Skin-specific expression of ank-3(93), a novel ankyrin-3 splice variant

Ankyrins represent a protein family whose members are associated with membrane proteins and the actin cytoskeleton. The principal ankyrin domain structure comprises an amino-terminal membrane-binding, a spectrin-binding, and a regulatory domain, and can be modulated by alternative splicing. In order to investigate the role of ankyrin-3 in skin, we have isolated three complete ankyrin-3 cDNA clones of 5.8 kb, 5.2 kb, and 2.5 kb by reverse transcription-polymerase chain reaction of mouse skin RNA. DNA sequencing confirmed the isolated clones to be splice variants of ankyrin-3. Of these, the smallest cDNA represents a novel ankyrin named ankyrin-3(93). Surprisingly, this novel ankyrin subtype lacks not only all ankyrin repeats, but also the first 75 amino acids of the spectrin-binding domain. Immuno-fluorescence analysis of mouse skin showed that ankyrin-3 is expressed in all living layers of mouse epidermis. Here, it predominates along the basal and lateral membranes of the basal layer in addition to an even cytoplasmic distribution. In primary mouse keratinocytes grown at elevated Ca2+ levels, ankyrin-3(93) was localized along the plasma membrane and throughout the cell in a Golgi-like fashion. Depending on fixation conditions, nuclear staining became apparent in many cells. In agreement with previous data, northern blotting revealed a widespread distribution of the two larger ankyrin splice variants. In contrast, the mRNA coding for ankyrin-3(93)was restricted to mouse skin. Reverse transcription-polymerase chain reaction of mouse skin RNA strongly suggested additional ankyrin isoforms in skin. Our data on ankyrin-3(93), which lacks a part of the spectrin-binding domain that regulates the affinity to spectrin, suggests a new function for this member of the ankyrin family.