Quick detection of firefly luciferase gene expression in live developing bovine embryos by photoncounting

The present study was designed, first to develop the new methodology to measure the bioluminescence activity easily in live developing bovine embryos by photoncounting, and secondly to compare the expression efficiency of four luciferase reporter genes in bovine embryos at four- to 16-cell stages. In experiment 1, equimolar pSVlacZ and pSVEluc were microinjected into the pronucleus of fertilized bovine oocytes. At 2 days after microinjection, bioluminescence activity of these embryos was measured by photoncounting with a luminometer for 1 min, and lacZ gene expression in the same embryos was assayed by X-gal staining. All the luciferase-positive oocytes showed some bacterial beta-galactosidase activity irrespective of the intensity. In experiment 2, four firefly luciferase genes (pTKEluc, pTK6WEIuc, pSVEluc and pMiwluc) were introduced by microinjection, and the injected embryos were cultured for the following 2 days. Detection of the luciferase gene expression was done by photoncounting at 5 to 55 min. Over the measurement period, the luciferase activity was almost constant irrespective of the transgenes microinjected. The luciferase activity and expression efficiency at 2 days after microinjection were not significantly affected by the difference in the microinjected transgenes. The present results demonstrated that the bioluminescence activity in live developing bovine embryos could be measured quickly by photoncounting.