Ricerc@Sapienza

Constitutive heterochromatin represents a significant portion of eukaryotic genomes,
but its functions still need to be elucidated. Even in the most updated genetics
and molecular biology textbooks, constitutive heterochromatin is portrayed
mainly as the ‘silent’ component of eukaryotic genomes. However, there may be
more complexity to the relationship between heterochromatin and gene expression.
In the fruit fly Drosophila melanogaster, a model for heterochromatin studies,
about one-third of the genome is heterochromatic and is concentrated in the
centric, pericentric, and telomeric regions of the chromosomes. Recent findings
indicate that hundreds of D. melanogaster genes can ‘live and work’ properly within
constitutive heterochromatin. The genomic size of these genes is generally larger
than that of euchromatic genes and together they account for a significant fraction
of the entire constitutive heterochromatin. Thus, this peculiar genome component
in spite its ability to induce silencing, has in fact themeans for being quite dynamic.
A major scope of this review is to revisit the ‘dogma of silent heterochromatin’.