The N-terminal Tail of C. elegans CENP-A Interacts with KNL-2 and is Essential for Centromeric Chromatin Assembly

Abstract

Centromeres are epigenetically defined by the presence of the centromere-specific histone H3 variant CENP-A. A specialized loading machinery, including the histone chaperone HJURP/Scm3, participates in CENP-A nucleosome assembly. However, Scm3/HJURP is missing from multiple lineages, including nematodes, which rely on a CENP-A-dependent centromere. Here, we show that the extended N-terminal tail of C. elegans CENP-A contains a predicted structured region that is essential for centromeric chromatin assembly. Removal of this region of the CENP-A N-Tail prevents loading, resulting in failure of kinetochore assembly and defective chromosome condensation. By contrast, the N-Tail mutant CENP-A localizes normally in the presence of endogenous CENP-A. The portion of the N-Tail containing the predicted structured region binds to KNL-2, a conserved SANTA and Myb domain-containing protein (referred to as M18BP1 in vertebrates), that is specifically involved in CENP-A chromatin assembly. This direct interaction is conserved in the related nematode C. briggsae, despite divergence of the N-Tail and KNL-2 primary sequences. Thus, the extended N-Tail of CENP-A is essential for CENP-A chromatin assembly in C. elegans and partially substitutes for the function of Scm3/HJURP, in that it mediates an interaction of the specialized histone fold of CENP-A with KNL-2. These results highlight an evolutionary variation on centromeric chromatin assembly in the absence of a dedicated CENP-A-specific chaperone/targeting factor of the Scm3/HJURP family.

Transgenerational inheritance of centromere identity requires the CENP-A N-terminal tail in the C. elegans maternal germ line

“…elegans ( Fig 2 ). These findings have recently been independently confirmed [ 34 ]. In chicken cells, the interaction between KNL-2 and CENP-A was shown to be dependent on a KNL-2 CENP-C motif [ 44 ].…”

“…Our results show that the interaction between KNL-2 and CENP-A depends on the central region of KNL-2 and the N-terminal tail of CENP-A in C. elegans (Fig 2). These findings have recently been independently confirmed [34]. In chicken cells, the interaction between KNL-2 and CENP-A was shown to be dependent on a KNL-2 CENP-C motif [44].…”

“…Based on our Y2H assay and the in vitro experiments, the central region of KNL-2 mediates this interaction (Figs 2A and S1A). These observations have recently been independently confirmed [34].…”

Small RNAs Worm Up Transgenerational Epigenetics Research

“…Although the nature of the positioning mark is still not clear, Steiner and colleagues determined that the de novo placement of CENP-A occurs during a strict developmental window preceding the first embryonic division of the zygote [ 80 ]. This process is dependent on the N-terminal tail of CENP-A [ 80 , 81 ]. Surprisingly, the N-terminal tail is dispensable for mitotic divisions during late embryogenesis, larval development, and germline proliferation [ 80 ].…”