673 ′UTR cyclin B1 mRNA. Cyclin B1, in contrast to Cripto-1 mRNA, is equally asso-
ciated with polyribosomes in animal and vegetal cells. These reporter mRNAs were
independently injected into either the animal or vegetal cells of 4–8 cell embryos that
were allowed to develop to the late blastula stage at which point they were harvested
Fig. 2.4 Spatial accumulation of the Cripto-1 protein in Xenopus embryos is controlled by regu-
lated translation of the Cripto-1 mRNA. In Xenopus, the Cripto-1 mRNA is uniformly distributed
throughout the egg and all embryonic cells. The Cripto-1 protein is only produced in animal cells
of embryos after fertilization, but not vegetal cells (Cragle and MacNicol 2014a). Differential
accumulation of the Cripto-1 protein in Xenopus embryos is due to the spatially regulated transla-
tion of the Cripto-1 mRNA. Translation is activated in animal cells and repressed in vegetal cells
(Heasman et al. 1994 ; Zhang et al. 2009 ). The Bicaudal-C (Bic-C) protein is responsible for
repression functions in the vegetal cells (Heasman 2006a; Houston 2013 ; Zhang et al. 2013 , 2014 ).
The Bic-C mRNA is localized to the vegetal cortex of developing oocytes, and as a consequence
after fertilization, Bic-C is restricted to vegetal cells (Schohl and Fagotto 2002 )
2 Controlling the Messenger...