pH variations enable guanine crystal formation within iridosomes

Area of Science:

• Biophysics
• Developmental Biology
• Cell Biology

Background:

• Animals create vibrant colors using guanine crystals in iridosomes.
• The process of guanine accumulation and crystallization within iridosomes is not well understood.

Purpose of the Study:

• To investigate the mechanisms of iridosome maturation and guanine crystal formation in zebrafish.
• To elucidate the role of pH regulation in biogenic crystal development.

Main Methods:

• Cryo-electron microscopy and synchrotron-based soft X-ray microscopy were used to visualize guanine crystal formation.
• Live-cell pH imaging and pharmacological perturbations (V-ATPase inhibition) were employed.
• Spectroscopy was utilized to analyze guanine properties.

Main Results:

• Amorphous guanine accumulates in a protonated state in early iridosomes.
• Iridosomes are initially acidic, with pH neutralizing during development.
• V-ATPase inhibition disrupts acidification and crystal formation, highlighting its role in pH regulation.

Conclusions:

• pH alterations are critical for the precise formation of guanine crystals in iridosomes.
• The study provides molecular insights into guanine biogenesis and crystallization.
• Understanding these mechanisms is key to understanding animal coloration.