As if you all needed one more reason to want Junk DNA to stay JUNK, I just read a couple of neato papers on the impact of wayward ERV and LINE activity in testes/sperm development:
Turns out that mice that lack MOV10L1 (a protein named after a retrovirus, but not retroviral– its totally a host protein, long story), grow up to be nice normal mice… except for the fact the males have tiny balls, and they are infertile (heh, cute picture in that first paper of these teeny-tiny mouse balls hehehe).
MOV10L1 is made in the testes, and is super useful during sperm development for shutting down active ERV and LINE elements via RNA interference (the cells cant do anything about the transcripts being made in this case, but they can keep the pirate RNA from causing any trouble). If these ERVs and LINEs are left to their own devices, the cells freak out and kill themselves (apoptosis), leaving you with no sperm.
So it could be that some kinds of male infertility are caused by dysfunctions of MOV10L1 (or somewhere along this pathway), so we could figure out how to cure them.
AND, since we know screwing with MOV10L1 screws around with sperm generation, we might be able to use this knowledge to figure out a male version of The Pill for birth control! Messing up MOV10L1 only messes up spermatogenesis, nothing else. So no surgery or cuts or stuff thats hard to reverse, no hormones or other stuff with off-target side effects– Just stops the sperm. I like this idea!