Required for the formation of cilia. Plays an indirect role in sonic hedgehog signaling, cilia being required for all activity of the hedgehog pathway. Has pro-apoptotic function via its interaction with HIP1, leading to recruit caspase-8 (CASP8) and trigger apoptosis. Has the ability to bind DNA sequence motif 5'-AAAGACATG-3' present in the promoter of caspase genes such as CASP1, CASP8 and CASP10, suggesting that it may act as a transcription regulator; however the relevance of such function remains unclear. Component of the IFT complex B, at least composed of IFT20, IFT22, HSPB11/IFT25, IFT27, IFT46, IFT52, TRAF3IP1/IFT54, IFT57, IFT74, IFT80, IFT81, and IFT88 (PubMed:19253336, PubMed:23810713). Interacts with IFT20 (PubMed:12821668). Interacts with IFT88 (PubMed:11062270, PubMed:19253336, PubMed:23810713). Interacts with IFT80, IFT-81, IFT74, IFT172, TTC30B and KIF17 (PubMed:23810713). Interacts with BLOC1S2 (PubMed:18188704). Interacts with RYBP (PubMed:17874297). Interacts with HOMER1; the interaction possibly prevents the pro-apoptotic effects of IFT57 (PubMed:17107665). Interacts with HIP1 (By similarity). In normal conditions, it poorly interacts with HIP1, HIP1 being strongly associated with HTT (By similarity). However, in mutant HTT proteins with a long poly-Gln region, interaction between HTT and HIP1 is inhibited, promoting the interaction between HIP1 and IFT57, leading to apoptosis (By similarity). Interacts with BFAR (By similarity). Interacts with TTC25 (PubMed:25860617). Interacts with USH1G (By similarity). Concentrates within the inner segment of cilia. Present in retina and testis. In brain, it is present in the cortex, striatum, globus pallidus, hypothalamus and cerebellum. Present at high level in neurons and neuropil throughout the brain (at protein level). Expressed in hippocampal neurons, where it colocalizes with HOMER1 at postsynaptic regions. Ubiquitous through the epiblast. Expression is detected in mesoderm and most strongly in ectoderm, but not in endoderm. Highly expressed in the region of the node, a depression at the surface of the embryo proposed to have a role in left-right axis patterning. At 8.5 dpc, it is widely expressed except in the heart. Stronger expression is observed in the anterior midline, the forebrain and the somites. Strong expression remains in the forebrain at 9.5 dpc and 10.5 dpc and extends to all regions of the neural tube. At those stages, high expression is also found in the branchial arches and in the limb buds. Embryo section at 9.5 dpc also shows expression throughout the neural tube and the mesoderm, but not in the surface ectoderm. The strongest expression is observed on the luminal edge of the neural tube and in the ventral foregut. The pseudo DED region (pDED) mediates the interaction with HIP1. Mice show randomization of the embryo turning process and heart looping, which are hallmarks of defective left-right (LR) axis patterning. Motile monocilia normally present at the surface of the embryonic node, and proposed to initiate the break in LR symmetry, are absent. Furthermore, defects in central nervous system development are observed. The Sonic hedgehog (Shh) pathway is down-regulated in the neural tube, resulting in failure to establish ventral neural cell fate. Belongs to the IFT57 family.