CNP-expressing progenitors display strikingly differential oligodendroglial or multipotent fates, as assessed by two Cre reporter lines

Abstract

In this study, I employ a mouse line in which Cre is knocked-in for the 2’,3’ -cyclic nucleotide 3’ –phosphodiesterase (CNP) gene and compare the fates of CNP-Cre ex-pressing OPCs between two Cre reporters: Z/EG and ROSA26/EYFP. CNPase is found only in mature oligodendrocytes; therefore a subpopulation of “late” or relatively differ-entiated OPCs which have presumably made the decision to differentiate into oligoden-drocytes are labelled with this experimental strategy.<br /> In the first section of this study, I present evidence of extensive oligodendrogliogenesis from CNP-Cre expressing OPCs in both experimental lines. I also show a small subset of reporter positive astrocytes and extensive neurogenesis in discrete regions of the CNP-Cre:ROSA26/EYFP line: ~12% of all EYFP+ cells in the ventral cortex represent an astrocytic phenotype with GFAP positivity and 55-70% reporter positive cells in the dorsal, ventral and piriform cortices are NeuN positive neurons. In striking contrast, no EGFP positive astrocytes or neurons are observed in the CNP-Cre:Z/EG line. <br /> In the second section I report Cnp promoter activity-dependent reporter labelling in em-bryonic radial-glia (RG) like cells which are known to display multipotency. I suggest that OPCs remain committed to an oligodendroglial fate and do not display lineage plasticity; while oligodendroglial genes are switched on transiently in RG-like cells at extremely low levels, only to be detected by sensitive Cre reporters. I thereby show that fate mapping studies can be strongly biased by the choice of Cre reporter strains, result-ing in stark differences in the progeny of oligodendroglial precursors as observed in this study.<br /> The last part of my thesis, is devouted to elucidating the functional role of the GluRB AMPA receptor subunit in influencing OPC physiology, by availing the GluRB floxed NG2creERTM:GluR-B2lox/2lox:ROSA26/EYFP mouse line. I demonstrate that removing the GluRB subunit from the OPC leads to a reduction in OPC proliferation in white matter regions. AMPA receptors are the principal mediators of glutamatergic signalling at the neuron-OPC synapse, and an insight into their effect on OPC development, as presented in this study, will further enhance our understanding of neuron-OPC cross-talk.