First report of Phytopythium vexans causing the “Avocado sadness” in Michoacan,Mexico

Mexico is the main producer, consumer and exporter of avocado in the world, being Michoacan the main producer state contributing more than 80% of the national production. There are phytopathogens that decimate the production causing the death of the tree. Root samples were collected in avocado trees that showed the characteristic symptomatology of the disease known as avocado sadness, the sampling was carried out in four of the main avocado producing towns, in the state of Michoacan, Mexico. The isolation consisted in sowing root tissue in Petri dishes with V8^®-PARPH culture medium, subsequently they were identified morphologically and for species level it was determined by molecular biology, with the PCR-ITS technique. Pathogenicity tests were performed in triplicate with avocado seedlings with more than six leaves. After 24 hours, the inoculated plants expressed decay in the apical part, after 120 hours the leaves showed yellowing and after 15 days there was a generalized wilt on the stem and leaves, re-isolating the phytopathogen Phytopythium vexans. This study confirms the first report of the oomycete P. vexans affecting avocado trees in the most important producing region of the Mexican Republic.     

Regulation of cellular adhesion molecule expression in murine oocytes, peri-implant ation and post-implantation embryos

Expression of the adhesion molecules, ICAM-1, VCAM-1, NCAM, CD44, CD49d (VLA-4, a chain), and CDlla (LFA-1, a chain) on mouse oocytes, and pre- and peri-implantation stage embryos was examined by quantitative indirect immunofluorescence microscopy. ICAM-1 was most strongly expressed at the oocyte stage, gradually declining almost to undetectable levels by the expanded blastocyst stage. NCAM, also expressed maximally on the oocyte, declined to undetectable levels beyond the morula stage. On the other hand, CD44 declined from highest expression at the oocyte stage to show a second maximum at the compacted 8-cell/morula. This molecule exhibited high expression around contact areas between trophecto-derm and zona pellucida during blastocyst hatching. CD49d was highly expressed in the oocyte, remained significantly expressed throughout and after blastocyst hatching was expressed on the polar trophecto-derm. Like CD44, CD49d declined to undetectable levels at the blastocyst outgrowth stage. Expression of both     

Microsatellite allele frequencies in humans and chimpanzees, with implications for constraints on allele size

The distributions of allele sizes at eight simple-sequence repeat (SSR) or microsatellite loci in chimpanzees are found and compared with the distributions previously obtained from several human populations. At several loci, the differences in average allele size between chimpanzees and humans are sufficiently small that there might be a constraint on the evolution of average allele size. Furthermore, a model that allows for a bias in the mutation process shows that for some loci a weak bias can account for the observations. Several alleles at one of the loci (Mfd 59) were sequenced. Differences between alleles of different lengths were found to be more complex than previously assumed. An 8-base-pair deletion was present in the nonvariable region of the chimpanzee locus. This locus contains a previously unrecognized repeated region, which is imperfect in humans and perfect in chimpanzees. The apparently greater opportunity for mutation conferred by the two perfect repeat regions in chimpanzees is reflected in the higher variance in repeat number at Mfd 59 in chimpanzees than in humans. These data indicate that interspecific differences in allele length are not always attributable to simple changes in the number of repeats.      

The immortalization of thymic nurse cells by SV40 virus

Thymic nurse cells (TNCs) are stromal elements that contain between 20 and 200 T cells within their cytoplasm. Because of this unique feature they are believed to play a role in thymocyte development. Unfortunately, it has been difficult to obtain pure TNCs in quantities sufficient for extensive evaluation of their thymic function. As a result, only a limited amount of information is available that characterizes TNCs or the T cell population(s) found within their cytoplasm. We have now used SV40 to infect and immortalize TNCs from C57BL/6 mice. SV40-transformed TNCs were found to specifically bind and internalize cells from an immature thymocyte line isolated in our laboratory. These results describe a method of obtaining pure populations of TNCs for future studies of their thymic function, and suggest that binding to specific subpopulations of lymphoblasts may be necessary for internalization.     

Fucosylated protein of retinal cone photoreceptor outer segments: morphological and biochemical analyses

Cone outer segments (OS) of the goldfish retina are diffusely labeled after intravitreal injection of [(3)H]fucose while rod OS remain unlabeled. By electron microscopic radioautography, the OS of red- and blue-sensitive cones are heavily labeled while green- sensitive cone OS are lightly labeled. The time-course and pattern of OS labeling in all cone types from 30 min to 24 h resemble that of incorporation of other sugars into rhodopsin in rod OS. The nature of the cone OS-specific fucosylated component(s) was examined using biochemical techniques. Cone OS were prelabeled by intravitreal injection of [(3)H]fucose 24 h before sacrifice. Photoreceptor OS were isolated using a discontinuous sucrose density gradient and it was verified by electron microscopic radioautography that the only source of radioactivity in the preparations was cone OS. The different cone types could be recognized by the heaviness of labeling, characteristic membrane spacing, and 'staining' of green cone OS in vitro with horseradish peroxidase. After acid hydrolysis of prelabeled photoreceptor membranes, 90 percent of the counts were in the neutral sugar fraction which was analyzed by thin-layer chromatography. Approximately 70 percent of the radioactivity co-chromatographed with authentic fucose. SDS-PAGE/fluorography of prelabeled photoreceptor membranes revealed a single radioactive component that was lightly stained with coomassie blue and showed an apparent molecular weight of 33,000. This cone-derived band was separated from unlabeled rod opsin which was well stained and showed an apparent mol wt of 38,000. Isoelectric focusing under denaturing conditions produced two major and one minor band of radioactivity with isoelectric points of 8.2, 8.6, and 8.8 respectively. No radioactivity was found in association with a stained band corresponding in isoelectric point to that of bovine opsin (pl, 6.2). The fucosylated component was readily digested by pronase, indicating its protein nature. Washing of the isolated OS with isotonic and hypotonic buffers failed to extract major amounts of the radioactivity, suggesting that the fucosylated component is an integral membrane protein. The presence of a fucosylated protein thus represents a major difference between cone and rod OS in the goldfish and has enabled us to identify cone OS in preparations of isolated photoreceptor membranes and to demonstrate the separation of a cone-derived glycoprotein from rod opsin.     

A strain of Fujinami sarcoma virus which is temperature-sensitive in protein phosphorylation and cellular transformation

Cells infected by one strain of Fujinami sarcoma virus (FSV) are transformed at 38 degrees C but are phenotypically normal at 41.5 degrees C. FSV encodes a 140,000 molecular weight protein (P140) with gag gene-related and FSV-specific peptide sequences. At 41.5 degrees C, P140 is weakly phosphorylated at serine residues, and is inactive in the immune complex protein kinase assay. At 38 degrees C, P140 is highly phosphorylated, contains phosphotyrosine in addition to phosphoserine, and in the immune complex kinase assay becomes phosphorylated at three tyrosine residues. Phosphorylation of cellular polypeptides at tyrosine residues in FSV-infected cells is also temperature-sensitive. These observations indicate that P140 is the transforming protein of FSV and that protein phosphorylation at tyrosine residues is involved in transformation by this virus.