Biology subjects

Co, M.

Publications and source records attributed to Co, M..

6 recordsLinked to original sources

bioRxiv2024

Detailed phenotyping of Tbr1-2A-CreER knock-in mice demonstrates significant impacts on TBR1 protein levels and axon development

Spatiotemporal control of Cre-mediated recombination has been an invaluable tool for understanding key developmental processes. For example, knock-in of Cre into cell type marker gene loci drives Cre expression under endogenous promoter and enhancer sequences, greatly facilitating the study of diverse neuronal subtypes in the cerebral cortex. However, insertion of exogenous DNA into the genome can have unintended effects on local gene regulation or protein function that must be carefully considered. Here, we analyze a recently generated Tbr1-2A-CreER knock-in mouse line, where a 2A-CreER cassette was inserted in-frame just before the stop codon of the transcription factor gene Tbr1. Heterozygous TBR1 mutations in humans and mice are known to cause autism or autism-like behavioral phenotypes accompanied by structural brain malformations, most frequently a reduction of the anterior commissure. Thus, it is critical for modified versions of Tbr1 to exhibit true wild-type-like activity. We evaluated the Tbr1-2A-CreER allele for its potential impact on Tbr1 function and complementation to Tbr1 loss-of-function alleles. In mice with one copy of the Tbr1-2A-CreER allele, we identified reduction of TBR1 protein in early postnatal cortex along with thinning of the anterior commissure, suggesting hypersensitivity of this structure to TBR1 dosage. Comparing Tbr1-2A-CreER and Tbr1-null heterozygous and homozygous mice to Tbr1-null complementation crosses showed reductions of TBR1 dosage ranging from 28.4% to 95.9%. Using these combinatorial genotypes, we found that low levels of TBR1 protein ([~]16%) are sufficient to establish cortical layer positioning, while greater levels (>50%) are required for normal suppression of layer 5 identity. In total, these results strongly support the conclusion that Tbr1-2A-CreER is a hypomorphic allele. We advise caution when interpreting experiments using this allele, such as transcriptomic studies, considering the sensitivity of various corticogenic processes to TBR1 dosage and the association of heterozygous TBR1 mutations with complex neurodevelopmental disorders.

developmental biology↗

bioRxiv2022

Shared and distinct functional effects of patient-specific Tbr1 mutations on cortical development

Predicted loss-of-function and missense heterozygous de novo mutations of TBR1 are strongly associated with intellectual disability and autism. The functional effects of these heterogeneous mutations on cortical development and genotype-phenotype relationships have yet to be explored. We characterized mouse models carrying patient mutations A136PfsX80 and K228E, finding convergent and discordant phenotypes. The A136PfsX80 mutation is loss-of-function and allelic to the Tbr1 knockout. In contrast, K228E causes significant upregulation of TBR1. Heterozygosity of either mutation produces axon defects, including reduction of the anterior commissure, and CTIP2 downregulation in adult cortex. While mice lacking TBR1 show extensive cortical apoptosis and inverted layering, K228E homozygotes show normal apoptosis levels and a complex layering phenotype--suggesting partial, yet abnormal, function of the allele. The construct and face validity of these Tbr1 patient mutation mice suggests they will be valuable translational models for studying the function of this essential brain transcription factor.

neuroscience↗

bioRxiv2022

Broadly-recognized, cross-reactive SARS-CoV-2 CD4 T cell epitopes are highly conserved across human coronaviruses and presented by common HLA alleles

Sequence homology between SARS-CoV-2 and common-cold human coronaviruses (HCoVs) raises the possibility that memory responses to prior HCoV infection can impact the T cell response in COVID-19. We studied T cells recognizing SARS-CoV-2 and HCoVs in convalescent COVID-19 donors, and identified a highly conserved SARS-CoV-2 sequence S811-831, with two overlapping epitopes presented by common MHC-II proteins HLA-DQ5 and HLA-DP4. These epitopes were recognized by CD4+ T cells from convalescent COVID-19 donors, mRNA vaccine recipients, and by low-abundance CD4+ T cells in uninfected donors. TCR sequencing revealed a diverse repertoire with public TCRs. CD4+ T cell cross-reactivity was driven by the remarkably strong conservation of T cell contact residues in both HLA-DQ5 and HLA-DP4 binding frames, with distinct patterns of HCoV cross-reactivity explained by MHC-II binding preferences and substitutions at secondary TCR contact sites. These data highlight S811-831 as a highly-conserved CD4+ T cell epitope broadly recognized across human populations.

immunology↗

bioRxiv2020

Functional Identification of Specialized Basal Ganglia Circuits that Regulate Vocal Motor Sequences

Disruption of the transcription factor FoxP2, which is enriched in the basal ganglia, impair vocal development in humans and songbirds. The basal ganglia are essential for the selection and sequencing of motor actions, but the circuit mechanisms governing accurate sequencing of learned vocalizations are unknown. Here, we show expression of FoxP2 in the basal ganglia is vital for the fluent initiation and termination of birdsong, and the maintenance of song syllable sequencing in adulthood. Knockdown of FoxP2 imbalances dopamine receptor expression across striatal direct-like and indirect-like pathways, suggesting a role of dopaminergic signaling in regulating vocal-motor sequencing. Confirming this prediction, we show that phasic dopamine activation, and not inhibition, during singing drives repetition of song syllables, thus also impairing fluent initiation and termination of birdsong. These findings demonstrate discrete circuit origins for the dysfluent repetition of vocal elements, a phenotype commonly observed in speech disorders.

neuroscience↗

bioRxiv2020

Autism-linked gene FoxP1 selectively regulates the cultural transmission of learned vocalizations

Autism spectrum disorders (ASD) are characterized by impaired learning of culturally transmitted behaviors like social skills, speech, and language1-3. These behaviors are learned by copying parents and other social models during development, a two-stage process that involves forming memories of appropriate behaviors during social experiences and then using those memories to guide imitation. How ASD-linked genes impair these often-intertwined aspects of learning is not known, thereby limiting our understanding of the developmental progression of ASD and the targeting of therapeutic interventions. Here we show that these aspects of learning are dissociable and that the ASD-linked gene FoxP1 selectively impairs learning from social experience, but not behavioral imitation. Haploinsufficiency of FOXP1 in humans causes FOXP1 syndrome, a neurodevelopmental disorder typified by severe disruptions in speech and language development, and other ASD-associated symptoms4,5. We tested how knockdown of FoxP1 (FP1-KD) affects the cultural transmission of vocal behaviors in zebra finches, a songbird that learns by memorizing and vocally copying the song of an adult song-tutor. We find that FP1-KD blocks song learning in juvenile birds by selectively impairing their ability to encode a memory during social experiences with a songtutor. These learning deficits are linked to disruptions in experience-driven structural and functional plasticity. However, if birds are exposed to tutor-song prior to FP1-KD, their ability to imitate that song during development is unaffected. Thus, FP1-KD impairs cultural transmission of vocalizations by disrupting the ability to form appropriate vocal memories, yet spares the ability to use previously acquired memories to guide vocal learning. This indicates that learning from social experience may be particularly vulnerable in FOXP1 syndrome.

neuroscience↗

bioRxiv2019

Cortical Foxp2 supports behavioral flexibility and developmental dopamine D1 receptor expression

Genetic studies have associated FOXP2 variation with speech and language disorders and other neurodevelopmental disorders involving pathology of the cortex. In this brain region, FoxP2 is expressed from development into adulthood, but little is known about its downstream molecular and behavioral functions. Here, we characterized cortex-specific Foxp2 conditional knockout mice and found a major deficit in reversal learning, a form of behavioral flexibility. In contrast, they showed normal activity levels, anxiety, and vocalizations, save for a slight decrease in neonatal call loudness. These behavioral phenotypes were accompanied by decreased cortical dopamine D1 receptor (D1R) expression at neonatal and adult stages, while general cortical development remained unaffected. Finally, using single-cell transcriptomics, we identified at least five excitatory and three inhibitory D1R-expressing cell types in neonatal frontal cortex, and we found changes in D1R cell type composition and gene expression upon cortical Foxp2 deletion. Strikingly, these alterations included non-cell-autonomous changes in upper-layer neurons and interneurons. Together these data support a role for Foxp2 in the development of dopamine-modulated cortical circuits and behaviors relevant to neurodevelopmental disorders.

neuroscience↗