Garver, T. | Search bioRxiv

bioRxiv2024

Loss of αBa-crystallin, but not αA-crystallin, increases age-related cataract in the zebrafish lens

The vertebrate eye lens is an unusual organ in that most of its cells lack nuclei and the ability to replace aging protein. The small heat shock protein -crystallins evolved to become key components of this lens, possibly because of their ability to prevent aggregation of aging protein that would otherwise lead to lens opacity. Most vertebrates express two -crystallins, A- and B-crystallin, and mutations in each are linked to human cataract. In a mouse knockout model only the loss of A-crystallin led to early-stage lens cataract. We have used the zebrafish as a model system to investigate the role of -crystallins during lens development. Interestingly, while zebrafish express one lens-specific A-crystallin gene (cryaa), they express two B-crystallin genes, with one evolving lens specificity (cryaba) and the other retaining the broad expression of its mammalian ortholog (cryabb). In this study we used individual mutant zebrafish lines for all three -crystallin genes to determine the impact of their loss on age-related cataract. Surprisingly, unlike mouse knockout models, we found that the loss of the Ba-crystallin gene cryaba led to an increase in lens opacity compared to cryaa null fish at 24 months of age. Loss of A-crystallin did not increase the prevalence of cataract. We also used single cell RNA-Seq and RT-qPCR data to show a shift in the lens expression of zebrafish -crystallins between 5 and 10 days post fertilization (dpf), with 5 and 6 dpf lenses expressing cryaa almost exclusively, and expression of cryaba and cryabb becoming more prominent after 10 dpf. These data show that cryaa is the primary -crystallin during early lens development, while the protective role for cryaba becomes more important during lens aging. This study is the first to quantify cataract prevalence in wild-type zebrafish, showing that lens opacities develop in approximately 25% of fish by 18 months of age. None of the three -crystallin mutants showed a compensatory increase in the expression of the remaining two crystallins, or in the abundant {beta}B1-crystallin. Overall, these findings indicate an ontogenetic shift in the functional importance of individual -crystallins during zebrafish lens development. Our finding that the lens-specific zebrafish Ba-crystallin plays the leading role in preventing age-related cataract adds a new twist to our understanding of vertebrate lens evolution.

developmental biology↗

bioRxiv2023

The autism-associated loss of δ-catenin functions disrupts social behaviors

{delta}-catenin is expressed in excitatory synapses and functions as an anchor for the glutamatergic AMPA receptor (AMPAR) GluA2 subunit in the postsynaptic density. The glycine 34 to serine (G34S) mutation in the{delta} -catenin gene is found in autism spectrum disorder (ASD) patients and induces loss of {delta}-catenin functions at excitatory synapses, which is presumed to underlie ASD pathogenesis in humans. However, how the G34S mutation causes loss of {delta}-catenin functions to induce ASD remains unclear. Here, using neuroblastoma cells, we discover that the G34S mutation generates an additional phosphorylation site for glycogen synthase kinase 3{beta} (GSK3{beta}). This promotes {delta}-catenin degradation and causes the reduction of {delta}-catenin levels, which likely contributes to the loss of {delta}-catenin functions. Synaptic {delta}-catenin and GluA2 levels in the cortex are significantly decreased in mice harboring the {delta}-catenin G34S mutation. The G34S mutation increases glutamatergic activity in cortical excitatory neurons while it is decreased in inhibitory interneurons, indicating changes in cellular excitation and inhibition. {delta}-catenin G34S mutant mice also exhibit social dysfunction, a common feature of ASD. Most importantly, inhibition of GSK3{beta} activity reverses the G34S-induced loss of {delta}-catenin function effects in cells and mice. Finally, using {delta}-catenin knockout mice, we confirm that {delta}-catenin is required for GSK3{beta} inhibition-induced restoration of normal social behaviors in {delta}-catenin G34S mutant animals. Taken together, we reveal that the loss of {delta}-catenin functions arising from the ASD-associated G34S mutation induces social dysfunction via alterations in glutamatergic activity and that GSK3{beta} inhibition can reverse {delta}-catenin G34S-induced synaptic and behavioral deficits. Significance Statement{delta}-catenin is important for the localization and function of glutamatergic AMPA receptors at synapses in many brain regions. The glycine 34 to serine (G34S) mutation in the{delta} -catenin gene is found in autism patients and results in the loss of {delta}-catenin functions. {delta}-catenin expression is also closely linked to other autism-risk genes involved in synaptic structure and function, further implying that it is important for the autism pathophysiology. Importantly, social dysfunction is a key characteristic of autism. Nonetheless, the links between {delta}-catenin functions and social behaviors are largely unknown. The significance of the current research is thus predicated on filling this gap by discovering the molecular, cellular, and synaptic underpinnings of the role of {delta}-catenin in social behaviors.

neuroscience↗