This family is the highly conserved central region of a number of metazoan proteins referred to as growth-arrest proteins. In mouse, Gas8 is predominantly a testicular protein, whose expression is developmentally regulated during puberty and spermatogenesis. In humans, it is absent in infertile males who lack the ability to generate gametes. The localization of Gas8 in the motility apparatus of post-meiotic gametocytes and mature spermatozoa, together with the detection of Gas8 also in cilia at the apical surfaces of epithelial cells lining the pulmonary bronchi and Fallopian tubes suggests that the Gas8 protein may have a role in the functioning of motile cellular appendages. Gas8 is a microtubule-binding protein localized to regions of dynein regulation in mammalian cells.