Biology subjects

Posner, M.

Publications and source records attributed to Posner, M..

5 recordsLinked to original sources

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↗

bioRxiv2021

Effects of α-crystallin gene knockout on zebrafish lens development

The -crystallin small heat shock proteins contribute to the transparency and refractive properties of the vertebrate eye lens and prevent the protein aggregation that would otherwise produce lens cataracts, the leading cause of human blindness. There are conflicting data in the literature as to what role the -crystallins may play in early lens development. In this study, we used CRISPR gene editing to produce zebrafish lines with null mutations for each of the three -crystallin genes (cryaa, cryaba and cryabb). The absence of normal protein was confirmed by mass spectrometry, and lens phenotypes were assessed with differential interference contrast microscopy and histology. Loss of A-crystallin produced a variety of lens defects with varying severity in larval lenses at 3 and 4 dpf but little substantial change in normal fiber cell denucleation. Loss of either Ba- or full-length Bb-crystallin produced no substantial lens defects. Mutation of each -crystallin gene did not alter the mRNA levels of the remaining two, suggesting a lack of genetic compensation. These data confirm a developmental role for A-crystallin in lens development, but the range of phenotype severity suggests that its loss simply increases the chance for defects and that the protein is not essential. Our finding that cryaba and cryabb mutants lack noticeable lens defects is congruent with insubstantial transcript levels in lens epithelial and fiber cells. Future experiments can explore the molecular consequences of cryaa mutation and causes of lens defects in this null mutant, as well as the roles of other genes in lens development and function.

developmental biology↗

bioRxiv2020

Single cell transcriptomics of the developing zebrafish lens and identification of putative controllers of lens development

The vertebrate lens is a valuable model system for investigating the gene expression changes that coordinate tissue differentiation due to its inclusion of two spatially separated cell types, the outer epithelial cells and the deeper denucleated fiber cells that they support. Zebrafish are a useful model system for studying lens development given the organs rapid development in the first several days of life in an accessible, transparent embryo. While we have strong foundational knowledge of the diverse lens crystallin proteins and the basic gene regulatory networks controlling lens development, no study has detailed gene expression in a vertebrate lens at single cell resolution. Here we report an atlas of lens gene expression in zebrafish embryos at single cell resolution through five days of development, identifying a number of novel regulators of lens development as potential targets for future functional studies. Our temporospatial expression data address open questions about the function of -crystallins during lens development and provides the first detailed view of {beta}- and {gamma}-crystallin expression in and outside the lens. We describe subfunctionalization in transcription factor genes that occur as paralog pairs in the zebrafish. Finally, we examine the expression dynamics of cytoskeletal, RNA-binding, and transcription factors genes, identifying a number of novel patterns. Overall these data provide a foundation for identifying and characterizing lens developmental regulatory mechanisms and revealing targets for future functional studies with potential therapeutic impact.

developmental biology↗

bioRxiv2020

Landscape of oncoviral genotype and co-infection via Human papilloma andHepatitis B viral tumor in-situ profiling

Hepatitis B virus (HBV) and human papillomavirus (HPV) infection are known risk factors for developing several cancers. However, the effect of viral genotype and co-infection in actually driving oncogenesis remains unclear. We have developed and deployed a new scalable, high throughput tool (ViralMine) for sensitive and precise oncoviral genotype deconvolution using tumor RNA sequencing data from 537 virally infected liver, cervical, and head and neck tumors. We provide the first comprehensive integrative landscape of tumor-viral gene expression, viral antigen immunogenicity, patient survival, and mutational profiling organized by tumor onco-viral genotype. We find that HBV and HPV genotype, and surprisingly high rates of multi-genotype co-infection, serve as significant predictors of patient survival, tumor immune responsiveness, and APOBEC activity modulation. Finally, we demonstrate that HPV genotype strongly associates with viral onco-gene expression over cancer type, implying expression may be similar across episomal and stochastic integration-based infections. Significance StatementWe demonstrate that scalable, high-accuracy oncoviral genotyping, gene expression, and co-infection estimation is feasible from legacy tumor RNA-seq data. While HBV and HPV genotype are known risk factors for oncogenesis, viral genotype and co-infection are shown to strongly associate with disease progression, patient survival, mutational signatures, and putative tumor neoantigen immunogenicity, facilitating novel clinical associations with infections.

cancer biology↗

bioRxiv2019

Why does the zebrafish cloche mutant develop lens cataract?

The zebrafish has become a valuable model for examining ocular lens development, physiology and disease. The zebrafish cloche mutant, first described for its loss of hematopoiesis, also shows reduced eye and lens size, interruption in lens cell differentiation and a cataract likely caused by abnormal protein aggregation. To facilitate the use of the cloche mutant for studies on cataract development and prevention we characterized variation in the lens phenotype, quantified changes in gene expression by qRT-PCR and RNA-Seq and compared the ability of two promoters to drive expression of introduced proteins into the cloche lens. We found that the severity of cloche embryo lens cataract varied, while the decrease in lens diameter and retention of nuclei in differentiating lens fiber cells was constant. We found very low expression of both B-crystallin genes (cryaba and cryabb) at 4 days post fertilization (dpf) by both qRT-PCR and RNA-Seq in cloche, cloche sibling and wildtype embryos and no significant difference in A-crystallin (cryaa) expression. RNA-Seq analysis of 4 dpf embryos identified transcripts from 25,281 genes, with 1,329 showing statistically significantly different expression between cloche and wildtype samples. Downregulation of eight lens {beta}- and {gamma}M-crystallin genes and 22 retinal related genes may reflect a general reduction in eye development and growth. Six stress response genes were upregulated. We did not find misregulation of any known components of lens development gene regulatory networks. These results suggest that the cloche lens cataract is not caused by loss of A-crystallin or changes to lens gene regulatory networks. Instead, we propose that the cataract results from general physiological stress related to loss of hematopoiesis. Our finding that the zebrafish A-crystallin promoter drove strong GFP expression in the cloche lens demonstrates its use as a tool for examining the effects of introduced proteins on lens crystallin aggregation and cataract prevention.

developmental biology↗