Fig. 6

Expression of tbx6 in sibling wild-type and no tail embryos. Staged embryos from matings between no tail/+ heterozygotes were processed to detect tbx6 transcripts (blue–black) by in situ hybridization. 6 and 9 h no tail mutant embryos were identified following immunohistochemical staining (brown) to detect the No Tail protein. At subsequent developmental stages, the no tail embryos could be identified unambiguously by morphological criteria. (A and B) Animal pole views of early gastrulae (6 h; * indicates dorsal) illustrate that tbx6 is initially expressed normally in no tail mutant embryos. (C and D) Dorsal views (animal pole up) of late gastrulae (90% epiboly, 9 h) show that the overall pattern of tbx6 expression in the hypoblast is normal. (E and F) Soon after the tail bud stage (12 h, posterior view), the domain of cells that express tbx6 and the extent of tbx6 expression appear diminished in no tail embryos. (G–J) As tail development proceeds, tbx6 expression is dramatically down-regulated in no tail embryos. Only a small population of cells near the yolk cell of mutant embryos continues to express tbx6 at 15 –16 h. By 18 h, only cells in the region of the intermediate cell mass continue to express the gene in mutant embryos.