Biomedical Engineering Reference
In-Depth Information
FIGURE 14.5
Schematic representations of three chemical genetics approaches. White
rectangles represent functional genes; black rectangles represent deleted genes. “Fitness”
refers to the growth rate of the deletant strain with respect to the wild-type strain. The black
star represents the active chemical compound.
dhMotC target in yeast, whose inhibition induces a decrease in ceramide levels. The
dhMotC effect on the ceramide cell content was also confirmed on human cells, thus
demonstrating that the drug way of action hypothesized in the yeast system can be
translated to higher eukaryotic cells. The use of the growth rate as a measure of the
effects of a compound is based on a considerable assumption: The phenotypic effect
of the compound tested has to be the variation in wild-type cells' growth rate. Thus,
this quantification is useful when the mode of action of anticancer or antifungal drugs
must be investigated. Nevertheless, the cell-based screening procedure proposed by
Baetz et al. can be adapted to screen numerous drug-induced phenotypes other than
growth rate variation, such as the activation of signaling pathways and of transcription
when an optically measurable reporter effect is modulated.
14.2.1.2 Homozygous Profiling
In contrast to haploinsufficiency profiling,
homozygous profiling (HOP) is based on deletion of the complete set of the gene.
In the HOP approach, yeast strains are used in a homozygote (diploid) or haploid
context (Figure 14.5). In the first case, both gene copies are deleted; in the latter, the
unique gene copy present is deleted. This approach is based on the idea that when the
target of a cytotoxic molecule is lacking (because of complete deletion of the gene
coding it), the yeast cell is not affected by the treatment. As is easily predictable,
only the effects on genes that are not essential for cell survival can be investigated
using this method. This limitation forbids the identification of entities whose target-
ing by a molecule induces cell death, thus resulting in a considerable restriction in
