Species-specific alternative splicing of transgenic RNA in the mammary glands of pigs, rabbits, and mice

Gene-farming techniques provide an effective tool for the production of recombinant proteins in livestock. Transgenes consisting of genomic DNA sequences are as a rule more efficiently expressed than those in which the product of interest is encoded by a cDNA. However, the processing of pre-mRNA from genomic constructs may yield unexpected messenger RNAs and subsequently protein variants. We describe the appearance of different alternative mRNA splice patterns of a gene construct in which a mutant human growth hormone (hGH-N) gene is transcriptionally controlled by 2.5 kb of mouse whey acidic protein (WAP2) regulatory sequences in the mammary gland of different livestock species. Compared to the transcription products in transgenic mice harboring the same gene construct and to cell transfection experiments, expression analysis in transgenic pigs and rabbits revealed different mRNA splice patterns with regard to the proportion of the processed transcripts. Apart from already-known physiological mRNA splice products, previously undescribed processed hGH transcripts were observed in these species. Sequence analysis of the transgenes suggests that the species-specific hGH mRNA patterns may be caused by species- and tissue-specific differences in trans-acting splice factors.