Magnetite-based Magnetoreception and Magnetic

Sensory Transduction in Chinook Salmon

Presentation to OHRC, September 20, 2010

M. Renee Bellinger & Michael BanksMarine Fisheries Genetics Laboratory

Hatfield Marine Science CenterOregon State University

Newport, Oregon200 nm

Overview• Magnetoreception is well-documented• Earth’s magnetic field and types of information provides

to organisms for orientation• Evidence for functionally different magnetoreceptors

– Inclination / polar compasses– Light-dependent / -independent processes

• The magnetic sensory organelle in fish, reptiles and amphibians has not been conclusively located

• Current limitations to understanding magnetic sensory transduction

• Research goals and objectives

Earth diagram from Freake et al. 2006

Magnetic FieldsMagnetic North Pole

Magnitude of Intensity

Angle of Magnetic Field Lines(inclination)

90°

90°

Magnetic South Pole

Polar and Inclination Compasses are

Functionally Different

(Ritz et al. 2000)

S T

Figure from T .Ritz website, UC Irvine

200 nmPhoto from Mann et al. (1988)

NS

Shüler (2008)

Fleissner et al. 2007

Radical Pairs Iron-Mineral

Earth diagram from Freake et al. 2006

Magnetoreception

http://www.mlahanas.de

https://91middleschoolscience.wikispaces.com

http://www.statesymbolsusa.org/images/South_Carolina

http://www.wildpacificsalmon.com

Weitkamp 2010 Figure 2

Magnetic Remanence & Sensory Pathways: Salmon

Moore et al. 1990

Olfactory Rosette

Dii Backtracing of ros-V Innervating Olfactory Rosette (Walker et al. 1997)

olfactory rosette (Kudo et al. 2009); drawing Baier et al. (1994)

Magnetite Reflectance In Basal Lamina

Walker et al. 1997

X 190 mag.

Chains SDM 1 μM

Locate candidate magnetoreceptors in situ and demonstrate their role in magnetic

sensory transduction

1. Identify genes unique to magnetosomes or other iron-mineral particles

2. Use these genes to develop probes that can be used to locate magnetosomes in situ

3. Link iron-minerals to sensory transduction

Cells containing magnetite can be separated from non-magnetic cells

Tissue homogenate

Non-magnetic cells sinkto bottom of tube

Magnetic cells collect at pole of magnet

Leading Hypothesis

Gene expression in magnetite- and non-magnetite containing tissue homogenates

will be similarReject null hypothesis: genes uniquely expressed or more abundantly expressed in magnetite-containing tissues, relative to non-magnetic tissues are considered “candidate genes”

Dependent Hypotheses –assuming leading Ho is rejected

1. Probes developed from candidate genes will hybridize to (a) extracts of mRNA from magnetite containing tissue and extracts of tissue that contain magnetite, but not to non-magnetic tissue/mRNA extracts, and (b) candidate magneto-receptor cells in situ

Pfister P, Rodriguez I PNAS 2005;102:5489-5494

Use genes uniquely associated with magnetosomes to locate candidate

magnetoreceptors in situExpression of V1r-like Transcripts in Zebrafish

Intact magnetosome(Walker 1997)

Contributions to Research• Understand mechanisms that underpin salmon’s ability

to navigate and home, and salmon ocean migratory patterns

• Findings generalized to other studies of orientation• Apply similar techniques to other vertebrates to better-

understand magnetoreception• Foundation for studies of magnetic field effects on

circadian rhythms and other neural processes• Understand impacts of electromagnetism on ocean (and

land) dwelling organisms