MURINE OSTEOCLASTS AND SPLEEN-CELL POLYKARYONS ARE DISTINGUISHED BY MESSENGER-RNA PHENOTYPING

To probe osteoclast gene expression, we combined the techniques of cel l microisolation and RT-PCR to develop a novel and sensitive method fo r the isolation and mRNA phenotyping of small numbers of authentic ost eoclasts and spleen cell polykaryons. Using this method we report (1) direct evidence for the presence of calcitonin receptor mRNA in osteoc lasts, (2) confirmation of the recent finding of osteopontin mRNA in o steoclasts, and (3) demonstration that the specific expression of mRNA for tartrate-resistant acid phosphatase, carbonic anhydrase II, calci tonin receptor, and osteopontin enable one to distinguish the osteocla st from the morphologically similar and developmentally related spleen cell polykaryon. We also show that mRNA associated with the osteoblas t phenotype, such as alkaline phosphatase, osteocalcin, and type I col lagen, are absent in osteoclasts. This is the first report in which su ch an approach has been used successfully to distinguish the mRNA expr ession pattern of an authentic osteoclast from a macrophage polykaryon , and as such it should provide an important new tool for evaluating t he results of various cell culture model systems designed to examine t he origin and ontogeny of osteoclasts. Our results also indicate that these procedures can be used as an alternative to in situ hybridizatio n methods for the cell-specific localization of specific MRNA in a mix ed cell preparation and for colocalization of multiple mRNA species to a single cell type.