Biomedical Engineering Reference
In-Depth Information
the hypothesis that the yeast apoptotic response is often dependent upon
Yca1p. Other studies however do not support such a hypothesis (Fahrenkrog
et al. 2004, Wysocki and Kron 2004, Maeta et al. 2005, Hauptmann et al.
2006). We can conclude from these studies that the metacaspase gene is
important, but is not the exclusive mechanism for the stimulation of PCD
in response to toxic stimuli.
Researchers Mousavi and Robson, 2004 found that factors such as
oxidative and amphotericin B-mediated stress were capable of inducing
apoptotic changes in
A. fumigatus
, without the induction of caspase-like
activity. These fi ndings would suggest the application of metacaspases in
biotechnological roles may not be as well-defi ned as necessary.
A study by Richie and coworkers, 2007 describes a metacaspase-defi cient
mutant
A. fumigatus
. The study reported that wild type
A. fumigatus
cultures
were associated with the appearance of typical markers of apoptosis such as
phosphatidylserine exposure on the outer leafl et of the membrane, elevated
proteolytic activity against caspase substrates and loss of viability but the
mutant strains of
A. fumigatus
were not associated with phosphatidylserine
exposure characteristic of apoptosis. The same study also reported that
caspase activity and cell viability were undistinguishable from the wild
type strain. Nevertheless, before the importance of the role of metacaspases
in the apoptotic process in
A. fumigatus
is dismissed other aspects should
be considered. The report by Richie and colleagues, 2007 remarks that the
possibility that a condition that would trigger a metacaspase-dependent
oxidative death response in
A. fumigatus
was not identifi ed. Alternatively,
A. fumigatus
may differ from yeast by the presence of redundant pathways
of PCD that can replace the metacaspases, analogous to what has been
described in higher eukaryotes (Broker et al. 2005, Kroemer and Martin
2005).
Fungal Metacaspase pathways; Applications as a Study Model
It has been noted by many of the scientists mentioned in this chapter,
that fungal pathways where metacaspase activity is in play seem to be
more complex than previously predicted, established on the presence of
the single metacaspase gene Yca1p present in the genome
Saccharomyces
cerevisiae
.
A study in 2010 by Mousavi and Robson is just one example that
supports the hypothesis that the more complex apoptotic process in
A.
fumigatus
compared with yeast may highlight the importance of using
fi lamentous fungi as a study model for more complex apoptotic pathways
which may elucidate fully the role of metacaspases. In this study the
translated amino acid sequence for
YCA1
, was used to perform a blast
