IFT27 Knockout Cell Line (HEK293)

Specific G-protein-coupled receptors (GPCRs) exist on the ciliary membrane. Hedgehog signaling activation triggers the import of Smoothened into and export of GPR161 from cilia. The BBSome, which comprises eight Bardet-Biedl syndrome (BBS) proteins, mediates GPCR export, together with the intraflagellar transport (IFT) machinery, containing the IFT-A and IFT-B complexes. The absence of any BBSome subunit or IFT27 (also known as BBS19) (an IFT-B subunit) impairs ciliary GPCR export, including that of GPR161. Plasma membrane GPCRs undergo phosphorylation by GPCR kinases (GRKs) and subsequent binding of β-arrestins [β-arrestin1 (ARRB1) and β-arrestin2 (ARRB2)], which is crucial for clathrin-mediated endocytosis. We here confirmed that GPR161 and β-arrestin are accumulated within cilia in the absence of IFT27 or the BBSome, and that ARRB1 and ARRB2 double-knockout impairs GPR161 export. Notably, we found that activation-mimetic β-arrestin mutants can interact with both the BBSome and ciliary GPCRs, and cause constitutive export of GPR161. Moreover, we demonstrated that GRK2 plays a crucial role in GPR161 export. We here propose that phosphorylated GPR161 recruits β-arrestins, converting them into their activated conformation. Activated β-arrestins then interact with the BBSome, which connects them to the IFT machinery to facilitate GPR161 export.

Intraflagellar transport (IFT) is an evolutionarily conserved mechanism essential for the assembly and maintenance of most eukaryotic cilia and flagella, including mammalian sperm tails. Depletion of IFT27, a component of the IFT complex, in male germ cells results in infertility associated with disrupted sperm flagella structure and motility. Leucine zipper transcription factor-like 1 (LZTFL1) is an IFT27 associated protein. LZTFL1, also known as BBS17, is a Bardet-Biedl syndrome (BBS) associated protein. Patients carrying biallelic variants of LZTFL1 gene exhibit the common BBS phenotypes. The global Lztfl1 knockout mice showed abnormal growth rate and retinal degeneration, typical of BBS phenotype. However, it is not clear if Lztfl1 has a role in male fertility. The LZTFL1 protein is highly and predominantly expressed in mouse testis. During the first wave of spermatogenesis, the protein is only expressed during spermiogenesis phase from the round spermatid stage and displays a cytoplasmic localization with a vesicular distribution pattern. At the elongated spermatid stage, LZTFL1 is present in the developing flagella and appears also close to the manchette. Fertility of Lztfl1 knockout mice was significantly reduced and associated with low sperm motility and a high level of abnormal sperm (astheno-teratozoospermia). In vitro assessment of fertility revealed reduced fertilization and embryonic development when using sperm from homozygous mutant mice. In addition, we observed a significant decrease of the testicular IFT27 protein level in Lztfl1 mutant mice contrasting with a stable expression levels of other IFT proteins, including IFT20, IFT81, IFT88 and IFT140. Overall, our results support strongly the important role of LZTFL1 in mouse spermatogenesis and male fertility.