Title

The Role of Adenylate Cyclase in Hydra Magnipapillata Phototransduction

Date of Award

Winter 2017

Project Type

Thesis

Program or Major

Biochemistry

Degree Name

Master of Science

First Advisor

David C Plachetzki

Second Advisor

Rick Cote

Third Advisor

Xuanmao Chen

Abstract

Cnidarians are members of an early branching phylum of animals with unexpectedly complex sensory capable of detecting light, chemical, and mechanical stimuli despite lacking the specialized sensory organs that bilaterian animals commonly possess. Although there are many obvious differences when comparing bilaterian sensory systems with that of Cnidarians, there is also a surprising degree of similarity. Recent studies reveal that in one species of Cnidaria, the freshwater polyp Hydra magnipapillata, there exists a phototransduction cascade mediated by the G-protein coupled receptor (GPCR) opsin and cyclic nucleotide-gated ion channels; features shared with the vertebrate phototransduction cascade. Other research has shown an increase in cytosolic cAMP levels in response to opsin signaling in heterologous gene expression studies of a jellyfish opsin, which in eukaryotic cells is mediated by the enzyme adenylate cyclase (AC). However, this is where our knowledge of cnidarian phototransduction ends. Here we investigate the possibility that AC plays an active role in hydra phototransduction. We show through a phylogenetic analysis of metazoan AC protein sequences that the hydra genome possesses an AC gene (hmAC) that is orthologous to human AC9. Next, we used in situ hybridization with riboprobes against hmAC to show its co-expression with opsin (hmOps2) in hydra sensory neurons. A photo-response experiment is then performed in the presence or absence of pharmacological agents that affect AC activity. To determine the functional relationship between hmAC and hmOps2, dark-adapted hydra animals are presented with various drug conditions, a light stimulus, and assayed for contraction. Our results support the view that AC plays an active role in the hydra photo-response, suggesting that AC may be a regulator of the cnidarian phototransduction cascade. This study advances our understanding of the early origins and diversification of animal phototransduction.

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