“Housekeeping” genes are expected to be expressed in all cells of an organism under normal conditions, irrespective of tissue type, developmental stage or cell cycle state. Interestingly, most of the genes affected are so-called “housekeeping” genes that are required for the maintenance of basic cellular function such as energy production or cell growth. Conversely, without Domino, H2A.Z is decreased on the chromatin, and transcription is severely reduced, resulting in lethality,” says Dafne Ibarra Morales. “Our data show that H2A.Z deposited by Domino is required for the transcriptional activation of thousands of genes at the onset of the Zygotic Genome Activation. It places a protein called histone variant H2A.Z on the chromatin. Domino also belongs to the material provided by the mother into the egg. In the newest study, the team found that another enzyme called Domino is essential for shaping chromatin in the very early stages of development. H2A.Z as an important regulator during zygote activation And this prompted us to question what other mechanisms could exist and how is the rest of the genes regulated,” explains Dafne Ibarra Morales, first author of the study. However, Zelda only regulates around ten percent of the genes in the early embryo. Lack of Zelda stops development and causes embryos to die just before ZGA. In the fruit fly, a pioneer factor called Zelda is crucial for coordinating Drosophila genome activation. “Specific proteins known as pioneer transcription factors are here essential and act as genome activators. The lab of Nicola Iovino wants to understand how the zygotic genome and epigenome is shaped to start its own transcription using the fruit fly Drosophila melanogaster as a model organism. This process in embryonic development during which the development comes under the exclusive control of the zygotic genome rather than the maternal genetic material stored in the egg is called Zygotic Genome Activation (ZGA) and involves the simultaneous transcriptional activation of thousands of genes. The chromatin remodeling to get everything ready for the takeover of the zygote takes place during the early transcriptional silence,” explains Nicola Iovino, group leader at the Max Planck Institute of Immunobiology and Epigenetics in Freiburg. Only this allows later that the single-cell embryo can give rise to the different cell lineages that would ultimately develop into all the different cell types present in the organism. “After fertilization, the chromatin, which is the packaging of the genome, needs to be remodeled to a naïve state. These same maternal products are also responsible for “preparing” or shaping the zygotic genome to get activated and produce its own RNA and proteins later on. It cannot produce its own RNA and proteins for hours or sometimes days after fertilization and only survives by relying on maternally supplied RNAs and proteins that have been stockpiled in the egg beforehand. Interestingly, the transcription of the new zygotic genome is initially silenced. Following fertilization, two highly specialized cells, the egg and the sperm, unite to create an entirely new organism with its own genome. In the first hours of life, all animals undergo a fascinating process. © MPI of Immunobiology and Epigenetics, Freiburg, Ibarra-Morales
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