In vivo roles of RORalpha and Sp4 in the regulation of murine prosaposin gene.

Prosaposin has a central role in intracellular glycosphingolipid catabolism and also has extracellular functions. This locus is regulated temporally and spatially. The highest mRNA expression occurs in the central nervous system (CNS) and reproductive system. In vitro, the CNS-expressed proteins Sp4 and RORalpha bind to Sp1 and RORE sites within a 310-bp fragment directly upstream of the transcription start site. These transcription factors exhibit negative cooperativity in vitro for prosaposin expression. Mice deficient in RORalpha and Sp4 (Staggerer [Sg(-/-)] and Sp4 knockout [Sp4 KO], respectively) containing selected prosaposin promoter deletion transgenes were used in comparative expression studies to evaluate this negative cooperativity in vivo. Constructs containing the RORE or Sp1/U cluster alone were independently stimulatory. Deletion of the Sp1/U site led to a decrease in reporter activity only in the cerebellum of Sg(-/-) mice. The deletion of RORE and Sp1/U sites did alter the increase of reporter activity in the brain and eye, but not in the spinal cord, of Sg(-/-) mice. These results indicate that Sp4 and RORalpha play minor and major roles, respectively, in regional expression of the prosaposin locus in the brain, whereas expression in the spinal cord is independent of RORalpha.