Complex sentence: Developmental and tissue specific expression has been studied in several mammalian species including humans, mice, rats, and rabbits however because FMO expression is unique to each animal species, it is difficult to make conclusions about human regulation based on other mammalian studies.
Split into simpler sentences: Developmental and tissue specific expression has been studied in several mammalian species, including humans, mice, rats, and rabbits. However, because FMO expression is unique to each animal species, it is difficult to make conclusions about human regulation based on other mammalian studies.