MORF (MOnonucleotide Repeat Frameshift) Genetic Sparse Cell Labeling

Type: Molecular / Cellular,

Keywords: MORF, TIGRE-MORF (Ai166), Mouse, Morphology, Astrocyte, MORF3, Sparse labeling, Cre, Neuron, Microglia

Resource ID: RRID: SCR_021125

MORF mouse lines confer genetically-directed labeling of brain cell morphology

The MORF strategy addresses the need for a simple, generalizable, and scalable method to sparsely label genetically-defined neuronal populations by developing reporter mouse lines conferring Cre-dependent sparse cell labeling methodology based on MOnonucleotide Repeat Frameshift (MORF) as a stochastic translational switch. The suite of MORF reporter mice labels about 1-5% of Cre+ neurons and glia distributed stochastically throughout the brain and can be imaged with endogenous fluorescence (mNeonGreen in MORF1 and EGFP in TIGRE-MORF/Ai166) or stained for a multivalent immunoreporter (Spaghetti Monster fluorescent protein V5, or smFP-V5, in MORF3). As a resource for both the BRAIN Initiative and general neuroscience communities, MORF enables the labeling and reconstruction of thousands of genetically defined cells per brain for large-scale, unbiased classification and quantitative analyses of CNS cell types brainwide.

* MORF mouse lines include the strong, ubiquitous CAG promoter, LoxP-STOP-LoxP cassette for Cre-dependent expression, an unstable, out-of-frame mononucleotide repeat that can undergo frameshift that functions as translational switch for stochastic expression of a reporter gene.
* Different MORF lines make use of various membrane-bound reporters, including mNeonGreen-F (MORF1), EGFP-F (TIGER-MORF), spaghetti monster Fluorescent Protein V5 (smFP-V5-F; MORF3).
* MORF is compatible with various tissue processing (iDISCO+ and stochastic electrotransport clearing and immunolabeling) and imaging modalities (light microscopy, confocal, light sheet, electron microscopy).
* MORF3 is is the most versatile line with highest signal-to-noise, capable of spare labeling neurons and glial cells at 1-5% labeling frequency (less than 1% with inducible Cre lines).

The MORF reporters permit visualization of the complete morphology of genetically-defined neurons and glial cells at single cell resolution. By labeling cells at less than 1% of a given genetically-defined population with a membrane-bound reporter that has an extremely high signal-to-noise ratio, MORF allows the full 3D reconstruction and high-resolution analyses of the complete local morphology (dendrites) and far-reaching projections (axons) of CNS cell-types. The complete morphological visualization of MORF-labeled cells can be captured through various time-points in the lifespan of a given cell-type, from development through aging.

* Dendritic reconstruction of single neurons.
* Tracing and reconstruction of axonal projections of single neurons.
* Visualization and analysis of dendritic spines and axonal terminals at single neuron resolution.

*MORF1 mice (JAX: 035400)
*MORF3 mice (JAX: 035403)
*TIGRE-MORF or Ai166 mice (JAX: 035404)

* Genetically-defined, high-resolution single-cell imaging of CNS-cell types.
* A generalizable and scalable method that makes use of the existing repository of Cre-mouse lines.
* Incorporates well validated reporters that make MORF amenable to most tissue processing and imaging protocols.

*Veldman et al. 2020, Brainwide Genetic Sparse Cell Labeling to Illuminate the Morphology of Neurons and Glia with Cre-Dependent MORF Mice. Neuron vol. 108,1: 111-127.e6. doi:10.1016/j.neuron.2020.07.019
*Peng et al. 2021, Morphological diversity of single neurons in molecularly defined cell types. Nature vol. 598,7879 (2021): 174-181. doi:10.1038/s41586-021-03941-1
*Muñoz-Castañeda et al. 2021, Cellular anatomy of the mouse primary motor cortex. Nature vol. 598,7879: 159-166. doi:10.1038/s41586-021-03970-w
*BRAIN Initiative Cell Census Network (BICCN) 2021, A multimodal cell census and atlas of the mammalian primary motor cortex. Nature. 2021;598(7879):86-102. doi:10.1038/s41586-021-03950-0


X. William Yang, Principal Investigator


David Geffen School of Medicine, University of California, Los Angeles (UCLA)



Matthew Veldman, Assistant Professor, Medical College of Wisconsin
Chang (Chris) Park, Project Scientist, University of California, Los Angeles (UCLA)
Hong-Wei Dong, Professor, University of California, Los Angeles (UCLA)
Hongkui Zeng, Executive Director, Allen Institute for Brain Science



NIH U01MH117079
NIH U01MH106008