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Hello. My name is Vincenzo Pirrotta,
and this talk is an introduction to Polycomb Epigenetic Mechanisms.
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So, a few basic concepts first.
Chromatin silence.
During development, certain genes may be turned off in a durable,
and long-lasting way that is transmitted to the progeny of the cells.
They may respond differently to activators,
depending on the previous history of the cell.
In other words, certain gene expression patterns
are affected by a sort of memory of earlier events.
Such heritable changes are epigenetic, that is,
they are transmitted to daughter cells,
but they do not entail mutations,
or changes in the DNA sequence itself.
They involve instead, changes or modifications in the proteins that make up,
or organize the chromatin.
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Polycomb complexes are multi protein structures
that organize and modify the structure of chromatin,
and reduce the transcriptional potential of genes in an epigenetic fashion.
The genes and proteins of the Polycomb group are
often referred to as PcG proteins, or genes.
They were first discovered in the fruitfly Drosophila,
for their role in the regulation of homeotic genes.
And they have often very dramatic morphological consequences.
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Drosophila homeotic genes determine the morphological structures of the fly.
They are very highly conserved in mammals, and humans.
They determine the morphological structure in the anterior-posterior axis.
They are responsible for the development of the head structure at the anterior end,
or the thoracic segments with their wings,
halteres, legs, and for the abdominal segments in the posterior heart.
The development of each structure is controlled by
the expression of the specific combination of homeotic genes.
Each of these must be expressed in its appropriate domain,
and repressed in other regions.
Thus, antennapedia specifies thoracic structures.
If it is expressed in the head region,
it will cause the development of thoracic structures in the head.
