July 1, 2002;
Cardiac specific expression of Xenopus Popeye-1.
Popeye genes code for putative transmembrane proteins that are predominantly expressed in heart
and skeletal muscle
. Here we report on the isolation and expression of a previously unknown Xenopus member of this family, Xenopus Popeye-1 (Xpop-1). Xpop-1 is 60-65% identical to other vertebrate Pop-1 genes at the protein level. Whole-mount in situ hybridization studies revealed a highly specific expression of Xpop-1 whose transcripts are restricted to the embryonic heart
and become enriched in the forming ventricle
. Interestingly, unlike other known vertebrate Popeye genes, Xpop-1 is exclusively expressed in cardiac tissue
and absent from skeletal muscle
[+] show captions
Fig. 2. Temporal and spatial expression of Xenopus Pop-1. (A) RT-PCR analyses of embryonic Xenopus Pop-1 expression during different developmental stages as indicated. RT-PCR was performed using total RNA isolated from embryos which were cultured until the indicated developmental stages. The temporal expression of Xpop-1 was compared to the developmental expression profile of other cardiac marker genes. Abbreviations used: CA, cardiac actin; MHC, myosin heavy chain α; ANF, atrial natriuretic factor; H4, histone 4. The RT-reaction was performed with H4 primers. (B) Expression of Xenopus Pop-1 in different adult tissues as indicated. RT-PCR was performed using total RNA isolated from the indicated adult tissues. Xpop-1 transcripts were only detected in the adult heart. (C) Spatial expression of Xpop-1 and Nkx2.5 at stage 30. Transverse sections demonstrate the specific expression of Xpop-1 in the myocardium (mc). Nkx2.5 transcripts are abundant in the myocardium but in contrast to Xpop-1, Nkx2.5 is additionally, albeit weaker, expressed in tissue fated to become the dorsal roof of the pericardium (pc) and in the pharyngeal pouches (arrow heads). (D) Expression pattern of Xpop-1 in the developing heart chambers at stages 33, 36, and 41. Abbreviations used: a, atrium; v, ventricle; o, outflow tract.
bves (blood vessel epicardial substance) gene expression in Xenopus laevis embryos, NF stage 33, as assayed by in situ hybridization. Lateral view: anterior left, dorsal up; also, transverse section of same at the plane of the heart