Predictability of dorso-ventral asymmetry in the cleavage stage zebrafish embryo: an analysis using lithium sensitivity as a dorso-ventral marker

The dorso-ventral axis in zebrafish first becomes apparent at gastrulation, when the future ventral side appears thinner than the dorsal side. The exa ct time of establishment of the dorso-ventral axis is not known. We show he re that the dorso-ventral axis is specified as early as the 32 cell stage. Using lithium as a marker for dorso-ventral asymmetry, we show that lithium -sensitivity is a characteristic of future ventral cell, but not future dor sal cells, and that there is an asymmetric lithium-sensitivity along the lo ng axis of the 32 cell stage embryo. Consequently, the dorso-ventral axis c orresponds to the long axis of the embryo. Because the effect of lithium tr eatment is short-lived, the dorso-ventral axis must be specified in zebrafi sh already at the 32 cell stage. (C) 1999 Elsevier Science ireland Ltd. All rights reserved.