Oligodendrocytes from Jimpy and Normal Mature Tissue Can Be 'Activated' when Transplanted in a Newborn Environment

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Abstract
Fragments of corpus callosum from P13 normal and jimpy (jp) mutant mice (containing only postmigrating precursors and differentiated oligodendrocytes (ODCs, some of them myelinating soon) have been transplanted into the thalamus of newborn shiverer (shi) mutant mice. The behaviour of transplanted ODCs has been assayed by immunohistochemistry of their myelin basic protein (MBP)-positive myelin synthesized in the host shi brain whose myelin is deprived of this component. ODCs and postmigrating precursors contained in P13 normal corpus callosum survived, migrated out of the graft and myelinated in the shi host parenchyme. The high ratio of positive cases observed was comparable to the one observed in previous experiments using fragments of newborn or embryonic normal tissue. When fragments of jp tissue were used as donors, postmigrating jp ODCs or precursors migrated on long distances out of the graft and synthesized large amounts of myelin as estimated by the size of the MBP-positive myelin patches present in the host shi brain. The extent of migration and the size of these myelin patches were more important than those observed in previous experiments using fragments of newborn or embryonic jp CNS as donors. By contrast, the low ratio of positive cases observed suggested that the survival of P13 jp ODCs or their postmigrating precursors cannot be restored by the newborn shi environment. In order to determine whether P13 jp ODCs were activated by a factor present in shi but absent in jp tissue, fragments of P13 jp corpus callosum were transplanted into newborn jp brains: large patches of MBP-positive myelin were observed around the graft and extending from the graft through the host brain. This last result compared with results obtained in previous experimental series using fragments of newborn or embryonic jp tissue suggests that the activation of postmigrating jp precursors or differentiated jp ODCs is not triggered by the soluble factor(s) which seems to modulate the survival of jp precursor cells during the embryonic life in vivo and during the perinatal period in vitro.

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