Progressive changes in the structure and dynamics of the phytoplankton community along a pollution gradient in a lowland river — a multivariate approach

The phytoplankton of the River Lujan (Buenos Aires, Argentina) was studied for a period of 18 months, together with physical and chemical variables, in relation to a pollution gradient. 167 taxa were recorded within a seasonal succession characterized by dominance of diatoms with a brief summer green algae facies. A combination of several biotic indices and multivariate analysis was employed to assess the impact of pollution on the phytoplankton community. The biotic indices used were species diversity and richness, algal quotients (green algae/diatom ratio, Centrales/Pennales ratio) and the SD succession rate index. Multivariate procedures included cluster analysis and ordination by PCA of both species and samples, stepwise discriminant analysis and multiple discriminant analysis of variance (MANOVA). Results indicate that community dynamism is attenuated at the more polluted sites, concomitant with an increased predominance of a broad-tolerance algal assemblage, co-dominated by Cyclotella meneghiniana and Nitzschia stagnorum. The changes in the community structure and dynamics described herein involved alterations in the distribution and relative proportions of the algae, rather than modifications in the basic species composition. These changes may not be readily detectable by methods which over-simplify the ecological information, such as systems of indicator species and biotic indices, designed to assess the degree of pollution. The suitability of multivariate analysis and biotic indices in river phytoplankton studies is further discussed.     

Melanocortin‐1 receptor (MC1R) genotypes do not correlate with size in two cohorts of medium‐to‐giant congenital melanocytic nevi

Congenital melanocytic nevi (CMN) are cutaneous malformations whose prevalence is inversely correlated with projected adult size. CMN are caused by somatic mutations, but epidemiological studies suggest that germline genetic factors may influence CMN development. In CMN patients from the U.K., genetic variants in MC1R, such as p.V92M and loss‐of‐function variants, have been previously associated with larger CMN. We analyzed the association of MC1R variants with CMN characteristics in two distinct cohorts of medium‐to‐giant CMN patients from Spain (N = 113) and from France, Norway, Canada, and the United States (N = 53), similar at the clinical and phenotypical level except for the number of nevi per patient. We found that the p.V92M or loss‐of‐function MC1R variants either alone or in combination did not correlate with CMN size, in contrast to the U.K. CMN patients. An additional case–control analysis with 259 unaffected Spanish individuals showed a higher frequency of MC1R compound heterozygous or homozygous variant genotypes in Spanish CMN patients compared to the control population (15.9% vs. 9.3%; p = .075). Altogether, this study suggests that MC1R variants are not associated with CMN size in these non‐UK cohorts. Additional studies are required to define the potential role of MC1R as a risk factor in CMN development.     

Cytosine-block telomeric type DNA-binding activity of hnRNP proteins from human cell lines

Following the observation of the presence in mammalian nuclear extracts of a DNA binding activity quite specific for the single-stranded C-rich telomeric motif, we have isolated from the K562 human cell line by affinity chromatography and identified by mass spectrometry a number of proteins able to bind to this sequence. All of them belong to different heterogeneous nuclear ribonucleoprotein subgroups (hnRNP). Whereas many of them, namely hnRNP K, two isoforms of hnRNP I, and the factor JKTBP, appear to bind to this sequence with limited specificity after isolation, an isoform of hnRNP D (alias AUF1) and particularly hnRNP E1 (alias PCBP-1) show a remarkable specificity for the (CCCTAA)n repeated motif. Both have been obtained also as recombinant proteins expressed in Escherichia coli and have been shown to retain their binding specificity toward the C-block repeated sequence. In the light of the current knowledge about these proteins, their possible involvement in telomere functioning is discussed.     

Successive episodes of synapses production in the developing rat nucleus tractus solitarii

In the rat nucleus tractus solitarii (NTS), synaptogenesis is thought to occur both pre- and postnatally. The present study was performed to precisely define the timetable of synapse formation in the NTS after birth. Changes in synapse morphology and densities were analyzed between postnatal day 3 (P3) and P28 using electron microscopy and ethanol phosphotungstic acid (E-PTA) staining. The proportion of morphologically immature synapses was high at P3 (38%) and P14 (30%) and low (8-14%) at the other ages investigated (P7, P21, and P28). Synaptic density significantly increased between P7 and P14 (60%) and between P21 and P28 (54%), but did not significantly change between P3 and P7 and between P14 and P21. Mean synaptic diameter also increased over the first postnatal month. Significant increases in synaptic size occurred between P3 and P7 (28%) and between P14 and P21 (15%). The present data indicate that, in the NTS, synaptogenesis occurs over a protracted period of time and involves distinct successive episodes of synapse production.     

Expression and function of the homeodomain-containing protein Hex in thyroid cells

The homeodomain-containing protein Hex (also named Prh) is expressed in primitive endoderm (during the early phases of development), in some endoderm-derived tissues and in endothelial and hematopoietic precursors. Hex expression is extinguished during terminal differentiation of endothelial and hematopoietic cells as well as in adult lung. Previous investigations have demonstrated that Hex is expressed during early thyroid gland development. No information has been reported on Hex expression in adult thyroid gland or on the function of this protein in follicular thyroid cells. These issues represent the focus of the present study. We demonstrate that Hex mRNA is present in rat and human adult thyroid gland as well as in differentiated follicular thyroid cell lines. In FRTL-5 cells TSH reduces Hex expression. In thyroid cell lines transformed by several oncogenes Hex expression is completely abolished. By using co-transfection assays we demonstrate that Hex is a repressor of the thyroglobulin promoter and that it is able to abolish the activating effects of both TTF-1 and Pax8. These data would suggest that Hex may play an important role in thyroid cell differentiation. Protein–DNA interaction experiments indicate that Hex is able to bind sites of the thyroglobulin promoter containing either the core sequence 5′-TAAT-3′ or 5′-CAAG-3′. The DNA binding specificity of the Hex homeodomain, therefore, is more ‘relaxed’ than that observed in the majority of other homeodomains.     

A proteomic approach to the bilirubin‐induced toxicity in neuronal cells reveals a protective function of DJ‐1 protein

Unconjugated bilirubin (UCB) is a powerful antioxidant and a modulator of cell growth through the interaction with several signal transduction pathways. Although newborns develop a physiological jaundice, in case of severe hyperbilirubinemia UCB may become neurotoxic causing severe long‐term neuronal damages, also known as bilirubin encephalopathy. To investigate the mechanisms of UCB‐induced neuronal toxicity, we used the human neuroblastoma cell line SH‐SY5Y as an in vitro model system. We verified that UCB caused cell death, in part due to oxidative stress, which leads to DNA damage and cell growth reduction. The mechanisms of cytotoxicity and cell adaptation to UCB were studied through a proteomic approach that identified differentially expressed proteins involved in cell proliferation, intracellular trafficking, protein degradation and oxidative stress response. In particular, the results indicated that cells exposed to UCB undertake an adaptive response that involves DJ‐1, a multifunctional neuroprotective protein, crucial for cellular oxidative stress homeostasis. This study sheds light on the mechanisms of bilirubin‐induced neurotoxicity and might help to design a strategy to prevent or ameliorate the neuronal damages leading to bilirubin encephalopathy.     

Subcellular localization of APE1/Ref-1 in human hepatocellular carcinoma: possible prognostic significance

APE1/Ref-1, normally localized in the nucleus, is a regulator of the cellular response to oxidative stress. Cytoplasmic localization has been observed in several tumors and correlates with a poor prognosis. Because no data are available on liver tumors, we investigated APE1/Ref-1 subcellular localization and its correlation with survival in 47 consecutive patients undergoing hepatocellular carcinoma (HCC) resection. APE1/Ref-1 expression was determined by immunohistochemistry in HCC and surrounding liver cirrhosis (SLC) and compared with normal liver tissue. Survival probability was evaluated using Kaplan-Meier curves (log-rank test) and Cox regression. Cytoplasmic expression of APE1/Ref-1 was significantly higher in HCC than in SLC (P = 0.00001); normal liver showed only nuclear reactivity. Patients with poorly differentiated HCC showed a cytoplasmic expression three times higher than those with well-differentiated HCC (P = 0.03). Cytoplasmic localization was associated with a median survival time shorter than those with negative cytoplasmic reactivity (0.44 compared with 1.64 years, P = 0.003), and multivariable analysis confirmed that cytoplasmic APE1/Ref-1 localization is a predictor of survival. Cytoplasmic expression of APE1/Ref-1 is increased in HCC and is associated with a lower degree of differentiation and a shorter survival time, pointing to the use of the cytoplasmic localization of APE1/Ref-1 as a prognostic marker for HCC.