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Biological Bulletin


This study identifies mRNAs located in oligodendrocyte (OL) processes of spiny dogfish and compares them with mRNAs that were previously identified in rat OL processes (1, 2). Because these two species have independent evolutionary histories covering hundreds of millions of years, mRNAs common to OL processes in both species likely represent proteins recruited to form the original myelin sheaths in the common gnathostome ancestor. Of the mRNAs present in rat OL processes, myelin basic protein (MBP) and myelin-associated oligodendrocytic basic protein (MOBP) mRNAs dominate (1, 2). Surprisingly, however, MBP mRNA is not located in spiny dogfish OL processes; rather it is restricted to OL soma as measured in both in situ hybridization and subcellular fractionation experiments (Gould, unpubl.). Thus, MBP synthesis must have moved from the OL soma to its processes sometime after the mammalian line diverged from elasmobranches.

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