Helicases DDX5 and DDX17 promote heterogeneity in HBV transcription termination in infected human hepatocytes.

BACKGROUND & AIMS: Transcription termination fine-tunes gene expression and contributes to the specification of RNA function in eukaryotic cells. Transcription termination of HBV is subject to the recognition of the canonical polyadenylation signal (cPAS) common to all viral transcripts. However, the regulation of this cPAS and its impact on viral gene expression and replication is currently unknown. METHODS: To unravel the regulation of HBV transcript termination, we implemented a 3' RACE (rapid amplification of cDNA ends)-PCR assay coupled to single molecule sequencing both in in vitro-infected hepatocytes and in chronically infected patients. RESULTS: The detection of a previously unidentified transcriptional readthrough indicated that the cPAS was not systematically recognized during HBV replication in vitro and in vivo. Gene expression downregulation experiments demonstrated a role for the RNA helicases DDX5 and DDX17 in promoting viral transcriptional readthrough, which was, in turn, associated with HBV RNA destabilization and decreased HBx protein expression. RNA and chromatin immunoprecipitation, together with mutation of the cPAS sequence, suggested a direct role of DDX5 and DDX17 in functionally linking cPAS recognition to transcriptional readthrough, HBV RNA stability and replication. CONCLUSIONS: Our findings identify DDX5 and DDX17 as crucial determinants of HBV transcriptional fidelity and as host restriction factors for HBV replication. IMPACT AND IMPLICATIONS: HBV covalently closed circular (ccc)DNA degradation or functional inactivation remains the holy grail for the achievement of HBV cure. Transcriptional fidelity is a cornerstone in the regulation of gene expression. Here, we demonstrate that two helicases, DDX5 and DDX17, inhibit recognition of the HBV polyadenylation signal and thereby transcriptional termination, thus decreasing HBV RNA stability and acting as restriction factors for efficient cccDNA transcription and viral replication. The observation that DDX5 and DDX17 are downregulated in patients chronically infected with HBV suggests a role for these helicases in HBV persistence in vivo. These results open new perspectives for researchers aiming at identifying new targets to neutralise cccDNA transcription.

Thematic Analysis of Coping Strategies Used by Parents of Children with Cleft Lip and Palate in El Salvador.

OBJECTIVE: The aim of this study was to describe coping strategies used by parents of children with cleft palate with or without a cleft (CP ± L) during the early development of their children in El Salvador. DESIGN: Qualitative interviews were completed with 16 parents of children born with CP ± L who were 6 months to 6 years old. Parents were questioned about their emotions and coping during eight time periods: prenatal, birth, social interaction before the first surgery, the beginning of surgeries, social interaction after the first surgery, early childhood education (ECE), speech-language therapy, and formal education. Thematic analysis (TA) was used to identify coping strategies as conceptualized by Lazarus and Folkman (1984). RESULTS: Four major themes emerged: (a) experienced emotions related to diagnosis, (b) interpretations related to the birth of a child with a cleft, (c) seeking and experiencing cleft treatment, and (d) social interaction of the children. During prenatal and birth stages, parents used emotion-focused strategies. A few hours to a week after birth, they used problem-focused strategies, which led them in search of treatment. Some parents used avoidance strategies during periods of social interaction before surgery, ECE, and formal education. Socioeconomic challenges impacted access to speech-language therapy. Sociocultural factors, such as discrimination, religion, and folk beliefs, appeared to influence some of the coping strategies used by parents. CONCLUSIONS: Problem-focused strategies appear to be helpful in seeking surgical treatments. The emotion-focused strategy of avoidance seemed to have adverse effects in minimizing opportunities for social interaction prior to surgery and early education.

Pre-Hispanic Evidence of Cleft Lip and/or Palate in Mesoamerica.

In this letter, the authors present archeological evidence of the presence of cleft lip and/or palate (CLP) in pre-Hispanic Mesoamerica. During years 2016 and 2017, the authors visited 5 anthropology museums in Mexico, Guatemala, and El Salvador, in search for pre-Hispanic archeological evidence of CLP, and 16 anthropomorphic figurines with evidence of CLP were identified; 9 at the Anahuacalli Museum, 6 at the National Anthropology Museum of Mexico, and 1 at the National Anthropology Museum of El Salvador. Fifteen of these ceramics originated from the shaft tombs (pre-Hispanic culture from western Mexico, Jalisco, Colima, and Nayarit; dating from 200 bc-600 ad), and 1 ceramic originated from the Cotzumalguapa (a pre-Hispanic culture from western El Salvador dating from 200 ad-900 ad).

Covalently closed circular DNA: The ultimate therapeutic target for curing HBV infections.

Current antiviral therapies, such as pegylated interferon-α and nucleos(t)ide analogues, effectively improve the quality of life of patients with chronic hepatitis B. However, they can only control the infection rather than curing infected hepatocytes. Complete HBV cure is hampered by the lack of therapies that can directly affect the viral minichromosome (in the form of covalently closed circular DNA [cccDNA]). Approaches currently under investigation in early clinical trials are aimed at achieving a functional cure, defined as the loss of HBsAg and undetectable HBV DNA levels in serum. However, achieving a complete HBV cure requires therapies that can directly target the cccDNA pool, either via degradation, lethal mutations or functional silencing. In this review, we discuss cutting-edge technologies that could lead to non-cytolytic direct cccDNA targeting and cure of infected hepatocytes.

Metabolic syndrome in indigenous communities in Mexico: a descriptive and cross-sectional study.

BACKGROUND: An Amerindian genetic background could play an important role in susceptibility to metabolic diseases, which have alarmingly increased in recent decades. Mexico has one of the highest prevalences of metabolic disease worldwide. The purpose of this study was to determine the prevalence of metabolic syndrome and its components in a population with high Amerindian ancestry. METHODS: We performed a descriptive, quantitative, and analytical cross-sectional study of 2596 adult indigenous volunteers from 60 different ethnic groups. Metabolic syndrome and its components were evaluated using the American Heart Association/National Heart, Lung, and Blood Institute Scientific Statement criteria. RESULTS: The overall prevalence of metabolic syndrome in the indigenous Mexican population was 50.3%. Although females had a higher prevalence than males (55.6% vs. 38.2%), the males presented with combinations of metabolic syndrome components that confer a higher risk of cardiovascular disease. The most frequent metabolic syndrome component in both genders was low HDL-cholesterol levels (75.8%). Central obesity was the second most frequent component in females (61%), though it had a low prevalence in males (16.5%). The overall prevalence of elevated blood pressure was 42.7% and was higher in males than females (48.8 vs. 40%). We found no gender differences in the overall prevalence of elevated triglycerides (56.7%) or fasting glucose (27.9%). CONCLUSIONS: We documented that individuals with Amerindian ancestry have a high prevalence of metabolic syndrome. Health policies are needed to control the development of metabolic disorders in a population with high genetic risk.

Intercellular Extensions Are Induced by the Alphavirus Structural Proteins and Mediate Virus Transmission.

Alphaviruses are highly organized enveloped RNA viruses with an internal nucleocapsid surrounded by a membrane containing the E2 and E1 transmembrane proteins. Alphavirus budding takes place at the plasma membrane and requires the interaction of the cytoplasmic domain of E2 with the capsid protein. Here we used WT alphaviruses and Sindbis virus in which E2 was fused to a fluorescent protein to characterize virus exit from host cells. Our results show that alphavirus infection induced striking modifications of the host cell cytoskeleton and resulted in the formation of stable intercellular extensions that emanated exclusively from the infected cell. The intercellular extensions were long (> 10 µM), contained actin and tubulin, and formed flattened contacts with neighboring cells, but did not mediate membrane or cytoplasmic continuity between cells. Receptor down-regulation studies indicated that formation of stable extensions did not require the virus receptor, and that extensions promoted cell-to-cell virus transmission to receptor-depleted cells. Virus mutant experiments demonstrated that formation of extensions required the E2-capsid interaction but not active particle budding, while intercellular transmission of infection required the production of fusion-active virus particles. Protein expression studies showed that even in the absence of virus infection, the viral structural proteins alone induced intercellular extensions, and that these extensions were preferentially targeted to non-expressing cells. Together, our results identify a mechanism for alphavirus cell-to-cell transmission and define the key viral protein interactions that it requires.

Prevalence and factors associated with supportive care needs among newly diagnosed Mexican breast cancer patients.

PURPOSE: Mexican breast cancer patients are generally diagnosed in advanced stages of the disease and often experience delays in cancer treatment delivery. Currently, little is known about these patients' psychological care needs. This study assessed levels and correlates of supportive care needs of Mexican breast cancer patients around the time of cancer diagnosis. METHODS: One hundred seventy-three newly diagnosed Mexican breast cancer patients participated in the study. Supportive care needs, anxiety, depression, and patients' sociodemographic and clinical characteristics were assessed. Multiple regression analyses were used to examine factors associated with care needs. RESULTS: Up to 44% of patients showed unmet care needs. Health system/information needs were the most prevalent (68%), while physical/daily living needs the least (19%). Level of depressive symptoms was most consistently related to care needs. Patients with higher levels of depressive symptoms had higher psychological (ß = 0.38), physical/daily living (ß = 0.43), patient care/support (ß = 0.17), and additional unmet care needs (ß = 0.30), than patients with lower levels of depressive symptoms. CONCLUSIONS: This study suggests that mainly health system/information needs arise at the time of cancer diagnosis among Mexican breast cancer patients. Patients suffering high levels of depressive symptoms reported the highest levels of unmet needs. Future studies should be conducted to elucidate the care needs throughout the disease trajectory, as such information can inform health care professionals and policy makers and lead to improvements in the organization and provision of health care services for Mexican breast cancer patients.

Tessier 3 Cleft in a Pre-Hispanic Anthropomorphic Figurine in El Salvador, Central America.

In 1976, Paul Tessier provided a numerical classification system for rare facial clefts, numbered from 0 to 14. The Tessier 3 cleft is a rare facial cleft extending from the philtrum of the upper lip through the wing of the nostril, and reaches the medial canthus of the eye. The aim of this document was to describe a pre-Hispanic anthropomorphic figurine dating from the classic period (200 A.D.-900 A.D.), which has a Tessier 3 cleft. We also discuss the documented pre-Hispanic beliefs about facial clefts.

Imaging the alphavirus exit pathway.

UNLABELLED: Alphaviruses are small enveloped RNA viruses with highly organized structures that exclude host cell proteins. They contain an internal nucleocapsid and an external lattice of the viral E2 and E1 transmembrane proteins. Alphaviruses bud from the plasma membrane (PM), but the process and dynamics of alphavirus assembly and budding are poorly understood. Here we generated Sindbis viruses (SINVs) with fluorescent protein labels on the E2 envelope protein and exploited them to characterize virus assembly and budding in living cells. During virus infection, E2 became enriched in localized patches on the PM and in filopodium-like extensions. These E2-labeled patches and extensions contained all of the viral structural proteins. Correlative light and electron microscopy studies established that the patches and extensions colocalized with virus budding structures, while light microscopy showed that they excluded a freely diffusing PM marker protein. Exclusion required the interaction of the E2 protein with the capsid protein, a critical step in virus budding, and was associated with the immobilization of the envelope proteins on the cell surface. Virus infection induced two distinct types of extensions: tubulin-negative extensions that were ∼2 to 4 µm in length and excluded the PM marker, and tubulin-positive extensions that were >10 µm long, contained the PM marker, and could transfer virus particles to noninfected cells. Tubulin-positive extensions were selectively reduced in cells infected with a nonbudding SINV mutant. Together, our data support a model in which alphavirus infection induces reorganization of the PM and cytoskeleton, leading to virus budding from specialized sites. IMPORTANCE: Alphaviruses are important and widely distributed human pathogens for which vaccines and antiviral therapies are urgently needed. These small highly organized viruses bud from the host cell PM. Virus assembly and budding are critical but little understood steps in the alphavirus life cycle. We developed alphaviruses with fluorescent protein tags on one of the viral membrane (envelope) proteins and used a variety of microscopy techniques to follow the envelope protein and a host cell PM protein during budding. We showed that alphavirus infection induced the formation of patches and extensions on the PM where the envelope proteins accumulate. These sites excluded other PM proteins and correlated with virus budding structures. Exclusion of PM proteins required specific interactions of the viral envelope proteins with the internal capsid protein. Together, our data indicate that alphaviruses extensively reorganize the cell surface and cytoskeleton to promote their assembly and budding.

[Treatment results for different categories of vaginal intraepithelial neoplasia with electrocoagulation, 5-fluorouracil and combined treatment]. / Resultados del tratamiento con esferolisis, 5 fluorouracilo y mixto de pacientes con diferentes categorías de neoplasia intraepitelial vaginal.

BACKGROUND: Vaginal intraepithelial neoplasia (VAIN) represents a variety of changes that initiate as an intraepithelial squamous lesion with the possibility of resulting in cancer. OBJECTIVE: To compare the results of the treatment for the different categories of VAIN with electrocoagulation, 5-fluorouracil and combined treatment. MATERIALS AND METHODS: Observational an analytical study. We stablished groups according to the category of VAIN evaluating and comparing remission, persistence, recurrence, or progression of the disease ac- cording to the received treatment, with a 1-year follow up. The results were compared by chi2 and Kruskal Wallis. The statistics analysis was done with the SPSS program version 20. RESULTS: One hundred thirty seven patients between 20 and 81 years of age (mean age: 52.49 years) were included. Seventy-four percent of the patients had a history of premalignant or malignant cervical lesions. Seventy-four patients had VAIN I, 34 patients had VAIN II, 22 patients had VAIN III and there were seven cases of vaginal carcinoma in situ. Fifty-eight patients were treated with electrocoagulation, 55 patients were treated with 5-FU, 16 patients had combined treatment, and eight patients received expectant management. Sixty three percent of patients had total remission of the lesion, 34% had persistence and 3% showed progression, and there were no cases of recurrence. Results were better in patients with VAIN I treated with 5-FU (bigger percentage of remission P .026), for the remaining categories of VAIN, no treatment showed superior results. CONCLUSIONS: The superior response occurs in patients with VAIN I treated with 5-FU. None of the treatments achieves a 100% remission. The VAIN frequency is high, patients with a history of malignant or premalignant cervical pathology should undergo a closer surveillance through cytocolposcopic control with respect to the remaining population.

[Contraception in women with chronic diseases]. / Anticoncepción en mujeres con enfermedades crónicas.

BACKGROUND: Almost 10% of women in reproductive age had a chronic disease, and contraception is frequently ignored by these patients. The lack of use of contraceptives methods has a higher repercussion in these patients; if pregnant, the risk is increased in morbidity and feto-maternal mortality. OBJECTIVES: to know the contraceptive coverage in women with chronic degenerative diseases, the kind of contraceptive methods and the unsatisfied demand. MATERIAL AND METHODS: A descriptive study was made with the application of a survey from the one elaborated by the IMSS. It explores contraception socio-demographic data, causes of non-protection and also explores Medical Doctor (MD) participation. Sample size was calculated in 385 women in reproductive age with a chronic disease. RESULTS: 428 women about 30-49 years old were interviewed, 53% of them were married, they had various diseases, the contraceptive coverage was 84%. The definitive methods were the most used with 47%, followed by the condom with 20%, intrauterine device with 13% and others in minor proportion. 38.5% of patients with sexual life have risk of pregnancy for lack of use of method or for using one of low effectiveness and continuity. Of 45 (16%) patients with sexual life that did not use methods, 29% because they wish pregnancy, 18% by collateral effects and the rest for other causes. From this same patients 21 wished getting pregnant and 24 did not, this is an unsatisfied demand of 53%. The MD's informed about risks in case of pregnancy of 83.4% of the patients. CONCLUSIONS: The contraceptive coverage is low and the unsatisfied demand is higher than in the general population. It requires the effective participation of health personal in this group of high reproductive risk.

Gastric adenocarcinoma in the context of X-linked agammaglobulinemia: case report and review of the literature.

The hallmarks of X-linked Agammaglobulinemia (XLA) are panhypogammaglobulinemia, absent B-cells, and recurrent sinopulmonary and gastrointestinal infections starting at an early age, as well as other infections like cellulitis, meningitis, arthritis and sepsis. A number of non-infectious complications have been reported in these patients, including autoimmune diseases and malignancy, especially lymphomas. Here, we report the case of a 30-year old man who developed gastric adenocarcinoma in the context of XLA. Previous reports of, and hypotheses addressing the development of cancer in patients with XLA, are also summarized. Solid cancer in XLA affects mainly the gastrointestinal tract and seems to be related to chronic infection. A natural evolution can be traced back from gastric adenocarcinoma to megaloblastic anemia due to achlorhydria in the context of chronic infection; periodic endoscopy thus seems justified to detect and treat carcinoma in early stages.

[Frequency factor Her-2/neu overexpression in patients with breast cancer]. / Frecuencia de sobrexpresión del factor Her-2/neu en pacientes con cáncer de mama.

BACKGROUND: Her-2/neu is an oncogen related with a poor prognosis and high agresivity when overexpressed in breast cancer. Main objective was analyze the frecuency of positivity or negativity ofller/neu in patients with breast cancer after surgery and their relationship with hormone receptors. We perfomed a longitudinal, retrospective, descriptive and observational trial in all patients included in the Patology Service with a determination of Her-2/neu and hormone receptors analysis, between January 1st 2007 and December 31 st 2009.We used descriptive stadistic and association tests with correlation coefficients. We analyze 893 patients. The age range was between 24 and 94 years. The 16.% of all cases overexpressed Her-2/neu (150 patients). The 4.8% (43 patients) were included in the FISII test resulting in 29 positives to Her-2/neu. There were a total of 179 cases overexpressed. Negative estrogen receptores cases were 23%, negative progesterone receptores cases were 28% and triple negative receptors cases were 19%. We analyzed independient variables with Student I resulting age with P = 0.294. We analyzed distribution variables with Pearson test resulting in negative estrogen receptors with a P = 0.0001 negative progesterone receptres with a P = 0.0001 and triple negative receptors P= 0.0001. Relationship between hormone receptors and Her-2/neu in proporlionaly inverse in other vvords when a high hormone receptors negativitvis present there is algo a Her-2/neu highly overexpressed.

S-layer proteins of Lactobacillus acidophilus inhibits JUNV infection.

It has been previously described that S-layer binds to the C-type lectin DC-specific ICAM-3-grabbing nonintegrin (DC-SIGN, CD209). It was also shown that DC-SIGN is a cell-surface adhesion factor that enhances viral entry of several virus families. Among those, Junin virus (JUNV) entry is enhanced in cells expressing DC-SIGN and for that reason surface-layer protein (S-layer) of Lactobacillus acidophilus ATCC 4365 was evaluated as a possible JUNV inhibitor. Experiments using 3T3 cells stably expressing DC-SIGN, showed an almost complete inhibition of JUNV infection when they were treated with S-layer in a similar extend as the inhibition shown by mannan. However no inhibition effect was observed in 3T3 wild type cells or in 3T3 cells expressing liver/lymph node-specific ICAM-3 grabbing nonintegrin (L-SIGN or DC-SIGNR or CD209L). Treatments with S-layer during different times in the infection demonstrated that inhibition was only observed when S-layer was presented in early stages of the viral infection. This inhibition does not involve the classic recognition of mannose by this C-type lectin as the S-layer showed no evidence to be glycosylated. In fact, the highly basic nature of the S-layer (pI>9.5) seems to be involved in electrostatic interactions between DC-SIGN and S-layer, since high pH abolished the inhibitory effect on infection cause by the S-layer. In silico analysis predicts a Ca(2+)-dependant carbohydrate recognition domain in the SlpA protein. This novel characteristic of the S-layer, a GRAS status protein, contribute to the pathogen exclusion reported for this probiotic strain and may be applied as an antiviral agent to inhibit several kinds of viruses.

Gene Editing Technologies to Target HBV cccDNA.

Hepatitis B virus (HBV) remains a significant cause of mortality and morbidity worldwide, since chronic HBV infection is associated with elevated risk of cirrhosis and hepatocellular carcinoma. Current licensed therapies against HBV efficiently suppress viral replication; however, they do not have significant effects on the intrahepatic covalently closed circular DNA (cccDNA) of the viral minichromosome responsible for viral persistence. Thus, life-long treatment is required to avoid viral rebound. There is a significant need for novel therapies that can reduce, silence or eradicate cccDNA, thus preventing HBV reemergence after treatment withdrawal. In this review, we discuss the latest developments and applications of gene editing and related approaches for directly targeting HBV DNA and, more specifically, cccDNA in infected hepatocytes.

CRISPR-Cas9 Targeting of Hepatitis B Virus Covalently Closed Circular DNA Generates Transcriptionally Active Episomal Variants.

Chronic hepatitis B virus (HBV) infection persists due to the lack of therapies that effectively target the HBV covalently closed circular DNA (cccDNA). We used HBV-specific guide RNAs (gRNAs) and CRISPR-Cas9 and determined the fate of cccDNA after gene editing. We set up a ribonucleoprotein (RNP) delivery system in HBV-infected HepG2-NTCP cells. HBV parameters after Cas9 editing were analyzed. Southern blot (SB) analysis and DNA/RNA sequencing (DNA/RNA-seq) were performed to determine the consequences of cccDNA editing and transcriptional activity of mutated cccDNA. Treatment of infected cells with HBV-specific gRNAs showed that CRISPR-Cas9 can efficiently affect HBV replication. The appearance of episomal HBV DNA variants after dual gRNA treatment was observed by PCR, SB analysis, and DNA/RNA-seq. These transcriptionally active variants are the products of simultaneous Cas9-induced double-strand breaks in two target sites, followed by repair and religation of both short and long fragments. Following suppression of HBV DNA replicative intermediates by nucleoside analogs, mutations and formation of smaller transcriptionally active HBV variants were still observed, suggesting that established cccDNA is accessible to CRISPR-Cas9 editing. Targeting HBV DNA with CRISPR-Cas9 leads to cleavage followed by appearance of episomal HBV DNA variants. Effects induced by Cas9 were sustainable after RNP degradation/loss of detection, suggesting permanent changes in the HBV genome instead of transient effects due to transcriptional interference. IMPORTANCE Hepatitis B virus infection can develop into chronic infection, cirrhosis, and hepatocellular carcinoma. Treatment of chronic hepatitis B requires novel approaches to directly target the viral minichromosome, which is responsible for the persistence of the disease. Designer nuclease approaches represent a promising strategy to treat chronic infectious diseases; however, comprehensive knowledge about the fate of the HBV minichromosome is needed before this potent tool can be used as a potential therapeutic approach. This study provides an in-depth analysis of CRISPR-Cas9 targeting of HBV minichromosome.

Transcriptional and Translational Dynamics of Zika and Dengue Virus Infection.

Zika virus (ZIKV) and dengue virus (DENV) are members of the Flaviviridae family of RNA viruses and cause severe disease in humans. ZIKV and DENV share over 90% of their genome sequences, however, the clinical features of Zika and dengue infections are very different reflecting tropism and cellular effects. Here, we used simultaneous RNA sequencing and ribosome footprinting to define the transcriptional and translational dynamics of ZIKV and DENV infection in human neuronal progenitor cells (hNPCs). The gene expression data showed induction of aminoacyl tRNA synthetases (ARS) and the translation activating PIM1 kinase, indicating an increase in RNA translation capacity. The data also reveal activation of different cell stress responses, with ZIKV triggering a BACH1/2 redox program, and DENV activating the ATF/CHOP endoplasmic reticulum (ER) stress program. The RNA translation data highlight activation of polyamine metabolism through changes in key enzymes and their regulators. This pathway is needed for eIF5A hypusination and has been implicated in viral translation and replication. Concerning the viral RNA genomes, ribosome occupancy readily identified highly translated open reading frames and a novel upstream ORF (uORF) in the DENV genome. Together, our data highlight both the cellular stress response and the activation of RNA translation and polyamine metabolism during DENV and ZIKV infection.

Trachelomonas (Euglenophyta) from a eutrophic reservoir in Central Mexico.

This study provides valuable information on the ultrastructure and environmental conditions of the Trachelomonas Ehr. (Euglenophyceae) genus in the Guadalupe Dam, a eutrophic reservoir located in the suburbs of Mexico City, which receives a considerable volume of wastewaters. Specimens were collected at surface level between November 2005 and May 2006. Using LM and SEM twelve taxa from phytoplankton were identified of which, 9 are new records for Mexico. The reservoir is warm monomictic, with basic pH values (7.4-10.1), a high concentration of chlorophyll a(18-101 microg l(-1), a permanent anoxic bottom, specific conductivity (K25) of 205 to 290 microS cm(-1), N-NO3, 0.19-1.2 mg l(-1) and P-PO4 0.22-1.6 mg l(-1). Water temperature was 15.6-23.0 degrees C. Most of the Trachelomonas species were found during the dry season, when concentrations of organic matter, nitrogen and phosphorus as well as the temperature were the highest. Higher species richness was also associated with the warmer months. This research contributes to increase our knowledge on Trachelomonas in Mexico and constitutes the first detailed description of lorica ultrastructure of 12 taxa that grow in a body of water with high concentration of nutrients and a moderate amount of mineral contents.

Temporal variation of phytoplankton from the tropical reservoir Valle de Bravo, Mexico.

Valle de Bravo reservoir is used for aquatic, fishing and as a source of drinking water to Mexico City. Annual data on composition, abundances, species richness and diversity of the phytoplankton surface community and some physical-chemical parameters variations were discussed. Results showed a spatial homogeneity for environmental descriptors and phytoplankton samples but a temporal significant difference between months. Pulses of high algal densities corresponded to late stratification (October, 103 x 10(3) cell ml(-1)), early stratification (April, 107 x 10(3) cell ml(-1)) and plenty stratification (June, 69 x 10(3) cell ml(-1)). Taxa that reached higher densities were: Microcystis spp., Snowella septentrionalis, Anabaena spp., Aphanizomenon yezoense and Fragilaria crotonensis. Contribution of each taxon to the total phytoplankton density showed that majorities were rare (41%) or dominants (40%). Frequent alternation between pulses and low densities and diversity of phytoplankton as well as a relative high number of taxa found (68), could be explained by daily strong winds, unstable epilimnion thickness and incorporation and extraction of substantial volumes of water occurred in the reservoir. Dominances of cyanobacteria and some chlorococcal species and a high temporal fluctuated Shannon-Wiener diversity index (0.45- 2.35 bits) pointing to eutrophic and perturbed conditions.