Biomedical subjects
Publications and source records attributed to J Gerritsma.
A problem-based learning programme for tuberculosis and leprosy supervisors is reported from Nigeria. It proved stimulating, motivating and enjoyable, and encouraged independent learning. The quality of their subsequent field work was average to good and showed sustained motivation.
We studied the regulation of the expression of the human c-sis/PDGF-B gene in the following panel of cell lines: K562 cells, in which expression is inducible by phorbol esters; cytotrophoblast-derived cell lines JEG-3 and JAR; carcinoma-derived cell lines PC3, T24 and HeLa, which show extensive differences in c-sis mRNA content; dermal fibroblasts, which do not express the gene. We demonstrate that the wide variety of levels of c-sis mRNA in these cells is mainly determined at the transcription level. Extensive gene rearrangements or amplifications, or significant differences in the stability of the c-sis transcript could not be found. In fibroblasts and placenta cell lines, inaccessibility of the c-sis promoter, rather than the absence of transcription factors that activate it, inhibits expression of the endogenous gene. Examination of the chromatin structure of the transcription unit and immediate flanking regions revealed several cell-type-specific DNase-I-hypersensitivity (DH) sites. Functional analysis of genomic fragments harbouring one or more DH sites showed the presence of negative regulatory elements within intron 1, and of an activating element downstream of the gene. A DH site, located immediately downstream of the promoter in dermal fibroblasts, may regulate accessibility of the promoter by means of specific nucleosome phasing.