We have measured levels of intracellular free calcium ([Ca2+]i) in albino Xenopus laevis embryos using recombinant aequorin and a photon-counting system. We observed sinusoidal oscillations in [Ca2+]i that had the same frequency as cleavage, with cleavage occurring when [Ca2+]i was lowest. An increase in calcium was seen to precede first cleavage. The cyclic changes in calcium were superimposed on a secondary pattern that increased, peaked between third and fifth cleavages and then slowly declined to a level similar to that measured before first cleavage. The amplitude of the oscillations was small during the first few cleavages but became larger with each cycle, with the largest oscillations occurring when the secondary pattern peaked (between third and fifth cleavage). As the secondary pattern declined, the amplitude of the oscillations also became smaller. The oscillations are due to release of calcium from intracellular stores, since the signal was the same in calcium-free solution as in normal medium. When cleavage was blocked with the microtubule-disrupting drugs colchicine or nocodazole, the [Ca2+]i oscillations persisted. Calcium oscillations of a similar magnitude and frequency were also present in artificially activated eggs. The secondary pattern was different in cleavage-blocked embryos and artificially activated eggs, the baseline increasing until about the third cycle and then remaining elevated for the rest of the recording (> 8 hours). By fixing embryos at various points in the calcium cycle, we determined that mitosis began shortly after calcium levels reached their peak and was complete before the calcium level dropped to its lowest point.(ABSTRACT TRUNCATED AT 250 WORDS)

Baker
P. F.
,
Warner
A. E.
(
1972
).
Intracellular calcium and cleavage in early embryos of Xenopus laevis.
J. Cell Biol
53
,
579
581
Berridge
M. J.
(
1993
).
Inositol trisphosphate and calcium signalling.
Nature
361
,
315
325
Blinks
J. R.
,
Wier
W. G.
,
Hess
P.
,
Prendergast
F. G.
(
1982
).
Measurement of Ca2+concentrations in living cells.
Prog. Biophys. Mol. Biol
40
,
1
114
Busa
W. B.
,
Nuccitelli
R.
(
1985
).
An elevated free cytosolic Ca2+wave follows fertilization in eggs of the frog, Xenopus laevis.
J. Cell Biol
100
,
1325
1329
Cork
R. J.
,
Cicerelli
M. F.
,
Robinson
K. R.
(
1987
).
A rise in cytosolic calcium is not necessary for maturation of Xenopus laevis oocytes.
Dev. Biol
121
,
41
47
Galione
A.
,
McDougall
A.
,
Busa
W. B.
,
Willmott
N.
,
Gillot
I.
,
Whitaker
M.
(
1993
).
Redundant mechanisms of calcium-induced calcium release underlying calcium waves during fertilization of sea urchin eggs.
Science
261
,
348
352
Gerhart
J.
,
Wu
M.
,
Kirschner
M.
(
1984
).
Cell cycle dynamics of an M-phase specific cytoplasmic factor in Xenopus laevis oocytes and eggs.
J. Cell Biol
98
,
1247
1255
Grandin
N.
,
Charbonneau
M.
(
1991
).
Intracellular free calcium oscillates during cell division of Xenopus embryos.
J. Cell Biol
112
,
711
718
Han
J.-K.
,
Fukami
K.
,
Nuccitelli
R.
(
1992
).
Reducing inositol lipid hydrolysis, Ins(1,4,5)P3receptor availability, or Ca2+gradients lengthens the duration of the cell cycle in Xenopus laevis blastomeres.
J. Cell Biol
116
,
147
156
Hara
K.
,
Tydeman
P.
,
Kirschner
M.
(
1980
).
A cytoplasmic clock with the same period as the division cycle in Xenopus eggs.
Proc. Nat. Acad. Sci. USA
77
,
462
466
Hepler
P. K.
(
1989
).
Calcium transients during mitosis: observations in flux.
J. Cell Biol
109
,
2567
2573
Keating
T. J.
,
Robinson
K. R.
(
1992
).
Intracellular free calcium levels in cleaving Xenopus embryos. Mol. Biol.
Cell
3
,
342
–.
Kubota
H. Y.
,
Yoshimoto
Y.
,
Hiramoto
Y.
(
1993
).
Oscillation of intracellular free calcium in cleaving and cleavage-arrested embryos of Xenopus laevis.
Dev. Biol
160
,
512
518
Maslanski
J. A.
,
Leshko
L.
,
Busa
W. B.
(
1992
).
Lithium-sensitive production of inositol phosphates during amphibian embryonic mesoderm induction.
Science
256
,
243
245
Miller
A. L.
,
Fluck
R. A.
,
McLaughlin
J. A.
,
Jaffe
L. F.
(
1993
).
Calcium buffer injections inhibit cleavage in Xenopus eggs.
J. Cell Sci
106
,
523
534
Murray
A. W.
(
1991
).
Cell cycle extracts.
Meth. Cell Biol
36
,
581
605
Newport
J.
,
Kirschner
M.
(
1982
).
A major developmental transition in early Xenopus embryos. I. Characterization and timing of cellular changes at the midblastula stage.
Cell
30
,
675
686
Nuccitelli
R.
,
Yim
D. L.
,
Smart
T.
(
1993
).
The sperm-induced Ca2+wave following fertilization of the Xenopus egg requires the production of Ins(1,4,5)P3.
Dev. Biol
158
,
200
212
Rink
T. J.
,
Tsien
R. Y.
,
Warner
A. E.
(
1980
).
Free calcium in Xenopus embryos measured with ion-sensitive microelectrodes.
Nature
283
,
658
660
Satoh
N.
(
1977
).
‘Metachronous’ cleavage and initiation of gastrulation in amphibian embryos.
Dev. Growth Differ
19
,
111
117
Shimomua
O.
(
1991
).
Preparation and handling of aequorin solutions for the measurement of cellular Ca2+.
Cell Calcium
12
,
635
643
Snow
P.
,
Nuccitelli
R.
(
1993
).
Calcium buffer injections delay cleavage in Xenopus laevis blastomeres.
J. Cell Biol
122
,
387
394
Speksnijder
J. E.
,
Miller
A. L.
,
Weisenseel
M. H.
,
Chen
T.-H.
,
Jaffe
L. F.
) (
1989
).
Calcium buffer injections block fucoid egg development by facilitating calcium diffusion.
Proc. Nat. Acad. Sci. USA
86
,
6607
6611
Stith
B. J.
,
Goalstone
M.
,
Silva
S.
,
Jaynes
C.
(
1993
).
Inositol 1,4,5-trisphosphate mass changes from fertilization through first cleavage in Xenopus laevis. Mol. Biol.
Cell
4
,
435
443
Sullivan
K. M. C.
,
Busa
W. B.
,
Wilson
K. L.
(
1993
).
Calcium mobilization is required for nuclear vesicle fusion in vitro: implications for membrane traffic and IP3receptor function.
Cell
73
,
1411
1422
Webb
D. J.
,
Nuccitelli
R.
(
1983
).
Direct measurement of intracellular pH changes in Xenopus eggs at fertilization and cleavage.
J. Cell Biol
91
,
562
567
This content is only available via PDF.