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1. Dipartimento di Biologia
Animale, Università di Pavia, Italia. 2. Dipartimento di Medicina Sperimentale,
Università di Parma, Italia. 3. Dipartimento di Bioogia Animale e dell'Uomo,
Università di Roma "La Sapienza" Italia.
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The studies here described
consider several aspects of the pericentromeric satellite-DNA (sat-DNA) biology
in the genus Mus and discuss how sat-DNA organization/composition
may influence karyotype structure which in turn can affect developmental and
microspeciation processes. The intra-genus comparative analysis of pericentromeric
DNAs shows that only in Mus domesticus one (the major) of the
two (the major and the minor) sat-DNA families allocated at the pericentromere
is highly amplified with a long-range organization of the cluster repeats. This
peculiar feature of major sat-DNA correlates with the proneness of domesticus
telocentric chromosomes to give rise to whole arm (Robertsonian, Rb)
translocations. In the pericentromeric regions of Rb chromosomes there are no
telomeric sequences and only 20-60 kb of minor sat-DNA organising a functionally
active kinetochore. The fusion point is constantly localised within the minor
sat-DNA which, when analysed with FIBER-FISH, shows low intermingling of the
tandem repeats with the major sat-DNA. Rb heterozygosity produces alteration
of the nuclear architecture as shown by whole chromosome painting in germ and
Sertoli cells of fertile and chromosomally-derived subfertile/sterile animals.
Thus, the mouse represents an excellent model animal to study the relationships
between the various hyerarchycal levels of life organisation, i.e. from molecular
to cytodifferentiation and from development to speciation. In the mouse, the
cascade of effects linking sat-DNA composition, chromosome translocations, cytodifferentiative
and developmental processes and microspeciation events, provides the conceptual
and experimental tools to further our understanding on the link between the
molecular and organismic worlds. The integration of these conceptual tools within
functional genomics and within an EVO-DEVO perspective will highlight those
functional aspects of the genome organisation (i.e. its size and composition)
useful to solve present-day paradoxes, e.g., C-values, number of structural
genes and heterochromatin biology. |
