TRANSLATIONAL CONTROL OF ARYLSULFATASE-A EXPRESSION IN MOUSE TESTIS

Arylsulfatase A is a lysosomal enzyme that is involved in the degradat ion of sulfated glycolipids. High levels of arylsulfatase A mRNA are f ound in germ cells of mouse testis. In late pachytene and secondary sp ermatocytes the level of arylsulfatase A mRNA is increased 20-fold whe n compared with other tissues. These high levels of arylsulfatase A mR NA are maintained in round spermatids and decrease in late elongating spermatids. The increase of arylsulfatase A mRNA levels is not accompa nied by a similar increase in enzyme activity or polypeptides. Subcell ular fractionation revealed that the majority of arylsulfatase A mRNA is not associated with polysomes but is found in fractions of lower bu oyancy. The failure to become translated is ascribed to the associatio n of arylsulfatase A mRNA with nonpolysomal ribonucleoproteins. This t ranslational repression may be due to proteins that bind to arylsulfat ase A mRNA and prevent its translation. Within the 639-nucleotide B'-u ntranslated region and the 700-nucleotide 3'-untranslated region of th e arylsulfatase A mRNA, we identified two regions that specifically bi nd proteins present in extracts prepared from testicular cells, These RNA binding proteins were absent from extracts prepared from liver or brain.