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First published online 2 April 2008
doi: 10.1242/dev.016576

Development 135, 1693-1702 (2008)
Published by The Company of Biologists 2008
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Tbx2b is required for the development of the parapineal organ

Corey D. Snelson1, Kirankumar Santhakumar2, Marnie E. Halpern2 and Joshua T. Gamse1,*

1 Department of Biological Sciences, Vanderbilt University, VU Station B, Box 35-1634, Nashville, TN 37235, USA.
2 Department of Embryology, Carnegie Institution of Washington, 3520 San Martin Drive, Baltimore, MD 21218, USA.

* Author for correspondence (e-mail: josh.gamse{at}vanderbilt.edu)

Accepted 10 March 2008

Structural differences between the left and right sides of the brain exist throughout the vertebrate lineage. By studying the zebrafish pineal complex, which exhibits notable asymmetries, both the genes and the cell movements that result in left-right differences can be characterized. The pineal complex consists of the midline pineal organ and the left-sided parapineal organ. The parapineal is responsible for instructing the asymmetric architecture of the bilateral habenulae, the brain nuclei that flank the pineal complex. Using in vivo time-lapse confocal microscopy, we find that the cells that form the parapineal organ migrate as a cluster of cells from the pineal complex anlage to the left side of the brain. In a screen for mutations that disrupted brain laterality, we identified a nonsense mutation in the T-box2b (tbx2b) gene, which encodes a transcription factor expressed in the pineal complex anlage. The tbx2b mutant makes fewer parapineal cells, and they remain as individuals near the midline rather than migrating leftward as a group. The reduced number and incorrect placement of parapineal cells result in symmetric development of the adjacent habenular nuclei. We conclude that tbx2b functions to specify the correct number of parapineal cells and to regulate their asymmetric migration.

Key words: Left-right asymmetry, Pineal complex, Diencephalon, Epithalamus, Zebrafish, from beyond mutant






© The Company of Biologists Ltd 2008