From dinosaurs to birds: the origins of feather formation
UNIGE scientists reveal the key role of specific genes in feather development, providing insights into their evolution from dinosaurs.
image:
At the 12th day of incubation, feather buds exhibit longitudinal domains of cell density that correspond to the barbs of the future down feather.
view moreCredit: © Rory Cooper & Michel Milinkovitch (CC BY)
Feathers are among the most complex cutaneous appendages in the animal kingdom. While their evolutionary origin has been widely debated, paleontological discoveries and developmental biology studies suggest that feathers evolved from simple structures known as proto-feathers. These primitive structures, composed of a single tubular filament, emerged around 200 million years ago in certain dinosaurs. Paleontologists continue to discuss the possibility of their even earlier presence in the common ancestor of dinosaurs and pterosaurs (the first flying vertebrates with membranous wings) around 240 million years ago.
Proto-feathers are simple, cylindrical filaments. They differ from modern feathers by the absence of barbs and barbules, and by the lack of a follicle—an invagination at their base. The emergence of proto-feathers likely marked the first key step in feather evolution, initially providing thermal insulation and ornamentation before being progressively modified under natural selection to give rise to the more complex structures that enabled flight.
The laboratory of Michel Milinkovitch, professor at the Department of Genetics and Evolution in the Faculty of Science at UNIGE, studies the role of molecular signaling pathways (communication systems that transmit messages within and between cells), such as the Sonic Hedgehog (Shh) pathway, in the embryonic development of scales, hair, and feathers in modern vertebrates. In a previous study, the Swiss scientists stimulated the Shh pathway by injecting an activating molecule into the blood vessels of chicken embryos and observed the complete and permanent transformation of scales into feathers on the bird’s feet.
Recreating the first dinosaur proto-feathers
‘‘Since the Shh pathway plays a crucial role in feather development, we wanted to observe what happens when it 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 the 9th day of embryonic development – just before feather buds appear on the wings – the two researchers observed the formation of unbranched and non-invaginated buds, resembling the putative early stages of proto-feathers.
However, from the 14th day of embryonic development, feather morphogenesis partially recovered. Furthermore, although the chicks hatched with patches of naked skin, dormant subcutaneous follicles were autonomously reactivated, eventually producing chickens with normal plumage.
‘‘Our experiments show that while a transient disturbance in the development of foot scales can permanently turn them into feathers, it is much harder to permanently disrupt feather development itself,’’ concludes Michel Milinkovitch. ‘‘Clearly, over the course of evolution, the network of interacting genes has become extremely robust, ensuring the proper development offeathers even under substantial genetic or environmental perturbations. The big challenge now is to understand how genetic interactions evolve to allow for the emergence of morphological novelties such as proto-feathers.’’
Journal
PLOS Biology
Method of Research
News article
Subject of Research
Animals
Article Title
"In vivo sonic hedgehog pathway antagonism temporarily results in ancestral proto-feather-like structures in the chicken"
Article Publication Date
20-Mar-2025
How feathers develop in chickens
The sonic hedgehog pathway may underlie the evolutionary emergence and diversity of feathers
image:
Alteration of the expression of the co-called 'Sonic Hedgehog' gene can transform feet scale and wing feathers. While a transient over-expression of the gene can permanently turn feet scales into feathers, it is much harder to disrupt feather development itself. The network of interacting genes determining feathers is very robust, ensuring their proper development even under substantial genetic or environmental perturbations.
view moreCredit: Fabrice Berger & Michel Milinkovitch 2025 (CC-BY 4.0, https://creativecommons.org/licenses/by/4.0/)
Inhibiting the sonic hedgehog (Shh) pathway strongly perturbs feather development in chickens by restricting feather bud outgrowth, invagination and branching, according to a study published March 20th, in the open-access journal PLOS Biology by Rory Cooper and Michel Milinkovitch from the University of Geneva, Switzerland.
Avian feathers are intricate appendages whose forms vary substantially across species and body areas, and between juvenile and adult stages. Understanding both the developmental and evolutionary mechanisms underpinning this morphological diversity has long fascinated biologists. The morphological intricacies of avian feathers make them an ideal model for investigating embryonic patterning. In particular, the Shh pathway is an important mediator of feather outgrowth and branching. However, functional in-vivo evidence regarding its role during feather development remains limited.
To fill this knowledge gap, Cooper and Milinkovitch used light sheet fluorescence microscopy imaging to study the normal patterning of embryonic feathers and how their shape develops. The authors also used precise intravenous injections of sonidegib to pharmacologically inhibit Shh pathway signaling during feather development at embryonic day 9, which precedes feather-bud outgrowth on the wings. This treatment temporarily modified Shh expression to produce striped domains instead of spots on the skin, temporarily stopped feather development, and resulted in unbranched and non-invaginated feather buds — akin to putative proto-feathers —until embryonic day 14.
Although feather development partially recovered later during development, hatched sonidegib-treated chickens exhibited naked regions of the skin surface with perturbed follicles. Remarkably, these follicles were subsequently reactivated by seven weeks post-hatching, highlighting the robustness of feather patterning as a developmental process. Overall, the study provides comprehensive functional evidence for the role of the Shh pathway in mediating feather development in chickens, supporting the idea that modified Shh signaling has contributed to the evolutionary diversification of feathers and other skin appendages such as feet scales. According to the authors, the study also demonstrates the importance of in-vivo experiments for obtaining a comprehensive understanding of developmental systems.
The authors add, “Our experiments show that while a transient disturbance in the development of feet scales can permanently turn them into feathers, it is much harder to disrupt feather development itself. The big challenge now is to understand how these genetic interactions have changed to allow for the emergence of protofeathers early in the evolution of dinosaurs."
In your coverage, please use this URL to provide access to the freely available paper in PLOS Biology: https://plos.io/3XLN4RU
Citation: Cooper RL, Milinkovitch MC (2025) In vivo sonic hedgehog pathway antagonism temporarily results in ancestral proto-featherlike structures in the chicken. PLoS Biol 23(3): e3003061. https://doi.org/10.1371/journal.pbio.3003061
Author countries: Switzerland
Funding: see manuscript
Journal
PLOS Biology
Method of Research
Experimental study
Subject of Research
Animals
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