The major horse satellite DNA family is associated with centromere competence

Background:
The centromere is the specialized locus required for correct chromosome segregation during cell
division. The DNA of most eukaryotic centromeres is composed of extended arrays of tandem repeats (satellite
DNA). In the horse, we previously showed that, although the centromere of chromosome 11 is completely devoid
of tandem repeat arrays, all other centromeres are characterized by the presence of satellite DNA. We isolated three
horse satellite DNA sequences (37cen, 2P1 and EC137) and described their chromosomal localization in four species
of the genus Equus.
Results:
In the work presented here, using the ChIP-seq methodology, we showed that, in the horse, the
37cen satellite binds CENP-A, the centromere-specific histone-H3 variant. The 37cen sequence bound by
CENP-A is GC-rich with 221 bp units organized in a head-to-tail fashion. The physical interaction of CENP-A
with 37cen was confirmed through slot blot experi
ments. Immuno-FISH on stretched chromosomes and
chromatin fibres demonstrated that the extension of sa
tellite DNA stretches is variable and is not related to
the organization of CENP-A binding domains. Finally, we proved that the centromeric satellite 37cen is
transcriptionally active.
Conclusions:
Our data offer new insights into the organization of horse centromeres. Although three
different satellite DNA families are cytogenetically lo
cated at centromeres, only the 37cen family is associated
to the centromeric function. Moreover, similarly to other species, CENP-A binding domains are variable in size.
The transcriptional competence of the 37cen satellit
e that we observed adds new evidence to the hypothesis
that centromeric transcripts may be required for centromere function