Molecular Genetics of Zebrafish Embryogenesis: from Nodal Signals to MicroRNAs

During early development, the embryo is faced with multiple challenges – the switch from maternally provided gene products to activating its own genome, the specification and patterning of tissue progenitors, and the rearrangement of cells to generate the embryonic axes. We have used genetics, molecular biology, embryology and in vivo imaging to address this problem in zebrafish. Our studies have revealed how the extracellular interplay of Nodal signals, EGF‐CFC proteins and Lefty antagonists controls mesoderm and endoderm formation and left‐right patterning in zebrafish. Nodal signals can act as morphogens and instruct cells to form mesoderm and endoderm and internalize; EGF‐CFC proteins act as essential coreceptors in this process; and Lefty attenuates mesoderm and endoderm induction by blocking Nodal signaling. More recently, we have identified a microRNA that regulates the degradation of a large number of maternal mRNAs and facilitates the maternal to zygotic transition. I will discuss how the interplay of microRNAs and signaling molecules regulates early development.