PhD defense by Anne Alsing – Niels Bohr Institutet - Københavns Universitet

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PhD defense by Anne Alsing

Models of Epigenetics. Bi- and multi-stability in biological systems

It is becoming increasingly clear that differences in DNA sequence can not be the sole carrier of the phenotypic differentiation that arises when a cell expresses different genes to different degrees.


A simple example, such as the cells of the human body, clearly shows that cells carrying the same genomic material can show diverse phenotypes characterized by organ specific gene expression patterns.


The mechanisms responsible for this phenotypic plasticity are characterized as epigenetic, as they inflict their effect ``epi-'' (Greek for ``above'' or ``on top'') of the genetic code. For a gene regulatory mechanism to be classified as epigenetic, it is required that it is self-sustainable. That is, the governed gene expression or repression should prevail for the lifetime of the cell and must be inherited by possible daughter cells.


In this thesis two different mechanisms of such epigenetic choices are examined; The bi-stable switch of temperate phage TP901-1 and the mutual exclusive expression among olfactory receptor genes in the olfactory sensory cells of mammals.