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Updated: Jul 27, 2025
High Throughput Microinjections of Sea Urchin Zygotes
Published on: January 21, 2014
ON THE SYSTEM CONTROLLING THE TIME OF MICROMERE FORMATION IN SEA URCHIN EMBRYOS
1Biology Department, Tokyo Metropolitan University, Setagayaku, Tokyo 158, and Misaki Marine Biological Station, Miurashi 238-02, Japan.
Abstract:
The previously reported observation that micromere formation after cleavage suppression is not linked with the number of blastomeres present but rather with the time schedule of the fourth cleavage of the normal embryos has been confirmed. A hypothesis is advanced that a rhythmical fluctuation of the sulfhydryl contents of the egg proteins is the clock system, and micromere formation is connected with the fourth SH cycle after fertilization. The hypothesis was tested under 3 conditions: (i) Conditions which stop the nuclear activities but preserve the SH cycle, followed by a release from these conditions. (ii) Conditions which "freeze" both nuclear and cytoplasmic rhythms, and later removal of the conditions. (iii) Conditions which leave nuclear activities intact but prevent the cytoplasmic rhythms, followed by normal culturing. The results came out as anticipated by the hypothesis.
Insights
The timing of the fourth embryonic cleavage, not blastomere count, dictates micromere formation. A sulfhydryl (SH) cycle in egg proteins likely acts as the biological clock regulating this process.
Area of Science:
- Developmental Biology
- Cell Biology
- Embryology
Background:
- Micromere formation in early embryos is a critical developmental event.
- Previous studies suggested a link between cleavage suppression and micromere formation, but the precise timing mechanism remained unclear.
Purpose of the Study:
- To confirm the role of the fourth cleavage timing in micromere formation.
- To investigate the hypothesis that rhythmic fluctuations in egg protein sulfhydryl (SH) content regulate embryonic development timing.
- To elucidate the relationship between nuclear activity, cytoplasmic rhythms, and micromere formation.
Main Methods:
- Experimental manipulation of nuclear and cytoplasmic activities during early embryonic development.
- Utilizing conditions to selectively inhibit or preserve nuclear and/or cytoplasmic rhythms.
- Observing micromere formation following the release from experimental conditions.
Main Results:
- Micromere formation was confirmed to be dependent on the timing of the fourth cleavage, independent of blastomere number.
- Experimental conditions supported the hypothesis that a sulfhydryl (SH) cycle acts as the embryonic clock.
- Results aligned with predictions regarding the interplay of nuclear and cytoplasmic rhythms in development.
Conclusions:
- The fourth cleavage timing is a critical determinant for micromere formation.
- Rhythmic fluctuations in egg protein sulfhydryl (SH) content are proposed as the underlying molecular clock mechanism.
- The study provides evidence for the coordinated regulation of embryonic development by nuclear and cytoplasmic temporal programs.
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