Distribution of Oct4 RNA in newly-divided blastomeres of 8-cell embryos. (A) The zona pellucida of embryos that had just reached the 8-cell stage (a) was perforated with three laser pulses (b). Gentle pipetting resulted in the extrusion of two groups of four connected cells from the zona (c). Each quartet was divided in two cell pairs (d) and, finally, in single blastomeres (e) by further up-and-down pipetting. (B) Oct4 RNA+DNA levels in the cells recovered from two embryos that had just reached the 8-cell stage (a and b) and one 7-cell embryo (c). All cells but one (n.r.) were recovered. Oct4 template measurements in cells deriving from pairs are shown by bars of the same color; the same hue (bluish or reddish) indicates cells originally forming a quartet. The 7-cell embryo was comprised by a quartet and a triplet of cells. Oct4 RNA+DNA levels in the largest cell of the triplet are shown by the orange bar (Bl. 5 in c). Oct4 RNA copy numbers were similar in the two cells of newly-formed pairs, with the exception of one higher-expressing blastomere per embryo.