Genetics. Published Articles Ahead of Print: February 16, 2005, Copyright © 2005
doi:10.1534/genetics.104.036434


A more recent version of this article appeared on May 1, 2005.

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The Zebrafish pob Gene Encodes a Novel Protein Required for Survival of Red Cone Photoreceptor Cells

Michael R Taylor 1, Satoshi Kikkawa 1, Antonio Diez-Juan 2, Visvanathan Ramamurthy 1, Koichi Kawakami 3, Peter Carmeliet 2 and Susan E Brockerhoff 1*

1 University of Washington
2 University of Leuven
3 National Institute of Genetics, Mishima, Shizuoka 411-8540, Japan

* To whom correspondence should be addressed. E-mail: sbrocker{at}u.washington.edu.

Submitted on September 16, 2004
Revised on November 12, 2004
Accepted on 18 January 2005


Abstract

The zebrafish mutant, partial optokinetic response b (pob), was isolated using an n-ethyl n-nitrosourea (ENU)-based screening strategy designed to identify larvae with defective optokinetic responses in red but not white light. Previous studies showed that red-light blindness in pob is due to the specific loss of long-wavelength photoreceptor cells via an apoptotic mechanism. Here, we used positional cloning to identify the mutated pob gene. We find that pob encodes a highly conserved 30kDa protein of unknown function. To demonstrate that the correct gene was isolated, we used the Tol2 transposon system to generate transgenic animals and rescue the mutant phenotype. The Pob protein contains putative transmembrane regions and protein sorting signals. It is localized to the inner segment and synapse in photoreceptor cells, and when expressed in COS-7 cells it localizes to intracellular compartments. We also show that the degeneration of red cone photoreceptors in the mutants occurs independently of light. Based on our findings, we propose that Pob is not involved in phototransduction but rather plays an essential role in protein sorting and/or trafficking.

Key Words: Tol2 transposon, Zebrafish, partial optokinetic response b (pob), positional cloning