EXTENT OF MOSAICISM IN EXPERIMENTALLY PRODUCED DIPLOID TRIPLOID CHIMERIC TROUT

Chimeric rainbow trout embryos have been produced by injecting isolate d blastomeres into intact recipient blastulae. In order for chimeric f ish to be useful in studies of development, it is necessary to determi ne whether the various organs or tissues of the resultant chimera have an equal probability of arising from the injected cells derived from donor embryos. The objective of this investigation is to determine the proportion of cells in the blood, liver, and brain tissues of rainbow trout chimeras that are derived from the injected cells. Blastomeres isolated from normal diploid blastulae were microinjected into age-mat ched triploid recipient embryos, and the treated embryos grown until 4 weeks post hatch. Samples of blood, liver, and brain tissues were dis persed; the cell nuclei were labeled with propidium iodide, and the sa mples subjected to flow cytometric analysis to determine the proportio ns of diploid and triploid nuclei. The proportion of cells that were d iploid varied among the resultant chimeric trout. Analysis of variance on the proportion of diploid cells in each sample indicated that ther e was no significant effect of tissue type. These results support the hypothesis that the isolated cells of the donor embryo are no more lik ely to colonize one tissue or organ type of a chimera than another.