当被攻击时,斑鱼产生一种柔软的,通过将粘液和螺纹喷射到海水中,在几分之一秒内产生纤维状的防御性粘液。粘液的快速设置和显着扩展使其成为一种非常有效和独特的防御形式。这种生物材料是如何进化的还不清楚,尽管间接证据表明表皮是粘液腺中产生线和粘液的细胞的起源。这里,我们描述了在一个假定的同源细胞类型内的大的细胞内线从黑鱼表皮。这些表皮线的平均长度为〜2mm,直径为〜0.5μm。整个盲鱼身体被一层致密的表皮线细胞覆盖,每平方毫米的皮肤总共存储约96厘米的线。实验引起的对盲鱼皮肤的损伤导致线的释放,连同粘液,形成粘性表皮粘液,比防御性粘液更纤维状,更稀。转录组分析进一步表明,表皮线是粘液线的祖先,线基因的复制和多样化与粘液腺的进化同时发生。我们的结果支持盲鱼粘液的表皮起源,这可能是由选择更强壮、更大量的粘液驱动的。
Hagfish是深海动物,它们代表着有脊骨的动物最古老的亲戚之一。为了抵御捕食者,它们会产生一种非凡的粘液,用纤维增强,会堵塞捕食者的g,挫败攻击。粘液在不到半秒钟的时间内展开,从盲鱼身体上的特殊腺体中渗出,并扩大到其喷射量的10,000倍。防御性粘液高度稀释,主要由海水组成,粘液浓度低且强烈,大约20厘米长的类似丝绸的线。盲鱼粘液在哪里以及如何进化仍然是一个谜。Zeng等人。着手回答食泥腺体的起源,以及它们是如何进化的。首先,Zeng等人。检查了斑驳鱼,发现它们皮肤表层(表皮)的细胞会产生大约两毫米长的线,当斑驳鱼的皮肤受损时,这些线就会释放出来。这些线与破裂的皮肤细胞产生的粘液混合,形成粘液,可能粘附在捕食者的嘴里。这种粘液可能是由专门腺体产生的粘液的前体。为了检验这个假设,Zeng等人。分析了在斑鱼的皮肤和粘液腺中哪些基因被打开和关闭。他们发现的模式与源自表皮的粘液腺一致。基于这些结果,Zeng等人。有人认为,古代河豚首先进化出了当它们的皮肤在攻击中受损时产生具有抗捕食者作用的粘液的能力。随着时间的推移,可以产生和储存更多粘液并将其积极地喷射到捕食者的嘴中的斑鱼可能有更好的生存机会。这种优势可能导致出现了可以执行这些功能的日益专业化的腺体。Zeng等人的发现。进化生物学家会感兴趣,海洋生物学家,以及那些研究捕食者-猎物相互作用生态学的人。由于其独特的材料特性,生物物理学家也对盲鱼粘液感兴趣,生物工程师和从事仿生研究的人员。盲鱼粘液腺的起源是一个新性状如何进化的有趣例子,并可能提供对其他适应性特征进化的见解。
When attacked, hagfishes produce a soft, fibrous defensive slime within a fraction of a second by ejecting mucus and threads into seawater. The rapid setup and remarkable expansion of the slime make it a highly effective and unique form of defense. How this biomaterial evolved is unknown, although circumstantial evidence points to the epidermis as the origin of the thread- and mucus-producing cells in the slime glands. Here, we describe large intracellular threads within a putatively homologous cell type from hagfish epidermis. These epidermal threads averaged ~2 mm in length and ~0.5 μm in diameter. The entire hagfish body is covered by a dense layer of epidermal thread cells, with each square millimeter of skin storing a total of ~96 cm threads. Experimentally induced damage to a hagfish\'s skin caused the release of threads, which together with mucus, formed an adhesive epidermal slime that is more fibrous and less dilute than the defensive slime. Transcriptome analysis further suggests that epidermal threads are ancestral to the slime threads, with duplication and diversification of thread genes occurring in parallel with the evolution of slime glands. Our results support an epidermal origin of hagfish slime, which may have been driven by selection for stronger and more voluminous slime.
Hagfishes are deep-sea animals, and they represent one of the oldest living relatives of animals with backbones. To defend themselves against predators, they produce a remarkable slime that is reinforced with fibers and can clog a predator’s gills, thwarting the attack. The slime deploys in less than half a second, exuding from specialized glands on the hagfish’s body and expanding up to 10,000 times its ejected volume. The defensive slime is highly dilute, consisting mostly of sea water, with low concentrations of mucus and strong, silk-like threads that are approximately 20 centimeters long. Where and how hagfish slime evolved remains a mystery. Zeng et al. set out to answer where on the hagfish’s body the slime glands originated, and how they may have evolved. First, Zeng et al. examined hagfishes and found that cells in the surface layer of their skin (the epidermis) produce threads roughly two millimeters in length that are released when the hagfish’s skin is damaged. These threads mix with the mucus that is produced by ruptured skin cells to form a slime that likely adheres to predators’ mouths. This slime could be a precursor of the slime produced by the specialized glands. To test this hypothesis, Zeng et al. analyzed which genes are turned on and off both in the hagfishes’ skin and in their slime glands. The patterns they found are consistent with the slime glands originating from the epidermis. Based on these results, Zeng et al. propose that ancient hagfishes first evolved the ability to produce slime with anti-predator effects when their skin was damaged in attacks. Over time, hagfishes that could produce and store more slime and eject it actively into a predator’s mouth likely had a better chance of surviving. This advantage may have led to the appearance of increasingly specialized glands that could carry out these functions. The findings of Zeng et al. will be of interest to evolutionary biologists, marine biologists, and those studying the ecology of predator-prey interactions. Because of its unique material properties, hagfish slime is also of interest to biophysicists, bioengineers and those engaged in biomimetic research. The origin of hagfish slime glands is an interesting example of how a new trait evolved, and may provide insight into the evolution of other adaptive traits.