Figure 6. tdTomato is not expressed by Schwann cells derived from Kir4.1-CreER^T2 mice that have been induced to myelinate in vitro.

A, Low-magnification images of DRG explant cultures show extensive tdTom+ SC associated with DRG after addition of TMX either before or after the induction of myelination by ascorbate. B, An MBP-positive MSC (outlined in white) associated with a neurofilament-M (NF-M)-reactive neurite expresses tdTom when TMX was added before ascorbate (top row), showing that Kir4.1 was robustly expressed in this cell before myelination was induced. In contrast, neurite-associated SC failed to express tdTom when TMX was added after ascorbate, demonstrating that Cre activity in Kir4.1-CreER^T2 mice was downregulated in response to myelination. C, Percentage of MBP+ Schwann cells expressing tdTom when tamoxifen was given before or after ascorbate; data in text. Expressing and non-expressing SC were defined as ones in which the tdTom fluorescence intensity within a 4 μm² square overlapping an MBP+ region was greater than 30 or less than 20 iu₈.