|Budget Amount *help
¥2,100,000 (Direct Cost : ¥2,100,000)
Fiscal Year 1993 : ¥400,000 (Direct Cost : ¥400,000)
Fiscal Year 1992 : ¥1,700,000 (Direct Cost : ¥1,700,000)
In order to determine the developmental relationships among the notochord, somites, and limbs, various micro-surgical manipulations were performed on chick embryos. When the notochord was transplanted onto the dorsal midline of the neural tube, the majority of the embryos developed without an abdominal wall and thus had exposed internal organs. In addition, their limbs grew toward the dorsal aspects of the embryo, as if the dorso-ventral orientation of the embryo had been changed. All such experimentally manipulated embryos were dead before embryonic day 10. Because transplantation of the notochord had such a deleterious effect on morphogenesis, it was impossible to determine the relationship between the notochord and limb development directly. Before we could address this issue, we firsts had to understand the developmental relationship between the notochord and somites. When somites were deprived from the influences of both the neural tube and notochord, all of the cells that compris
e the somites were dead within 10 hours of operation ; after 24 hours, neither dermomyotomes nor sclerotomes were observed adjacent to the neural tube. However, when the somites were deprived of the notochord, the sclerotome cells had died within 24 hours, leaving a void surrounded by the dermomyotomes. The vertebral columns and ribs did not develop on the operated side because they derived from sclerotomes. Though the arrangement of muscle cells was quite irregular, however, they developed above the mesonephros by day 7. In contrast, when only the neural tube was eliminated, small dermomyotomes appeared distal to the neural tube ; these ultimately differentiated to small clusters of muscle cells.
These results indicated that myotomes development requires influences from either neural tube or notochord, and sclerotome development requires only influences from the notochord. More data is required before the developmental relationship between the myotomes and the neural tube and notochord can be fully appreciated. Less