DNA dendrimers localize MyoD mRNA in presomitic tissues of the chick embryo

MyoD expression is thought to be induced in somites in response to factors released by surrounding tissues; however, reverse transcription-PCR and cel l culture analyses indicate that myogenic cells are present in the embryo b efore somite formation. Fluorescently labeled DNA dendrimers were used to i dentify MyoD expressing cells in presomitic tissues in vivo. Subpopulations of MyoD positive cells were found in the segmental plate, epiblast, mesode rm, and hypoblast. Directly after laying, the epiblast of the two layered e mbryo contained similar to 20 MyoD positive cells. These results demonstrat e that dendrimers are precise and sensitive reagents for localizing low lev els of mRNA in tissue sections and whole embryos, and that cells with myoge nic potential are present in the embryo before the initiation of gastrulati on.