. Finally, our modelling approach opens opportunities for integrating additional effects as the spatial distribution of competitors.     

Human CD14 mediates recognition and phagocytosis of apoptotic cells

Cells undergoing programmed cell death (apoptosis) are cleared rapidly in vivo by phagocytes without inducing inflammation. Here we show that the glycosylphosphatidylinositol-linked plasma-membrane glycoprotein CD14 on the surface of human macrophages is important for the recognition and clearance of apoptotic cells. CD14 can also act as a receptor that binds bacterial lipopolysaccharide (LPS), triggering inflammatory responses. Overstimulation of CD14 by LPS can cause the often fatal toxic-shock syndrome. Here we show that apoptotic cells interact with CD14, triggering phagocytosis of the apoptotic cells. This interaction depends on a region of CD14 that is identical to, or at least closely associated with, a region known to bind LPS. However, apoptotic cells, unlike LPS, do not provoke the release of pro-inflammatory cytokines from macrophages. These results indicate that clearance of apoptotic cells is mediated by a receptor whose interactions with 'non-self' components (LPS) and 'self' components (apoptotic cells) produce distinct macrophage responses.     

Proficiency-Adapted Information Browsing and Filtering in Hypermedia Educational Systems

We present a framework for proficiency-adapted information browsing and filtering in educational hypermedia systems. In hyperdocuments, information is acquired by browsing through highly interconnected sets of information nodes. In order to find specific information, users follow links to nodes they judge to be relevant. In order to help users find relevant information and new learning material that match their levels of domain knowledge, we present a framework for adapting the information nodes, and the links leading to them, to the user's proficiency in the subject matter. Such a proficiency-adapted, user-centered educational environment is intended to enhance learning. We believe that learning in educational hypertext-based applications cannot be reduced to traversing a static information space. Navigating through any space, be it a physical or an information space, normally requires that users have a prior degree of proficiency in the domain knowledge. Learning is an evolving dynamic process through which users progress from a situation of unfamiliarity to one of mastery of a knowledge corpus. Therefore, we propose a model of proficiency-adapted learning and information browsing in which the presented choices (links and the textual context of links) are selected based on the user's knowledge state. Ultimately, such an adaptive course not only guides the learning process of the student, but it gradually transforms itself into a reference guide. This revised version was published online in July 2006 with corrections to the Cover Date.     

Pattern of spontaneous and post-stimulation FSH and LH in male adolescents with thalassemia

BACKGROUND: In the last years thalassemic patients gained a good improvement in prognosis and life style. However, short stature and hypogonadism are still frequent endocrine problems in this population. METHODS: In a group of eleven thalassemic males (14-18 years old), the spontaneous nocturnal endocrine patterns of LH and FSH and plasma gonadotropins in response to GnRH were studied. The profiles were analyzed using a computer program (PULSAR) to determine the secretion pattern (number and amplitude of peaks) and the area under the curve above the secretion baseline (AUC). The endocrine status was compared with liver fibrosis, iron overload and transfusional regimen. RESULTS: A regular and homogeneous transfusion and chelation management often does not prevent pubertal failure; it is related with the degree of liver fibrosis and often it is due to hypothalamic and/or pituitary dysfunction. CONCLUSIONS: Spontaneous gonadotropin profiles can be useful to evaluate hypogonadotropic hypogonadism in order to start the correct treatment.     

Use of D gene segments with irregular spacers in terminal deoxynucleotidyltransferase (TdT)+/+ and TdT-/- mice carrying a human Ig heavy chain transgenic minilocus

D gene segments with irregular spacers (DIR) are D gene segments that are specific to higher primates. Their use is controversial because of their G+C-rich long sequences. In the human, it has always been tempting to assume that a complementarity-determining region 3 sequence has been added by terminal deoxynucleotidyltransferase (TdT) activity and is not derived from DIR recombination. Herein, we examine the use of human DIR gene segments by cross-breeding the human Ig heavy chain minilocus pHC1 transgenic mice and TdT-deficient mice. In the absence of TdT and with a defined set of human D gene segments, it is relatively easy to demonstrate that DIR2 is used to form human Ig heavy chains, contributing to 7% of the human heavy chain rearrangements. VHDJH rearrangements (where H is heavy chain) in the minilocus TdT-/- mice use small portions of DIR2 located throughout the coding sequence. These results constitute the strongest evidence to date that DIR gene segments are used to form human antibodies. Additionally, we show that direct and inverted DIR2JH and VHDIR2 rearrangements occur in the minilocus transgenic mice. During these rearrangements, DM2 3' signal sequence and a new DIR2 5' signal sequence are used. These rearrangements generally follow the 12/23 recombination rule. Our results at the VHDJH, DJH, and VHD levels indicate that DIR2 is used to form human heavy chains in transgenic mice. The rearrangement of this gene segment likely involves, however, other mechanisms in addition to the classical VHDJH recombination.     

Simultaneous onset of primary cutaneous B-cell lymphoma and human herpesvirus 8-associated Kaposi's sarcoma

We report the simultaneous occurrence of Kaposi's sarcoma (KS) and primary cutaneous B-cell lymphoma (CBCL) of the leg in a 79-year-old woman, seronegative for HIV-1, HTLV-1 and HTLV-2. The CBCL underwent complete clinical remission after local radiotherapy, whilst the KS became disseminated within a year following diagnosis. However, 2 years after the diagnosis of KS, the patient died with neurological symptoms. These were presumed to be due to involvement of the central nervous system by lymphoma, although in the absence of an autopsy, this could not be proven. Skin biopsies from the original KS and CBCL lesions, as well as short-term culture of spindle cells from the KS lesion and peripheral blood mononuclear cells (PBMC), were studied by semiquantitative polymerase chain reaction (PCR) using primers specific for DNA sequences of a novel gamma-herpesvirus-8 (HHV-8). PCR studies were strongly positive for the virus on KS cells and PBMC; conversely, a low viral load was found on CBCL cells. A high titre of serum IgG antibodies reacting with the nuclei of the HHV-8 positive cell line BCP-1 was found. These data suggest that reactivation of latent infection with HHV-8 had occurred in this patient, and that HHV-8 is directly involved in KS, but not in CBCL of the leg, an aggressive variant of CBCL.     

Techniques for Traceable Measurements of Small Currents

The Italian national standard of direct current is being extended down to the femtoampere range. Two current sources have been developed. The first one, working in the 100 pA to 100 fA range, is based on a low-frequency trapezoidal wave generator, measured with a sampling digital voltmeter at regular time intervals, which charges and discharges a gas-dielectric capacitor. The second, working in the 10-muA to 10-pA range, makes use of a calibrated resistor to generate a known current. Current is traceable to national standards of voltage, resistance or capacitance, and frequency