In situ hybridization to detect spatial gene expression in medaka

Area of Science:

• Comparative genomics
• Fish biology
• Molecular endocrinology

Background:

• Understanding differential gene expression in whole organisms is crucial for toxicological and developmental studies.
• Japanese medaka (Oryzias latipes) is a valuable model organism for aquatic research due to its small size and oviparous nature.
• Aromatase (CYP19a) plays a key role in sexual development and is known for its tissue- and gender-specific expression.

Purpose of the Study:

• To develop and validate a whole-animal tissue section in situ hybridization (ISH) system for detecting differential gene expression in Japanese medaka.
• To utilize gonadal aromatase (CYP19a) as a model gene to demonstrate the system's capability in analyzing tissue-specific gene regulation.
• To assess the impact of an aromatase inhibitor on gene expression and gonadal morphology in medaka.

Main Methods:

• Development of a whole-animal ISH system using radio-labeled probes for gene expression analysis in Japanese medaka.
• Validation of the ISH system by exposing fish to fadrozole, a known aromatase inhibitor.
• Confirmation of ISH results using quantitative real-time-polymerase chain reaction (RT-PCR) and histological evaluation of gonadal tissues.

Main Results:

• The ISH system successfully detected tissue-specific gene expression patterns in Japanese medaka.
• Fadrozole exposure significantly up-regulated CYP19a gene expression in ovaries but did not affect expression in testes.
• Histological analysis showed that high-dose fadrozole exposure inhibited oocyte maturation in female medaka, while male gonadal morphology remained unaffected.

Conclusions:

• The developed whole-animal ISH method provides high-resolution, tissue-specific gene expression analysis in a whole organism model.
• The system effectively demonstrated the differential regulation of aromatase gene expression in response to endocrine disruption.
• This ISH approach allows for the simultaneous assessment of gene expression and cellular morphology, offering a comprehensive tool for toxicological and biological research.