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A growing body of work suggests that the activity of ion channels and pumps is an important regulatory factor in embryonic development. We are beginning to identify functional roles for proteins suggested by a survey of expression of ion channel and pump genes in Xenopus and chick embryos (Rutenberg et al. [2002] Dev Dyn 225, this issue). Here, we report that the ATP-sensitive K(+) channel protein is present in the hatching gland of Xenopus embryos; moreover, we show that its activity is necessary for hatching in Xenopus. Pharmacologic inhibition of K(ATP) channels not only specifically prevents the hatching process but also greatly reduces the endogenous expression of Connexin-30 in the hatching gland. Based on recent work which showed that gap-junctional communication mediated by Cx30 in the hatching gland was required for secretion of the hatching enzyme, we propose that K(ATP) channel activity is upstream of Cx30 expression and represents a necessary endogenous step in the hatching of the Xenopus embryo.
Fig. 1. KATP channels are involved in hatching gland function. A,B:
Immunohistochemistry using an antibody to Kir6.1 reveals the presence
of KATP channels in the Y-shaped tissue of the hatching gland. C: SUR1
protein is strongly expressed in the head but is strikingly absent from the
hatching gland cells, the cement gland, and the tissue between the two
frontal arms of the hatching gland Y shape. D: SUR2 is present in the
hatching gland. E: Control embryos hatch by stage 29. F: In contrast,
embryos exposed to Nicorandil, an opener of KATP channels, remain in
the vitelline membrane and are unable to hatch. G: Individual embryo
showing morphology at stage 38. H: Individual embryo manually freed
from the membrane shows normal development to this late stage, despite
confinement to the vitelline membrane. I: Connexin30 is normally strongly
expressed in the hatching gland. J: Embryos exposed to Nicorandil show
a much reduced expression of Cx30 in the same tissue (white arrow).
Compared with control embryos (K), the expression of the hatching
enzyme is equally strong in Nicorandil-exposed embryos (L), showing
that the tissue is alive and that the cells maintain hatching gland identity.
Red arrows indicate expression. Green arrows indicate lack of expression
abcc8 (ATP-binding cassette, sub-family C (CFTR/MRP), member 8) gene expression in a Xenopus laevis embryo, NF stage 29, as assayed by immunohistochemistry. Anterior view: dorsal up.
abcc9 (ATP-binding cassette, sub-family C (CFTR/MRP), member 9) gene expression in a Xenopus laevis embryo, NF stage 29, as assayed by immunohistochemistry. Anterior view: dorsal up.
kcnj8 (potassium inwardly rectifying channel subfamily J member 8) gene expression in a Xenopus laevis embryo, NF stage 29, as assayed by immunohistochemistry. Lateral view: anteriorright, dorsal up.
