before hatching. Maternal CHD1 is required for the incorporation of H3.3 into the male pronucleus during decondensation after fertilization. Failure to incorporate H3.3 may render the paternal genome unable to participate in mitosis in the zygote, resulting in non-viable haploid embryos65. Interestingly, mutation of both genes encoding H3.3 in D. melanogaster recapitulates the Chd1 loss-of-function phenotype — that is, viable adults are completely sterile66 — suggesting that this remodeller is specifically dedicated to H3.3 incorporation during early development after fertilization.
