Larabell CA et al. (2004), A PKC wave follows the calcium wave after activ...

XB-ART-3873

Differentiation 2004 Feb 01;721:41-7.

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A PKC wave follows the calcium wave after activation of Xenopus eggs.

Larabell CA , Rowning BA , Moon RT .

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Calcium waves are well-known hallmarks of egg activation that trigger resumption of the cell cycle and development of the embryo. These waves rapidly and efficiently assure that activation signals are transmitted to all regions of the egg. Although the mechanism by which the calcium wave propagates across an egg as large as that of Xenopus is not known, two models prevail. One model is a wave of calcium-induced calcium release (CICR) and the other is propagation by inositol-induced calcium release (IICR). IICR requires a wave of phosphatidylinositol 4,5-bisphosphate (PIP2) hydrolysis, generating two second messengers, IP3, which then releases calcium and DAG, which activates protein kinase C (PKC). We show here that a wave of PKC-green fluorescent protein travels across the egg immediately following, and at the same velocity as, the calcium wave. This is the first example of a PKC wave in a vertebrate egg and supports the IICR model of wave propagation.

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Species referenced: Xenopus laevis
Genes referenced: actb prkca prkcb
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	Fig. 1 Calcium and PKC waves at Xenopus egg activation. The increase in intracellular free calcium is detected by the dye calcium crimson (left column) as it travels from the site of activation (right) across the egg; a wave of PKC is seen crossing the egg using PKCGFP (center column). The merged image shows that the PKC wave follows the calcium wave (right column).
	Fig. 2 Relative change in levels of intracellular free calcium after egg activation compared with those of PKC-GFP. Calcium levels reach a maximum within 2 min after artificial egg activation then slowly decrease toward baseline; PKC levels begin to increase with a lag of 30 s after the calcium rise and steadily continue to rise.
	Fig. 3 Wave of PKC-GFP in egg cortex. The increase in PKC-GFP is seen in one region of the cell periphery at high magnification (60 lens) before activation (A) and at 30 s intervals thereafter (B–I). PKC is slowly seen as it encircles cortical granules (1–3 mm diameter secretory granules), moving from the right to left of each frame and slowly increasing in intensity.
	Fig. 4 Egg cortex labeled with anti-PKC antibodies. (A) PKC can be seen surrounding the cortical granules in the unactivated egg. (B) Activated egg showing that PKC labels granules in the egg periphery at 15 min post-activation.
	Fig. 5 PKC-labeled secretory granules after egg activation. Shortly after egg activation, PKC-labeled granules (white circles) are detected as they are propelled from the egg surface to the interior of the egg by actin comet tails. (A, B) Eggs fixed 5 min after activation. (C) Eggs fixed 10 min after activation. (D) Egg fixed 15 min after activation.