Sonic Hedgehog Gene Determines Whether Bird Has Scales or Feather

Vertebrate skin appendages, which are a surprisingly varied collection of microorganisms, include scales, spines, feathers, and hair.

These appendages have many different natural shapes, but they all go through the same early developmental stages while they are embryos.

By deliberately altering the expression of key genes, two University of Geneva (UNIGE) researchers have found a way to permanently change the scales that ordinarily cover chicken feet into feathers.

Feather or scales are Gene dependent

(Photo : OLI SCARFF/AFP via Getty Images)

Terrestrial vertebrates have a variety of keratinized appendages covering their skin, including hair, feathers, and scales, as per Phys.org.

Even though there are many different forms seen within and across species, the embryonic development of skin appendages usually starts off relatively similarly.

In fact, cells that form a localized thickening on the skin's surface and express certain genes give rise to all of these structures.

A signaling pathway-a communication mechanism that permits the transfer of signals both inside and between cells-is controlled by one of these genes, known as Sonic hedgehog (Shh).

The neural tube, limb buds, and skin appendages are only a few of the structures that are developed as a result of Shh signaling.

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Understanding development of skin appendages

The physical and biological mechanisms that result in the variety of skin appendages in vertebrates are of interest to Michel Milinkovitch's group, a professor in the Department of Genetics and Evolution at the Faculty of Science at the UNIGE.

His group has specifically shown that scales, hair, and feathers are homologous features that were passed down from a common ancestor among reptiles.

Scientists utilize chicken embryonic feathers as a model system to comprehend the evolution of skin appendages.

While the existence of feathered legs and dorsal foot surfaces in some breeds of chickens, such as the Brahma and Sablepoot types, is well recognized, the genetic basis of this characteristic is still not entirely understood.

Feathered feet originated in scaly feet

Chickens descended from creatures with scale-covered fingers and tarsometatarsus, as per Oxford Academic.

Feathered legs, feathered feet, shank feathering, or ptilopody are genetic conditions that result in some of those scales developing into feathers.

Previous research has demonstrated that chromosomes 13 and 15 include two key loci that regulate feathered leg.

Transition for gene modification

Michel Milinkovitch's team looked into how the Shh pathway may be involved because the signaling pathways that are totally responsible for this metamorphosis have not yet been identified.

The two researchers noted that just one stage-specific treatment is necessary to cause the development of many juvenile down-type feathers in places that are ordinarily coated in scales.

Surprisingly, because they regenerate and are subsequently and independently replaced by adult feathers, these artificially produced feathers are equivalent to those covering the rest of the body.

RNA sequencing research revealed that the Shh pathway is promptly and continuously activated once the active molecule is injected into embryos as compared to embryos that received a control solution lacking the active molecule.

This demonstrates that the Shh pathway is activated during the transformation of scales into feathers.

The findings suggested that a change in genome makeup or expression is not necessary for an evolutionary leap, such as from scales to feathers.

Instead, the creation of feathers as opposed to scales can result from a brief alteration in the expression of the Shh gene.

This work, which at first aimed to understand how scales and feathers evolve, has profound ramifications for our knowledge of the evolutionary processes that produce the tremendous range of animal forms found in nature.