Zebrafish Lacking Circadian Gene per2 Exhibit Visual Function Deficiency

Area of Science:

• Neuroscience
• Chronobiology
• Ophthalmology

Background:

• The retina possesses an intrinsic circadian clock, but its role in visual function remains unclear.
• Zebrafish are a valuable model for studying vertebrate vision and circadian rhythms.

Purpose of the Study:

• To investigate the function of the zebrafish period 2 (per2) gene, a light-regulated gene, in visual behavior.
• To elucidate the molecular mechanisms by which per2 influences visual processing in the retina.

Main Methods:

• Optokinetic response (OKR) and visual motor response (VMR) assays were used to assess visual behavior in per2 mutant zebrafish larvae.
• Immunofluorescence and electron microscopy were employed to examine retinal morphology and photoreceptor synapse structure.
• Quantitative real-time PCR (qRT-PCR) was utilized to analyze the expression of cone opsins and clock genes.

Main Results:

• Per2 mutant zebrafish larvae exhibited reduced contrast sensitivity and visual acuity.
• Mutants displayed normal OFF responses but abnormal ON responses in VMR assays.
• Abnormalities in photoreceptor ribbon synapses and decreased arciform density were observed, leading to a retinal ON pathway defect.
• Expression of long-wave-sensitive opsin (opn1lw) and short-wave-sensitive opsin (opn1sw) was reduced, along with down-regulation of cry1ba and bmal1b clock genes in adult mutant eyes.

Conclusions:

• The study identifies a mechanism linking circadian clock genes to visual function.
• The zebrafish per2 gene plays a critical role in retinal information processing and visual behavior.
• Disruption of per2 impacts photoreceptor synapse structure and the retinal ON pathway, affecting visual performance.