The cytosolic chaperonin subunit TRiC-P5 begins to be expressed at the two-cell stage in mouse embryos.

The cytosolic chaperonin TRiC is a large protein complex involved in the folding of newly synthesized actin and tubulin. The fertilization of the mouse oocyte is followed by a remodelling of the actin and tubulin filaments. The TRiC subunit TCP1 is expressed only from the 4-cell stage on, even though actin and tubulin are synthesized in the previous stages. We investigated the onset of synthesis of another subunit, TRiC-P5, during early mouse embryogenesis. We report that TRiC-P5 is synthesized at the 2-cell stage in an alpha-amanitin sensitive manner. Thus, it is expressed before TCP1 and is one of the first proteins to be synthesized after zygotic genome activation.