Molecular development of fibular reduction in birds and its evolution from dinosaurs
Authors:
Botelho et al
Abstract:
Birds have a distally reduced, splinter-like fibula that is shorter than the tibia. In embryonic development, both skeletal elements start out with similar lengths. We examined molecular markers of cartilage differentiation in chicken embryos. We found that the distal end of the fibula expresses Indian hedgehog (IHH), undergoing terminal cartilage differentiation, and almost no Parathyroid-related protein (PTHrP), which is required to develop a proliferative growth plate (epiphysis). Reduction of the distal fibula may be influenced earlier by its close contact with the nearby fibulare, which strongly expresses PTHrP. The epiphysis-like fibulare however then separates from the fibula, which fails to maintain a distal growth plate, and fibular reduction ensues. Experimental downregulation of IHH signaling at a postmorphogenetic stage led to a tibia and fibula of equal length: The fibula is longer than in controls and fused to the fibulare, whereas the tibia is shorter and bent. We propose that the presence of a distal fibular epiphysis may constrain greater growth in the tibia. Accordingly, many Mesozoic birds show a fibula that has lost its distal epiphysis, but remains almost as long as the tibia, suggesting that loss of the fibulare preceded and allowed subsequent evolution of great fibulo–tibial disparity.
pop sci link.
Genetic material from ancient viral infections is critical to human development, according to researchers at the Stanford University School of Medicine.
They've identified several noncoding RNA molecules of viral origins that are necessary for a fertilized human egg to acquire the ability in early development to become all the cells and tissues of the body. Blocking the production of this RNA molecule stops development in its tracks, they found.
The discovery comes on the heels of a Stanford study earlier this year showing that early human embryos are packed full of what appear to be viral particles arising from similar left-behind genetic material.
"We're starting to accumulate evidence that these viral sequences, which originally may have threatened the survival of our species, were co-opted by our genomes for their own benefit," said Vittorio Sebastiano, PhD, an assistant professor of obstetrics and gynecology. "In this manner, they may even have contributed species-specific characteristics and fundamental cell processes, even in humans."
Sebastiano is a co-lead and co-senior author of the study, which will be published online Nov. 23 in Nature Genetics. Postdoctoral scholar Jens Durruthy-Durruthy, PhD, is the other lead author. The other senior author of the paper is Renee Reijo Pera, PhD, a former professor of obstetrics and gynecology at Stanford who is now on the faculty of Montana State University.
Sebastiano and his colleagues were interested in learning how cells become pluripotent, or able to become any tissue in the body. A human egg becomes pluripotent after fertilization, for example. And scientists have learned how to induce other, fully developed human cells to become pluripotent by exposing them to proteins known to be present in the very early human embryo. But the nitty-gritty molecular details of this transformative process are not well understood in either case.
Are the new Ediacaran Doushantuo embryo-like fossils early metazoans? A reply
Authors:
Chen et al
Abstract:
Chen et al. (2014) described a suite of one-celled, Parapandorina-stage, Megaclonophycus-stage (some with dyads and tetrads), and matryoshka-stage fossils from the Doushantuo Formation, and interpreted them as representing a sequence of ontogenetic stages of the animal embryo-like fossil Megasphaera. Tang (2015) argues that the matryoshkas might have been parasites or symbionts, rather than developmental products of dyads and tetrads in Megaclonophycus-stage fossils. Assessing Tang's (2015) arguments against available evidence, we conclude that the matryoshkas likely represent an ontogenetic stage of Megasphaera. As such, they have the potential to illuminate the developmental biology, life cycle, and phylogenetic affinity of the enigmatic fossil Megasphaera.
Are the new Ediacaran Doushantuo Megasphaera-like acritarchs early metazoans?
Author:
Tang
Abstract:
A recent report by Chen et al. (Chen, L., Xiao, S., Pang, K., Zhou, C.M., Yuan, X.L., 2014. Cell differentiation and germ-soma separation in Ediacaran animal embryo-like fossils. Nature 516, 238-241) describes the new Ediacaran Doushantuo acritarchs with fascinating features. Nested within Megaclonophycus-like fossils that exhibit palintomic cell division are multicellular spheroid structures termed matryoshkas, which are interpreted to be germ cells. Such distinctive features of cellular differentiation and germ-soma separation suggest affinities of these with early stem group metazoans. In this commentary, I suggest some alternative interpretations to those elaborated by Chen et al. (2014).
A molecular mechanism for the origin of a key evolutionary innovation, the bird beak and palate, revealed by an integrative approach to major transitions in vertebrate history
Authors:
Bhullar et al
Abstract:
The avian beak is a key evolutionary innovation whose flexibility has permitted birds to diversify into a range of disparate ecological niches. We approached the problem of the mechanism behind this innovation using an approach bridging paleontology, comparative anatomy, and experimental developmental biology. First we used fossil and extant data to show the beak is distinctive in consisting of fused premaxillae that are geometrically distinct from those of ancestral archosaurs. To elucidate underlying developmental mechanisms, we examined candidate gene expression domains in the embryonic face: the earlier frontonasal ectodermal zone (FEZ) and the later midfacial Wnt-responsive region, in birds and several reptiles. This permitted the identification of an autapomorphic median gene expression region in Aves. In order to test the mechanism, we used inhibitors of both pathways to replicate in chicken the ancestral amniote expression. Altering the FEZ altered later Wnt responsiveness to the ancestral pattern. Skeletal phenotypes from both types of experiments had premaxillae that clustered geometrically with ancestral fossil forms instead of beaked birds. The palatal region was also altered to a more ancestral phenotype. This is consistent with the fossil record and with the tight functional association of avian premaxillae and palate in forming a kinetic beak.
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Lungs of the first amniotes: why simple if they can be complex?
Authors:
Lambertz et al
Abstract:
We show—in contrast to the traditional textbook contention—that the first amniote lungs were complex, multichambered organs and that the single-chambered lungs of lizards and snakes represent a secondarily simplified rather than the plesiomorphic condition. We combine comparative anatomical and embryological data and show that shared structural principles of multichamberedness are recognizable in amniotes including all lepidosaurian taxa. Sequential intrapulmonary branching observed during early organogenesis becomes obscured during subsequent growth, resulting in a secondarily simplified, functionally single-chambered lung in lepidosaurian adults. Simplification of pulmonary structure maximized the size of the smallest air spaces and eliminated biophysically compelling surface tension problems that were associated with miniaturization evident among stem lepidosaurmorphs. The remaining amniotes, however, retained the multichambered lungs, which allowed both large surface area and high pulmonary compliance, thus initially providing a strong selective advantage for efficient respiration in terrestrial environments. Branched, multichambered lungs instead of simple, sac-like organs were part and parcel of the respiratory apparatus of the first amniotes and pivotal for their success on dry land, with the sky literally as the limit.
Cell differentiation and germ–soma separation in Ediacaran animal embryo-like fossils
Authors:
Chen et al
Abstract:
Phosphorites of the Ediacaran Doushantuo Formation (~600 million years old) yield spheroidal microfossils with a palintomic cell cleavage pattern. These fossils have been variously interpreted as sulphur-oxidizing bacteria, unicellular protists, mesomycetozoean-like holozoans, green algae akin to Volvox and blastula embryos of early metazoans or bilaterian animals. However, their complete life cycle is unknown and it is uncertain whether they had a cellularly differentiated ontogenetic stage, making it difficult to test their various phylogenetic interpretations. Here we describe new spheroidal fossils from black phosphorites of the Doushantuo Formation that have been overlooked in previous studies. These fossils represent later developmental stages of previously published blastula-like fossils, and they show evidence for cell differentiation, germ–soma separation, and programmed cell death. Their complex multicellularity is inconsistent with a phylogenetic affinity with bacteria, unicellular protists, or mesomycetozoean-like holozoans. Available evidence also indicates that the Doushantuo fossils are unlikely crown-group animals or volvocine green algae. We conclude that an affinity with cellularly differentiated multicellular eukaryotes, including stem-group animals or algae, is likely but more data are needed to constrain further the exact phylogenetic affinity of the Doushantuo fossils.
Cell differentiation and germ–soma separation in Ediacaran animal embryo-like fossils
Authors:
Chen et al
Abstract:
Phosphorites of the Ediacaran Doushantuo Formation (~600 million years old) yield spheroidal microfossils with a palintomic cell cleavage pattern. These fossils have been variously interpreted as sulphur-oxidizing bacteria, unicellular protists4, mesomycetozoean-like holozoans green algae akin to Volvox and blastula embryos of early metazoans or bilaterian animals. However, their complete life cycle is unknown and it is uncertain whether they had a cellularly differentiated ontogenetic stage, making it difficult to test their various phylogenetic interpretations. Here we describe new spheroidal fossils from black phosphorites of the Doushantuo Formation that have been overlooked in previous studies. These fossils represent later developmental stages of previously published blastula-like fossils, and they show evidence for cell differentiation, germ–soma separation, and programmed cell death. Their complex multicellularity is inconsistent with a phylogenetic affinity with bacteria, unicellular protists, or mesomycetozoean-like holozoans. Available evidence also indicates that the Doushantuo fossils are unlikely crown-group animals or volvocine green algae. We conclude that an affinity with cellularly differentiated multicellular eukaryotes, including stem-group animals or algae, is likely but more data are needed to constrain further the exact phylogenetic affinity of the Doushantuo fossils.
Recent advances in imaging technology are transforming how scientists see the cellular universe, showing the form and movement of once grainy and blurred structures in stunning detail. But extracting the torrent of information contained in those images often surpasses the limits of existing computational and data analysis techniques, leaving scientists less than satisfied.
Now, researchers at the Howard Hughes Medical Institute’s Janelia Research Campus have developed a way around that problem. They have developed a new computational method that can rapidly track the three-dimensional movements of cells in such data-rich images. Using the method, the Janelia scientists can essentially automate much of the time-consuming process of reconstructing an animal's developmental building plan cell by cell.
Philipp Keller, a group leader at Janelia, led the team that developed the computational framework. He and his colleagues, including Janelia postdoc Fernando Amat, Janelia group leader Kristin Branson and former Janelia lab head Eugene Myers, who is now at the Max Plank Institute of Molecular Cell Biology and Genetics, have used the method to reconstruct cell lineage during development of the early nervous system in a fruit fly. Their method can be used to trace cell lineages in multiple organisms and efficiently processes data from multiple kinds of fluorescent microscopes.
The scientists describe their approach in a paper published online this week in Nature Methods.
The developmental cycles of early Cambrian Olivooidae fam. nov. (?Cycloneuralia) from the Yangtze Platform (China)
Authors:
Steiner et al
Abstract:
Eggs, embryos, and hatchlings of olivooids are common and distinctive components of the earliest Cambrian small shelly fossil assemblage (Anabarites trisulcatus–Protohertzina anabarica Zone) at the northern and northwestern edge of the Yangtze Platform. Embryos are preserved in 3D as phosphatized permineralizations with superficial cellular structures. Nanofocus X-ray computed tomography reveals that diagenetic structures characterize the interior of most phosphatized eggs and embryos. The Olivooidae fam. nov. is herein distinguished from the possibly related hexaconulariids. Statistical size investigations and morphological studies indicate that at least three, but possibly five or more species of olivooids occur in the early Cambrian of South China. Fossilized smooth egg stages reflect a high biodiversity, encompassing 8–10 or more biological species. Eggs and embryos of Olivooides multisulcatus, Olivooides mirabilis and Quadrapyrgites quadratacris are represented by distinct and characteristic size clusters. The size ranges of embryonic parts of hatchlings roughly correspond to the size clusters of the embryos. From reconstruction of the developmental series of Olivooides multisulcatus it appears that the cleavage mode of olivooids was transitional between superficial and total cleavage. Late embryos and hatchlings of Olivooides multisulcatus and Olivooides mirabilis are characterized by pentaradial symmetry, whereas tubes of Quadrapyrgites quadratacris exhibit tetraradial symmetry. Tubular hatchlings of olivooids may represent larval or adult stages, or perhaps, nonfeeding larvae. Although the biological affinity of olivooids is weakely constrained, we hypothesize that they belong within an extinct clade of the Cycloneuralia. Their assignment to the Cnidaria is considered unlikely.
The search for Orsten-type fossils in southern China
Authors:
Shen et al
Abstract:
Orsten-type fossils, mainly arthropod juveniles and even tiny embryos exquisitely preserved in apatite, have been well documented from several localities in southern China. This particular type of Lagerstätte is known from just a few places around the world but has led to significant breakthroughs in the understanding of the early diversity of animals and evolution of metazoans. The original ‘orsten’ from southern Sweden are limestone concretions within black shales, whereas in China this kind of preservation occurs in lime mudstone thin beds and nodules interbedded with shale. Thus there is a taphonomic bias in that this kind of preservation is localized to a deeper water carbonate facies which can be regarded as concretionary due to early cementation under shallow burial. Nonetheless, we observe that even within a laterally extensive bed of the seemingly appropriate lithofacies, preservation may be highly localized. Thus, in addition to the extreme rarity of Orsten-type preservation globally, serendipity in discovering fossiliferous localities plays a significant role. Because of their predominant occurrence in the Cambrian they are also a temporally restricted window. To extract Orsten-type material from the limestone matrix, mild acetic acid digestion has been widely applied, but certain procedures can be employed to aid recovery by limiting damage to these delicate but fragile specimens. Here, we describe our method for etching out specimens and review some of the discoveries recently made in southern China.
