Human osteogenesis involves differentiation-dependent increases in the morphogenically active 3 ' alternative splicing variant of acetylcholinesterase

The extended human acetylcholinesterase (AChE) promoter contains many bindi ng sites for osteogenic factors, including 1,25-(OH)(2) vitamin D-3 and 17 beta-estradiol. In differentiating osteosarcoma Saos-2 cells, both of these factors enhanced transcription of the AChE mRNA variant 3' terminated with exon 6 (E6-AChE mRNA), which encodes the catalytically and morphogenically active E6-AChE isoform. In contrast, antisense oligodeoxynucleotide suppre ssion of E6-AChE mRNA expression increased Saos-2 proliferation in a dose- and sequence-dependent manner. The antisense mechanism of action was most l ikely mediated by mRNA destruction or translational arrest, as cytochemical staining revealed reduction in AChE gene expression. In vivo, we found tha t E6-AChE mRNA levels rose following midgestation in normally differentiati ng, postproliferative fetal chondrocytes but not in the osteogenically impa ired chondrocytes of dwarf fetuses with thanatophoric dysplasia. Taken toge ther, these findings suggest morphogenic involvement of E6-AChE in the prol iferation-differentiation balance characteristic of human osteogenesis.