Organization, ontogenetic differentiation and evolution of the inverted rod photoreceptor nuclei

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Initially the project was a combination of two projects covering two major research directions, (i) Functional organization of inverted rod nuclei and (ii) Evolution of vision biology and Adaptive organization of nocturnal retinas. The first one was predominantly led by Dr. Irina Solovei and the second one - by late Dr. Boris Joffe. Generally, the project is focused on investigation of inverted nuclei of rod photoreceptors in nocturnal animals. These nuclei had acquired a dramatically changed nuclear architecture in comparison to all other conventional nuclei, which allows them to function as microlenses to improve nocturnal vision (Solovei et al. 2009). The objectives of the project are (1) to describe large scale chromatin folding in the inverted nuclei that determines their difference from the conventional nuclei; (2) to study molecular mechanisms underlying remodeling of conventional nuclei to the inverted ones during postnatal terminal differentiation of the rod photoreceptor cells and (3) to prove the hypothesis that adaptation to nocturnal vision can drive the evolution of the karyotype and the genome towards accumulation of heterochromatin necessary to build heterochromatin microlenses. During the two grant periods, considerable progress was made in all three parts of the projects. Our main achievement during the first three years was identification of the major mechanisms of peripheral heterochromatin binding, which is a key element in establishment and maintenance of the conventional nuclear organization in eukaryotes (Solovei et al 2013). The current application consists of a report on results obtained over the last two year period and a proposal of experimental work needed to continue and complete some of the topics outlined below. The continuation will be performed by one person, Irina Solovei.