# Intron V, not intron I of human thrombopoietin, improves expression in the milk of transgenic mice regulated by goat beta-casein promoter

## TL;DR

This study shows that intron V of human thrombopoietin improves gene expression in transgenic mice milk more effectively than intron I.

## Contribution

The study reveals that intron V, not intron I, enhances hTPO expression in transgenic mice regulated by a strong promoter.

## Key findings

- Intron V significantly improves hTPO expression in transgenic mice milk.
- Intron I does not enhance hTPO expression when regulated by the β-casein promoter.
- Deleting uAUG7 in TUR does not improve hTPO expression.

## Abstract

Introns near 5′ end of genes generally enhance gene expression because of an enhancer /a promoter within their sequence or as intron-mediated enhancement. Surprisingly, our previous experiments found that the vector containing the last intron (intron V) of human thromobopoietin (hTPO) expressed higher hTPO in cos-1 cell than the vector containing intron I regulated by cytomegalovirus promoter. Moreover, regulated by 1.0 kb rat whey acidic protein promoter, hTPO expression was higher in transgenic mice generated by intron V-TPOcDNA than in transgenic mice generated by TPOcDNA and TPOgDNA. However, it is unknown whether the enhancement of hTPO expression by intron I is decreased by uAUG7 at 5′-UTR of hTPO in vivo. Currently, we constructed vectors regulated by stronger 6.5kb β-casein promoter, including pTPOGA (containing TPOcDNA), pTPOGB (containing TUR-TPOcDNA, TUR including exon1, intron I and non-coding exon2 of hTPO gene), pTPOGC (containing ΔTUR-TPOcDNA, nucleotides of TUR from uAUG7 to physiological AUG were deleted), pTPOGD (containing intron V-TPOcDNA) and pTPOGE (containing TPOgDNA), to evaluate the effect of intron I on hTPO expression and to further verify whether intron V enhances hTPO expression in the milk of transgenic mice. The results demonstrated that intron V, not intron I improved hTPO expression.