Expression of the proliferation-related Ki-67 mRNA in the early development of murine embryo

In a search for early lymphoid-specific genes, we isolated a cDNA clone (LL7) encoding a murine homologue of Ki-67 protein, a proliferation-related nuclear antigen. LL7 transcript appears preferentially in lymphoid organs as the bone marrow, spleen, and the thymus. Here, we studied the expression of murine Ki-67 (mKi-67) mRNA among various organs or tissues during the early development of fetus. In fetus, mKi-67 mRNA appears developmentally as early as day 11 and is expressed maximally at day 15. In situ hybridization on the section revealed that the expression of mKi-67 mRNA is preferential in the area of active organ formation such as neurological system and the fetal liver. These results suggest that mKi-67 plays an important role in the proliferation of early embryonic precursor cells of neurological and immune systems.