Table 1.

Exploring the Impact of a Gene on Heart Development in Xenopus

	Spatiotemporal pattern of expression	Gene loss	Addition of a gene product
Pros	Comparative analysis of sequential developmental stages	Antisense oligonucleotide mediated reduction of gene expression is simple and reversible using microinjection.	Simple injection protocol for normal or mutant mRNA injections.
Cons	Xenopus laevis genome is not sequenced (but coding regions are very similar to those sequenced only in Xenopus tropicalis).	Efficacy of antisense compounds is temporally limited. Antisense compounds will be inherited in cells outside the heart field.	Injected mRNA has a restricted half life. Timing and spatial expression of protein from mRNA will likely be broader than endogenous mRNA.
Best use of model	Understanding developmental appearance of mRNA in the embryo and comparison with other mRNAs and morphological features. Defining regulatory regions of promoters by transgenesis.	Testing loss of expression of genes critical for cardiac development through tube closure.	Testing gene misexpression or the effects of mutant protein on early heart development.