The present invention is one gene construct or a combination of two gene constructs or expression vectors incorporating a Cypridina luciferase gene and a copepod luciferase under the control of distinct promoters. These gene constructs and expression vectors are useful for making a mammalian cell incorporating the Cypridina luciferase gene and the copepod luciferase to be capable of stably expressed and extracellularly secreted under the control of the distinct promoters.