Adrenergic neurotransmitters and calcium ionophore‐induced situs inversus viscerum in Xenopus laevis embryos

Abstract

Xenopus laevis embryos at the blastula-early tail bud stage were exposed to norepinephrine or octopamine dissolved in culture saline until they reached the larval stage. The left-right asymmetry of the heart and gut was then examined. We found that these adrenergic neurotransmitters induced situs inversus in the heart and/or gut in up to 35% of tested neurula embryos. Norepinephrine-induced situs inversus was blocked by the alpha-1 adrenergic antagonist prazosin. Furthermore, A23187, a calcium ionophore, also increased the incidence of situs inversus up to 54% when late-neurula embryos were exposed to the solution. A23187 treatment initiated before neural groove formation was less effective. The incidence of situs inversus induced by these reagents decreased towards the control level (2.2%, 25 untreated embryos out of 1127 embryos in total) in embryos past the stage of neural tube closure. In the present experiments we obtained 22 gut-only situs inversus embryos having an inverted gut and a normal heart. In contrast, such embryos were not observed among the 1127 untreated embryos. An adrenergic signal mediated by an increase in intracellular free calcium may be involved in the asymmetrical visceral morphogenesis of Xenopus embryos.

H,K-ATPase protein localization and Kir4.1 function reveal concordance of three axes during early determination of left–right asymmetry

“…In chick, the appearance of asymmetric calcium at the node is regulated by the H + /K + -ATPase , and Ca ++ channels have been implicated in mouse (Pennekamp et al, 2002) and zebrafish (Sarmah et al, 2005) asymmetry. However, prior data suggest that the roles of calcium in Xenopus asymmetry are likely to occur much later than the events we describe in the early embryo (Toyoizumi et al, 1997). Another likely possibility is that the H + /K + -ATPase/Kir4.1 component in Xenopus is a key aspect of the machinery that sets up the voltage gradients powering LR-asymmetric serotonin transport at later stages (Esser et al, 2006;Fukumoto et al, 2005a,b;Levin et al, 2006).…”

Xenopus nodal related-1 is indispensable only for left-right axis determination

“…At this stage, left-right orientation of the heart and visceral organs was examined and the incidence of left-right reversal in the injected embryos was scored according to the criteria as previously described (Toyoizumi et al, 1997(Toyoizumi et al, , 2000Mogi et al, 2003). To more precisely judge the gut asymmetry, the laterality of the ventral pancreas was also checked.…”

Na,K-ATPase α2 and Ncx4a regulate zebrafish left-right patterning

“…The fish-specific sodium calcium exchanger Ncx4a is required for LR patterning Calcium signaling has been implicated as an early determinant of LR patterning (Fujinaga et al, 1994;Toyoizumi et al, 1997;Raya et al, 2004). One well-characterized function of Na,K-ATPase is to regulate the intracellular Ca 2+ level by modulating the activity of NCX (Blanco and Mercer, 1998;Blaustein and Lederer, 1999).…”