Observations and Introduction

• The study investigated how exposure to magnetic fields can change the timing of cell division in early sea urchin embryos.
• Both alternating current (AC) and direct current (DC) magnetic fields were used.
• Researchers examined effects at low frequencies (such as 60 Hz) and over a wide range (up to 600 kHz).
• The focus was on how these fields can either speed up (advance) or slow down (delay) the mitotic cycle (the process of cell division).
• Key terms:
  • Mitotic cycle: The sequence of events that leads to cell division.
  • AC field: A magnetic field produced by alternating current where the direction changes periodically.
  • DC field: A constant magnetic field produced by direct current.

Experimental Setup and Methods (Step-by-Step “Cooking Recipe” Style)

• Step 1: Preparing the Embryos
  • Fertilized sea urchin eggs (from Strongylocentrotus purpuratus) were collected and pooled to minimize individual differences.
  • Successful fertilization was confirmed by the rapid elevation of the fertilization membrane.
• Step 2: Setting Up the Magnetic Field
  • A copper wound cylindrical coil was used to generate a homogenous magnetic field (within 5% variation).
  • The field strengths ranged from as low as 1.7 mT up to 8.8 mT at 60 Hz and 2.5–6.5 mT for other frequencies.
  • Controls were in place to ensure that heating from the coil did not affect the embryos.
• Step 3: Embryo Culture Conditions
  • Embryos were cultured in 250 ml beakers with stirring in filtered sea water at a constant 12°C.
  • Temperature and environmental magnetic conditions were continuously monitored to ensure consistency.
• Step 4: Sampling and Scoring
  • Samples of approximately 200 embryos were taken every 15 minutes during the first and second cell divisions.
  • Embryos were fixed with 3% formaldehyde and then scored for the number of cells (blastomeres) present.
  • Data were plotted to compare the timing of cell divisions between exposed and control groups.
• Step 5: Data Analysis
  • The timing of the first and second cell divisions was determined from the plots.
  • Results were expressed as a percentage advance or delay relative to control cultures.
  • Multiple experiments were performed to ensure reproducibility.

Key Findings and Results

• Exposure to a 60 Hz AC magnetic field advanced the timing of both the first and second cell divisions.
• The degree of advancement increased with field strength:
  • No effect was seen at 1.7 mT.
  • At 3.4 mT, cell divisions were about 12–14% faster than controls.
  • At 8.8 mT, the first division was advanced by up to 32% and the second by up to 35%.
• When exposing embryos to other frequencies (from 0 up to 420 Hz and even into kHz ranges):
  • Some frequencies (like 60 Hz, 240 Hz, and 360 Hz) caused significant advancement.
  • Higher frequencies above the ELF range (beyond a few kHz) eventually led to delays in cell division.
• Shorter exposure durations (even as brief as 15% of the cell cycle) produced a measurable advance in division timing.
• Exposing only the sperm (before fertilization) did not affect the timing, indicating the effect occurs in the fertilized egg/embryo.
• The overall cell cycle shortening appears to be due to an earlier entry into mitosis rather than a faster mitosis itself.
• Exposed embryos exhibited less natural variation in division times compared to control groups.

Interpretations and Possible Mechanisms

• The magnetic fields seem to “push” the embryo’s cell cycle toward a faster pace, almost like turning up the heat in a recipe to speed up cooking.
• Possible mechanisms include:
  • Changes in calcium ion dynamics, which are crucial for triggering cell division.
  • Alterations in the cell membrane potential that may influence when cells start dividing.
  • An increase in the synthesis of regulatory proteins (such as cyclins) that control the cell cycle.
• The study ruled out ion cyclotron resonance (ICR) effects for common ions based on the frequency response observed.
• Overall, the effect appears cumulative—the longer the exposure during the cell cycle, the greater the advancement in cell division timing.

Conclusions and Implications

• Both AC and DC magnetic fields can significantly alter the timing of early cell divisions in sea urchin embryos.
• The effect is dependent on field strength, frequency, and duration of exposure.
• The findings suggest that magnetic fields may accelerate the developmental clock of embryos, pushing them toward a lower limit of the cell cycle duration.
• This research provides insights into how electromagnetic fields might affect cellular processes and embryonic development in other organisms as well.
• Further studies are needed to clarify the precise biochemical mechanisms involved.

Additional Notes

• The experimental design included extensive controls to rule out factors like heating and stray magnetic fields.
• Advanced data analysis techniques (using software like Matlab) were used to accurately determine the timing shifts.
• These results may help inform safety guidelines and further research on environmental electromagnetic field exposure.

观察与引言

• 本研究探讨了磁场暴露如何改变海胆胚胎早期细胞分裂的时机。
• 使用了交流（AC）和直流（DC）磁场。
• 研究考察了低频（如60 Hz）以及宽频范围（最高达600 kHz）的磁场效应。
• 重点在于磁场是使细胞分裂提前（加速）还是延迟（减缓）。
• 关键术语：
  • 有丝分裂周期：细胞分裂过程中依次发生的一系列事件。
  • 交流磁场：由交流电产生的磁场，其电流方向周期性改变。
  • 直流磁场：由直流电产生的恒定磁场。

实验设置与方法（详细步骤说明）

• 步骤1：准备胚胎
  • 收集并受精海胆（Strongylocentrotus purpuratus）的卵子，并混合以减少个体差异。
  • 通过受精膜的迅速抬起确认受精成功。
• 步骤2：搭建磁场设备
  • 利用铜线缠绕的圆柱形线圈产生均匀磁场（变化范围在5%以内）。
  • 在60 Hz下，磁场强度范围为1.7 mT到8.8 mT；在其他频率下，使用2.5–6.5 mT的磁场。
  • 采取严格控制措施，确保线圈发热不会影响胚胎。
• 步骤3：胚胎培养条件
  • 在250毫升烧杯中用过滤海水培养胚胎，并持续搅拌，温度保持在12°C。
  • 实时监控温度和环境磁场，确保实验条件一致。
• 步骤4：采样与计数
  • 在第一和第二次细胞分裂期间，每15分钟采集约200个胚胎的样本。
  • 用3%甲醛固定胚胎，并计数各胚胎内的细胞数（卵裂球）。
  • 将数据绘制成曲线，比较处理组与对照组细胞分裂的时机差异。
• 步骤5：数据分析
  • 确定第一和第二次细胞分裂的时间点。
  • 以百分比形式表示处理组相对于对照组的提前或延迟程度。
  • 重复多次实验以确保结果具有重复性。

主要发现与结果

• 60 Hz的交流磁场使第一和第二次细胞分裂时间均提前。
• 提前的程度随磁场强度增加而增大：
  • 在1.7 mT下未观察到明显效应。
  • 在3.4 mT时，细胞分裂提前约12%–14%。
  • 在8.8 mT时，第一分裂提前可达32%，第二分裂提前达35%。
• 在其他频率下（0至420 Hz甚至到kHz范围）：
  • 某些频率（如60 Hz、240 Hz、360 Hz）显著提前细胞分裂。
  • 而高于极低频（ELF）范围的高频磁场则导致细胞分裂延迟。
• 即使较短的暴露时间（约占细胞周期的15%）也能引起明显的分裂时机变化。
• 仅暴露精子（未受精）不影响细胞分裂时机，说明效应主要发生在受精卵或胚胎中。
• 整体来看，缩短的是细胞周期中两次分裂之间的间期，而不是分裂本身的过程。
• 暴露组胚胎的分裂时机比对照组更为一致，变异性较小。

解释与可能机制

• 磁场似乎使胚胎的细胞周期加速，就像在烹饪时提高火力使食物更快成熟一样。
• 可能的机制包括：
  • 改变钙离子（对触发细胞分裂至关重要）的动态平衡。
  • 改变细胞膜电位，从而影响细胞开始分裂的时机。
  • 增加调控细胞周期的蛋白质（如周期蛋白）的合成。
• 实验数据排除了常见离子的离子回旋共振（ICR）效应。
• 总体而言，效应呈累积性——暴露时间越长，细胞分裂提前的幅度越大。

结论与启示

• 交流和直流磁场都能显著改变海胆胚胎早期细胞分裂的时机。
• 这种效应依赖于磁场强度、频率以及暴露时长。
• 结果表明，磁场暴露使胚胎的发育时钟提前，将细胞周期压缩到可能的最短时长。
• 该研究为理解电磁场如何影响细胞过程和胚胎发育提供了重要线索，也可能对其他生物体具有参考价值。
• 需要进一步研究以明确其分子和生化机制。

附加说明及未来展望

• 实验设计中严格控制了温度、线圈发热和环境磁场等干扰因素。
• 采用Matlab等软件进行数据处理，精确计算了细胞分裂时机的变化。
• 这些发现有助于指导未来关于环境电磁场暴露安全性和生物发育影响的研究。