Martin H. Johnson

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Reactive astrocytes adjacent to a forebrain stab injury were selectively ablated in adult mice expressing HSV-TK from the Gfap promoter by treatment with ganciclovir. Injured tissue that was depleted of GFAP-positive astrocytes exhibited (1) a prolonged 25-fold increase in infiltration of CD45-positive leukocytes, including ultrastructurally identified(More)
The division of single cells, isolated from an 8-cell mouse embryo, to give 2 x 1/16 cells has been studied by sampling cells for analysis at defined stages during and after the division. Cells were analyzed for evidence of polarity in their surface organization as assessed by fluorescent ligand binding and distribution of microvilli. Individual 1/8 cells(More)
To investigate the roles of astroglial cells, we targeted their ablation genetically. Transgenic mice were generated expressing herpes simplex virus thymidine kinase from the mouse glial fibrillary acidic protein (GFAP) promoter. In adult transgenic mice, 2 weeks of subcutaneous treatment with the antiviral agent ganciclovir preferentially ablated(More)
The development of the early 2-cell mouse embryo to the late 2-cell stage is marked by the appearance between 23 and 26 h post-insemination of a complex of polypeptides of mol. wt. approximately 67 K. Addition of alpha-amanitin between 18 and 21 h post-insemination prevents or reduces the subsequent appearance of these polypeptides. Addition of(More)
We describe a fluorimetric method for measuring the level of H2O2 in individual mouse oocytes and early embryos. Levels of H2O2 are low but detectable in unfertilized oocytes recovered freshly from the female reproductive tract. The levels in early cleaving embryos (1-cell to 8-cell stages) immediately after recovery from the female tract seem to be(More)
The influence of mouse oocyte chromosomes on their immediate environment has been investigated following their dispersal by dissolution of the metaphase spindle with nocodazole. Small clusters of chromosomes become redistributed around the egg cortex in a microfilament-dependent process. Each cluster has the capacity, on removal from nocodazole, to organize(More)
On fertilisation of mouse oocytes, the fusing spermatozoon triggers a series of repetitive calcium (Ca2+) spikes. The Ca2+ spikes seem to be necessary for successful progression through the cell cycle and are regulated in a cell-cycle-dependent manner. The spikes appear to require the linkage of continuous Ca2+ influx to the periodic release of Ca2+ from(More)
The development of the polarized surface binding of the fluoresceinated ligand concanavalin A (FITC-Con A) was studied in blastomeres of the early mouse embryo. Single 8-cell blastomeres, natural 8-cell couplets derived from the in vitro division of individual 4-cell blastomeres, and reagregated couplets made from dissociated 8-cells were cultured for(More)
The distal portion of mouse chromosome 12 is imprinted. To date, however, Gtl2 is the only imprinted gene identified on chromosome 12. Gtl2 encodes multiple alternatively spliced transcripts with no apparent open reading frame. Using conceptuses with maternal or paternal uniparental disomy for chromosome 12 (UPD12), we found that Gtl2 is expressed from the(More)
The effect on the microtubule system of human oocytes of cooling to room temperature for either 10 or 30 minutes has been investigated. Changes in spindle organization were found in all oocytes cooled for 30 minutes compared with control oocytes kept at 37 degrees C throughout. These changes included reduction in spindle size, disorganization of(More)