Medrano Emmanuel, Jendrick Karen, McQuirter Julian, Moxham Claire, Rajic Dominique, Rosendorf Lila, Stilman Liraz, Wilright Dontrel, Collins Kevin M
Department of Biology, University of Miami, 1301 Memorial Drive, Coral Gables, FL 33146.
These authors contributed equally and are listed in alphabetical order.
bioRxiv. 2024 Dec 31:2024.12.30.630790. doi: 10.1101/2024.12.30.630790.
Animals alter their behavior in response to changes in the environment. Upon encountering hyperosmotic conditions, the nematode worm initiates avoidance and cessation of egg-laying behavior. While the sensory pathway for osmotic avoidance is well-understood, less is known about how egg laying is inhibited. We analyzed egg-laying behavior after acute and chronic shifts to and from hyperosmotic media. Animals on 400 mM sorbitol stop laying eggs immediately but then resume ~3 hours later, after accumulating additional eggs in the uterus. Surprisingly, the hyperosmotic cessation of egg laying did not require known osmotic avoidance signaling pathways. Acute hyperosmotic shifts in hyperosmotic-resistant mutants overproducing glycerol also blocked egg laying, but these animals resumed egg laying more quickly than similarly treated wild-type animals. These results suggest that hyperosmotic conditions disrupt a 'high-inside' hydrostatic pressure gradient required for egg laying. Consistent with this hypothesis, animals adapted to hyperosmotic conditions laid more eggs after acute shifts back to normosmic conditions. Optogenetic stimulation of the HSN egg-laying command neurons in hyper-osmotic treated animals led to fewer and slower egg-laying events, an effect not seen following direct optogenetic stimulation of the postsynaptic vulval muscles. Hyperosmotic conditions also affected egg-laying circuit activity with the vulval muscles showing reduced Ca transient amplitudes and frequency even after egg-laying resumes. Together, these results indicate that hyperosmotic conditions regulate egg-laying via two parallel mechanisms: a sensory pathway that acts to reduce HSN excitability and neurotransmitter release, and a biophysical mechanism where a hydrostatic pressure gradient reports egg accumulation in the uterus.
动物会根据环境变化改变其行为。遇到高渗环境时，线虫会启动回避行为并停止产卵。虽然渗透压回避的感觉通路已为人熟知，但对于产卵是如何被抑制的却知之甚少。我们分析了线虫在急性和慢性转移至高渗培养基以及从高渗培养基转移出来后的产卵行为。处于400 mM山梨醇环境中的线虫会立即停止产卵，但在子宫中积累了更多卵子后，约3小时后又会恢复产卵。令人惊讶的是，高渗导致的产卵停止并不需要已知的渗透压回避信号通路。在过量产生甘油的抗高渗突变体中，急性高渗转移也会阻断产卵，但这些动物比同样处理的野生型动物恢复产卵的速度更快。这些结果表明，高渗环境破坏了产卵所需的“内部高压”静水压力梯度。与这一假设一致的是，适应高渗环境的线虫在急性转移回等渗环境后会产下更多卵子。对经高渗处理的动物的HSN产卵指令神经元进行光遗传学刺激会导致产卵事件减少且速度变慢，而直接对突触后外阴肌肉进行光遗传学刺激则不会出现这种效果。高渗环境还影响产卵回路的活动，即使在恢复产卵后，外阴肌肉的钙瞬变幅度和频率也会降低。总之，这些结果表明，高渗环境通过两种平行机制调节产卵：一种感觉通路，其作用是降低HSN的兴奋性和神经递质释放；另一种生物物理机制，即静水压力梯度反映子宫内卵子的积累情况。
