human or mouse H1/U6 promoter? - (Jul/25/2007 )

Hi, I am trying to use the shRNA system and need to decide which promoter to use.
I will be using both mouse and human cell lines.
Is there a species specificity for the H1 and U6 promoter?
I already have the mouse H1 promoter clone from previous lab member, but according to the literature it seems that most ppl use the human one. would there be a big difference in expression?
I also heard of the 7SK promoter system. is there an advantage for that? does that promoter work in both mouse and human?

Thanks a lot~~

we have used human H1 in a rat invivo and invitro and it worked very efficiently. Also we have used in human cell lines. seems to work nicely.