A Markerless Pose Estimator Applicable to Limbless Animals

Patient-specific mutation of contact site protein Tomm70 causes neurodegeneration

TOMM70 is a receptor at the contact site between mitochondria and the endoplasmic reticulum, and TOMM70 has been identified as a risk gene for hereditary spastic paraplegia. Furthermore, de novo missense variants of TOMM70 have been identified to cause neurological impairments in two unrelated patients. Here, we show that mutant zebrafish ruehreip25ca also harbour a missense mutation in tomm70, affecting the same conserved isoleucine residue as in one of the human patients. Using this model, we demonstrate how loss of Tomm70 function leads to impairment. At the molecular level, the mutation affected the interaction of Tomm70 with the endoplasmic reticulum protein Lam6, a known sterol transporter. At the neuronal level, the mutation impaired mitochondrial transport to the axons and dendrites, leading to demyelination of large calibre axons in the spinal cord. These neurodegenerative defects in zebrafish were associated with reduced endurance and swimming efficiency, and alterations in the C-start escape response, which correlated with decreased spiking in giant Mauthner neurons. Thus, in zebrafish, a mutation in the endoplasmic reticulum-mitochondria contact site protein Tomm70 recreates some of the neurodegenerative phenotypes characteristic of hereditary spastic paraplegia.

Axon demyelination and degeneration in a zebrafish spastizin model of hereditary spastic paraplegia

Hereditary spastic paraplegias (HSPs) are a diverse set of neurological disorders characterized by progressive spasticity and weakness in the lower limbs caused by damage to the axons of the corticospinal tract. More than 88 genetic mutations have been associated with HSP, yet the mechanisms underlying these disorders are not well understood. We replicated the pathophysiology of one form of HSP known as spastic paraplegia 15 (SPG15) in zebrafish. This disorder is caused in humans by mutations in the ZFYVE26 gene, which codes for a protein called SPASTIZIN. We show that, in zebrafish, the significant reduction of Spastizin caused degeneration of large motor neurons. Motor neuron degeneration is associated with axon demyelination in the spinal cord and impaired locomotion in the spastizin mutants. Our findings reveal that the reduction in Spastizin compromises axonal integrity and affects the myelin sheath, ultimately recapitulating the pathophysiology of HSPs.

Diving deep: zebrafish models in motor neuron degeneration research

In the dynamic landscape of biomedical science, the pursuit of effective treatments for motor neuron disorders like hereditary spastic paraplegia (HSP), amyotrophic lateral sclerosis (ALS), and spinal muscular atrophy (SMA) remains a key priority. Central to this endeavor is the development of robust animal models, with the zebrafish emerging as a prime candidate. Exhibiting embryonic transparency, a swift life cycle, and significant genetic and neuroanatomical congruencies with humans, zebrafish offer substantial potential for research. Despite the difference in locomotion-zebrafish undulate while humans use limbs, the zebrafish presents relevant phenotypic parallels to human motor control disorders, providing valuable insights into neurodegenerative diseases. This review explores the zebrafish's inherent traits and how they facilitate profound insights into the complex behavioral and cellular phenotypes associated with these disorders. Furthermore, we examine recent advancements in high-throughput drug screening using the zebrafish model, a promising avenue for identifying therapeutically potent compounds.

The caloric value of food intake structurally adjusts a neuronal mushroom body circuit mediating olfactory learning in Drosophila

Associative learning enables the adaptive adjustment of behavioral decisions based on acquired, predicted outcomes. The valence of what is learned is influenced not only by the learned stimuli and their temporal relations, but also by prior experiences and internal states. In this study, we used the fruit fly Drosophila melanogaster to demonstrate that neuronal circuits involved in associative olfactory learning undergo restructuring during extended periods of low-caloric food intake. Specifically, we observed a decrease in the connections between specific dopaminergic neurons (DANs) and Kenyon cells at distinct compartments of the mushroom body. This structural synaptic plasticity was contingent upon the presence of allatostatin A receptors in specific DANs and could be mimicked optogenetically by expressing a light-activated adenylate cyclase in exactly these DANs. Importantly, we found that this rearrangement in synaptic connections influenced aversive, punishment-induced olfactory learning but did not impact appetitive, reward-based learning. Whether induced by prolonged low-caloric conditions or optogenetic manipulation of cAMP levels, this synaptic rearrangement resulted in a reduction of aversive associative learning. Consequently, the balance between positive and negative reinforcing signals shifted, diminishing the ability to learn to avoid odor cues signaling negative outcomes. These results exemplify how a neuronal circuit required for learning and memory undergoes structural plasticity dependent on prior experiences of the nutritional value of food.