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The histone H3.3 chaperone HIRA is essential for chromatin assembly in the male pronucleus


In sexually reproducing animals, a crucial step in zygote formation is the decondensation of the fertilizing sperm nucleus into a DNA replication-competent male pronucleus. Genome-wide nucleosome assembly on paternal DNA implies the replacement of sperm chromosomal proteins, such as protamines, by maternally provided histones1,2. This fundamental process is specifically impaired in sésame (ssm), a unique Drosophila maternal effect mutant that prevents male pronucleus formation3. Here we show that ssm is a point mutation in the Hira gene, thus demonstrating that the histone chaperone protein HIRA is required for nucleosome assembly during sperm nucleus decondensation. In vertebrates, HIRA has recently been shown to be critical for a nucleosome assembly pathway independent of DNA synthesis that specifically involves the H3.3 histone variant4,5. We also show that nucleosomes containing H3.3, and not H3, are specifically assembled in paternal Drosophila chromatin before the first round of DNA replication. The exclusive marking of paternal chromosomes with H3.3 represents a primary epigenetic distinction between parental genomes in the zygote, and underlines an important consequence of the critical and highly specialized function of HIRA at fertilization.

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Figure 1: Hira is the ssm gene.
Figure 2: Maternal HIRA accumulates in the male nucleus.
Figure 3: H3.3 is specifically deposited in paternal chromatin.
Figure 4: Di- or tri-methylation of H3 on lysine 4 and lysine 9 marks maternal chromosomes.


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We thank P. Fisher for anti-PCNA antibodies and the European Drosophila Genome Project for cosmid clones. We are grateful to B. Durand and B. Horard for helpful discussions. We also thank J. Schmitt and the CTµ microscopy center for technical assistance. This work was supported by the C.N.R.S. and the French Ministry of Research.

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Correspondence to Benjamin Loppin.

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Supplementary information

Supplementary Figure 1

RT-PCR analysis of Hira expression (PDF 735 kb)

Supplementary Figure 2

Western Blot analysis of HIRA-FLAG, H3.3-FLAG and H3-FLAG proteins. (PDF 283 kb)

Supplementary Figure 3

Pronuclei replicate their DNA by the time they appose. (PDF 532 kb)

Supplementary Table 1

Complementation of the ssm185b phenotype with Hira transgenes. (PDF 783 kb)

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Loppin, B., Bonnefoy, E., Anselme, C. et al. The histone H3.3 chaperone HIRA is essential for chromatin assembly in the male pronucleus. Nature 437, 1386–1390 (2005).

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