Developmental Timing in Fertilized Merogones of the Sand Dollar, <i>Clypeaster japonicus</i>

Yoneda, Masafumi; Nomura, Akihiro

doi:10.1111/j.1440-169x.1991.00391.x

Cited by 2 publications

(1 citation statement)

References 19 publications

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“…It is apparent that neither the reduction of ploidy nor the surgical treatment affects the time of the first cleavage or the start of gastrulation. These findings agree with a report on the development of haploid sea urchin embryos by Yoneda and Nomura (1991), who showed that haploid embryos undergo cleavage with nearly the same periodicity as diploid embryos, although first cleavage occurs slightly later in the haploid than in the diploid embryos. Delay in the first cleavage or the start of gastrulation in haploid eggs relative to the delay in diploid eggs.…”

Section: Effect Of Egg Ploidy On the Timing Of The Start Of Gastrulationsupporting

confidence: 92%

Timing system for the start of gastrulation in the Xenopus embryo

Itoh

Shinagawa

2003

Dev Growth Differ

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This study examined which component of the egg, the nucleus or cytoplasm, is involved in the timing of the start of gastrulation in the Xenopus embryo, and when it starts to measure time. First, nuclei of cells of 256-cell stage embryos were transplanted to enucleated eggs 60 min after activation. These eggs showed first cleavage 20-30 min later than control eggs fertilized at the same time as the activation of recipient eggs, and started gastrulation 25-35 min later than control embryos (depending on the delay in the first cleavage). Second, eggs whose nuclei were temporarily isolated by the extrusion of the portion containing the nucleus out of the fertilization envelope showed first cleavage 60-90 min later than sibling control eggs, because of delayed introduction of the nucleus from the extruded portion. They started gastrulation 60-90 min later than sibling control embryos (depending on the delay in the first cleavage). The portion inside the envelope underwent two to three rounds of oscillation in cell cycle relevant activities before the first cleavage, while the portion outside underwent the same rounds of cleavage as the inside portion. From the present and previous results it is concluded that the putative timing system for the start of gastrulation in the Xenopus embryo, whether it consists of a single or of multiple clocks, starts measuring time at or around the first cleavage, and that the presence of both the nucleus and the cytoplasm in the same cell and occurrence of mitosis and/or cleavage there are indispensable for the timing system to work, although the role of the cytoplasm is superior to that of the nucleus.

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Section: Effect Of Egg Ploidy On the Timing Of The Start Of Gastrulationsupporting

confidence: 92%

Timing system for the start of gastrulation in the Xenopus embryo

Itoh

Shinagawa

2003

Dev Growth Differ

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Relative Timing of Stiffening with Various Combinations of Nucleate and Enucleated Egg Fragments of Xenopus laevis

Shinagawa

1992

Dev Growth Differ

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Previously, I found that in Xenopuseggs, the surface contraction wave (SCW) can arise at a point close to a male, a female or a zygote nucleus or a top portion of the egg (9). This finding suggested that all types of nucleus and cytoplasm of a Xenopus egg have the potential to determine the point of initiation of the SCW. Since stiffening is closely associated with the SCW, to determine the factors governing this phenomenon, I compared the times of egg stiffening of pairs of fragments containing different types of nuclei or cytoplasm. I found that the stiffening occurs earlier in fragments containing any type of nucleus than in those containing no nucleus, and earlier in fragments containing a male nucleus than in those containing a female nucleus. These results are consistent with the notion that either a nucleus or cytoplasm that induces the SCW earliest determines the point of initiation of the SCW close to itself. I also found that DNA replication is essential for the earlier occurrence of stiffening in a fragment containing a nucleus.

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Developmental Timing in Fertilized Merogones of the Sand Dollar, Clypeaster japonicus

Cited by 2 publications

References 19 publications

Timing system for the start of gastrulation in the Xenopus embryo

Timing system for the start of gastrulation in the Xenopus embryo

Relative Timing of Stiffening with Various Combinations of Nucleate and Enucleated Egg Fragments of Xenopus laevis

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