肠道肌肉的性别与生殖可塑性决定肠道大小

亮点
    肠道肌肉主动控制成年肠道的大小
    雌性肠道肌肉在生殖期间发生重塑
    肌肉的性别决定因子塑造器官的大小与结构
    生殖相关的肌肉重塑可适应性地减缓肠道转运速度

Summary
Adult organs enlarge or regress in response to functional demands: changes commonly attributed to the dynamics of their resident stem cells. A striking example is the intestine, whose length varies with diet and reproductive status. We find that the size of the adult gut is extrinsically controlled by its surrounding muscles. In Drosophila, intestinal muscle differs in size and structure between sexes and grow in females during reproduction. By altering the sex or reproductive status of gut muscle cells, we establish that muscle-intrinsic sex determinants determine baseline sex differences in muscle myofibril width and organ size. Female muscles integrate hormonal and nutritional inputs during reproduction to elongate their sarcomeres; this reduces intestinal transit and further increases organ size. Such remodeling is adaptive and also occurs in mice. Our findings redefine the intestinal muscle as a responder to specific signals that adjust adult organ-level features and sustain reproductive demands.

摘要

成年器官会根据功能需求而增大或缩小——这种变化通常归因于其驻留干细胞的动态行为。肠道是一个典型例子，其长度随饮食和生殖状态而变化。我们发现，成年肠道的大小由其周围的肌肉外在控制。在果蝇中，肠道肌肉在性别间存在大小和结构的差异，并且在雌性生殖期间会生长。通过改变肠道肌肉细胞的性别或生殖状态，我们证实肌肉内在的性别决定因子决定了肌肉肌原纤维宽度和器官大小的基础性别差异。雌性肌肉在生殖期间整合激素和营养信号，以延长其肌节；这会降低肠道转运速度并进一步增加器官大小。这种重塑具有适应性，且在小鼠中同样发生。我们的研究重新定义了肠道肌肉——它是一个对特定信号做出响应的组织，能够调整成年器官层面的特征，并支持生殖需求。

Keywords
Drosophila, sex differences, reproduction, intestinal visceral muscles, organ remodeling, Mus musculus, juvenile hormone, peristalsis, intestine, plasticity

关键词

果蝇，性别差异，生殖，肠道内脏肌，器官重塑，小鼠，保幼激素，蠕动，肠道，可塑性

Introduction
The process of building an organ does not end in adult life; fully developed organs grow and shrink in adult animals to adapt to a changing environment and/or fulfill new physiological roles. A striking example of adult organ remodeling is provided by the intestinal tract. In many animals, including flies, reptiles, and mammals, the intestinal tract elongates or shortens dramatically in response to diet.[1,2] In females, it grows further during reproduction.[3–8] In light of the key roles of the intestine in modulating food intake and energy balance,[9–11] understanding its adult plasticity is both valuable from a fundamental perspective and of potential therapeutic significance.

器官的构建过程并不终止于成年期；已完全发育的器官在成年动物中会生长或萎缩，以适应变化的环境和/或满足新的生理需求。肠道是成年器官重塑的一个突出例子。在许多动物（包括蝇类、爬行动物和哺乳动物）中，肠道会因饮食而发生显著伸长或缩短[1,2]。在雌性中，肠道在生殖期间进一步生长[3–8]。鉴于肠道在调节食物摄入和能量平衡中的关键作用[9–11]，理解其成年可塑性既有基础研究价值，也有潜在的治疗意义。

Our current conceptual framework of intestinal plasticity is largely epithelial. Work over the past few decades in several animal models, including flies and mice, has shown that stem cells endow the intestinal epithelium with the ability to self-renew, regenerate, and resize in response to challenges; changes in the size of the organ ensue from changes in the rates of epithelial proliferation, differentiation, and death.[1,12] But this intestinal epithelium is surrounded by muscles that can provide niche signals.[13–19] Are these muscles passive bystanders in the resizing of the intestinal epithelium?

目前关于肠道可塑性的概念框架主要集中于上皮层。过去几十年，在果蝇和小鼠等多个动物模型中的研究表明，干细胞赋予肠道上皮自我更新、再生和响应挑战而改变大小的能力；器官大小的变化源于上皮增殖、分化和死亡速率的改变[1,12]。然而，肠道上皮被肌肉包裹，且这些肌肉能够提供微环境信号[13–19]。那么，这些肌肉在肠道上皮重塑过程中是否只是被动旁观者？

In contrast to skeletal or cardiac muscle,[20–22] intestinal muscle is not well characterized: its ability to remodel in response to physiological changes remains unexplored, and potential sex differences or reproductive plasticity have not been considered. Mechanistic interrogation of these questions relies on the ability to genetically target intestinal muscle specifically, without affecting other muscle types, and on assessing effects across scales from the subcellular to the organismal level. An opportunity to do so is provided by the intestine of Drosophila: a well-established model organ for the study of adult organ plasticity and the crosstalk between intestinal epithelial stem cells and their niche.[23–25]

与骨骼肌或心肌不同[20–22]，肠道肌肉的特征尚未被充分研究：其对生理变化的响应重塑能力尚待探索，且潜在的性别差异或生殖可塑性也未被考虑。对这些问题的机制性探究依赖于能否特异性地靶向肠道肌肉（不影响其他肌肉类型），并能在从亚细胞到生物体多个层面上评估效应。果蝇肠道为此提供了机会：它是一个成熟的模型器官，用于研究成年器官可塑性以及肠道上皮干细胞与其微环境之间的对话[23–25]。

Here, we discover and characterize sex differences and reproductive plasticity in intestinal muscle. We reveal that such plasticity also occurs in mice and has instructive effects at the organ and organismal level. Indeed, intestinal muscle does not passively respond to changes in the intestinal epithelium: it is actively remodeled by a hormone to adjust organ size and function, sustaining the female’s ability to reproduce.

在此，我们发现了肠道肌肉中的性别差异和生殖可塑性，并对其进行了表征。我们揭示这种可塑性同样存在于小鼠中，并对器官和生物体层面具有指导性影响。实际上，肠道肌肉并非被动地响应肠道上皮的变化；它受到激素的主动重塑，以调整器官大小和功能，从而支持雌性的生殖能力。

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Feeding assays using FlyPAD
FlyPAD assays were performed as described in Itskov et al.[133] FlyPAD arenas were filled with 2.4 μL of food (5% w/v sucrose (granulated sugar, Tate & Lyle), 10% w/v Brewer’s yeast (#903312, MP Biomedicals), 1.5% w/v agar (Sigma A7002)). For all experiments, 4- to 7-day-old virgin or mated females were individually transferred to FlyPAD arenas by mouth aspiration and allowed to feed for 1.5 hrs at 25°C, 65% relative humidity. The total number of sips per animal over this period was acquired using the Bonsai framework,[134] and analyzed in MATLAB using previously described custom-written software.[133] Non-eating flies (defined as having fewer than 2 activity bouts during the assay) were excluded from the analysis. All FlyPAD experiments were performed during the day from 10:00 until 14:00. Data for experimental and control genotypes used for comparison were always acquired in the same FlyPAD assay. Comparisons between two conditions were analyzed with the Mann-Whitney-Wilcoxon rank sum test using GraphPad Prism 10.1.

进食实验 – FlyPAD

FlyPAD 实验按照 Itskov 等人[133]的描述进行。FlyPAD 活动室中注入 2.4 μL 食物（5% w/v 蔗糖（颗粒糖，Tate & Lyle），10% w/v 啤酒酵母（#903312，MP Biomedicals），1.5% w/v 琼脂（Sigma A7002））。所有实验中，4–7 日龄的处女蝇或交配雌蝇通过口吸法单独转移至 FlyPAD 活动室，在 25°C、65% 相对湿度下自由取食 1.5 小时。使用 Bonsai 框架[134]采集每只动物在此期间的总摄食次数，并使用先前描述的定制软件在 MATLAB 中进行分析[133]。不进食的蝇（定义为在测定期间活动次数少于 2 次）被排除分析。所有 FlyPAD 实验均在白天 10:00–14:00 进行。用于比较的实验基因型和对照基因型数据始终在同一 FlyPAD 测定中采集。两组间比较采用 Mann-Whitney-Wilcoxon 秩和检验，使用 GraphPad Prism 10.1 进行分析。