Cholinesterase in larvae of the ascidian,Ciona intestinalis, developing from fragments cut from centrifuged eggs.

UnfertilizedCiona eggs were centrifuged, stratifying their mitochondria and some other cytoplasmic components. Each centrifuged egg had a mitochondria-free, centripetal clear layer that was contiguous with centrifugal layers containing mitochondria. By cutting centrifuged eggs in two at various levels along the centripetal-centrifugal axis, it was possible to obtain centripetal fragments including virtually no mitochondria, about one-tenth of the uncut egg's mitochondria or about one-fourth of the uncut egg's mitochondria. Most of these centripetal fragments, when fertilized, developed into larvae. However, only the centripetal fragments that included about one-fourth of the uncut egg's mitochondria developed into larvae giving the cytochemical reaction for cholinesterase, a convenient indicator of muscle cell differentiation inCiona. Therefore, the inclusion of a minimum number of mitochondria (more than one-tenth but less than one-fourth the number in the uncut egg) is correlated with muscle cell differentiation in larvae developing from the centripetal fragments. The possible influences of mitochondria and of other cytoplasmic components on muscle differentiation are discussed.