Biology subjects

Klar, A.

Publications and source records attributed to Klar, A..

5 recordsLinked to original sources

bioRxiv2025

Temporal control of axonal floor plate crossing through a combination of incoherent feedforward and feedback loops of gene regulatory network regulating Robo3 expression

Spinal commissural neurons play a fundamental role in motor control and sensory perception. Robo3, a receptor expressed on pre-crossing commissural axons, is required for midline crossing. Its downregulation in post-crossing axons is essential for forming synapses with contralateral CNS targets. We demonstrate that, at the transcriptional level, the dynamic expression of Robo3 in pre-crossing neurons is controlled by incoherent feed-forward loops (iFFLs) and negative feedback loops (NFLs) that precisely regulate its transience and thereby determine midline crossing. Lhx2 and Lhx9 activate Robo3 while also inducing its repressor, Barhl2. Additionally, negative feedback loops fine-tune the transience of Robo3 expression by adjusting the relative strength of the activation and repression modules. Our genomic analysis reveals that this regulatory circuitry converges on an enhancer element of the Robo3 gene. These findings imply that diverse iFFLs, together with NFLs, are essential for regulating the extent of midline crossing across different spinal commissural subtypes.

developmental biology↗

bioRxiv2025

Transcriptional and cellular maturation of the chick spinal cord in the context of distinct neuromuscular circuits

The chicken spinal cord is a classic model system to study the early specification of neuronal cell types along its anterior-posterior axis. Here, we follow the ensuing maturation dynamics at limb levels with single cell resolution and contrast neuronal populations innervating appendages of distinct form and function. We use gene co-expression modules to identify rare cell populations with specific biological functions, and show that appendages with different motor outputs - wings and legs - rely on largely similar spinal cord cell type repertoires. Challenging the system with experimental alterations to the peripheral limb musculature reveals limited transcriptional changes, but spatially restricted plasticity in spinal cord motor neuron numbers. Collectively, our results provide a resource to investigate the molecular and cellular basis of neuronal maturation in the avian spinal cord and highlight the plastic nature of embryonic cells to adapt to changes in the limb periphery at both developmental and evolutionary timescales. HighlightsO_LICellular and transcriptional maturation of the developing chicken spinal cord at single-cell resolution C_LIO_LISingle-cell weighted gene co-expression network analysis isolates transcriptional maturation dynamics in different neuronal populations C_LIO_LIIn silico identification and in situ verification of novel markers for cerebrospinal fluid-contacting neurons C_LIO_LIMolecular characterization of the avian glycogen body C_LIO_LITranscriptional and compositional changes of spinal cord cell types in the context of different neuromuscular circuits C_LI

developmental biology↗

bioRxiv2021

Natural loss of function of ephrin-B3 shapes spinal flight circuitry in birds

Flight in birds evolved through patterning of the wings from forelimbs and transition from alternating gait to synchronous flapping. In mammals, the spinal midline guidance molecule ephrin-B3 instructs the wiring that enables limb alternation, and its deletion leads to synchronous hopping gait. Here we show that the ephrin-B3 protein in birds lacks several motifs present in other vertebrates, diminishing its affinity for the EphA4 receptor. The avian ephrin-B3 gene lacks an enhancer that drives midline expression, and is missing in Galliformes. The morphology and wiring at brachial levels of the chick spinal cord resemble those of ephrin-B3 null mice. Importantly, dorsal midline decussation, evident in the mutant mouse, is apparent at the chick brachial level, and is prevented by expression of exogenous ephrin-B3 at the roof plate. Our findings support a role for loss of ephrin-B3 function in shaping the avian brachial spinal cord circuitry and facilitating synchronous wing flapping. TeaserWalking vs flying: Deciphering the organization and evolution of the neuronal network that controls wing flapping in birds.

neuroscience↗

bioRxiv2020

A subpopulation of spinocerebellar tract neurons regulates the stability of bipedal stepping

Peripheral and intraspinal feedback is required to shape and update the output of spinal networks that execute motor behavior. We report that lumbar dI2 spinal interneurons of the chick receive synaptic input from afferents and pre-motoneurons. They innervate contralateral premotor networks in the lumbar and brachial spinal cord and their ascending projections innervate the cerebellum. These findings suggest that dI2 neurons function as interneurons in local lumbar circuits and involved in lumbo-brachial coupling and that part of them deliver peripheral and intraspinal feedback to the cerebellum. Silencing of dI2 neurons leads to destabilized stepping in P8 hatchlings with occasional collapses, variable step-profiles and wide-base walking, suggesting that the dI2 neurons may contribute to stabilization of the bipedal gait.

neuroscience↗

bioRxiv2018

The endosomal sorting adaptor HD-PTP is required for ephrin-B:EphB signalling in cell collapse and motor axon guidance

The signalling output of many transmembrane receptors that mediate cell-cell communication is restricted by the endosomal sorting complex required for transport (ESCRT), but the impact of this machinery on Eph tyrosine kinase receptor function is unknown. We identified the ESCRT-associated adaptor protein HD-PTP as part of an EphB2 BioID interactome, and confirmed this association using co-immunoprecipitation. Although HD-PTP loss does not change EphB2 expression, it attenuates the ephrin-B2:EphB2 signalling-induced collapse of cultured cells and axonal growth cones, and results in aberrant guidance of chick spinal motor neuron axons in vivo HD-PTP depletion abrogates ligand-induced EphB2 clustering, and EphB2 and Src family kinase activation. HD-PTP deficiency also accelerates ligand-induced EphB2 degradation, contrasting the phenotypes reported for other cell surface receptors. Our results link Eph signalling to the ESCRT machinery and demonstrate a role for HD-PTP in the earliest steps of ephrin-B:EphB signalling, as well as in obstructing premature receptor depletion.

cell biology↗