Biology subjects

Froberg, J. E.

Publications and source records attributed to Froberg, J. E..

4 recordsLinked to original sources

bioRxiv2026

Sequestration of growth cone surface proteins by cytoplasmic Lrrtm2 induces de novo amygdala innervation by cerebral cortex associative neurons

Precise establishment of distinct cerebral cortex circuits is essential for sensorimotor function, high-level cognition, and cross-modality integration and association. Although an increasing set of molecular controls over subtype-specific cortical wiring have been identified, much less is known about how molecules in growth cones (GCs) regulate precise long-range projection of axons through complex environments, or how dysregulation of GC molecular machinery disrupts precision of circuit formation. Here, we discover a generalizable mechanism for regulation of precise circuit wiring by focusing on callosal projection neurons (CPN), which link cortical hemispheres via the corpus callosum. CPN are centrally involved in associative and cognitive function, and are often disrupted in people with autism spectrum disorders (ASD) and intellectual disabilities (ID). We identify dysregulated subcellular CPN GC proteomes in vivo after CPN-specific deletion of Bcl11a/Ctip1, a transcription factor (TF) with variants that cause ASD/ID in humans, and validate localization of dysregulated proteins to CPN GCs ex vivo. We identify that disruption of Lrrtm2 - a canonically postsynaptic transmembrane protein - in CPN GCs specifically induces de novo innervation of the amygdala, an evolutionarily ancient regulator of social behavior, cognition, and anxiety that is abnormally activated in humans with ASD. Mechanistically, we identify that deletion of Bcl11a from CPN disrupts targeting of Lrrtm2 to CPN GC membranes, causing cytoplasmic sequestration of key CPN GC surface proteins, and resulting in aberrant innervation of basolateral amygdala (BLA), which is typically targeted by evolutionarily older archicortex. Together, this work connects deletion of a causal ASD/ID TF, dysregulation of a non-canonical control over GC surface protein remodeling, and formation of a de novo, subtype-specific circuit between cerebral cortex and BLA - similar mechanisms likely generalize across neuron subtypes. These results expand conceptual understanding of how diverse circuits are precisely constructed and potentially evolve, and how coordinated dysregulation of GC molecules can disrupt precise subtype-specific circuitry, contributing to diverse neurodevelopmental and neuropsychiatric disorders.

neuroscience↗

bioRxiv2024

Cortical projection neurons with distinct axonal connectivity employ ribosomal complexes with distinct protein compositions

Diverse subtypes of cortical projection neurons (PN) form long-range axonal projections that are responsible for distinct sensory, motor, cognitive, and behavioral functions. Translational control has been identified at multiple stages of PN development, but how translational regulation contributes to formation of distinct, subtype-specific long-range circuits is poorly understood. Ribosomal complexes (RCs) exhibit variations of their component proteins, with an increasing set of examples that confer specialized translational control. Here, we directly compare the protein compositions of RCs in vivo from two closely related cortical neuron subtypes-cortical output "subcerebral PN" (SCPN) and interhemispheric "callosal PN" (CPN)- during establishment of their distinct axonal connectivity. Using retrograde labeling of subtype-specific somata, purification by fluorescence-activated cell sorting, ribosome immunoprecipitation, and ultra-low-input mass spectrometry, we identify distinct protein compositions of RCs from these two subtypes. Strikingly, we identify 16 associated proteins reliably and exclusively detected only in RCs of SCPN. 11 of these proteins have known interaction with components of ribosomes; we further validated ribosome interaction with protein kinase C epsilon (PRKCE), a candidate with roles in synaptogenesis. PRKCE and a subset of SCPN-specific candidate ribosome-associated proteins also exhibit enriched gene expression by SCPN. Together, these results indicate that ribosomal complexes exheq]ibit subtype-specific protein composition in distinct subtypes of cortical projection neurons during development, and identify potential candidates for further investigation of function in translational regulation involved in subtype-specific circuit formation.

neuroscience↗

bioRxiv2022

Development of ultra-low-input nanoRibo-seq enables quantification of translational control, revealing broad uORF translation by subtype-specific neurons

While increasingly powerful approaches enable investigation of transcription using small samples of RNA, approaches to investigate translational regulation in small populations of specific cell types, and/or (sub)-cellular contexts are lacking. Comprehensive investigation of mRNAs actively translated into proteins from ultra-low input material would provide important insight into molecular machinery and mechanisms underlying many cellular, developmental, and disease processes in vivo. Such investigations are limited by the large input required for current state-of-the-art Ribo-seq. Here, we present an optimized, ultra-low input "nanoRibo-seq" approach using 102 - 103-fold less input material than standard approaches, demonstrated here in subtype-specific neurons. nanoRibo-seq requires as few as 2.5K neurons, and exhibits rigorous quality control features: 1) strong enrichment for CDS versus UTRs and non-CDS; 2) narrow, distinct length distributions over CDS; 3) ribosome P-sites predominantly in-frame to annotated CDS; and 4) sufficient ribosome-protected fragment (RPF) coverage across thousands of mRNAs. As proof-of-concept, we calculate translation efficiencies from paired Ribo-seq and alkaline fragmented control libraries from "callosal projection neurons" (CPN), revealing divergence between mRNA abundance and RPF abundance for hundreds of genes. Intriguingly, we identify substantial translation of upstream ORFs in the 5 UTRs of genes involved in axon guidance and synapse assembly. nanoRibo-seq enables previously inaccessible investigation of translational regulation by small, specific cell populations in normal or perturbed contexts.

molecular biology↗

bioRxiv2018

Megadomains and superloops form dynamically but are dispensable for X chromosome inactivation and gene escape

The mammalian inactive X-chromosome (Xi) is structurally distinct from all other chromosomes and serves as a model for how the 3D genome is organized. The Xi shows weakened topologically associated domains and is instead organized into megadomains and superloops directed by the noncoding loci, Dxz4 and Firre. Their functional significance is presently unclear, though one study suggests that they permit Xi genes to escape silencing. Here, we find that megadomains do not precede Xist expression or Xi gene silencing. Deleting Dxz4 disrupts megadomain formation, whereas deleting Firre weakens intra-megadomain interactions. Surprisingly, however, deleting Dxz4 and Firre has no impact on Xi silencing and gene escape. Nor does it affect Xi nuclear localization, stability, or H3K27 methylation. Additionally, ectopic integration of Dxz4 and Xist is not sufficient to form megadomains on autosomes, further uncoupling megadomain formation from chromosomal silencing. We conclude that Dxz4 and megadomains are dispensable for Xi silencing and escape from X-inactivation.

genomics↗