Differential Roles of the Chib Chitinase in Autolysis and Cell Death of Aspergillus Nidulans - Essay Example

It was ascertained in the course of the study that ChiB, a gene coding for endo Chitinase B, is in part responsible for the induction of autolysis by the flbA gene. Also though ChiB was found to be necessary for ∆flbA-induced autolysis its overexpression did not accelerate or enhance hyphal disintegration thus suggesting that ChiB is necessary but not sufficient for autolysis in submerge-cultured A.nidulans. Alamar Blue reduction test which corresponds to the activity of the living cell mitochondria was employed to assess the dispensability of the ChiB gene in autolysis. By AB reduction it was seen that both Wild Type strain and ChiB deletion ∆ChiB mutant showed the same death pattern from day 1 to day 8. Thus though ChiB was required for autolysis it was not essential.

To study the proteins involved in autolysis, the proteins upregulated in ∆flbA and ∆flbA∆ChiB were studied and five proteins were found to be upregulated. These were identified as chitinase (ChiB), dipeptidyl peptidase V (DppV), O-glycosyl compound hydrolase, -N-acetylhexosaminidase (NagA), and myo-inositol-1-phosphate synthase (InoB) on SDS PAGE after Liquid chromatography-tandem mass spectroscopy. Of these 5 proteins NagA was speculated to be associated with cell death. This was because ∆the NagA mutant showed a significantly higher percentage reduction in Alamar Blue as compared to other proteins on day 2 of incubation indicating more viable cells.

The absence of InoB or AN2395.2 (a probable hydrolase) was seen to cause accelerated cell death and disorganization of mycelial pellets suggesting that these proteins might be needed for the controlled progression of cell death. FlbA gene negatively controls G protein-mediated proliferation signaling likely by acting as GTPase activating protein for FadAGα. It was also concluded in other studies that FadA and SfaD signaling negatively regulate the cell wall chitin content and cell wall structure in A.nidulans.

FadA was also found to mediate signaling involved in the initiation of apoptosis by another study. Finally, yet another study concluded that the FadA heterotrimeric G protein complex was found to be a part of the signal transduction pathway that promotes apoptosis in hyphae exposed to chemical farnesol. Thus on the same lines, the research in this paper lead to the formulation of a working model which suggested that FadA and SfaD were constitutively activated in the absence of regulating flbA gene which resulted in accelerated autolysis and that ChiB and NagA “ play differential roles in these interconnected, yet separate biological processes” as aptly summarized in Toto from the paper. Read More