Toxoplasma gondii: determinants of tachyzoite to bradyzoite conversion

Apicomplexa are primarily obligate intracellular protozoa that have evolved complex developmental stages important for pathogenesis and transmission. Toxoplasma gondii, responsible for the disease toxoplasmosis, has the broadest host range of the Apicomplexa as it infects virtually any warm-blooded vertebrate host. Key to T. gondii’s pathogenesis is its ability to differentiate from a rapidly replicating tachyzoite stage during acute infection to a relatively non-immunogenic, dormant bradyzoite stage contained in tissue cysts. These bradyzoite cysts can reconvert back to tachyzoites years later causing serious pathology and death if a person becomes immune-compromised. Like the sexual stage sporozoites, bradyzoites are also orally infectious and a major contributor to transmission. Because of the critical role of stage conversion to pathogenesis and transmission, a major research focus is aimed at identifying molecular mediators and pathways that regulate differentiation. Tachyzoite to bradyzoite development can occur spontaneously in vitro and be induced in response to exogenous stress including but not limited to host immunity. The purpose of this review is to explore the potential contributors to stage differentiation in infection and how a determination is made by the parasite to differentiate from tachyzoites to bradyzoites.     

The degradation of cell cycle regulators by SKP2/CKS1 ubiquitin ligase is genetically controlled in rodent liver cancer and contributes to determine the susceptibility to the disease

Previous work showed a genetic control of cell cycle deregulation during hepatocarcinogenesis. We now evaluated in preneoplastic lesions, dysplastic nodules and hepatocellular carcinoma (HCC), chemically induced in genetically susceptible F344 and resistant Brown Norway (BN) rats, the role of cell cycle regulating proteins in the determination of a phenotype susceptible to HCC development. p21^WAF1, p27^KIP1, p57^KIP2 and p130 mRNA levels increased in fast growing lesions of F344 rats. Lower/no increases occurred in slowly growing lesions of BN rats. A similar behavior of RassF1A mRNA was previously found in the 2 rat strains. However, p21^WAF1, p27^KIP1, p57^KIP, p130 and RassF1A proteins exhibited no change/low increase in the lesions of F344 rats and consistent rise in dysplastic nodules and HCC of BN rats. Increase in Cks1‐Skp2 ligase and ubiquitination of cell cycle regulators occurred in F344 but not in BN rat lesions, indicating that posttranslational modifications of cell cycle regulators are under genetic control and contribute to determine a phenotype susceptible to HCC. Moreover, proliferation index of 60 human HCCs was inversely correlated with protein levels but not with mRNA levels of P21^WAF1, P27^KIP1, P57^KIP2 and P130, indicating a control of human HCC proliferation by posttranslational modifications of cell cycle regulators.     

A novel MYH7 mutation occurring independently in French and Norwegian Laing distal myopathy families and de novo in one Finnish patient

Laing early-onset distal myopathy is a rare autosomal dominant myopathy and caused by mutations in the MYH7 gene, encoding the slow beta myosin heavy chain. We report the first molecularly verified Laing distal myopathy in a French family caused by a novel p.Glu1508del mutation in the MYH7 gene. Interestingly, we identified the identical mutation in an unrelated Norwegian family and, as a de novo mutation, in one sporadic Finnish patient. Described in detail are the clinical and electrophysiological characteristics of 5 patients from the French family. The phenotype in the Finnish patient and the Norwegian patients is largely similar. This mutation causes a benign myopathy within the range of previously reported Laing myopathy phenotype variations. Onset of weakness in the tibialis anterior (TA) muscles occurred in early childhood in all patients. Finger extensor and neck flexor weakness together with Achilles tendon retractions were other frequent findings. The independent recurrence of the identical mutation without any founder background may reflect a mutational susceptibility of this residue, in accordance with some other MYH7 mutations previously reported. De novo mutations seem to be frequent in Laing distal myopathy. This is of clinical importance since a dominant family history is missing, which may confuse differential diagnostic efforts.     

Blur adaptation and myopia.

Previous studies have demonstrated a significant improvement in visual resolution during sustained periods of retinal defocus. This appears to result from perceptual adaptation designed to restore the perceived contrast of the degraded image. However, it is unclear whether perceptual adaptation to sustained blur is present in all individuals or only in certain subgroups, such as those who have been chronically exposed to sustained periods of blur due to uncorrected ametropia. Accordingly, the present study examined the effects of sustained retinal defocus on both high-and low-contrast visual acuity in emmetropes (n = 13) and myopes (n = 18). Subjects were required to view through +2.50-D spherical lenses worn over their distance refractive correction for a continuous 2-hour period. A significant improvement in both Landolt C and grating visual acuity measured through the fogging lenses was observed in both refractive groups. Although the mean change in grating visual acuity was significantly greater for the myopic subjects, the improvements in Landolt C acuity observed in the emmetropes and myopes were statistically equivalent. We hypothesize that the improvement in visual acuity results from perceptual adaptation to the blurred images, which may occur at central sites within the visual cortex.     

Background radiation and childhood leukemia: A nationwide register‐based case‐control study

High doses of ionizing radiation are an established cause of childhood leukemia. However, substantial uncertainty remains about the effect of low doses of radiation, including background radiation and potential differences between genetic subgroups of leukemia have rarely been explored. We investigated the effect of the background gamma radiation on childhood leukemia using a nationwide register‐based case‐control study. For each of the 1,093 cases, three age‐ and gender matched controls were selected (N = 3,279). Conditional logistic regression analyses were adjusted for confounding by Down syndrome, birth weight (large for gestational age), and maternal smoking. Complete residential histories and previously collected survey data of the background gamma radiation in Finland were used to assess the exposure of the study subjects to indoor and outdoor gamma radiation. Overall, background gamma radiation showed a non‐significant association with the OR of childhood leukemia (OR 1.01, 95% CI 0.97, 1.05 for 10 nSv/h increase in average equivalent dose rate to red bone marrow). In subgroup analyses, age group 2–<7 years displayed a larger effect (OR 1.27, 95% CI 1.01, 1.60 for 1 mSv increase in equivalent cumulative dose to red bone marrow). Suggestive difference in OR by genetic subtype was found. Our results provide further support to the notion that low doses of ionizing radiation increase the risk for childhood leukemia, particularly at age 2–<7 years. Our findings suggest a larger effect of radiation on leukemia with high hyperpdiploidy than other subgroups, but this result requires further confirmation.     

p73 beta-expressing recombinant adenovirus: a potential anticancer agent

Tumor suppressor p53-based gene therapy strategy is ineffective in certain conditions. p73, a p53 homologue, could be a potential alternative gene therapy agent as it has been found to be an important determinant of chemosensitivity in cancer cells. Previously, we have reported the generation of a replication-deficient adenovirus expressing p73 beta (Ad-p73). In this study, we evaluated the therapeutic potential of Ad-p73 against a panel of cancer cells (n=12) of different tissue origin. Ad-p73 infected all the cell lines tested very efficiently resulting in several-fold increase in p73 beta levels, which is also functional as it activated the known target gene p21(WAF1/CIP1). Infection with Ad-p73 resulted in potent cytotoxicity in all the cell lines tested. The mechanism of p73-induced cytotoxicity in these cell lines is found to be due to a combination of cell cycle arrest and induction of apoptosis. In addition, exogenous overexpression of p73 by Ad-p73 infection increased the chemosensitivity of cancer cells by many fold to commonly used drug adriamycin. Moreover, Ad-p73 is more efficient than Ad-p53 in enhancing the chemosensitivity of mutant p53 harboring cells. Furthermore, Ad-p73 infection did not induce apoptosis in human normal lung fibroblasts (HEL 299) and human immortalized keratinocytes (HaCaT). These results suggest that Ad-p73 is a potent cytotoxic agent specifically against cancer cells and could be developed as a cancer gene therapy agent either alone or in combination with chemotherapeutic agents.     

Histopathologic Variants of Basal Cell Carcinoma Correlation with Sex, Age and Localization

During the 6-year period (January 1, 1993 to December 31, 1998) in the Laboratory for Dermatopathology of Department of Dermatovenereology in Clinical Hospital Split, 1616 basal cell carcinomas (BCC) of a total of 323 investigated specimens were diagnosed. The incident rate varies from 92 to 114 BCC per 100,000 inhabitants in the Split region. The sex ratio in material is 1.2:1 in favor of males. The frequence of BCC increases with the advanced age in both sexes with the peak in the age group from 70 to 79 years. The most frequent location in both sexes is the nose followed by cheeks and trunk. Statistic analysis showed a significantly higher occurrence of BCC in temporal region in the males and perioral region in the females; respectively. The solid variant is the most frequent followed by superficial multicentric and solid-adenoid. Pure variants are found in 83.1% specimens, and mixed variants in 16.9%. Solid and adenoid variants are the most frequent on the nose and cheeks. According to statistics cystic variant is significantly higher on the forehead, and morpheic variant on the nose. Superficial multicentric variant is statistically more frequent on the trunk than on other locations. All specimens were reexamined and histopathologic variants were obtained. Over 2000 data are comprised which is a sufficient examination sample. In programs such as SPSS, and Graph master ver 1.12, Win95, MO'97 (Word, Excel, Access) on Pentium II 200 MHz, floppy, 64 MB RAM, HDD 2.1 GB, CD x24, HP LJet 6L, a comprehensive analysis has been performed.