The expression of prosaposin is temporally and spatially regulated at transcriptional and post-translational levels. Transgenic mice with various 5′-flanking deletions of the prosaposin promoter fused to luciferase (LUC) reporters were used to define its temporal regulatory region. LUC expression in the transgenic mice carrying constructs with 234bp (234LUC), 310bp (310LUC) or 2400bp (2400LUC) of the 5′-flanking region was analysed in the central nervous system and eye throughout development. For 310LUC and 2400LUC, low-level LUC activity was maintained until embryonal day 18 in brain, eye and spinal cord. The peak level of LUC activity was at birth, with return to a plateau (1/3 of peak) throughout adulthood. Deletion of the region that included the retinoic acid-receptor-related orphan receptor (RORα)-binding site and sequence-specific transcription factor (Sp1) cluster sites (44—310bp) suppressed the peak of activity. By comparison, the peak level for 234LUC was shifted 2 weeks into neonatal life in the brain, but not in the eye, and no peak of activity was observed in the spinal cord. The endogenous prosaposin mRNA in eye, spinal cord and cerebellum had low-level expression before birth and continued to increase into adulthood. In cerebrum, the endogenous mRNA showed similar expression profile to constructs 310LUC, 2400LUC and 234LUC, with the peak expression at 1 week and a decreased level in adult. In the brain of the newborn, 2400LUC was highly expressed in the trigeminal ganglion and brain stem regions when compared with the generalized expression pattern for endogenous prosaposin mRNA. These results suggest that the modifiers (RORα- and Sp1-binding sites) residing within 310bp of the 5′-flanking region mediate developmental regulation in the central nervous system and eye. Additional regulatory elements outside the 5′ region of the 2400bp promoter fragment appear to be essential for the physiological control of the prosaposin locus.
The expression of prosaposin is temporally and spatially regulated at the transcriptional and post-translational levels. In vitro , the mouse prosaposin promoter contains functional RORE [retinoic acid-receptor-related orphan receptor α subunit (RORα)-binding element], Sp1 and U (unknown) sites within 310bp directly 5′ to the transcription start site and additional elements within 2400bp 5′ to the transcription start site. To elucidate promoter regions important to tissue-preferential expression in vivo , transgenic mice were created with 5′-flanking deletions of the prosaposin gene fused to a luciferase reporter. Nearly exclusive expression was observed in cerebrum, cerebellum and eyes of adult transgenic mice containing constructs with 234–310bp of 5ƀ-flanking DNA. This central nervous system (CNS) expression was due to the presence of RORE and overlapping Sp1 sites in this region. Internal deletion of RORE and the Sp1 cluster from the longer constructs with 2400bp of 5ƀ-flanking DNA significantly diminished expression in the CNS. The appearance of substantial visceral tissue (e.g. liver, spleen, lung, kidney, thymus and heart) expression was obtained with transgenic mice bearing constructs with 742–2400bp of 5ƀ-flanking DNA. The cellular localization of luciferase reporter-gene expression from these constructs corresponded closely with that for prosaposin. These results define important CNS and visceral regulatory regions in the promoter in vivo and may be sufficient to account for the majority of prosaposin's tissue-preferential expression.