[论文解读] Native climate uniformly influences temperature-dependent growth rate in Drosophila embryos

Steven Kuntz, Michael Eisen|arXiv (Cornell University)|Jun 22, 2013

Physiological and biochemical adaptations被引用 1

一句话总结

本研究揭示，尽管果蝇物种和温度之间存在广泛的胚胎发育时间差异，从细胞化到孵化的关键发育里程碑的相对时间保持恒定。通过在11个物种中使用时间延时成像及人工/自动标注，作者发现了一种保守的、与温度无关的发育时钟，调控着来自不同气候起源的胚胎发育过程。

ABSTRACT

Temperature affects both the timing and outcome of animal development, but the detailed effects of temperature on the progress of early development have been poorly characterized. To determine the impact of temperature on the order and timing of events during Drosophila melanogaster embryogenesis, we used time-lapse imaging to track the progress of embryos from shortly after egg laying through hatching at seven precisely maintained temperatures between 17.5C and 32.5C. We employed a combination of automated and manual annotation to determine when 36 milestones occurred in each embryo. D. melanogaster embryogenesis takes ~33 hours at 17.5C, and accelerates with increasing temperature to 16 hours at 27.5C, above which embryogenesis slows slightly. Remarkably, while the total time of embryogenesis varies over two fold, the relative timing of events from cellularization through hatching is constant across temperatures. To further explore the relationship between temperature and embryogenesis, we expanded our analysis to cover ten additional Drosophila species of varying climatic origins. Six of these species, like D. melanogaster, are of tropical origin, and embryogenesis time at different temperatures was similar for them all. D. mojavensis, a sub-tropical fly, develops slower than the tropical species at lower temperatures, while D. virilis, a temperate fly, exhibits slower development at all temperatures. The alpine sister species D. persimilis and D. pseudoobscura develop as rapidly as tropical flies at cooler temperatures, but exhibit diminished acceleration above 22.5C and have drastically slowed development by 30C. Despite ranging from 13 hours for D. erecta at 30C to 46 hours for D. virilis at 17.5C, the relative timing of events from cellularization through hatching is constant across all species and temperatures, suggesting the existence of a timer controlling embryogenesis.

研究动机与目标

• 表征果蝇胚胎在广泛温度范围内的温度依赖性发育进程。
• 确定具有不同气候起源的物种之间发育时间是否保守。
• 探究尽管绝对发育速度存在差异，关键事件的相对时间顺序是否保持恒定。
• 检验一种与温度无关的发育时钟控制胚胎发育的假设。

提出的方法

• 在七个精确温度（17.5°C 至 32.5°C）下，对果蝇胚胎从卵产出到孵化进行时间延时成像。
• 在多个温度下对个体胚胎的36个发育里程碑进行人工和自动标注。
• 对11个具有不同气候起源的果蝇物种（包括热带、亚热带、温带和高山物种）的胚胎发育时间进行比较分析。
• 对绝对发育时间及不同物种和温度下里程碑的相对时间进行定量比较。
• 通过统计分析评估在温度和系统发育变异下相对时间一致性的程度。

实验结果

研究问题

• RQ1 温度如何影响黑腹果蝇（D. melanogaster）胚胎中发育里程碑的绝对时间？
• RQ2 在D. melanogaster中，胚胎事件的相对序列和时间是否在不同温度下保持保守？
• RQ3 在相同热条件下，具有不同气候起源的果蝇物种的发育轨迹有何差异？
• RQ4 是否存在一种保守的发育时钟，能够在绝对发育速度变化的情况下维持相对时间？
• RQ5 热带、温带和高山果蝇物种在温度依赖性胚胎发育方面有何不同？

主要发现

• D. melanogaster 胚胎发育在17.5°C时需33小时，在27.5°C时缩短至16小时，且在27.5°C以上略有减慢。
• 尽管总胚胎发育时间存在两倍的差异，从细胞化到孵化的发育里程碑的相对时间在所有测试温度下均保持不变。
• 六个热带果蝇物种表现出相似的温度依赖性胚胎发育时间，表明其热响应具有保守性。
• D. mojavensis（亚热带）在低温下发育速度慢于热带物种，而D. virilis（温带）在所有温度下均发育缓慢。
• D. persimilis 和 D. pseudoobscura（高山）在低温下发育迅速，但在22.5°C以上加速减弱，且在30°C时显著减慢。
• 在所有11个物种中，从13小时（D. erecta 在30°C时）到46小时（D. virilis 在17.5°C时）的范围内，从细胞化到孵化的事件相对时间保持恒定，支持一种保守发育时钟的存在。