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The development and evolution of vertebrate electroreceptors

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 system of fishes and aquatic 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, which are flanked on the head by electrosensory ampullary organs that respond to weak electric fields (used for hunting). 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 and frogs (zebrafish and Xenopus both lack electroreceptors). We are using a comparative “evo-devo” approach to understand electroreceptor development and evolution (e.g. the paddlefish, a non-teleost fish: Modrell et al., 2011, Nature Communications PMID:21988912; the axolotl, a urodele amphibian: Modrell & Baker, 2012, Evol. Dev. PMID:23017075; the little skate, a cartilaginous fish: Gillis et al., 2012, Development PMID:21988912).

We have used RNA-seq in late-larval paddlefish to generate a lateral line organ-enriched dataset of over 400 genes. Validation of selected candidates showed expression in both ampullary organs and neuromasts of transcription factors, signalling pathway members, and genes involved in synaptic transmission, suggesting significant conservation. We also identified a few genes expressed in ampullary organs but not neuromasts, which may be important for electroreceptor development or function (manuscript in preparation).

The PhD student will investigate whether expression of these genes is conserved in skate and/or axolotl lateral line organs, and study the expression (and ideally function, using CRISPR) of additional candidates from the paddlefish dataset in a related, experimentally amenable non-teleost fish (sturgeon).

Relevant references

Modrell MS, Bemis WE, Northcutt RG, Davis MC, Baker CVH (2011) Electrosensory ampullary organs are derived from lateral line placodes in bony fishes. Nature Communications 2, 496. (PMID: 21988912)

Baker CVH, Modrell MS, Gillis JA (2013) The evolution and development of vertebrate lateral line electroreceptors. Journal of Experimental Biology 216: 2515–2522. (PMID: 23761476)

Piotrowski T, Baker CVH (2014) The development of lateral line placodes: Taking a broader view. Developmental Biology 389: 68–81. (PMID: 24582732)

 

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