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Connexins are a family of proteins that assemble to form gap junction channels. Cell-cell communication through gap junctions mediates many important events in embryogenesis, including limb patterning, lens physiology, neuronal function, left-right asymmetry, and secretion from gland tissue. We studied the expression of connexin 30 (Cx30) in the Xenopus embryo and find that it is expressed in the developing hatching gland and pronephros. To determine whether its expression plays a functional role in the activity of the hatching gland, we exposed pre-hatching embryos to drugs that block gap junctional communication. This resulted in a continuation of normal growth and development but specifically abolished hatching. The treatment did not affect Cx30 or Xenopus hatching enzyme transcription, suggesting a post-transcriptional effect on Cx30 gap junctions. We conclude that junctional communication, possibly mediated by Cx30, is involved in secretion of hatching enzyme in Xenopus.
Fig. 1. Cx30 is expressed in the Xenopus embryo. A: At stage 17, the Cx30 signal is detected in the anterior dorsal portion of the closing neural tube. B: Sectioning reveals expression in the endoderm. C: Cx30 is expressed in a stripe on the anterior most dorsal part of the neural tube and in two semicircular stripes on the most anterior part of the embryo. D: Sectioning confirms the ectodermal localization of Cx30 mRNA in the hatching gland. E: Signal is also detected at stage 26 in a small spot near pronephros precursor cells. F: The signal remains at stage 31, as seen in section. In all figure parts, red arrowheads indicate expression.
Fig. 2. Cx30 is expressed in the hatching gland.
A,B: Xenopus hatching enzyme (XHE) is expressed
in a vertical stripe on the anterior dorsal
aspect of the neural tube and in semicircular stripes
on the face (hatching gland cells). C,D: Cx30 is
expressed in an identical pattern at these stages. In
all figure parts, red arrowheads indicate expression.
Fig. 3. Cx30 expression in hatching gland cells is necessary for
hatching gland function. A: Control embryos all hatch from the vitelline
membrane by stages 26–27. B: In contrast, embryos exposed from stage
22 to drugs that inhibit the action of connexins are unable to hatch at the
normal time. C: The same effect is observed when embryos are injected
with H7, a dominant-negative construct that interferes with the function of
endogenous connexins. D: At stages 37–38, control embryos are always
hatched and develop normally. E: In contrast, embryos exposed to the
GJC-reducing drug anandamide remain in the vitelline membrane
through this very late stage; this panel shows a close-up view of a stage
41 embryo trapped within the vitelline membrane because of continued
exposure to anandamide. F: Embryo from panel E manually freed with
forceps to allow clearer staging.
Fig. 4. Reduction of hatching gland function by inhibition of GJC takes
place post-transcriptionally with respect to Cx30 and XHE. A: Control
embryos show normal expression of Cx30. B: Embryos exposed to
glycyrrhetinic acid do not show detectable differences in the expression
of Cx30 mRNA. C: Control embryos show normal expression of XHE.
D: Embryos exposed to glycyrrhetinic acid do not show detectable differences
in the expression of XHE mRNA.
