Biology subjects

Greig, L. C.

Publications and source records attributed to Greig, L. C..

4 recordsLinked to original sources

bioRxiv2024

Bcl11b orchestrates subcerebral projection neuron axon development via cell-autonomous, non-cell-autonomous, and subcellular mechanisms

Both cell-intrinsic competency and extracellular cues regulate axon projection, but mechanisms that coordinate these elements remain poorly understood. Subcerebral projection neurons (SCPN) extend their primary axons from cortex through subcortical structures, including the striatum, targeting the brainstem and spinal cord. We identify that the transcription factor Bcl11b/Ctip2 functions in multiple independent neuron populations to control SCPN axon development. Bcl11b expressed by SCPN is required cell-autonomously for axonal outgrowth and efficient entry into the internal capsule within the striatum, while Bcl11b expressed by medium spiny neurons (MSN) non-cell-autonomously regulates SCPN axon fasciculation within the internal capsule and subsequent pathfinding. Further, integrated investigation of Bcl11b-null SCPN with transcriptomic, immunocytochemical, and in vivo growth cone purification approaches identifies that Cdh13 is localized along axons and on growth cone surfaces of SCPN in vivo, and mediates Bcl11b regulation of SCPN axonal outgrowth. Together, these results demonstrate that Bcl11b controls multiple aspects of SCPN axon development by coordinating intrinsic SCPN cell autonomous subcellular mechanisms and extrinsic MSN non-cell-autonomous mechanisms.

neuroscience↗

bioRxiv2024

Symmetry in levels of axon-axon homophilic adhesion establishes topography in the corpus callosum and development of connectivity between brain hemispheres

Specific and highly diverse connectivity between functionally specialized regions of the nervous system is controlled at multiple scales, from anatomically organized connectivity following macroscopic axon tracts to individual axon target-finding and synapse formation. Identifying mechanisms that enable entire subpopulations of related neurons to project their axons with regional specificity within stereotyped tracts to form appropriate long-range connectivity is key to understanding brain development, organization, and function. Here, we investigate how axons of the cerebral cortex form precise connections between the two cortical hemispheres via the corpus callosum. We identify topographic principles of the developing trans-hemispheric callosal tract that emerge through intrinsic guidance executed by growing axons in the corpus callosum within the first postnatal week in mice. Using micro-transplantation of regionally distinct neurons, subtype-specific growth cone purification, subcellular proteomics, and in utero gene manipulation, we investigate guidance mechanisms of transhemispheric axons. We find that adhesion molecule levels instruct tract topography and target field guidance. We propose a model in which transcallosal axons in the developing brain perform a "handshake" that is guided through co-fasciculation with symmetric contralateral axons, resulting in the stereotyped homotopic connectivity between the brains hemispheres.

neuroscience↗

bioRxiv2023

BEAM: a combinatorial recombinase toolbox for binary gene expression and mosaic analysis

Genetic mosaic analysis, in which mutant cells reside intermingled with wild-type cells, is a powerful experimental approach, but has not been widely used in mice because existing genome-based strategies require complicated and protracted breeding schemes. We have developed an alternative approach termed BEAM (for Binary Expression Aleatory Mosaic) that relies on sparse recombinase activation to generate two genetically distinct, non-overlapping populations of cells for comparative analysis. Following delivery of DNA constructs by transfection or viral transduction, combinatorial recombinase activity generates two distinct populations of cells labeled with either green or red fluorescent protein. Any gene of interest can be mis-expressed or deleted in one population for comparison with intermingled control cells. We have extensively optimized and characterized this system both in vitro and in vivo, and demonstrate its power for investigating cell autonomy, identifying temporally or spatially aberrant phenotypes, revealing changes in cell proliferation or death, and controlling for procedural variability.

genetics↗

bioRxiv2022

ASD gene Bcl11a regulates subcellular RNA localization, associative circuitry, and social behavior

Precise, area-specific connectivity of interhemispheric callosal projection neurons (CPN) in the cerebral cortex is critical for sensory, associative, and behavioral functions. CPN circuitry, which connects and integrates the cerebral hemispheres via the corpus callosum, is centrally implicated in autism spectrum disorder (ASD) and intellectual disability (ID). Though transcriptional controls regulating CPN subtype and areal development are partially understood, downstream subcellular molecular machinery that implements CPN circuitry is essentially unknown. Here, we identify that the highly penetrant ASD/ID risk gene Bcl11a/Ctip1 is critical developmentally for appropriate and precise areal targeting of superficial layer CPN (CPNSL) projections, and that its deletion strikingly re-routes some CPNSL projections subcortically, causes dramatic disruption to subcellular CPNSL growth cone (GC) molecular machinery, and disrupts social behavior and cognition in mice. CPNSL-specific embryonic deletion of Bcl11a causes loss of correct homotopic targeting in the contralateral cortex, re-routes a substantial proportion of axonal projections through the anterior commissure, and induces strikingly aberrant, but specific and precise, projections to the basolateral amygdala. Importantly, bilateral deletion of Bcl11a from CPNSL results in abnormal social behavior and working memory. Mechanistically, we identify dysregulation of the CPNSL axonal GC-localized transcriptome in Bcl11a nulls, due to either aberrant transcription or trafficking of individual transcripts. These molecular mis-localizations disrupt axon guidance and CPNSL circuitry formation. Together, this work identifies critical functions for Bcl11a in CPNSL axonal connectivity, development of functional associative-social circuitry, and regulation of subtype-specific subcellular molecular machinery in vivo, revealing novel GC-localized transcripts that regulate precise axonal targeting and circuit formation. These results elucidate development and ASD/ID disease-related circuit disruption of CPNSL, and the importance of understanding circuit-specific subcellular molecular machinery by neurons.

neuroscience↗