Expression of proteins supporting visual function in heterobranch gastropods.

Area of Science:

• Molecular and Cellular Biology
• Neuroscience
• Vision Research

Background:

• Animals use visual pigments (opsin and retinal) for light sensing, triggering phototransduction.
• Molluscan Gq-coupled rhodopsin (Gq-rhodopsin) is bistable, regenerating 11-cis-retinal via light or retinochrome.
• Retinal binding protein (RALBP) facilitates retinal transport, but the necessity for other bistable opsins (Opn5, xenopsin) is unclear.

Purpose of the Study:

• To investigate whether Opn5 and xenopsin in mollusks rely on RALBP and retinochrome for 11-cis-retinal regeneration.
• To explore the cellular localization of RALBP and retinochrome in photoreceptors expressing Opn5 and Xenopsin.
• To compare the molecular composition of different photoreceptor types in Limax and Peronia.

Main Methods:

• Examined the expression of RALBP and retinochrome in Opn5- and Xenopsin-expressing photoreceptors in gastropods Limax and Peronia.
• Utilized immunohistochemistry to detect protein presence in specific neuronal and ciliary cell types.
• Investigated the expression of β-arrestin, Gq, and Go in various photoreceptor types.

Main Results:

• Retinochrome was detected in some Opn5A-positive neurons in Limax, but RALBP was absent.
• Photoreceptors expressing Xenopsin2 in Peronia lacked both retinochrome and RALBP.
• Variations in the expression of β-arrestin, Gq, and Go were observed across different photoreceptor types.

Conclusions:

• Bistable opsins in mollusks do not universally depend on the RALBP-retinochrome system.
• This study highlights cellular diversity in visual pigment regeneration mechanisms.
• Differences in molecular composition suggest functional specialization among mollusk photoreceptors.