The PCR technique and highly degenerate oligonucleotide primers were used to amplify a 282 bp fragment of the horse (Equus caballus) epidermal growth factor (EGF) cDNA. The clone corresponded to 94 amino acids of the EGF precursor molecule. The deduced amino acid sequence of the 53 residue EGF mitogenic peptide within the precursor sequence showed 60-70% identity with five other published EGF sequences. The PCR cDNA fragment hybridized to a 4.9 kb transcript in horse kidney and endometrial RNA which was of a similar size to the mature EGF transcript found in other mammalian species. The horse cDNA clone was used in Northern blots to monitor EGF expression in the endometrium of pregnant mares up to day 83 of gestation (term = 330-340 days). The level of expression increased from day 33 and showed a further dramatic increase between days 35 and 45, which coincides with the onset of implantation and placentation in this species. Levels remained elevated up to day 83. The horse DNA sequence was used to design sense and antisense oligonucleotide probes (45-mers) for in situ hybridization studies. The antisense probe showed specific hybridization to the glandular, but not lumenal, epithelial cells of the endometrium and there was no signal in fetal membranes. The in situ hybridization signal increased between days 35 and 45 to a similar degree to that observed in the Northern blot analysis. This dramatic increase in EGF expression in the glandular epithelium of the mare's endometrium during pregnancy may provide a mitogenic stimulus to the endometrium and/or trophoblast to facilitate placental differentiation and attachment. Alternatively, the precursor could be involved in the endometrial gland secretory process which is necessary to produce uterine milk for fetal sustenance. The PCR cloning methods used in this study should be generally applicable to the cloning of EGF cDNAs from other species.
Caspase 3 activation has been implicated in cell death following a number of neurodegenerative insults. To determine whether caspase genes can affect the susceptibility of cells to neurodegeneration, a transgenic mouse line was created, expressing human caspase 3 under control of its own promoter. The human gene was regulated by the murine homeostatic machinery and human procaspase 3 was expressed in the same tissues as mouse caspase 3. These novel transgenic mice appeared phenotypically and developmentally normal and survived in excess of 2 years. Behavioural assessment using the 5-choice serial reaction time task found no differences from wild-type littermates. Caspase activity was found to be tightly regulated under physiological conditions, however, significantly larger lesions were obtained when transgenic mice were subjected to focal cerebral ischaemia/reperfusion injury compared to wildtype littermates. These data demonstrate that mice overexpressing human caspase 3 are essentially normal, however, they have increased susceptibility to degenerative insults.
The regulation of human cytomegalovirus (hCMV) and human immunodeficiency virus (HIV) gene expression has been studied in single intact mammalian cells. Viral promoters were placed upstream of the firefly luciferase reporter gene and the resulting hybrid reporter constructs were stably integrated into the HeLa cell genome. A highly sensitive photon-counting camera system was used to study the level of gene expression in single intact cells. Luciferase expression was studied in the absence of activators of viral gene expression, in the presence of the HIV-1 TAT transactivator protein, or in the presence of sodium butyrate, a non-viral activator of gene expression. In the absence of any activator of gene expression, while expression was undetectable in most cells, significant levels of basal luciferase activity were observed in a few cells, indicating heterogeneity in gene expression in the cell population. In the presence of the general activator of viral gene expression, sodium butyrate, transcriptional activation from the viral promoters gave rise to significant and relatively homogeneous levels of luciferase expression in a majority of cells. The luciferase imaging technology was used for the real-time analysis of changes of gene expression within a single cell. This non-invasive reporter assay should become important for studies of the temporal regulation of gene expression in single cells.
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