The feathers of birds may have originally been filaments from ancient dinosaurs, but a team of Swiss researchers is delving into the genetics of feather formation by experimenting with chicken embryos. By manipulating a key signaling pathway, they reconstructed a structure similar to that of the original feather, revealing the elasticity and evolutionary refinement of the feather development process. Feather growth often recovers even when disturbed – hinting at the astonishing complexity and stability of this evolutionary innovation.

On day 12 of incubation, the pinnately buds take on longitudinal areas of cell density that correspond to the future fluffy branches. Image Credits: © Rory Cooper and Michel Milinkovitch (CC BY)

羽毛是动物身上最复杂的皮肤结构之一。它们的进化起源一直存在争议，但化石和发育生物学的证据表明，羽毛有一个共同的起源：简单的毛发状结构，称为原羽毛。这些早期的羽毛前体由一根管状细丝组成，据信最早出现在大约 2 亿年前的某些恐龙身上。

一些科学家认为，原始羽毛可能进化得更早，可能是在大约 2.4 亿年前，在恐龙和翼龙的共同祖先中进化而来，翼龙是第一种具有膜状翅膀的飞行脊椎动物。原始羽毛的出现可能标志着羽毛进化的第一步关键。

Unlike modern feathers, primitive feathers were unbranched, cylindrical filaments. They lacked the complex branches and small branches that made up the structure of today's feathers, nor did they have hair follicles (small sacs of feather growth in the skin). These early structures, which may have served functions such as thermal insulation and display, were gradually reshaped by natural selection into more complex flight-friendly shapes.

At the University of Geneva (UNIGE), Professor Michel Milinkovitch and his team study how molecular signaling pathways – systems that allow cells to communicate – affect the development of features such as scales, hair, and feathers in vertebrate embryos.

In earlier studies, the team activated a key pathway called Sonic Hedgehog (Shh) in chicken embryos. By injecting an activating molecule into the embryo's veins, they triggered a dramatic transformation: the scales on the bird's feet permanently turned into feathers.

Recreate the original feathers of the first dinosaur

"Since the Shh pathway plays a vital role in feather development, we wanted to see what happens when this pathway is inhibited," explains Rory Cooper, a postdoctoral researcher in Michel Milinkovitch's lab and co-author of the study. By injecting a molecule that blocks the SHH signaling pathway on day 9 of embryonic development, just before the pinnoid bud appears on the wings, the two researchers observed the formation of unbranched and non-invaginated pinnate, similar to the putative early stage of the original feather.

However, from day 14 of embryonic development, feather morphogenesis partially resumes. In addition, although the chicks hatch with bare skin, dormant subcutaneous hair follicles reactivate on their own, eventually producing chicks with normal feathers.

Michel Milinkovich concludes: "Our experiments show that while a brief disturbance during the development of foot scales can permanently turn it into a feather, it is much more difficult to permanently disrupt the developmental process of a feather. "Obviously, during evolution, the network of interacting genes has become very strong, ensuring the proper development of feathers even in the event of significant genetic or environmental disturbances. The biggest challenge now is to understand how genetic interactions have evolved to allow morphological novelties such as primitive feathers to emerge. ”

编译自/ScitechDaily