Crippled Growth occurs only on media containing
high amounts of Yeast Extract. It does not promote death but serious health
impairment. Crippled Growth sectors appear
spontaneously during growth as depicted in the animation, which
recapitulates the evolution of a culture during one week.
Comparison of the Normal and
Crippled Growth of the filamentous fungus Podospora anserina (AS6-5
We have identified several genes
involved either in the development of Crippled Growth (their mutation
prevent the development of the growth alteration: genes IDC), or on the
contrary genes that facilitate the development of Crippled Growth (their
mutations permit the development of
the growth alteration on medium lacking yeast extract: genes PDC).
The cloning of some IDC genes revealed that they code for proteins implied in
the transduction of the signal from the outside of the cell towards the
interior. The pathway contains a MAP kinase module (PaASK1, PaMKK1 et
PaMpk1) as well as a NADPH oxidase (PaNox1). This data enabled us to
formulate a hypothesis as for the nature of the infectious element.
cascade could present two states on and off. The off state would be the
normal state of the cells in growth and the on state that of the cells in
stationary phase. Normally, during the resumption of growth the cascade
must be inactivated. That would not be the case on yeast extract
containing medium. A loop of positive self-regulation would make it
possible to sustain the activation of the cascade during growth. Such a
phenomenon of sustained activity is called hysteresis and could be a
phenomenon present in several signalling pathways. The transmission of
the two states on and off would be done then in a faithful way during
cellular divisions, the active state involving an altered growth.
We have also identified some PDC genes. They code for proteins involved in cytosolic
translation and the PDC mutations trigger an increase in translation
accuracy! We are currently investigation this unexpected relationship
between translation fidelity and signal transduction.