celsr1a is essential for tissue homeostasis and onset of aging phenotypes in the zebrafish

Effect of nonsense-mediated mRNA decay factor SMG9 deficiency on premature aging in zebrafish

SMG9 is an essential component of the nonsense-mediated mRNA decay (NMD) machinery, a quality control mechanism that selectively degrades aberrant transcripts. Mutations in SMG9 are associated with heart and brain malformation syndrome (HBMS). However, the molecular mechanism underlying HBMS remains unclear. We generated smg9 mutant zebrafish (smg9oi7/oi7) that have a lifespan of approximately 6 months or longer, allowing for analysis of the in vivo function of Smg9 in adults in more detail. smg9oi7/oi7 zebrafish display congenital brain abnormalities and reduced cardiac contraction. Additionally, smg9oi7/oi7 zebrafish exhibit a premature aging phenotype. Analysis of NMD target mRNAs shows a trend toward increased mRNA levels in smg9oi7/oi7 zebrafish. Spermidine oxidase (Smox) is increased in smg9oi7/oi7 zebrafish, resulting in the accumulation of byproducts, reactive oxygen species, and acrolein. The accumulation of smox mRNA due to NMD dysregulation caused by Smg9 deficiency leads to increased oxidative stress, resulting in premature aging.

Systematic Characterization of the Disruption of Intestine during Liver Tumor Progression in the xmrk Oncogene Transgenic Zebrafish Model

The crosstalk between tumors and their local microenvironment has been well studied, whereas the effect of tumors on distant tissues remains understudied. Studying how tumors affect other tissues is important for understanding the systemic effect of tumors and for improving the overall health of cancer patients. In this study, we focused on the changes in the intestine during liver tumor progression, using a previously established liver tumor model through inducible expression of the oncogene xmrk in zebrafish. Progressive disruption of intestinal structure was found in the tumor fish, displaying villus damage, thinning of bowel wall, increase in goblet cell number, decrease in goblet cell size and infiltration of eosinophils, most of which were observed phenotypes of an inflammatory intestine. Intestinal epithelial cell renewal was also disrupted, with decreased cell proliferation and increased cell death. Analysis of intestinal gene expression through RNA-seq suggested deregulation of genes related to intestinal function, epithelial barrier and homeostasis and activation of pathways in inflammation, epithelial mesenchymal transition, extracellular matrix organization, as well as hemostasis. Gene set enrichment analysis showed common gene signatures between the intestine of liver tumor fish and human inflammatory bowel disease, the association of which with cancer has been recently noticed. Overall, this study represented the first systematic characterization of the disruption of intestine under the liver tumor condition and suggested targeting intestinal inflammation as a potential approach for managing cancer cachexia.

Aging Activates the Immune System and Alters the Regenerative Capacity in the Zebrafish Heart

Age-associated organ failure and degenerative diseases have a major impact on human health. Cardiovascular dysfunction has an increasing prevalence with age and is one of the leading causes of death. In contrast to humans, zebrafish have extraordinary regeneration capacities of complex organs including the heart. In addition, zebrafish has recently become a model organism in research on aging. Here, we have compared the ventricular transcriptome as well as the regenerative capacity after cryoinjury of old and young zebrafish hearts. We identified the immune system as activated in old ventricles and found muscle organization to deteriorate upon aging. Our data show an accumulation of immune cells, mostly macrophages, in the old zebrafish ventricle. Those immune cells not only increased in numbers but also showed morphological and behavioral changes with age. Our data further suggest that the regenerative response to cardiac injury is generally impaired and much more variable in old fish. Collagen in the wound area was already significantly enriched in old fish at 7 days post injury. Taken together, these data indicate an ‘inflammaging’-like process in the zebrafish heart and suggest a change in regenerative response in the old.

Interleukin-10 regulates goblet cell numbers through Notch signaling in the developing zebrafish intestine

Cytokines are immunomodulatory proteins that orchestrate cellular networks in health and disease. Among these, interleukin (IL)-10 is critical for the establishment of intestinal homeostasis, as mutations in components of the IL-10 signaling pathway result in spontaneous colitis. Whether IL-10 plays other than immunomodulatory roles in the intestines is poorly understood. Here, we report that il10, il10ra, and il10rb are expressed in the zebrafish developing intestine as early as 3 days post fertilization. CRISPR/Cas9-generated il10-deficient zebrafish larvae showed an increased expression of pro-inflammatory genes and an increased number of intestinal goblet cells compared to WT larvae. Mechanistically, Il10 promotes Notch signaling in zebrafish intestinal epithelial cells, which in turn restricts goblet cell expansion. Using murine organoids, we showed that IL-10 modulates goblet cell frequencies in mammals, suggesting conservation across species. This study demonstrates a previously unappreciated IL-10-Notch axis regulating goblet cell homeostasis in the developing zebrafish intestine and may help explain the disease severity of IL-10 deficiency in the intestines of mammals.

The RNA helicase Ddx52 functions as a growth switch in juvenile zebrafish

Vertebrate animals usually display robust growth trajectories during juvenile stages, and reversible suspension of this growth momentum by a single genetic determinant has not been reported. Here, we report a single genetic factor that is essential for juvenile growth in zebrafish. Using a forward genetic screen, we recovered a temperature-sensitive allele, pan (after Peter Pan), that suspends whole-organism growth at juvenile stages. Remarkably, even after growth is halted for a full 8-week period, pan mutants are able to resume a robust growth trajectory after release from the restrictive temperature, eventually growing into fertile adults without apparent adverse phenotypes. Positional cloning and complementation assays revealed that pan encodes a probable ATP-dependent RNA helicase (DEAD-Box Helicase 52; ddx52) that maintains the level of 47S precursor ribosomal RNA. Furthermore, genetic silencing of ddx52 and pharmacological inhibition of bulk RNA transcription similarly suspend the growth of flies, zebrafish and mice. Our findings reveal evidence that safe, reversible pauses of juvenile growth can be mediated by targeting the activity of a single gene, and that its pausing mechanism has high evolutionary conservation.

Zebrafish models of sarcopenia

Sarcopenia - the accelerated age-related loss of muscle mass and function - is an under-diagnosed condition, and is central to deteriorating mobility, disability and frailty in older age. There is a lack of treatment options for older adults at risk of sarcopenia. Although sarcopenia's pathogenesis is multifactorial, its major phenotypes - muscle mass and muscle strength - are highly heritable. Several genome-wide association studies of muscle-related traits were published recently, providing dozens of candidate genes, many with unknown function. Therefore, animal models are required not only to identify causal mechanisms, but also to clarify the underlying biology and translate this knowledge into new interventions. Over the past several decades, small teleost fishes had emerged as powerful systems for modeling the genetics of human diseases. Owing to their amenability to rapid genetic intervention and the large number of conserved genetic and physiological features, small teleosts - such as zebrafish, medaka and killifish - have become indispensable for skeletal muscle genomic studies. The goal of this Review is to summarize evidence supporting the utility of small fish models for accelerating our understanding of human skeletal muscle in health and disease. We do this by providing a basic foundation of the (zebra)fish skeletal muscle morphology and physiology, and evidence of muscle-related gene homology. We also outline challenges in interpreting zebrafish mutant phenotypes and in translating them to human disease. Finally, we conclude with recommendations on future directions to leverage the large body of tools developed in small fish for the needs of genomic exploration in sarcopenia.