Cytoplasmic membrane transplants in early Xenopus embryos indicate cell-cycle-specific effects

Fragments of rough endoplasmic reticulum or Golgi complex isolated from normal adult rat liver homogenates were injected into one cell of cleaving two-cell Xenopus laevis embryos and the effects on development were monitored during early cleavage by morphological analysis. Scanning electron microscopy revealed the formation of large cells on the injected side of the embryos. Such large cells were not present in controls and thus were considered to have been formed as a consequence of delayed cleavage. Delay of cleavage was obtained with as little as 1 ng of membrane protein giving a ratio of membrane protein to embryo protein of 1:10(5). Cytological observations of microinjected embryos confirmed the occurrence of delayed cytokinesis and suggested that nuclear division became asynchronous. Since rough microsomes from proliferating tissues (i.e., livers with primary tumors and livers undergoing regeneration) showed little or no effect on cytokinesis after microinjection into early embryos, we conclude that cytoplasmic membranes may exhibit cell-cycle-specific properties important for normal development.