Recycling of signaling proteins is a common phenomenon in diverse signaling pathways. In photoreceptors of Drosophila, light absorption by rhodopsin triggers a phospholipase Cβ-mediated opening of the ion channels transient receptor potential (TRP) and TRP-like (TRPL) and generates the visual response. The signaling proteins are located in a plasma membrane compartment called rhabdomere. The major rhodopsin (Rh1) and TRP are predominantly localized in the rhabdomere in light and darkness. In contrast, TRPL translocates between the rhabdomeral plasma membrane in the dark and a storage compartment in the cell body in the light, from where it can be recycled to the plasma membrane upon subsequent dark adaptation. Here, we identified the gene mutated in trpl translocation defective 14 (ttd14), which is required for both TRPL internalization from the rhabdomere in the light and recycling of TRPL back to the rhabdomere in the dark. TTD14 is highly conserved in invertebrates and binds GTP in vitro. The ttd14 mutation alters a conserved proline residue (P75L) in the GTP-binding domain and abolishes binding to GTP. This indicates that GTP binding is essential for TTD14 function. TTD14 is a cytosolic protein and binds to PtdIns(3)P, a lipid enriched in early endosome membranes, and to phosphatidic acid. In contrast to TRPL, rhabdomeral localization of the membrane proteins Rh1 and TRP is not affected in the ttd14 P75L mutant. The ttd14 P75L mutation results in Rh1-independent photoreceptor degeneration and larval lethality suggesting that other processes are also affected by the ttd14 P75L mutation. In conclusion, TTD14 is a novel regulator of TRPL trafficking, involved in internalization and subsequent sorting of TRPL into the recycling pathway that enables this ion channel to return to the plasma membrane.

NK cells are functionally controlled by the killer immunoglobulin-like receptor (KIR) family that comprises inhibitory (iKIR) and activating (aKIR) members. Genetic association studies suggest that donors expressing aKIRs next to iKIRs will be superior donors in the setting of hematopoietic stem cell transplantation of patients with leukemia. However, contrary evidence states that aKIR expression may be irrelevant or even detrimental. Using a complex methodology incorporating KIR-Q-PCR, double fluorescence and viSNE analysis, we characterized subset distribution patterns and functionality in haplotype A donors which lack aKIRs and haplotype B donors that express a variety of B-specific genes. Here, we show that the alloreactive KIR2DS1+ NK cell subset in HLA-C1/C2 donors is highly responsive towards C2-expressing targets but quantitatively small and as such does not significantly contribute to cytotoxicity. Thus, we fail to find a direct link between haplotype allocation status and NK cell cytotoxicity at least in HLA-C1/C2 heterozygous donors.

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