Maternal Control of Development at the Midblastula Transition and beyond

Abstract

Many maternal factors in the oocyte persist in the embryo. They are required to initiate zygotic transcription but also function beyond this stage, where they interact with zygotic gene products during embryonic development. In a four-generation screen in the zebrafish, we identified 47 maternal-effect and five paternal-effect mutants that manifest their phenotypes at the time of, or after, zygotic genome activation. We propagated a subset of 13 mutations that cause developmental arrest at the midblastula transition, defects in cell viability, embryonic morphogenesis, and establishment of the embryonic body plan. This diverse group of mutants, many not previously observed in vertebrates, demonstrates a substantial maternal contribution to the "zygotic" period of embryogenesis and a surprising degree of paternal control. These mutants provide powerful tools to dissect the maternal and paternal control of vertebrate embryogenesis.

Mlh1 Deficiency in Zebrafish Results in Male Sterility and Aneuploid as Well as Triploid Progeny in Females

“…The difference in this model is that after fertilization the embryo makes little use of its own genome initially, but instead develops on maternally supplied mRNAs and proteins from the yolk. Transcription from the zygotic genome does not commence before $3 hpf (Duffy et al 2005) and maternal supplies are active until much later (Wagner et al 2004). In this respect, severe aneuploidy would be tolerable during the first hours of development.…”

Zebrafish: A model system for the study of eye genetics

“…This latter result raises an important issue; if brg1 is essential for early stages of murine development, then how did the zebrafish embryos survive? In zebrafish, transcripts for many genes involved in early development such as brg1 are expressed maternally (Gregg et al, 2003;Dosch et al, 2004;Wagner et al, 2004). These maternal stores likely permit embryos to progress through the early stages of development thereby uncovering the novel function of the gene in eye development.…”

Analysis of axis induction mutant embryos reveals morphogenetic events associated with zebrafish yolk extension formation

“…Even though morphogenetic movements begin after the initiation of zygotic transcription, perduring maternal gene products can affect post-MBT processes, including cell movements (Pelegri et al, 2004;Wagner et al, 2004). Thus, mutant phenotypes for maternal factors can lend insight into the complexities of development and demonstrate how later processes build upon early cell fate decisions.…”