The expression of selenoprotein biosynthesis genes Selenop and Sephs2 increases during mouse development, with Selenop rising over 500-fold in the liver and Sephs2 showing a linear increase from embryonic day 12.5 to postnatal day 90, indicating that the machinery for selenium utilization is established early and amplified to meet the heightened demand for selenoprotein synthesis during rapid postnatal growth.

As a mouse grows after birth, its liver starts making much more of a protein that carries selenium to other organs, and it also makes more of a molecule that puts selenium into all the proteins that need it. This happens because the body needs more of these selenium proteins to protect cells from damage caused by increased oxygen use after birth, and to help organs like the brain and kidneys function properly. The liver begins this process early in development and keeps increasing it as the mouse grows rapidly.