Cell degeneration in the model system Podospora anserina

Podospora anserina is a filamentous fungus used in many studies of fundamen tal cell biology, including cell ageing. In this organism, ageing is define d as a diminution of cell ability to proliferate and/or differentiate. This may or may not culminate with cell death. Two different ageing processes a re intensively studied. The 'Senescence phenomenon is present in all wild-t ype strains, results in cell death and is caused by a yet undefined cytopla smic and infectious element. It is associated with extensive mitochondrial DNA modifications. Longevity of the strains is controlled by a highly compl ex network of genes. Among these, those involved in cytosolic translation a nd respiratory metabolism an of special importance. The 'Crippled Growth' p henomenon is present only in strains with elevated translational accuracy. It does not result in cell death but in a severe impairment of cell growth, an acceleration of Senescence and a diminution of differentiation potencie s. No mitochondrial DNA modification is associated with Crippled Growth. An other cytoplasmic and infectious element with peculiar properties, C, is ca usally involved in the set up of this cell degeneration. The study of P. an serina degenerative processes provides a conceptual framework to understand ageing in more complex organisms. Especially, it emphasises the complex co ntrol exerted by genes on longevity, the multiplicity of degenerative proce sses that may occur to cells with identical genotype and the potential role of non-conventional infectious elements in cell ageing.