Kinesin and kinectin can associate with the melanosomal surface and form alink with microtubules in normal human melanocytes

Microtubuli play an important role in the organization of organelles and me mbrane traffic. They are present in melanocytic dendrites through which mel anosomes are transported towards keratinocytes. Besides the actin-based mot ility systems, microtubuli-associated motor proteins also play a critical r ole in melanosome movement, as has recently been confirmed in mouse melanoc ytes. We investigated the in vitro expression of two forms of human convent ional kinesin and its receptor kinectin in normal human epidermal melanocyt es, keratinocytes, and dermal fibroblasts by reverse transcription polymera se chain reaction and northern blot analysis. In an attempt to gain insight into the subcellular distribution of kinesin and kinectin in melanocytes, double immunofluorescent staining and immunogold electron microscopy were p erformed. In all studied skin cells ubiquitous and neuronal kinesin are exp ressed, as well as the kinectin receptor. Immunofluorescent staining shows distinct but partially overlapping distributions for kinesin heavy chain an d melanosomes, suggesting that kinesin is associated with some but not all of the melanosomes. Similar observations for kinectin indicate that this re ceptor can colocalize with melanosomes, which was confirmed by immunoelectr on microscopy. The latter technique allowed us to demonstrate a close assoc iation between kinesin heavy chain, microtubuli, and melanosomes. The combi ned data from reverse transcription polymerase chain reaction, northern blo t analysis, double immunofluorescent staining, and immunogold electron micr oscopy suggest that kinesins and kinectin have an important role in microtu buli-based melanosome transport in human melanocytes.