Figure 3
Dynamics of head mesoderm cell clusters during individualization of the head muscles See also Figures S4 and S5.
(A–L) 3D reconstructions and laser scanning images of stage 24 (A–D), 25 (E–H), and 26 (I–L) lamprey embryos. The area enclosed by the white dotted line in (K) indicates velum mesoderm. Pink, mesoderm; light blue, dorsal inner mandibular mesoderm; green, ventral mandibular arch mesoderm; yellow, cavity in the mandibular mesoderm. Images show sagittal views.
(M) Comparison of rosettes and head mesoderm cell clusters in lamprey and amphioxus embryos. Right blue, somite rosette; blue, distinct head mesodermal cell clusters. DIMM, dorsal inner mandibular mesoderm; EOM, extraocular muscle; GS, gill slit; GV, ganglion trigeminal; HyAM, hyoid arch mesoderm; HyM, hyoid mesoderm; LLM, lower lip mesoderm; LPM, lateral plate mesoderm; MM, mandibular mesoderm; NHP, nasohypophyseal plate; Op, optic vesicle; OPM, oropharyngeal membrane; OV, otic vesicle; PHM, pharyngeal mesoderm; PMM, premandibular mesoderm; PP, pharyngeal pouch; S, somite; ULM, upper lip mesoderm; Vel, velum; VMAM, ventral mandibular arch mesoderm.
Dynamics of head mesoderm cell clusters during individualization of the head muscles See also Figures S4 and S5.
(A–L) 3D reconstructions and laser scanning images of stage 24 (A–D), 25 (E–H), and 26 (I–L) lamprey embryos. The area enclosed by the white dotted line in (K) indicates velum mesoderm. Pink, mesoderm; light blue, dorsal inner mandibular mesoderm; green, ventral mandibular arch mesoderm; yellow, cavity in the mandibular mesoderm. Images show sagittal views.
(M) Comparison of rosettes and head mesoderm cell clusters in lamprey and amphioxus embryos. Right blue, somite rosette; blue, distinct head mesodermal cell clusters. DIMM, dorsal inner mandibular mesoderm; EOM, extraocular muscle; GS, gill slit; GV, ganglion trigeminal; HyAM, hyoid arch mesoderm; HyM, hyoid mesoderm; LLM, lower lip mesoderm; LPM, lateral plate mesoderm; MM, mandibular mesoderm; NHP, nasohypophyseal plate; Op, optic vesicle; OPM, oropharyngeal membrane; OV, otic vesicle; PHM, pharyngeal mesoderm; PMM, premandibular mesoderm; PP, pharyngeal pouch; S, somite; ULM, upper lip mesoderm; Vel, velum; VMAM, ventral mandibular arch mesoderm.
Despite the almost daily claims in the social media by creationist dupes that mainstream biologists are abandoning the Theory of Evolution (TOE) in favour of creationism because it doesn't explain the facts, there is no sign whatsoever in the scientific literature of that happening. No serious biologist has ever published a peer-reviewed paper proposing that magic by a supernatural designer better explains the facts than the TOE.
Instead, just about every paper dealing with origins and development of species and their relationship to other species, has evolution firmly and inextricably embedded within it and the conclusions only ever make sense as the result of an evolutionary process. The belief that the TOE has been or is in the process of being, overthrown by creationism is a lie promulgated by the Deception Institute to claim success for the 'Wedge Strategy', which has been a monumental failure as fewer Americans now believe in creationism than did at the start of the campaign.
The paper recently published with open access in iScience illustrates just have firmly embedded the TOE is in biology. It concerns the early development of the vertebrate head, which has been a matter of conjecture in biology:
Some believe that the vertebrate head has developed as a result of modification of the segmental elements of the trunk, such as the vertebrae and somites. On the other hand, others believe that the vertebrate head has evolved as a new, unsegment body part, unrelated to other widely observed embryonic segments somites. Interestingly, previous studies on embryos have revealed the presence of some vestiges of somites in the head mesoderm (e.g., head cavities and somitomeres). However, homology between trunk somites and such head segments has been controversial.Note the complete absence of any notion of magic creation in the controversy. The issue is over which tissues evolved into the beginnings of the vertebrate head.
The paper, by Japanese scientists led by Assistant Professor Takayuki Onai, of the Department of Anatomy, University of Fukui, School of Medical Sciences, Fukui, Japan, resolves that controversy by showing how the head of a lamprey embryo develops.
As the University of Fukui news release explains:
Scientists study developing lamprey embryos to clarify the origin of vertebrate head, paving the way to a better understanding of ancestral vertebrates.Did anyone notice the abandonment of the TOE in favour of creationism in that description? Me neither!
Since the 18th century, several theories regarding the origin of the vertebrate head have been proposed. However, owing to the lack of molecular and morphological studies, the question of whether the vertebrate head evolved as a modified embryonic segment or originated as an independent unsegmented head remains unanswered. Now, scientists from Japan have investigated lamprey embryos using cutting-edge microscopic techniques to reveal interesting insights about vertebrate head evolution, clarifying an unresolved mystery in basic science.
The failure to understand the evolutionary origins of the vertebrate head is also attributable to the lack of studies on extant species such as lampreys, which are known to share several traits with fossil jawless vertebrates and retain primitive traits related to the head mesoderm. While some studies have focused on the embryonic morphology of lampreys, they have often fallen short because of challenges like tissue destruction and acidic fixation during examination, making it difficult to observe the formation of head mesoderm and trunk somites.
Now, however, a research team led by Assistant Professor Takayuki Onai from the University of Fukui, Japan, has utilized advanced techniques like transmission electron microscopy and serial block-face scanning electron microscopy (SBF-SEM) to understand the development of the head mesoderm and somites in lamprey embryos. The researchers also analyzed the morphology and gene expression patterns of cephalochordate and hemichordate (both being invertebrates) to understand the origins of somites and head mesoderm from an evolutionary perspective. This paper was made available online in iScience on November 13, 2023, and is co-authored by Dr. Noritaka Adachi from Aix-Marseille Université, Dr. Hidetoshi Urakubo from the National Institute for Physiological Sciences (NIPS), Dr. Fumiaki Sugahara from Hyogo Medical University, Dr. Toshihiro Aramaki from Osaka University, Dr. Mami Matsumoto from NIPS and Nagoya City University, and Dr. Nobuhiko Ohno from NIPS and Jichi Medical University.
To clarify the presence or absence of somites in the head mesoderm during early stages of diversification, the researchers focused on rosettes, which are major somite patterns and are important for the subsequent development of vertebrae. Their initial observations of lamprey embryos showed that the tissue closely related to the formation of facial muscles and other elements of the skull, known as the head mesoderm, did have cell clusters with features similar to somite rosettes. To clarify if these cell clusters were indeed rosettes, they conducted ultrastructural experiments, including the SBF-SEM and gene expression analysis. This examination of the cellular morphology and gene expression revealed that the cell clusters were clearly distinct from rosettes. “The cell clusters we observed are likely lamprey-specific features, as they are not recognizable in the head mesoderm of both hagfish and shark embryos,” explains Dr. Onai.
Furthermore, gene expression analysis also revealed the absence of segmental expression of somitogenesis-related genes, indicating their distinctiveness from somites. These findings indicate that the rosette pattern typically seen in somites is not necessarily the essential or most basic feature that defines the process of bodily segmentation.
Moreover, the experiments provide evidence that the vertebrate head mesoderm diverged during the early phases of vertebrate evolution. Furthermore, comparison of embryos of hemichordates (a basal deuterostome), amphioxus (a basal chordate), and vertebrates revealed that the somites likely arose from the “endomesoderm” tissue of an ancient deuterostome ancestor. The evolutionary origin of somites has been the central question in zoology for more than 150 years, and in this study, Onai et al., revealed the enigma. Regarding the evolutionary mechanism for the emergence of head mesoderm, they found that the head mesoderm emerged upon the segregation of mesodermal genes between the front and back parts (rostro-caudal axis) of organisms.
“Taken together, our findings revealed a different evolutionary origin for the vertebrate head mesoderm, suggesting that it evolved from the repatterning of an ancient mesoderm and diversified even before the emergence of jawed vertebrates,” concludes Dr. Onai.
In summary, the finding that the cell clusters present in the head mesoderm are distinct morphologically and molecularly from somites, favors a new model where the vertebrate head mesoderm diverged during early evolution. This sheds more light on the age-old debate on the evolution of the vertebrate head and can help us advance the understanding of our own origins.
Perhaps it's in the peer-reviewed paper in iScience:
It look very much then like your head has evolved not from a modified first segment of your segmented deuterostome ancestor, but from a structure which evolved and diversified from other tissues early on in your primitive ancestry.HighlightsGraphical abstract
- Rosette pattern seen in somites is not a primal identity of segmentation
- The vertebrate head mesoderm diverged during the early phase of evolution
- Rostro-caudal segregation of mesodermal genes enabled to evolve the head mesoderm
- Somites arose from an ancient deuterostome endomesoderm during gastrulation
Summary
The cranial muscle is a critical component in the vertebrate head for a predatory lifestyle. However, its evolutionary origin and possible segmental nature during embryogenesis have been controversial. In jawed vertebrates, the presence of pre-otic segments similar to trunk somites has been claimed based on developmental observations. However, evaluating such arguments has been hampered by the paucity of research on jawless vertebrates. Here, we discovered different cellular arrangements in the head mesoderm in lamprey embryos (Lethenteron camtschaticum) using serial block-face scanning electron and laser scanning microscopies. These cell populations were morphologically and molecularly different from somites. Furthermore, genetic comparison among deuterostomes revealed that mesodermal gene expression domains were segregated antero-posteriorly in vertebrates, whereas such segregation was not recognized in invertebrate deuterostome embryos. These findings indicate that the vertebrate head mesoderm evolved from the anteroposterior repatterning of an ancient mesoderm and developmentally diversified before the split of jawless and jawed vertebrates.
Introduction
After Goethe proposed in the 18th century that skulls were derived from trunk vertebrae,1 the vertebrate head has been considered to have evolved from the modification of trunk segmental elements such as vertebrae and somites (a view of segmentalists).2,3,4 Contrary to Goethe’s idea, the vertebrate head is assumed to have evolved as a new unsegmented head (a view of non-segmentalists).5,6 To date, no definite solution to this debate has been obtained,7 and the main controversy centers on the origin of the pre-otic head mesoderm.2,5,7 Three pairs of head cavities, which have been repeatedly regarded as serial homologs of trunk somites, develop during embryogenesis in elasmobranchs and lampreys (Figures 1A–1C and S1B)8,9 and have been proposed as homologs of rostral somites in the cephalochordate amphioxus (Figure S1A).10,11 Furthermore, vestiges of somites, known as somitomeres, have been discovered in the head mesoderm of early chicken embryos12 before the formation of the head cavity (Figure S1C).5 Somitomeres were also found in the teleost (Oryzias latipes), Chondrichthyes (Squalus acanthias), and mouse embryos.13,14,15 However, replication studies of somitomeres did not detect such morphological structures, nor did gene expression profiles of head mesoderm fit well with somitomere patterns.16,17,18,19 Although the presence of such segmental features of the head has been denied by some researchers,20,21,22 there have been insufficient molecular and morphological studies to resolve this dichotomy.10,19,23,24,25,26,27,28
Extant cyclostomes (lampreys and hagfish) share several traits with fossil jawless vertebrates, making them useful for understanding the origin of vertebrates.29,30,31 Moreover, conflicts on the origin of the vertebrate head have been unsettled partly due to the poor understanding of the lamprey head mesoderm.2,7 On the early vertebrate evolution, there has been two major hypotheses about the position of lampreys and hagfishes, craniate, and cyclostome hypotheses.29 Based on morphological data, lampreys are considered to be a closer relative to gnathostomes than to hagfishes, and hagfishes are regarded to retain primitive traits in the craniate hypothesis.32 On the other hand, the cyclostome hypothesis supported by molecular data indicates that hagfishes are anatomically derived lineage.33 Recent fossil study on hagfishes from the Cretaceous Tethys sea, as well as a comparative developmental study on lampreys, hagfishes, and gnathostomes also strength the cyclostome hypothesis.34,35 Hagfishes are marine fishes living in deep sea, and the developmental sequences of the head mesoderm seem to be highly modified because of the degenerated eyes and the loss of extraocular muscles.36,37 Therefore, it is considered that they experienced long selective time which related to evolve highly derived characters.33 On the other hand, lampreys possess eyes and extraocular muscles and are more likely to retain their ancestral condition of the head mesoderm.9
Figure 1 Formation of the head/trunk mesoderm in lamprey (Lethenteron camtschaticum) embryos.
See also Figure S1.
(A–C) Comparison of the chordate heads. Somites are located at the rostral end of the amphioxus (A), and three pairs of somite homologs have been suggested in the head mesoderm of lampreys (B) and gnathostomes (C).
(D–H) 3D reconstruction of lamprey embryos. The blue (mandibular mesoderm), green (hyoid mesoderm), and orange (somites) lines in the left panels correspond to the optical sections analyzed in (J–L). The left panels are side views anterior to the left; the center panels are left anterior oblique views, and the right panels are posterior views.
(I–L) Quantitative analysis of lamprey morphology in terms of mandibular mesoderm (blue), hyoid mesoderm (green), and somites (orange). (I) Scheme of the inner product (x), calculation of the paraxial mesoderm, axial mesoderm, and neural plate. (J–L) Time sequences of the inner products (J), distance between the paraxial and axial mesoderm (K), and the distance between the axial mesoderm and neural plate (tube) (L). AM, axial mesoderm; Br, brain; CV, cerebral vesicle; GS, gill slit; HyM, hyoid mesoderm; LAGD, left anterior gut diverticulum; LPM, lateral plate mesoderm; MM, mandibular mesoderm; Not, notochord; NP, neural plate; NT, neural tube; OV, otic vesicle; PCP, pre-chordal plate; PHM, paraxial head mesoderm; PM, paraxial mesoderm; PMM, premandibular mesoderm; PP, pharyngeal pouch; S, somite.
In 1902, Koltzoff observed head somites of lamprey embryos in paraffin sections, but the tissues tended to peel off during sectioning because of a large number of yolk granules, and the acidic fixative distorted the embryonic morphology.9,38,39 Subsequent studies on the lamprey head mesoderm were insufficient to determine whether it contains somites.39,40 Therefore, we reinvestigated the formation of the head mesoderm and trunk somites in lamprey embryos using confocal laser scanning microscopy, which prevents tissue destruction by yolk granules, and examined the tissue ultrastructures using transmission electron microscopy (TEM), which is useful for detecting tiny cavities. Furthermore, we performed serial block-face scanning electron microscopy (SBF-SEM) to reconstruct and compare cellular morphology and arrangements between somites and the head mesoderm, especially the mandibular and hyoid mesoderm, located in anatomically comparable positions in the embryo. To understand the evolutionary history of the somites and head mesoderm in the deuterostome phylogeny, we also analyzed morphology and gene expression patterns of cephalochordate (Branchiostoma floridae), which is the most basal living chordate, and hemichordate (Ptychodera flava), which is a member of ambulacraria phyla, one of the two superphyla in deuterostomes.
Video S1. Serial block-face–scanning electron microscopy of the trunk somite related to Figure 2
L. The cells were radially distributed from the somite center. The columnar cells were located antero-posteriorly. Sectioning was started from the lateral to the medial side of the embryo. The anterior to the left.Video S2. Serial block-face–scanning electron microscopy of the mandibular cell cluster 1 related to Figure 2
M. Mandibular cell cluster 1 is covered by neural crest cells. Cluster 1 had many cavities and acellular spaces among the cells. Sectioning was started from the lateral to the medial side of the embryo. The anterior to the right.Video S3. Serial block-face–scanning electron microscopy of the mandibular cell cluster 2 related to Figure 2
N. Mandibular cell cluster 2 was situated near the neural crest cells. There were many spaces and cavities among the cells of cluster 2. Sectioning was initiated from the medial to the lateral side of the embryo. The anterior to the right.Video S4. Serial block-face–scanning electron microscopy of the hyoid cell cluster related to Figure 2
O. The hyoid cell cluster was beneath the otic vesicle anterior to the pharyngeal pouch 2. This cell cluster was observed above the hyoid arch mesoderm. Similar to other cell clusters, acellular spaces were observed among the cells. Sectioning was started from the lateral to the medial side of the embryo. The anterior to the left.Video S5. 3D reconstruction of the trunk somite related to Figure 2
T. The somite in video 1 was 3D reconstructed. Typical rosette cell arrangements can be observed.Video S6. 3D reconstruction of the mandibular cell cluster 1 related to Figure 2
U. The mandibular cell cluster 1 in video 2 was 3D reconstructed.Video S7. 3D reconstruction of the mandibular cell cluster 2 related to Figure 2 V. 3D reconstruction of the mandibular cell cluster 2 in video 3. Near pharyngeal pouch 1, columnar cells were lined along the dorsal/ventral axis.Video S8. 3D reconstruction of the hyoid cell cluster related to Figure 2
W. 3D reconstruction of the hyoid cell cluster in video 4. The hyoid cell cluster consisted of amorphous cells. Above pharyngeal pouch 2, there were a small number of mesodermal cells that were post-hyoid dorsal head mesoderm.
Onai, Takayuki; Adachi, Noritaka; Urakubo, Hidetoshi; Sugahara, Fumiaki; Aramaki, Toshihiro; Matsumoto, Mami; Ohno, Nobuhiko
Ultrastructure of the lamprey head mesoderm reveals evolution of the vertebrate head
iScience, 26(12). DOI: 10.1016/j.isci.2023.108338
Copyright: © 2024 The authors.
Published by Elsevier Inc. Open access.
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)
And no! There is no sign of the scientists thinking magic is required to explain the facts there either. They still think the TOE is the perfect tool for that.
I wonder how creationist fools got the idea that they're winning the debate! But in almost any debate with a creationist you can legitimately ask, "Did someone fool you into believing that, or are you trying to fool me?".
Why are so many creationists so obviously either fools or frauds?
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