Effects of the Brachyury (T) mutation on morphogenetic movement in the mouse embryo |
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Authors: | K.O. Yanagisawa H. Fujimoto Hideko Urushihara |
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Affiliation: | Mitsubishi-Kasei Institute of Life Sciences, 11 Minamiooya, Machida-shi, Tokyo 194, Japan |
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Abstract: | embryos have been first distinguishable at 8 days post coitum by their gross morphological abnormalities. By quantitative morphometry of histological sections, anomalies in the homozygotes were expressed numerically. At 8 days p.c., morphologically identifiable T-homozygotes had an increased number of ectodermal and a reduced number of mesodermal cells compared to the wild type. At 7 days p.c., embryos with a low mesoderm/ectoderm ratio were found only in litters of matings at the expected frequency. At 6 days p.c., one-fourth of the embryos in litters showed a delay in the transition from cuboidal to squamous endoderm. No such embryos were found in the +/+ × +/+ matings. In 6-, 7-, and 8-day mutant embryos, cells proliferated at statistically normal rates. Therefore, it may be said that advanced morphological irregularities of 8-day homozygotes cannot be accounted for by anomalies in cell proliferation. When the total cell number was 5 × 104/embryo (8 days), a sudden change was observed in the regional distribution of mesodermal and ectodermal cells along the anteroposterior axis of embryos. Since no regional difference in the cell cycle time was observed, these abnormalities may best be explained by anomalies in cell migration. These results strongly suggest abnormal morphology of mutants resulting from defects in morphogenetic movement. |
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