Structure and expression of Xenopus tropicalis BMP-2 and BMP-4 genes

The Xenopus tropicalis BMP-2 and BMP-4 genes have been cloned and sequenced. A comparison with the corresponding genes from X. laevis reveals that the BMP-4 genes are conserved at a higher extent than the BMP-2 genes. This is especially evident for the intron sequences, but is also reflected by the exon sequences. While the amino acids of X. tropicalis and X. laevis BMP-4 proteins diverge at about 4%, those of BMP-2 proteins diverge at about 7%. By reverse transcriptase polymerase chain reaction analyses and whole mount in situ hybridizations, we demonstrate the temporal and spatial expression patterns of X. tropicalis BMP-2 and BMP-4 genes. BMP-2 is found to be expressed maternally, and later in development, in migrating heart progenitor cells as well as in the final heart, within the pineal gland and the olfactory placodes. BMP-4 is zygotically activated within the ventral marginal zone and later found in the eye, the otic vesicle, the heart and within blood islands. Although the overall patterns are very similar to those found in X. laevis, there is some distinct difference which might result from the accelerated development in X. tropicalis.