The Drosophila DAXX-Like Protein (DLP) Cooperates with ASF1 for H3.3 Deposition and Heterochromatin Formation

ABSTRACT

Histone variants are nonallelic isoforms of canonical histones, and they are deposited, in contrast to canonical histones, in a replication-independent (RI) manner. RI deposition of H3.3, a histone variant from the H3.3 family, is mediated in mammals by distinct pathways involving either the histone regulator A (HIRA) complex or the death-associated protein (DAXX)/α-thalassemia X-linked mental retardation protein (ATRX) complex. Here, we investigated the function of the Drosophila DAXX-like protein (DLP) by using both fly genetic approaches and protein biochemistry. DLP specifically interacts with H3.3 and shows a prominent localization on the base of the X chromosome, where it appears to act in concert with XNP, the Drosophila homolog of ATRX, in heterochromatin assembly and maintenance. The functional association between DLP and XNP is further supported by a series of experiments that illustrate genetic interactions and the DLP-XNP-dependent localization of specific chromosomal proteins. In addition, DLP both participates in the RI deposition of H3.3 and associates with anti-silencing factor 1 (ASF1). We suggest, in agreement with a recently proposed model, that DLP and ASF1 are part of a predeposition complex, which is recruited by XNP and is necessary to prevent DNA exposure in the nucleus.

KEYWORDS:

• DLP
• heterochromatin
• histone variant
• H3.3
• XNP
• ASF1

ACKNOWLEDGMENTS

We thank Kami Ahmad, Ounissa Aït-Ahmed, Asifa Akhtar, Sarah Elgin, François Karch, and Peter Verriijzer for gifts of antibodies and flies. We thank Claude Delaporte for generating transgenic lines. We thank Chrysa Latrick and Christian Bronner for critical reading of the manuscript.

We declare that we have no conflicting interests relevant to the study.

C.F.-R., P.R., and A.H. conceived of and designed the experiments. C.F.-R., P.R., and A.H. analyzed the data and wrote the paper. C.F.-R. and P.R. performed the experiments. A.H. acquired funding.

This work was supported by institutional funds from the Université de Strasbourg (UDS), CNRS, and INSERM (grant Plan Cancer) and by grants from INCA (INCa_4496, INCa_4454, and INCa PLBIO15-245) (A.H.), ANR (VariZome) (A.H.), USIAS-2015-42 (A.H.), and La Ligue Nationale contre le Cancer Équipe Labelisée (A.H.).