and it all starts in the nucleus! Warning: This does NOT apply to prokaryotes. You are in eukaryote-only territory, and don't you forget it.
Most eukaryotic cells have a nucleus throughout their entire life cycles, but there are a few notable exceptions. Human red blood cells (the good ol' RBCs), for example, get rid of their nuclei as they mature. Rebels without a cause. Or actually, with a cause, because, with their nuclei removed, red blood cells have more space to carry oxygen throughout the body.