EXPRESSION OF GENE-GUN INJECTED PLASMID DNA IN THE OVINE MAMMARY-GLAND AND IN LYMPH-NODES DRAINING THE INJECTION SITE

A jet-injection based gene-gun delivery system has been evaluated as a means to transiently transfect the lactating mammary gland in vivo. T he model expression plasmid contained the human growth hormone (hGH) s tructural gene driven by the human cytomegalovirus immediate early gen e 1 promoter/enhancer region (CMV). Expression from plasmid DNA jet in jected into lactating mammary glands of sheep was at a level sufficien t to allow detection by Northern blot analysis when tissue was obtaine d 48 hours post-transfection. In contrast, mRNA expression following D NA transfer by needle and syringe was detectable by RT PCR, but not by Northern blot analysis. Furthermore, specific mRNA was detected by RT -PCR in lymph nodes draining the mammary gland injection sites. Jet-in jection of CMV-hGH into either muscle or mammary gland resulted in the development of serum antibodies to hGH. The ability to transiently tr ansfect lactating mammary tissue in vivo may circumvent the difficulti es encountered with in vitro culture techniques and provide a method f or examining mammary regulatory elements and testing fusion gene const ructs.