Figure 2.

Distribution of key maternal factors in the oocyte. Studies in different organisms have shown that maternal mRNAs are organized in cytoplasmic granules together with several regulatory proteins responsible for their post‐transcriptional processing and thus translational regulation. In fish and amphibians, a large structure known as mitochondrial cloud or Balbiani body is present at the vegetal pole of the oocyte. This structure consists of a large accumulation of mitochondria and cytoplasmic granules (specifically termed germ granules) containing silenced mRNAs. The mitochondrial cloud serves as a vehicle for transporting and localizing maternal factors to the vegetal cortex during oogenesis by means of microtubule network and motor proteins (yellow arrows). At egg activation and fertilization, Sybu and Wnt8 are translocated to the future dorsal axis through microtubule‐mediated transport (blue arrows).