Birds are useful models in developmental biology, given their large, external eggs and an array of classic embryology techniques, but the study of avian development has been dominated by a single species, the chicken Gallus gallus.
The emu, Dromaius novaehollandiae(left), and a comparison of emu and chicken eggs (right)
While a few other bird varieties have been studied for purposes of comparison, these have all been from the “modern” species (neognaths), such as quail, duck and pheasant. A number of more basal bird species (palaeognaths), including ostrich, rhea, kiwi, and emu survive, but their development has remained unstudied.
Now, in a report published in Developmental Dynamics, Hiroki Nagai of the Laboratory of Early Embryogenesis (Guojun Sheng, Team Leader) and colleagues from the same lab as well as the Laboratory for Sensory Development (Raj Ladher, Team Leader) provide a comparative description of the development of the emu, Dromaius novaehollandiae, with that of the better-known chick. The team found that while the two birds’ proceed through similar embryonic stages, a number of differences in timing and pace set them on the widely diverging courses manifested in their adult forms.
Nagai’s approach centered on identifying emu equivalents for Hamilton-Hamburger stages in the chick. The Hamburger-Hamilton (HH) system uses definitive morphological characteristics to determine the state of development, and is the gold standard in staging chick embryos. As a general rule, emus take 2–3 times longer than chicks to reach the same HH stage.
The early development of the emu resembles that of the chick until HH7. During subsequent stages in which somites form, however, the emu forms a greater number of these structures than the chick. The emu somitogenic period was calculated to be 100–110 min, slightly longer than the 90 minutes in chick embryos.
The forelimbs in adult emus are diminutive, which is reflected in development as well. The forelimb buds form and undergo initial patterning, but these appendages fail to grow apace with the rest of the embryo body, including the hindlimbs. Interestingly, adult emus also have fewer forelimb digits than do other birds, a difference that is also observable at the stage of the limb’s patterning. Once the limb buds have formed, the emu embryo begins a growth spurt that results in the enormous size differential with the chick.
In addition to their comprehensive morphological observations, the team looked at the expression of a number of genes, such as Sonic hedgehog (Shh), Brachyury, and Chordin, known to be important in early development. Expression patterns were similar to those in chick up to stage 7, when the first somite appears, with the single exception that the Brachyury expression begins slightly later in emu.
“Since a brief description by Haswell in 1887, there has not been any published study of emu development,” says Sheng. “In staging these embryos, we learned of the high level of conservation of developmental routines across bird orders, which suggests that findings from the chick may well apply generally to birds. That said, we also saw heterochrony in the development of specific tissues and structures between chick and emu, so we look forward to studying these embryos in more detail through cell labeling, transplants, and imaging techniques.”
Molecular microscopy illuminates molecular motor motion
26.07.2017 | Penn State
New virus discovered in migratory bird in Rio Grande do Sul, Brazil
26.07.2017 | Fundação de Amparo à Pesquisa do Estado de São Paulo
Strong light-matter coupling in these semiconducting tubes may hold the key to electrically pumped lasers
Light-matter quasi-particles can be generated electrically in semiconducting carbon nanotubes. Material scientists and physicists from Heidelberg University...
Fraunhofer IPA has developed a proximity sensor made from silicone and carbon nanotubes (CNT) which detects objects and determines their position. The materials and printing process used mean that the sensor is extremely flexible, economical and can be used for large surfaces. Industry and research partners can use and further develop this innovation straight away.
At first glance, the proximity sensor appears to be nothing special: a thin, elastic layer of silicone onto which black square surfaces are printed, but these...
3-D shape acquisition using water displacement as the shape sensor for the reconstruction of complex objects
A global team of computer scientists and engineers have developed an innovative technique that more completely reconstructs challenging 3D objects. An ancient...
Physicists have developed a new technique that uses electrical voltages to control the electron spin on a chip. The newly-developed method provides protection from spin decay, meaning that the contained information can be maintained and transmitted over comparatively large distances, as has been demonstrated by a team from the University of Basel’s Department of Physics and the Swiss Nanoscience Institute. The results have been published in Physical Review X.
For several years, researchers have been trying to use the spin of an electron to store and transmit information. The spin of each electron is always coupled...
What is the mass of a proton? Scientists from Germany and Japan successfully did an important step towards the most exact knowledge of this fundamental constant. By means of precision measurements on a single proton, they could improve the precision by a factor of three and also correct the existing value.
To determine the mass of a single proton still more accurate – a group of physicists led by Klaus Blaum and Sven Sturm of the Max Planck Institute for Nuclear...
26.07.2017 | Event News
21.07.2017 | Event News
19.07.2017 | Event News
26.07.2017 | Physics and Astronomy
26.07.2017 | Life Sciences
26.07.2017 | Earth Sciences