Identification of eight-cell tw32 homozygous lethal mutants by aberrant compaction.

Early cleavage stage (4- and uncompacted 8-cell) embryos from experimental (+/tw32 X +/t32) and control (male +/tw32 X female +/T) matings were recovered at 56 hours post coitum, cultured, separated into uncompacted and compacted 8-cell embryo groups, and either analyzed histologically for cytoplasmic lipids or cultured through the morula-to-blastocyst transformation. Abnormal compaction was associated with excess cytoplasmic lipids at the 8-cell stage (P less than 0.01). Also, 89.2% (33/37) of the original uncompacted experimental embryos underwent developmental arrest characteristic of tw32 homozygous lethals. Thus, aberrant compaction, a newly reported symptom of the tw32/tw21 syndrome, affords a visual means to identify tw32 homozygotes at 8-cell stages.