KI-67 EXPRESSION DURING RAT-LIVER REGENERATION AFTER PARTIAL-HEPATECTOMY

Antibodies to the cell-cycle-associated Ki-67 protein have been widely used for more than a decade as markers of proliferative cells. The pr ototype antibody Ki-67 reacted only with snap-frozen human tissue, but a novel antibody, MIB-1, was able to detect the Ki-67 antigen in para ffin wax-embedded human tissue. The ability of MIB-5, a novel antibody reactive with the rat equivalent Ki-67 protein, to immunohistochemica lly detect cycling parenchymal and littoral cells in the regenerating rat liver is reported. Rats underwent a standard two-thirds partial he patectomy (PH), and groups of three animals were killed at intervals f or up to 192 hours after PH. DNA synthesis was monitored by flash labe ling with bromodeoxyuridine, and the response was as expected with a s ignificant upsurge in hepatocyte labeling at 16 to 17 hours after PH. On the other hand, MIB-5 labeled a relatively constant percentage of h epatocytes (4%-8%) during the first 16 hours after PH, before a large proportion became labeled, also at 17 hours. The temporal pattern of M IB-5 labeling was similar to that of bromodeoxyuridine labeling, altho ugh, as expected, MIB-5 indices were higher. Semiquantification of Ki- 67 messenger RNA (mRNA) levels by reverse-transcription polymerase cha in reaction showed modest (fourfold to fivefold) increases in abundanc e during the first 12 hours after PH, but then levels increased dramat ically to be at least 15-fold those of intact liver at 36 hours after PH. Much higher than normal levels of Ki-67 mRNA persisted throughout the period of study and even at 96 hours after PH they were still nine fold greater than normal. This study has shown the usefulness of the M IB-5 antibody to monitor proliferation in the rat liver, and furthermo re, the pattern of expression of both the mRNA and the protein suggest that the Ki-67 protein, with hitherto unknown function, is more abund ant in DNA synthesis and mitosis than in the early or even very late f irst G1 phase.