Light in early life: understanding the mechanisms of embryonic photoreception to improve poultry welfare and production

This project will use state of the art technology to investigate the mechanism by which light exposure during artificial incubation of bird eggs exerts positive effects on embryonic development, hatchability and post-hatch outcomes.

Poultry production is a major component of the agricultural sector in the UK and worldwide. Over 90 million eggs are set for incubation each month in the UK alone. Environmental conditions during incubation are vital for proper development and can have long lasting consequences post-hatch. Hatchability and hatch synchrony are two areas of major industry concern, as low hatchability and asynchronous hatch result in chick loss. Reduction of hatch asynchrony and improvement of hatchability represents a key means to improve animal welfare and efficiency.

In commercial settings eggs are incubated in darkness but light exposure during incubation has emerged as a potential means of improving hatchability and hatch synchrony. Our understanding of how light exposure acts during incubation, and how it can be optimized remains limited. Our recent work has shown that extra-retinal photoreceptors (non-visual opsins) represent a widespread and evolutionarily ancient form of light detection and response that could readily mediate these developmental effects. Our data has shown that extra-retinal photoreceptor expression begins at least several days before that of visual opsin expression and displays marked changes across the developmental time course.

The project has 3 specific objectives:

1. Determine the anatomical localization and ontogeny of extra-retinal photoreceptors across development to establish the optimal wavelengths and timing of light delivery during incubation.

2. By using transcriptomic analysis, identify the neural and developmental pathways activated by light exposure during incubation focusing on identification of pathways related to hatch synchronicity. Specifically we will identify genes that show changes in expression in response to incubation under light versus dark conditions.

3. Elucidate if light detection by the extra retinal photoreceptors (VA opsin and melanopsin) mediate the positive effects of light exposure during incubation using gene edited opsin knockout chicken lines. Identify linkages between opsin mediated light detection and the endocrine system e.g. thyroid, melatonin and glucocorticoid systems as well as hatchability and synchrony of hatch.

These studies will provide unique insights into the mechanisms by which embryos are able to detect and respond to light cues. This understanding will inform not only commercial egg incubation, but inform a more detailed appreciation of how nocturnal light exposure may impact wild bird populations.

This timely project is relevant to the BBSRC strategic priorities: Welfare of Managed Animals, Animal Health, Sustainably Enhancing Agricultural Production, Healthy Ageing Across the Life Course and Technology Development for the Biosciences and the Roslin Institute's BBSRC funded Institute Strategic Program: Improving Animal Production and Welfare.

This project brings together a strong multidisciplinary team with exceptional skills in avian physiology as well as novel avian gene targeting and germ line transmission of mutated germ cells to generate a gene-edited line that can be used as a sterile host (due to absence of primordial germ cells) for transferred gene edited primordial germ cells. This technology will lead to highly efficient production of birds carrying the desired opsin mutation.

We will provide important new information on how light signals are detected during incubation. Elucidation of these mechanisms, will provide a powerful alternative method to identifying optimal lighting regimes (wavelength and timing of exposure) to improve hatchability and hatch synchrony.

The project will provide valuable information for real application for industrial stakeholders for the management of eggs and chicks in the poultry hatchery industry. Our findings will advance our understanding of the underlying basic biology and the rules of life as non-retinal photoreceptors are also implicated in mammalian and human health and well-being.

We propose to use the latest chicken gene editing technology to determine the ontogeny of extra-retinal photoreceptors in the domestic chicken chick, the genes and gene networks altered by exposure to light during incubation and the role of extra-retinal photoreceptors in mediating the developmental response to light exposure.

Immunohistochemistry for photoreceptors (e.g. neuropsin, VA-opsin, melanopsin, and pinopsin) will be used to determine the ontogeny and localization of extra-retinal photoreceptors across development. To identify the neural and developmental pathways activated by light exposure during incubation, discovery oriented RNAseq will be used and analysis will focus on identification of candidate genes and gene pathways.

Crispr-Cas editing of avian primordial germ cells will be used to generate VA opsin and melanopsin (a key photoreceptor) knockout embryos from sterile surrogate hosts. Outcome metrics will include morphology (i.e. embryo mass and bone formation), hatchability, hypothalamic TSHb a reliable indicator of light exposure and melatonin across development. RT-PCR and western blot analysis of neural tissue will be used to probe the involvement of neural thyroid signaling in transducing the light signal and to confirm knockout of the opsins.

Immediate Beneficiaries:
Scientists working in the fields of extra-retinal photodetection, developmental biology, neuroendocrinology, photobiology, and poultry welfare. This study will provide technological advances in experimental avian photobiology. The development of an extra-retinal photoreceptor avian knockout model is unique, and will be a global first for avian biology. This has power to not only deliver major impact for the field of avian developmental biology but to transform the broader field of photobiology. It will enable an avenue of research into the mechanisms of seasonality, circadian rhythms, and the negative effects of nocturnal light exposure in avian species through experimental testing of causal hypotheses. With the presence of extra-retinal photoreceptors identified across vertebrates, including recently mammals, these findings also have the potential to inform cross taxa investigations. The findings published in high impact journals, communicated at national and international conferences, and delivered directly via in person meetings with industry stakeholders will benefit those managing commercial hatchery and bird breeding facilities.

Professional Development and Training:
This project will provide high impact training in bioinformatics analyses and cutting edge gene editing approaches to support the named researcher's, Dr. Perez, continuing development as a leading integrative organismal biologist. Furthermore, it will retain an experienced integrative biologist with expertise in in vivo manipulation of neurophysiology and physiology, considered vulnerable skill areas by the UKRI. The experience and training received during this grant will prepare the Research Co-Investigator to take up an independent research position to build a world leading program in photobiology.

Improving Animal Health and Welfare:
This research directly addresses the BBSRC strategic priorities of understanding Animal Health and Welfare as well as Sustainably Enhancing Agricultural Production by understanding how light exposure can alter avian development. This integrative research approach will clearly elucidate the time course of light sensitivity and response by the developing brain. In turn this will inform our understanding of how light exposure can alter pre- and post-hatch phenotypes. This understanding will in turn lead to new potential strategies for using light in incubation that could potentially improve the welfare outcomes of the 90 million eggs incubated every month in the UK. Improvements in hatchability and hatch synchrony will potentially result in the increased sustainability of poultry production by increasing hatchery efficiency, reducing the total number of eggs needed to meet demand

Industrial stakeholders:
These findings will have practical implications for management of poultry production. A mechanistic understanding will inform optimal timing of light conditions based on knowledge of when light can be functionally detected and when specific gene networks are responding. This will allow for targeted use of lighting. Formation of industry contacts to cultivate future partnerships is a key aim of the grant. Prof. Meddle has recently established a partnership with the hatchery and incubation industry (Petersime).

Public Engagement:
Animal welfare and sustainability of production are areas of keen and growing public interest, as is understanding how environmental lighting can shape physiology and behaviour (e.g shift work disorders). This research will be widely disseminated to the public through a coordinated effort involving media engagement through the University press office, direct communication through Twitter, and public workshops and outreach activities. This project focus on response to light is timely, given public interest in effects of light at night on humans and the environment.