Project description:The function and retention/reprogramming of epigenetic marks during the germline-to-embryo transition is a key issue in developmental and cellular biology, with relevance to stem cell programming and trans-generational inheritance. In zebrafish, DNAme patterns are programmed in transcriptionally-quiescent early cleavage embryos; paternally-inherited patterns are maintained, whereas maternal patterns are reprogrammed to match the paternal pattern. Here we show that a ‘placeholder’ nucleosome, containing the histone H2A variant H2A.Z(FV) and H3K4me1, occupies virtually all regions lacking DNAme in both sperm and cleavage embryos – residing at promoters encoding housekeeping and early embryonic transcription factors. Upon genome-wide transcriptional onset, genes with the Placeholder become either active H3K4me3-marked or silent H3K4me3/K27me3-marked (bivalent). Importantly, functional perturbation causing Placeholder loss confers DNAme acquisition, whereas acquisition/expansion of Placeholder confers DNA hypomethylation and improper gene activation. Thus, during transcriptionally quiescent stages (gamete-zygote-cleavage), an H2A.Z(FV)/H3K4me1-containing Placeholder nucleosome deters DNAme, poising parental genes for either gene-specific activation or facultative repression.
Project description:The function and retention/reprogramming of epigenetic marks during the germline-to-embryo transition is a key issue in developmental and cellular biology, with relevance to stem cell programming and trans-generational inheritance. In zebrafish, DNAme patterns are programmed in transcriptionally-quiescent early cleavage embryos; paternally-inherited patterns are maintained, whereas maternal patterns are reprogrammed to match the paternal pattern. Here we show that a ‘placeholder’ nucleosome, containing the histone H2A variant H2A.Z(FV) and H3K4me1, occupies virtually all regions lacking DNAme in both sperm and cleavage embryos – residing at promoters encoding housekeeping and early embryonic transcription factors. Upon genome-wide transcriptional onset, genes with the Placeholder become either active H3K4me3-marked or silent H3K4me3/K27me3-marked (bivalent). Importantly, functional perturbation causing Placeholder loss confers DNAme acquisition, whereas acquisition/expansion of Placeholder confers DNA hypomethylation and improper gene activation. Thus, during transcriptionally quiescent stages (gamete-zygote-cleavage), an H2A.Z(FV)/H3K4me1-containing Placeholder nucleosome deters DNAme, poising parental genes for either gene-specific activation or facultative repression.
Project description:The function and retention/reprogramming of epigenetic marks during the germline-to-embryo transition is a key issue in developmental and cellular biology, with relevance to stem cell programming and trans-generational inheritance. In zebrafish, DNAme patterns are programmed in transcriptionally-quiescent early cleavage embryos; paternally-inherited patterns are maintained, whereas maternal patterns are reprogrammed to match the paternal pattern. Here we show that a ‘placeholder’ nucleosome, containing the histone H2A variant H2A.Z(FV) and H3K4me1, occupies virtually all regions lacking DNAme in both sperm and cleavage embryos – residing at promoters encoding housekeeping and early embryonic transcription factors. Upon genome-wide transcriptional onset, genes with the Placeholder become either active H3K4me3-marked or silent H3K4me3/K27me3-marked (bivalent). Importantly, functional perturbation causing Placeholder loss confers DNAme acquisition, whereas acquisition/expansion of Placeholder confers DNA hypomethylation and improper gene activation. Thus, during transcriptionally quiescent stages (gamete-zygote-cleavage), an H2A.Z(FV)/H3K4me1-containing Placeholder nucleosome deters DNAme, poising parental genes for either gene-specific activation or facultative repression.
Project description:Humans and animals have problems producing eggs with high embryo developmental competence, but the causes of poor egg quality are usually unknown. This study delivered the first proteomic portraits of egg quality in zebrafish, a leading model for vertebrate development. Egg batches of good and poor quality, evidenced by embryo survival for 24 h, were used to create pooled or replicated sample sets subjected to different levels of fractionation before LC-MS/MS. Obtained spectra were searched against a custom zebrafish proteome database and detected proteins were annotated, categorized and quantified based on their normalized spectral counts. Manual and automated enrichment analyses were highly confirmative, showing that good and poor quality eggs have disparate proteomes. Proteins involved in protein synthesis, energy metabolism, and lipid metabolism, and certain vitellogenin products were strikingly underrepresented in poor quality eggs. Poor quality eggs also had significantly higher representation of proteins related to immune system and endosome/lysosome functioning, oncogenes, and apoptosis, as well as lectins and egg envelope proteins. Quantitative comparisons of highly abundant proteins revealed 9 candidate egg quality markers warranting further study. In conclusion, the zebrafish egg proteome appears to be linked to embryo developmental potential, a phenomenon that begs further investigation.
Project description:Humans and animals have problems producing eggs with high embryo developmental competence, but the causes of poor egg quality are usually unknown. This study delivered the first proteomic portraits of egg quality in zebrafish, a leading model for vertebrate development. Egg batches of good and poor quality, evidenced by embryo survival for 24 h, were used to create pooled or replicated sample sets subjected to different levels of fractionation before LC-MS/MS. Obtained spectra were searched against a custom zebrafish proteome database and detected proteins were annotated, categorized and quantified based on their normalized spectral counts. Manual and automated enrichment analyses were highly confirmative, showing that good and poor quality eggs have disparate proteomes. Proteins involved in protein synthesis, energy metabolism, and lipid metabolism, and certain vitellogenin products were strikingly underrepresented in poor quality eggs. Poor quality eggs also had significantly higher representation of proteins related to immune system and endosome/lysosome functioning, oncogenes, and apoptosis, as well as lectins and egg envelope proteins. Quantitative comparisons of highly abundant proteins revealed 9 candidate egg quality markers warranting further study. In conclusion, the zebrafish egg proteome appears to be linked to embryo developmental potential, a phenomenon that begs further investigation.