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The evolution and development of vertebrate lateral line sense organs (Clare Baker)

Supervisor: Clare Baker

Fundamental questions in biology include how different cell types and organs are specified during development, and how novel cell types and organs evolve. An excellent model for both questions is the lateral line sensory system of fishes and amphibians. Ancestrally, this comprises lines of mechanosensory neuromasts on the head and trunk, containing hair cells (like those in the inner ear) that respond to local water movement; these are flanked on the head by electrosensory ampullary organs that respond to weak electric fields in water (generated e.g. by ion leakage across mucous membranes), allowing prey detection. Neuromasts and ampullary organs, and the neurons that innervate them both, arise embryonically from the same primordia: elongating lateral line placodes on the head.

The electrosensory component of the lateral line system was independently lost in the lineages leading to teleost fishes, frogs and amniotes (zebrafish and Xenopus both lack electroreceptors). We are using a comparative “evo-devo” approach to understand the development and evolution of electroreceptors (e.g. the paddlefish, a non-teleost fish: Modrell et al., 2011, Nature Communications 2, 496; the little skate, a cartilaginous fish: Gillis et al., 2012, Development 139, 3142-6; the axolotl, a urodele amphibian: Modrell and Baker, 2012, Evol. Dev. 14: 277–85).

We are also working with the sea lamprey, a jawless fish from the most basal lineage of living vertebrates, via a collaboration with Prof. Marianne Bronner (Caltech, USA) (Modrell et al., 2014, Dev. Biol. 385: 405–16). Intriguingly, lamprey lateral line organs also mediate a light-avoidance reflex. It is currently unclear whether neuromast hair cells or electroreceptors (or both) are photoreceptive, but neuromast hair cells in zebrafish and Xenopus were recently shown to express opsin genes. The PhD project will investigate lateral line neuromast and electroreceptor development in the lamprey, including the molecular basis for the light-avoidance reflex.

Relevant references

Baker CVH, Modrell MS, Gillis JA (2013) The evolution and development of vertebrate lateral line electroreceptors. J. Exp. Biol. 216: 2515–2522.

Piotrowski T, Baker CVH (2014) The development of lateral line placodes: Taking a broader view. Developmental Biology 389: 68–81.

Baker GE, de Grip WJ, Turton M, Wagner H-J, Foster RG, Douglas RH (2015) Light sensitivity in a vertebrate mechanoreceptor? J. Exp. Biol. 218: 2826–2829.

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