Nonspecific labeling limits the utility of Cre-Lox bred CST-YFP mice for studies of corticospinal tract regeneration

J Comp Neurol. 2015 Dec 15;523(18):2665-82. doi: 10.1002/cne.23809. Epub 2015 Aug 10.


Studies of axon regeneration in the spinal cord often assess regeneration of the corticospinal tract (CST). Emx1-Cre x Thy1-STOP-YFP mice have been reported to have yellow fluorescent protein (YFP) selectively expressed in forebrain neurons leading to genetic labeling of CST axons in the spinal cord, and it was suggested that these CST-YFP mice would be useful for studies of CST regeneration. Because regeneration past a lesion may involve only a few axons, the presence of labeled non-CST axons compromises interpretation. We show here that in CST-YFP mice, some YFP-labeled axons are not from the CST. Specifically, YFP-labeled axons are present in regions beyond those with anterogradely labeled CST axons, most YFP-labeled axons beyond established CST locations do not undergo Wallerian degeneration following a large lesion of the sensorimotor cortex, some rubrospinal and reticulospinal neurons are labeled with YFP, and some YFP-labeled cells in the spinal gray matter have YFP-labeled projections into the spinal cord white matter. We further demonstrate that the density of YFP-labeled axon arbors hinders tracing of single axons to their point of origin in the main descending tracts. In light of recent advances in 3D imaging for visualizing axons in unsectioned blocks of spinal cord, we also assessed CST-YFP mice for 3D imaging and found that YFP fluorescence in CST-YFP mice is faint for clearing-based 3D imaging in comparison with fluorescence in Thy1-YFP-H mice and fluorescence of mini-ruby biotinylated dextran amine (BDA). Overall, the nonspecific and faint YFP labeling in CST-YFP mice limits their utility for assessments of CST axon regeneration.

Keywords: AB_91337; CST; Cre; Emx1; MGI_2156086; MGI_3497947; MGI_3707420; RRIDs: MGI_2684610; nif-0000-00508; nif-0000-30467; rid_000081; spinal cord injury; transgenic.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Bacterial Proteins / genetics
  • Bacterial Proteins / metabolism
  • Biotin / analogs & derivatives
  • Biotin / metabolism
  • Brain Injuries / complications
  • Brain Injuries / pathology
  • Dextrans / metabolism
  • Female
  • Functional Laterality
  • Homeodomain Proteins / genetics
  • Homeodomain Proteins / metabolism
  • Imaging, Three-Dimensional
  • Luminescent Proteins / genetics
  • Luminescent Proteins / metabolism
  • Male
  • Mice
  • Mice, Inbred C57BL
  • Mice, Transgenic
  • Microscopy, Confocal
  • Motor Cortex / pathology
  • Nerve Regeneration / physiology*
  • Neurons / metabolism
  • PTEN Phosphohydrolase / genetics
  • PTEN Phosphohydrolase / metabolism
  • Pyramidal Tracts / metabolism*
  • Pyramidal Tracts / pathology
  • Pyramidal Tracts / physiopathology*
  • Stilbamidines / metabolism
  • Transcription Factors / genetics
  • Transcription Factors / metabolism
  • Wallerian Degeneration / etiology
  • Wallerian Degeneration / physiopathology*


  • 2-hydroxy-4,4'-diamidinostilbene, methanesulfonate salt
  • Bacterial Proteins
  • Dextrans
  • Homeodomain Proteins
  • Luminescent Proteins
  • Stilbamidines
  • Transcription Factors
  • biotinylated dextran amine
  • empty spiracles homeobox proteins
  • yellow fluorescent protein, Bacteria
  • Biotin
  • PTEN Phosphohydrolase
  • Pten protein, mouse