Why does the zebrafish cloche mutant develop lens cataract?

PLoS One. 2019 Mar 12;14(3):e0211399. doi: 10.1371/journal.pone.0211399. eCollection 2019.

Abstract

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 αB-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 αA-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 β- and γM-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 αA-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 αA-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.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Basic Helix-Loop-Helix Transcription Factors / genetics*
  • Basic Helix-Loop-Helix Transcription Factors / physiology*
  • Cataract / genetics*
  • Crystallins / genetics
  • Crystallins / physiology
  • Disease Models, Animal
  • Hematopoiesis / physiology
  • Lens, Crystalline / metabolism
  • Lens, Crystalline / physiology
  • Mutation
  • Phenotype
  • Zebrafish / genetics
  • Zebrafish Proteins / genetics*
  • Zebrafish Proteins / physiology*
  • alpha-Crystallin A Chain / genetics
  • alpha-Crystallin B Chain / genetics

Substances

  • Basic Helix-Loop-Helix Transcription Factors
  • Crystallins
  • Zebrafish Proteins
  • alpha-Crystallin A Chain
  • alpha-Crystallin B Chain
  • npas4l protein, zebrafish

Grants and funding

This work was supported by an R15 AREA grant from the National Eye Institute (EY013535; nei.nih.gov) to MP. Support was also provided by the Provost Office of Ashland University and a summer student research stipend was provided as part of a Choose Ohio First scholarship grant to Ashland University to KLM. None of these funders played a role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.