Complex sentence: Understanding the mechanism by which protein p11 regulates serotonin sheds some light on this mystery, as research has shown that low levels of Protein p11 directly correlates with depression in humans and mice.
Split into simpler sentences: Understanding the mechanism by which protein p11 regulates serotonin sheds some light on this mystery. Research has shown that low levels of protein p11 directly correlates with depression in humans and mice.