Greig, L. C. | bioRxiv Science

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↗