Biology subjects

Lai, H. C.

Publications and source records attributed to Lai, H. C..

6 recordsLinked to original sources

bioRxiv2026

Deep Cellular and Spatial Profiling of the Mouse Spinal Cord Reveals Sex-Specific Neuron Types and the Ascending Projection Neuron Repertoire

The spinal cord gives rise to central somatosensation and orchestrates autonomic and motor control. How its cellular diversity achieves functions across sex, longitudinal axis and links the spinal cord to the brain remains poorly understood. Here we used retrograde viral tracing with spatial transcriptomics and multiomic profiling of over 750,000 mouse spinal cord neurons to define its output logic and functional cellular repertoire. We identified 78 ascending spinal projection neuron classes that link it to hind-, mid-, and forebrain centers for itch, touch, and pain revealing its output wiring logic. Furthermore, we characterized >500 anatomically and transcriptomically distinct neuron types with extensive ([~]55%) rostro-caudal specialization as well as first sex specific spinal neurons. Finally, we assembled a cell-type-to-phenotype map of spinal output neurons based on genetically defined interventions. Consequently, we deliver an anatomically and functionally annotated atlas of the adult mouse spinal cord to guide future interrogation of the organ.

neuroscience↗

bioRxiv2025

Unbiased Quantification of Persistent Postural and Motor Deficits Following Spinal Cord Injury in Mice

Spinal cord injury (SCI) causes multifaceted postural and motor impairments that are challenging to quantify. Conventional behavioral tests, such as the Basso mouse scale (BMS), rely on qualitative observations, which do not detect subtle yet significant functional deficits. To perform unbiased and quantitative evaluation of motor function and posture after SCI, we employed high-speed video tracking with machine learning-based whole body pose estimation and weight-bearing analyses using the Blackbox system in freely moving mice. We found enduring alterations in posture induced by SCI not captured by conventional metrics. Postural deficits included reduced hindpaw spacing with concomitant increased forepaw spacing, narrowed femur width, and altered hind paw angles, which remained evident beyond 42 days post-injury (dpi). Furthermore, sustained deficits in locomotor activity were identified as decreased distance traveled, decreased exploratory behavior, and disrupted fore-to-hindpaw speed ratio. Additionally, we analyzed behavioral motifs using Keypoint MoSeq software and found frequency changes in unique motor syllables correlating with forward acceleration and turning after SCI. Interestingly, while motor deficits persisted, sensory deficits, such as thermal and mechanical sensitivity, returned to baseline levels by 21 days after injury in C57Bl/6J mice, with no subsequent hypersensitivity. Lastly, we developed a web-based application to assist in visualization and analyses of Blackbox-based kinematic data. Altogether, our study identifies distinct postural and motor deficits pre- and post-SCI using accurate, unbiased, and quantitative behavioral assessments. By tracking the unique features of motor recovery trajectories, researchers can more accurately assess the effectiveness of SCI therapeutic strategies.

neuroscience↗

bioRxiv2021

Nociceptor subtypes are born continuously over DRG development peaking at E10.5 - E11.5.

Sensory neurogenesis in the dorsal root ganglion (DRG) occurs in two waves of differentiation with larger, myelinated proprioceptive and low-threshold mechanoreceptor (LTMR) neurons differentiating before smaller, unmyelinated (C) nociceptive neurons. This temporal difference was established from early birthdating studies based on DRG soma cell size. However, distinctions in birthdates between molecular subtypes of sensory neurons, particularly nociceptors, is unknown. Here, we assess the birthdate of lumbar DRG neurons in mice using a thymidine analog, EdU, to label developing neurons exiting mitosis combined with co-labeling of known sensory neuron markers. We find that different nociceptor subtypes are born on similar timescales, with continuous births between E9.5 to E13.5, and peak births from E10.5 to E11.5. Notably, we find that thinly myelinated A{delta}-fiber nociceptors and peptidergic C-fibers are born more broadly between E10.5 and E11.5 than previously thought and that non-peptidergic C-fibers and C-LTMRs are born with a peak birth date of E11.5. Moreover, we find that the percentages of nociceptor subtypes born at a particular timepoint are the same for any given nociceptor cell type marker, indicating that intrinsic or extrinsic influences on cell type diversity are occurring similarly across developmental time. Overall, the patterns of birth still fit within the classical "two wave" description, as touch and proprioceptive fibers are born primarily at E10.5, but suggest that nociceptors have a slightly broader wave of birthdates with different nociceptor subtypes continually differentiating throughout sensory neurogenesis irrespective of myelination.

developmental biology↗

bioRxiv2020

Loss of Prdm12 during development, but not in mature nociceptors, causes defects in pain sensation.

Prdm12 is as a key transcription factor in nociceptor neurogenesis. Mutations of Prdm12 cause Congenital Insensitivity to Pain (CIP) due to failure of nociceptor development. However, precisely how deletion of Prdm12 during development or adulthood affects nociception is unknown. Here, we employ tissue- and temporal-specific knockout mouse models to test the function of Prdm12 during development and in adulthood. We find that constitutive loss of Prdm12 causes deficiencies in proliferation during sensory neurogenesis. We also demonstrate that conditional knockout from dorsal root ganglia (DRGs) during embryogenesis causes defects in nociception. In contrast, we find that in adult DRGs, Prdm12 is dispensable for pain sensation and injury-induced hypersensitivity. Using transcriptomic analysis, we found unique changes in adult Prdm12 knockout DRGs compared to embryonic knockout, and that PRDM12 is likely a transcriptional activator in the adult. Overall, we find that the function of PRDM12 changes over developmental time.

neuroscience↗

bioRxiv2020

Evidence for genetically distinct direct and indirect spinocerebellar pathways mediating proprioception.

Proprioception, the sense of limb and body position, generates a map of the body that is essential for proper motor control, yet we know little about precisely how neurons in proprioceptive pathways are wired. Defining the anatomy of secondary neurons in the spinal cord that integrate and relay proprioceptive and potentially cutaneous information from the periphery to the cerebellum is fundamental to understanding how proprioceptive circuits function. Here, we use genetic tools in both male and female mice to define the unique anatomical trajectories of long-range direct and indirect spinocerebellar pathways as well as local intersegmental spinal circuits. We find that Clarkes column (CC) neurons, a major contributor to the direct spinocerebellar pathway, has mossy fiber terminals that diversify extensively in the cerebellar cortex with axons terminating bilaterally, but with no significant axon collaterals within the spinal cord, medulla, or cerebellar nuclei. By contrast, we find that two of the indirect pathways, the spino-lateral reticular nucleus (spino-LRt) and spino-olivary pathways, are in part, derived from cervical Atoh1-lineage neurons, while thoracolumbar Atoh1-lineage neurons project mostly locally within the spinal cord. Notably, while cervical and thoracolumbar Atoh1-lineage neurons connect locally with motor neurons, no CC to motor neuron connections were detected. Silencing of caudal Atoh1- lineage neurons results in a subtle motor impairment consistent with a defect in local proprioceptive circuitry. Altogether, we define anatomical differences between long-range direct, indirect, and local proprioceptive subcircuits that likely mediate different components of proprioceptive-motor behaviors. Significance StatementWe define the anatomy of long-range direct and indirect spinocerebellar pathways as well as local spinal proprioceptive circuits. We observe that mossy fiber axon terminals of Clarkes column (CC) neurons diversify proprioceptive information across granule cells in multiple lobules on both ipsilateral and contralateral sides sending no significant collaterals within the spinal cord, medulla, or cerebellar nuclei. Strikingly, we find that cervical spinal cord Atoh1-lineage neurons form mainly the indirect spino- lateral reticular nucleus and spino-olivary tracts and thoracolumbar Atoh1-lineage neurons project locally within the spinal cord while only a few Atoh1-lineage neurons form a direct spinocerebellar tract. Altogether, we define the development, anatomical projections, and some behavioral consequences of silencing spinal proprioceptive pathways.

neuroscience↗

bioRxiv2020

Motor neurons involved in fine motor control are labeled by tracing Atoh1-lineage neurons in the spinal cord

Motor neurons (MNs) innervating the digit muscles of the intrinsic hand and foot (IH and IF) control fine motor movements. Previous studies suggest that the IH and IF MN pools have a unique developmental history in comparison to limb MN pools. Consistent with having this unique development, we find that the IH and IF MN pools are labeled postnatally using a CRE knock-in mouse line of Atoh1, a developmentally expressed basic helix-loop-helix (bHLH) transcription factor, while limb-innervating MN pools are not. Approximately 60% of the IH and IF MN pools are labeled and are a mixture of alpha and gamma-MNs. In addition, because Atoh1 is known developmentally to specify many cerebellar-projecting neurons, we tested the hypothesis that IH and IF MNs can send axon collaterals to the cerebellum as a mechanism of corollary discharge. Using intersectional genetic, viral labeling, and retrograde labeling strategies, we were unable to provide evidence in support of this idea. As a secondary finding of our viral labeling experiments, we report here that injection of both AAV and Lentiviruses in the periphery can cross the blood-brain barrier to infect Purkinje cells within the central nervous system. Altogether, though, we find that labeling of the IH and IF motor neurons using the Atoh1 CRE knock-in mouse suggests that IH and IF MNs have a unique developmental history and that this mouse strain might be a useful tool to target these specific sets of neurons allowing for functional studies of fine motor control. Significance StatementMotor neurons (MNs) of the intrinsic hand and foot (IH and IF) are labeled postnatally using a CRE knock-in mouse line of the basic helix-loop-helix (bHLH) transcription factor Atoh1 indicating a unique developmental history. We tested whether IH and IF MNs send axon collaterals rostrally to the cerebellum as a mechanism of direct corollary discharge from MNs, but the question remains unresolved. As a resource for the community, we report that injection of both AAV and Lentiviruses in the periphery can cross the blood-brain barrier and infect Purkinje cells within the central nervous system.

developmental biology↗