Immediate-early gene. Plays an important role in embryonic development as well as in cellular growth and proliferation; its long-term silencing affects cell survival and cell cycle distribution as well as decreases CDK1 activity correlated with reduced phosphorylation of CDK1. Plays a role as a positive regulator of the sonic hedgehog pathway, acting downstream of PTCH1. Plays an important role in the regulation of centriole duplication. Required for the onset of procentriole formation and proper mitotic progression. During procentriole formation, is essential for the correct loading of SASS6 and CENPJ to the base of the procentriole to initiate procentriole assembly (By similarity). Homodimer (By similarity). Interacts with PIN1 via its WW domain. This interaction is dependent on Stil mitotic phosphorylation (PubMed:16024801). Interacts with CENPJ. Interacts with RBM14 and this interaction interferes with the interaction of STIL with CENPJ. Forms a complex with CENPJ and SASS6 (By similarity). Ubiquitously expressed in adult and fetal tissues. Highly expressed in hematopoietic tissues such as thymus, bone marrow and spleen. Down-regulated during cell terminal differentiation. Accumulates during G2 phase and falls at completion of the cell cycle. Ubiquitinated. Phosphorylated following the activation of the mitotic checkpoint. Death during embryonic development between days 8.5 and 10.5. Embryos are reduced in size and display delayed development. They have axial midline defects, and randomized cardiac looping. The midline sonic hedgehog signaling is blocked in these mice.