OptoSeason: decoding seasonal reproduction in vertebrates using a next-gen optogenetic tool

Artificial light at night (ALAN) is throwing nature out of sync. Many animals rely on the length of daylight (photoperiod), to time their reproduction for when conditions are just right. Disrupting this natural signal, whether through urban lighting or aquaculture practices, can have serious consequences for animal life or survival. My project aims to uncover the biological mechanisms behind seasonal reproduction to better predict and mitigate these impacts. I will investigate the role of a key hormone in the thyroid function, called thyroid-stimulating hormone (TSH), in regulating seasonal reproduction in animals, using the Japanese medaka fish as a model. This small fish is perfect for genetic studies, as many tools and protocols exist to study in detail the cellular and molecular mechanisms involved in essential body functions such as reproduction in this species. To explore this, I will use advanced genetic tools and optogenetics, a method that uses light to control cell activity, to uncover the mechanism regulating the seasonal timing of reproduction. By decoding how animals adapt their reproduction to changing seasons, this project promises to illuminate how we can safeguard biodiversity and develop sustainable aquaculture practices.

Seasonal reproduction in vertebrates ensures offspring survival by aligning reproductive timing with photoperiod as the primary cue. However, artificial light at night (ALAN) disrupts these cues, posing a threat to species survival. Similarly, continuous light used in aquaculture to inhibit fish reproduction may have unintended physiological effects. OptoSeason seeks to decode the mechanisms underlying seasonal reproduction as a critical step toward predicting and mitigating the impact of these environmental disturbances. Research in mammals and birds suggests that thyroid-stimulating hormone (TSH) in the pituitary pars tuberalis (PT-TSH) regulates seasonal reproduction. However, the role of PT-TSH remains controversial due to the challenges of knocking out the Tshb gene without affecting essential thyroid functions. Thanks to the teleost-specific whole-genome duplication (WGD), we can now study a TSH gene specifically involved in seasonal reproduction using teleost fish models. Our previous findings indicate that tshbb plays a crucial role in this process. To unravel these mechanisms, OptoSeason will develop a next-gen optogenetic tool in Japanese medaka, a seasonally breeding teleost suitable for genetic manipulation and knockout studies. Considering its potential, this tool also has broader applications across various biological research areas. We will also employ advanced techniques such as CRISPR/Cas9-mediated knockout/knock-in, receptor assays, laser microdissection, transcriptomics, calcium imaging, and patch clamping to explore the tshbb pathway and its link to reproduction. Understanding this pathway will help identify markers for out-of-season spawning risks due to ALAN and provide insights into environmental and genetic influences on reproduction. This research will address challenges like early puberty in aquaculture, advance scientific knowledge, and develop tools to tackle key environmental and industrial issues.