Molecular and developmental alterations in circadian clock function in various strains of the Mexican blind cavefish, Astyanax mexicanus. (360G-Wellcome-087257_Z_08_A)

A major environmental cue for most organisms is the daily cycle of light and darkness Consequently, most organisms have developed a system, synchronised by the light/dark cycle coordinating physiology and behaviour with the environment. This system is known as the circadian clock and was proposed to be a neural phenomenon residing in a region of the central nervous system: the SCN. Over the last decade, research has led to a decentralisation of the circadian clock with discoveries of independent peripheral oscillators both in vivo (Whitmore et al, 1998) and in vitro cell culture (Whitmore et al, 2000; Welsh et al, 2004). Additionally, zebrafish cells can detect light and use this to set the phase of the circadian clock. Recent research in our lab has begun to investigate the workings of the circadian clock in a species of fish that lives in perpetual darkness, and is therefore missing the major environmental cue for most living organisms. This work has been performed using the Mexican tetra, Astyanax mexicanus; a single teleost species consisting of a sighted surface-dwelling form and several independent cave dwelling forms. Cavefish have lost eyes and pigmentation, as well as gaining constructive feature: such as increased jaw size and taste bud number. Selective pressures for retaining light adaptive features such as pigmentation are relaxed in the absence of light, and it is believed that pigmentation is lost through neutral mutations in the Oca2 gene (Protas et al, 2006). Little research has been performed on circadian clocks in cave animals, and particularly not on cave animals with living con-specific surface dwelling ancestors. This is important because when the ancestral surface form is still present, a direct comparison can be made between ancestral and derived developmental states. Astyanax is thus an important model for understanding the molecular basis of developmental changes in the context microevolution. Jeffery suggested "cavefish can be compared with surface fish in essentially the same way as mutants are compared with wild-type phenotypes" (Jeffery, 2008). We possess a model in which we can investigate a range of clock phenotypes. We will use surface fish and the two different populations of cavefish (Pachon and Steinhard) in our proposed research to further understand clock mechanisms in a dark adapted animal and assess whether cavefish really are clock mutants. If they are mutants in the clock me