Histone variant H3.3–mediated chromatin remodeling is essential for paternal genome activation in mouse preimplantation embryos

Abstract

Derepressionof chromatin-mediated transcriptional repression of paternal and maternal genomes is considered the first major step that initiates zygotic gene expression after fertilization. The histone variant H3.3 is present in both male and female gametes and is thought to be important for remodeling the paternal and maternal genomes for activation during both fertilization and embryogenesis. However, the underlying mechanisms remain poorly understood. Using our H3.3B-HA-tagged mouse model, engineered to report H3.3 expression in live animals and to distinguish different source of H3.3 protein in embryos, we show here that sperm-derived H3.3 protein (sH3.3) is removed from the sperm genome shortly after fertilization and extruded from the zygotes via the second polar bodies (PB II) during embryogenesis. We also found that the maternal H3.3 (mH3.3) protein is incorporated into the paternal genome as early as 2h postfertilization and is detectable in the paternal genome until the morula stage. Knockdown of maternal H3.3 resulted in compromised embryonic development both of fertilized embryos and of androgenetic haploid embryos. Furthermore, we report that mH3.3 depletion in oocytes impairs both activation of the Oct4 pluripotency marker gene and global de novo transcription from the paternal genome important for early embryonic development. Our results suggest that H3.3-mediated paternal chromatin remodeling is essential for the development of preimplantation embryos and the activation of the paternal genome during embryogenesis. [1,2]. At the time of fertilization, both the sperm and oocyte genomes are transcriptionally repressed, whereas the maternal stored factors in the oocyte support and control the process of early embryogenesis. Maternal-to-zygotic transition (MZT) is an embryonic development stage under the exclusive control of the newly formed zygotic genome. This developmental process requires the zygotic genome activation (ZGA) to allow for the transition from specified germ cells to a totipotent embryo, in which both paternal and maternal genomes undergo dramatic epigenetic reprogramming regulated by maternal factors [3]. Overcoming chromatin-mediated transcriptional repression of paternal and maternal genomes is thought to be the first major step to initiate zygotic gene expression after fertilization [4][5][6][7][8][9].The mammalian sperm genome is packaged into highly condensed chromatin consisting primarily of protamine but 5-15% residual histones. Following fertilization, ZGA occurs first in the paternal genome (male pronucleus) at the 1-cell stage embryo, while activation of the maternal genome is usually delayed and occurs at the 2-cell stage in mice [10][11][12][13]. Soon after fertilization, protamine is removed from the sperm genome. The paternal genomes subsequently undergoes chromatin remodeling through a massive and highly regulated exchange of canonical and variant histones including H1FOO, H3.3, microH2A and H2A.Z. The incorporation of histone variants into paternal genome is ...

Listening to mother: Long‐term maternal effects in mammalian development

“…Although present in both sperm and egg, paternally derived H3.3 is lost after fertilization (Kong et al, 2018). Maternally derived H3.3 associates with the paternal chromatin, remains detectable in the nuclei until the morula stage, and is essential for correct transcription from the paternally derived chromosomes, the correct expression of the key pluripotency gene Oct4/Pou5f1 , and embryo preimplantation viability (Kong et al, 2018). This latter effect on Oct4/Pou5f1 suggests a possible long‐term maternal effect of oocyte‐derived H3.3 level on progeny phenotype.…”

Phosphorylation of the ancestral histone variant H3.3 amplifies stimulation-induced transcription

“…However, because there are only two genes for the histone H3.3 variant containing the S31 residue ( H3f3a and H3f3b ) we were able to target these genes by CRISPR. H3.3 is required for embryogenesis 25–28 and spermatogenesis 29 . Further, as we find here (fig.…”

Differential Expression of Histone H3.3 Genes and Their Role in Modulating Temperature Stress Response inCaenorhabditis elegans

“…This signal is normally obscured by maternally provided HIS-72 and HIS-74 , which is incorporated into paternal chromatin shortly after fertilization and prior to pronuclear fusion, but becomes visible when the H3.3::GFP fusions are only transmitted through the paternal germ line by sexual crossing of H3.3::GFP-carrying males to nontagged feminized hermaphrodites. These findings indicate that the H3.3 dynamics in nematodes differ slightly from mammalian systems, where paternally provided H3.3 is removed from the zygote with the second polar body and replaced by maternal copies of the histone ( Kong et al 2018 ). Moreover, it has been shown that epigenetic patterns established during worm spermatogenesis, including the ones associated with H3 and H3.3, are retained in the early embryo in C. elegans ( Arico et al 2011 ).…”