TUNEL analysis in embryos injected with braEnR or hairy2a mRNAs.

Sibling embryos were injected with 1 or 2 ng of braEnR mRNA or with 1 or 2 ng of hairy2a mRNA into 1 ventral cell at the 4-cell stage, or into the most ventral-vegetal blastomere (CD4) at the 16-cell stage, or were left uninjected (controls). At neural plate stage, embryos were fixed and processed for TUNEL analysis, and were classified into three categories, according to the appearance of TUNEL+ cells in the posterior region, as follows: TUNEL+/− (low or none), TUNEL++ (moderate), and TUNEL+++ (high).