The green fluorescent protein is an efficient biological marker for cardiac myocytes

There is a need for a non-toxic marker for cardiac myocytes in studies of c ardiac development and in experimentally induced pathophysiologic stales in adult animals, We investigated the possibility of using the enhanced green fluorescent protein (EGFP) gene as such a biological marker for cardiac my ocytes in both whole animal and cell culture systems. Several lines of tran sgenic mice were constructed harboring an EGFP gene directed by a 2.38-kb p romoter fragment of the hamster beta-myosin heavy chain gene. The transgene was preferentially expressed in the cardiac progenitor cells of embryos at E7.5, a developmental stage that precedes the formation of the cardiomyotu be, It was specifically expressed in the cardiomyotube and myotomes along t he somites of embryos at E8.5. The EGFP transgene expression continued in t he heart throughout gestation and became very intense at birth. When neonat al cardiac cells were fractionated into myocytes and non-myocytes by a diff erential plating procedure, only myocytes from the transgenic mice showed s pecific green fluorescence of the transgene product that carl be used as a marker for now cytometry analysis. Although the expression levels were hete rogeneous, EGFP expression persisted in the hearts of postnatal animals. In addition to the heart, some skeletal and smooth muscles from transgenic an imals also expressed the transgene, The transgenic mice were healthy and ha d a normal life span, identical to their non-transgenic littermates. These results demonstrate that EGFP is an efficient non-toxic biological marker f or cardiac myocytes. (C) 1999 Academic Press.