Name: a reverse genetic approach to test functional redundancy during embryogenesis
Uploaded: 2010-08-11T17:00:00
Description: Watch this Scientific Journal Video about A Reverse Genetic Approach to Test Functional Redundancy During Embryogenesis at JoVE.com

We thank members of the Evans laboratory for their help in preparing this presentation. The morpholinos used here were originally validated by Dr. Audrey Holtzinger. T.E. is supported by grants from the National Institutes of Health (HL064282 and HL056182). Experiments on animals were performed in accordance with the guidelines and regulations set forth by the Institute for Animal Care and Use Committee, of the Weill Cornell Medical College.

Our goal here is to test the functional redundancy of two transcription factors for specification of cardiomyocyte progenitors. The factors are encoded by the two related genes gata5 and gata6 and we are using the zebrafish model to understand their relative functions1. Our strategy is to block gene function using morpholinos2. We will inject morpholinos for one or the other gene into fertilized eggs, and compare the embryonic phenotype with embryos derived from eggs injected simul...

<ol>
	<li>Heicklen-Klein, A., McReynolds, L. J., Evans, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Using+the+zebrafish+model+to+study+GATA+transcription+factors.">Using the zebrafish model to study GATA transcription factors.</a> Semin Cell Dev Biol. 16, 95-106 (2005).</li><li>Bill, B. R., Petzold, A. M., Clark, K. J., Schimmenti, L. A., Ekker, S. C. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=A+primer+for+morpholino+use+in+zebrafish.">A primer for morpholino use in zebrafish.</a> Zebrafish. 6, 69-77 (2009).</li><li>Holtzinger, A., Evans, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Gata5+and+Gata6+are+functionally+redundant+in+zebrafish+for+specification+of+cardiomyocytes.">Gata5 and Gata6 are functionally redundant in zebrafish for specification of cardiomyocytes.</a> Dev Biol. 312, 613-622 (2007).</li><li>Peterkin, T., Gibson, A., Patient, R. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Redundancy+and+evolution+of+GATA+factor+requirements+in+development+of+the+myocardium.">Redundancy and evolution of GATA factor requirements in development of the myocardium.</a> Dev Biol. 311, 623-635 (2007).</li><li>Holtzinger, A., Evans, T. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Gata4+regulates+the+formation+of+multiple+organs.">Gata4 regulates the formation of multiple organs.</a> Development. 132, 4005-4014 (2005).</li><li>Sorrentino, R. P., Gajewski, K. M., Schulz, R. A. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=GATA+factors+in+Drosophila+heart+and+blood+cell+development.">GATA factors in Drosophila heart and blood cell development.</a> Semin Cell Dev Biol. 16, 107-116 (2005).</li></ol>

In the experiment described here, we combined two morpholinos, each of which alone generate a distinct range of phenotypes, and found an entirely different phenotype when they were co-injected together. Of course, we needed a justification for doing this experiment in the first place. We suspected that the two genes might compensate each other for an earlier function, in this case cardiac specification. This is because the genes are highly related (and capable of binding to the same DNA sequences) and are expressed in ov...

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a reverse genetic approach to test functional redundancy during embryogenesis

Gene function during embryogenesis is typically defined by loss-of-function experiments, for example by targeted mutagenesis (knockout) in the mouse. In the zebrafish model, effective reverse genetic techniques have been developed using microinjection of gene-specific antisense morpholinos. Morpholinos target an mRNA through specific base-pairing and block gene function transiently by inhibiting translation or splicing for several days during embryogenesis (knockdown). However, in vertebrates such as mouse or zebrafish, some gene functions can be obscured by these approaches due to the presence of another gene that compensates for the loss. This is especially true for gene families containing sister genes that are co-expressed in the same developing tissues. In zebrafish, functional compensation can be tested in a relatively high-throughput manner, by co-injection of morpholinos that target knockdown of both genes simultaneously. Likewise, using morpholinos, a genetic interaction between any two genes can be demonstrated by knockdown of both genes together at sub-threshold levels. For example, morpholinos can be titrated such that neither individual knockdown generates a phenotype. If, under these conditions, co-injection of both morpholinos causes a phenotype, a genetic interaction is shown. Here we demonstrate how to show functional redundancy in the context of two related GATA transcription factors. GATA factors are essential for specification of cardiac progenitors, but this is revealed only by the loss of both Gata5 and Gata6. We show how to carry out microinjection experiments, validate the morpholinos, and evaluate the compensated phenotype for cardiogenesis.

Watch this Scientific Journal Video about A Reverse Genetic Approach to Test Functional Redundancy During Embryogenesis at JoVE.com

A Reverse Genetic Approach to Test Functional Redundancy During Embryogenesis

Gene function can be obscured in loss-of-function experiments if there is compensation by another gene. The zebrafish model provides a relatively high-throughput means to reveal such functional redundancy in living embryos.

Gene function during embryogenesis is typically defined by loss-of-function experiments, for example by targeted mutagenesis (knockout) in the mouse. In ...

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