Truly epigenetic: A centromere finds a "neo" home

Abstract

Murillo-Pineda and colleagues (2021. J. Cell Biol.https://doi.org/10.1083/jcb.202007210) use CRISPR-Cas9-based genetic engineering in human cells to induce a new functional centromere at a naive chromosomal site. Long-read DNA sequencing at the neocentromere provides firm evidence that centromere establishment is a truly epigenetic event.

Figure 1.

Establishment of a human neocentromere on chromosome 4 (Chr4). (A) CRISPR-Cas9 is used to remove an 8-Mb region of Chr4 containing the endogenous centromere and surrounding pericentric heterochromatin. This approach generates an acentric Chr4. These cells are cultured and screened by immunofluorescent microscopy for neocentromere formation. A stable neocentromere, Neo4p13, is established on the p (short) arm at a frequency of one in eight million cells. (B) Comparison of the features of the canonical centromere versus neocentromere Neo4p13. Chr4 (left) normally contains a centromere that is epigenetically specified by the histone H3 variant CENP-A. The underlying centromeric DNA contains a higher order array of α satellite repeats, flanked by pericentric heterochromatin. CENP-B binds to α satellite DNA via the CENP-B box, and it is sufficient to reform a centromere (via CENP-C) in the absence of CENP-A (11). In contrast, de novo centromere formation at Neo4p13 (right) occurs at sites void of α satellite DNA, CENP-B binding, and proximal heterochromatin. This indicates that centromere establishment is truly an epigenetic event, independent of centromeric DNA contribution.