T-Catenin is a recently identified member of the -catenin family of cell-cell adhesion molecules. For decades it was thought that -catenins mediate solid cell-cell adhesion by linking the cadherin-mediated cell-cell adhesion complex with the actin cytoskeleton. However, the roles of -catenins in this classical adhesion model have been questioned recently. T-Catenin has a restricted expression pattern, in contrast to the ubiquitously expressed E-catenin. High levels of T-catenin were detected in heart and testis. Northern and Western blot experiments indicated that besides the standard full-length T-catenin transcript, smaller alternative transcripts are expressed in testis. We report the cloning of two alternative transcripts of the mouse T-catenin gene (transcript-B and -X), both of which are expressed in a testis-restricted manner from two putative alternative promoters. Alternative transcript-X encodes a smaller protein, isoform-X, which lacks the amino-terminal -catenin binding domain of the standard mouse T-catenin protein, and is therefore unable to restore cell-cell adhesion in an -catenin-negative colon carcinoma cell line. Immunohistochemical analysis showed specific localization of the T-catenin isoform-X in the differentiating germ cells. In contrast to the standard full-length T-catenin protein, this shortened isoform-X can bind to l-afadin, an important component of the nectin/afadin/ponsin adhesion complex that reportedly is essential for spermatogenesis.--Goossens, S., Janssens, B., Vanpoucke, G., De Rycke, R., van Hengel, J., van Roy, F. Truncated isoform of mouse T-catenin is testis-restricted in expression and function.