Unique alternative translation from two open reading frames on Acpin1 mRNA yields an acrosomal protein and a salivary-gland-specific protein

Objective: To examine the expression profiles of the proteins translated from Acpin1 mRNA in germ cells. Methods: Northern and western blotting of various tissues and immunohistochemical analysis of germ cells were carried out in a mouse model. Results: ACPIN1 protein was transcribed from the longer, 3′ open reading frame (ORF) of Acpin1. An alternative‐splicing variant, Acpin1vs, contained only the smaller, 5′ ORF of the full‐length Acpin1 gene. Its gene product, SAGSIN1, was expressed specifically in salivary glands. Retrotransposed regions of Acpin1 homology were also detected in various chromosomes, and intronless paralogous genes on the X chromosome were expressed in the testis and other tissues. The genomic structure of Acpin1 is highly conserved in mammals. Conclusion: The two ORFs on the Acpin1 mRNA are independently translated in differentiated cells. Analysis of gene Acpin1 might clarify the molecular mechanism of spermatogenesis.