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Updated: Jun 25, 2026

High Resolution Whole Mount In Situ Hybridization within Zebrafish Embryos to Study Gene Expression and Function
Published on: October 19, 2013
Gag proteins encoded by endogenous retroviruses are required for zebrafish development
Ni-Chen Chang1, Jonathan N Wells1, Andrew Y Wang1
1Department of Molecular Biology and Genetics, Cornell University, Ithaca, NY 14850.
None:
Transposable elements (TEs) make up the bulk of eukaryotic genomes and examples abound of TE-derived sequences repurposed for organismal function. The process by which TEs become coopted remains obscure because most cases involve ancient, transpositionally inactive elements. Reports of active TEs serving beneficial functions are scarce and often contentious due to difficulties in manipulating repetitive sequences. Here, we show that recently active TEs in zebrafish encode products critical for embryonic development. Knockdown and rescue experiments demonstrate that the endogenous retrovirus family BHIKHARI-1 (Bik-1) encodes a Gag protein essential for mesoderm development. Mechanistically, Bik-1 Gag associates with the cell membrane, and its ectopic expression in chicken embryos alters cell migration. Similarly, depletion of BHIKHARI-2 Gag, a relative of Bik-1, causes defects in neural crest development in zebrafish. We propose an "addiction" model to explain how active TEs can be integrated into conserved developmental processes.
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