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Heat shock of Zebrafish (Danio rerio) embryo causes disruptions in somite development


Jessica Zagory
Swarthmore College , 2004
Swarthmore, PA


Segmentation during development is a common phenomenon in vertebrates. It involves the anterior/posterior body axis dividing into repeating segments that provides a body plan (Holley and Takeda, 2002). Structures such as rhombomeres of the hindbrain, branchial arches, and trunk somites are created through segmentation (Roy et al., 1999).

Somites in vertebrates are formed most commonly through the epithelial-mesenchymal transition of the cells lying within the segmental plate mesoderm. Beginning at the conclusion of gastrulation of zebrafish, one pair of somites forms from the presomitic mesoderm by migration of cells within the extending tailbud every 30 minutes until there are 30 pairs (Holley and Takeda, 2002). The hairy gene, expressed in a dynamic pattern during somitogenesis, correlates with the positioning of where a somite will separate from the unsegmented mesoderm (Gilbert, 2000). However, it is still somewhat unclear how a series of similar, repeated units differentiate to produce individually fated structures in a precisely coordinated fashion.

Recent study suggests that there is an oscillator mechanism that mediates repeated cycles of gene expression and repression of the Notch gene (Holley and Takeda, 2002). In Notch and Notch pathway mutations, the proper segmentation of somites fails and somite boundaries are absent or irregular (Jiang et al., 2000). Forsberg and colleagues have found in mice that Lunatic fringe expression precede somite boundary formation (1998). Indeed, Fringe genes regulate the Notch signaling pathway, and L-fringe is expressed as a dynamic and repetitive wave that takes four hours to complete one cycle. Termination of the wave occurs immediately prior to somite boundary formation.

It has been shown that heat shock treatments affect not the next somite that forms, but leaves a zone in which there is normal somite development before a defective somite appears (Roy et al., 1999). After the defect, normal development resumes. In conjunction with research in the Notch pathway, heat shock will provide a method of investigation into the somite formation mechanism.

©Cebra-Thomas, 2000

Last Modified: 10 May 2004

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