title: Nonspecific labeling limits the utility of Cre-Lox bred CST-YFP mice for studies of corticospinal tract regeneration.
abstract: 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.
authors.affiliation: Reeve-Irvine Research Center, University of California at Irvine, Irvine, California, 92697.|Department of Anatomy & Neurobiology, University of California at Irvine, Irvine, California, 92697.
authors.forename: Rafer
authors.initials: R
authors.lastname: Willenberg
authors.affiliation: Reeve-Irvine Research Center, University of California at Irvine, Irvine, California, 92697.|Department of Anatomy & Neurobiology, University of California at Irvine, Irvine, California, 92697.|Department of Neurobiology & Behavior, University of California at Irvine, Irvine, California, 92697.|Department of Neurosurgery, University of California at Irvine, Irvine, California, 92697.
authors.forename: Oswald
authors.initials: O
authors.lastname: Steward
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism; D001710:Biotin / Q000031:analogs & derivatives / Q000378:metabolism; D001930:Brain Injuries / Q000150:complications / Q000473:pathology; D003911:Dextrans / Q000378:metabolism; D005260:Female; D007839:Functional Laterality; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism; D021621:Imaging, Three-Dimensional; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D018613:Microscopy, Confocal; D009044:Motor Cortex / Q000473:pathology; D009416:Nerve Regeneration / Q000502:physiology*; D009474:Neurons / Q000378:metabolism; D051059:PTEN Phosphohydrolase / Q000235:genetics / Q000378:metabolism; D011712:Pyramidal Tracts / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology*; D013266:Stilbamidines / Q000378:metabolism; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014855:Wallerian Degeneration / Q000209:etiology / Q000503:physiopathology*; D000099260:Empty Spiracles Homeobox Proteins
chemical_list: D001426:Bacterial Proteins; D001710:Biotin; D003911:Dextrans; D018398:Homeodomain Proteins; D008164:Luminescent Proteins; D051059:PTEN Phosphohydrolase; D013266:Stilbamidines; D014157:Transcription Factors; D000099260:Empty Spiracles Homeobox Proteins; C049774:2-hydroxy-4,4'-diamidinostilbene, methanesulfonate salt; C076397:biotinylated dextran amine; C054562:yellow fluorescent protein, Bacteria; C487757:Pten protein, mouse
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