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Cytoplasmic epigenetics: inheritance by cytoplasmic continuity
A selection of talks on Biochemistry
The ERK1/2 MAPK cascade
- Prof. Melanie H. Cobb
- University of Texas Southwestern Medical Center at Dallas, USA
Amino acid conjugation: mechanism and enzymology
- Dr. Kathleen Knights
- Flinders University, Australia
Phillipe Silar and Fabienne Malagnac of University of Paris 7 will present a talk on cytoplasmic epigenetic, and will mostly focus on inheritance by cytoplasmic continuity.
It was demonstrated about 50 years ago, that DNA is the major carrier of information that pass from mother to daughter cells. This DNA-based information accounts for the classical Mendelian inheritance, but also for the cytoplasmic inheritance brought about by DNA contained within mitochondria and plasmids, but also by viruses and other infectious factors present within the cytoplasms. However, at about the same time, several examples of non-DNA based inheritance were postulated and later on discovered. Two broad classes of such phenomena were made: structural inheritance, whereby your preexisting structure is necessary for the correct folding of a newly formed one and regulatory inheritance in which the state of a metabolic or regulatory network, directs the status of the same network in the daughter cells. The hallmarks of this inheritance are that the characters are frequently unstable, and may switch spontaneously and with high frequency between several so-called states, and that this inheritance is achieved by cellular continuity. This means that when extracted from the cell, this information loses its coding capacity. As we shall see, these are general properties of this phenomena, but may not be fulfilled in all cases.
We will now explore several examples of structural inheritance. We shall first start with cortical inheritance in paramecium, which was the first example of such phenomenon and was described in 1965 by Beisson and Sonneborn. Wild-type paramecium exhibit the characteristic swimming behavior. Beisson and Sonneborn describe a twisty mutant, with an exaggerated twisty swimming behavior, that can easily be seen under the binocular. They could trace back the abnormal swimming back to the structure of the cilia. In wild-type paramecium, cilia are arranged in rows and can be in a mutant form to some structure at the birth of the cilium, here depicted in red. They showed that this twisty mutant exhibited some inverted rows of cilia which would not beat in the correct orientation, hence the abnormal swimming. Interestingly, the cilia are not found in a row but are precisely inserted and oriented with respect to pre-existent cilias. In wild-type, this ensures correct growth of the cell before division. In mutant, this permits the abnormal orientation to be copied. In the long-term, thanks to this property,