Translational control of arylsulfatase A expression in mouse testis

Abstract

Arylsulfatase A is a lysosomal enzyme that is involved in the degradation of sulfated glycolipids. High levels of arylsulfatase A mRNA are found in germ cells of mouse testis. In late pachytene and secondary spermatocytes the level of arylsulfatase A mRNA is increased 20-fold when compared with other tissues. These high levels of arylsulfatase A mRNA are maintained in round spermatids and decrease in late elongating spermatids. The increase of arylsulfatase A mRNA levels is not accompanied by a similar increase in enzyme activity or polypeptides. Subcellular fractionation revealed that the majority of arylsulfatase A mRNA is not associated with polysomes but is found in fractions of lower buoyancy. The failure to become translated is ascribed to the association of arylsulfatase A mRNA with nonpolysomal ribonucleoproteins. This translational repression may be due to proteins that bind to arylsulfatase A mRNA and prevent its translation. Within the 639-nucleotide 5'-untranslated region and the 700-nucleotide 3'-untranslated region of the arylsulfatase A mRNA, we identified two regions that specifically bind proteins present in extracts prepared from testicular cells. These RNA binding proteins were absent from extracts prepared from liver or brain.