For the biogenesis and maintenance of cilia, bidirectional protein trafficking within cilia is crucial, and is conducted by intraflagellar transport (IFT) trains containing the IFT-A and IFT-B complexes that are powered by dynein-2 and kinesin-II motors. We have recently shown that before the assembly of anterograde IFT trains, the IFT-A, IFT-B, and dynein-2 complexes are independently recruited to the mother centriole/basal body. The IFT-B complex, which consists of 16 subunits, can be divided into the IFT-B1 and IFT-B2 subcomplexes, and IFT-B1 can be further divided into the IFT-B1a and IFT-B1b subgroups. Here we investigated how the IFT-B complex is assembled and recruited to the mother centriole for ciliogenesis. Analyses using cells with knockouts of individual IFT-B subunits, and analyses of proteins coimmunoprecipitated with EGFP-fused IFT-B2, IFT-B1b, and IFT-B1a subunits expressed in these knockout cells demonstrated the following: (i) although IFT-B2 is dispensable for the linkage between IFT-B1b and IFT-B1a, it is essential for their localization to the mother centriole; (ii) IFT-B1b is essential both for bridging IFT-B2 and IFT-B1a, and for their localization to the mother centriole; (iii) IFT-B1a is not required for the linkage between IFT-B2 and IFT-B1b nor for their localization to the mother centriole; and (iv) all IFT-B components (IFT-B2, IFT-B1b, and IFT-B1a) are essential for ciliogenesis. Thus, although ciliogenesis is not a prerequisite for the recruitment of the IFT-B complex to the mother centriole, the linkage between IFT-B2 and IFT-B1b is crucial for the mother centriole localization of the IFT-B complex for ciliogenesis.

Key words: cilia, ciliogenesis, distal appendages, IFT-B complex, mother centriole

As the outermost organ, the skin is particularly susceptible to physical damage. Keratinocytes are a major component of the epidermis, and their migration plays a crucial role in skin wound healing. Supersulfides contribute to energy production to sustain the life activities of organisms and are anticipated to play a role in various physiological functions; however, minimal studies have investigated their presence and functions in the skin. This study aimed to determine the presence of supersulfides in the skin and investigate their effect on keratinocyte migration. Using sulfane sulfur probe 4 (SSP4), a fluorescent probe that detects sulfane sulfur, the presence of supersulfides in both skin tissue and keratinocytes was revealed. Moreover, the primary supersulfide biosynthetic enzyme, cysteinyl-tRNA synthetase 2 (CARS2), was expressed at both the tissue and cellular levels. CARS2 expression and SSP4 fluorescence intensity in keratinocytes increased during wound healing, suggesting that supersulfide is involved in the regulation of cell migration. Knockdown of CARS2 suppressed keratinocyte migration and markedly downregulated gene expression of various chemokines. Protein expression analysis revealed that supersulfides regulate E-cadherin and matrix metalloproteinase (MMP)-9 via extracellular signal-regulated kinase (ERK) and protein kinase B (Akt). Furthermore, Na₂S₄ treatment of keratinocytes with CARS2 knockdown restored cell migration. We propose that supersulfide in the skin represents a novel mechanism of re-epithelialization and may serve as a therapeutic target for skin wounds.

Key words: supersulfide, cysteinyl-tRNA synthetase 2, keratinocyte, cell migration, wound healing