Abstract
Following fertilization, the genomes of the germ cells are reprogrammed to form the totipotent embryo. Pioneer transcription factors are required for remodeling the chromatin and driving the initial wave of zygotic gene expression. In Drosophila melanogaster, the pioneer factor Zelda is essential for development through this dramatic period of reprogramming, known as the maternal- to-zygotic transition (MZT). However, it was unknown whether additional pioneer factors were necessary for this transition. We identified an additional maternally encoded factor required for development through the MZT, GAGA Factor (GAF). GAF is needed to activate widespread zygotic transcription and to remodel the chromatin accessibility landscape. We demonstrated that Zelda preferentially controls expression of the earliest transcribed genes, while genes expressed during widespread activation are predominantly dependent on GAF. Thus, progression through the MZT requires coordination of multiple pioneer factors, and we propose that as development proceeds transcriptional control is gradually transferred from Zelda to GAF.
Competing Interest Statement
The authors have declared no competing interest.
