Chromosphaera perkinsii resembles the early stages of animal embryo development during its multicellular life stage
DudinLab
Scientists believe they may have cracked the chicken and egg 'problem' that creationists have been fooled into thinking is a killer problem for the Theory of Evolution. With their child-like understanding of evolution, creationists can't imagine how species emerge over time from earlier species by a process of evolution and think that their mythical magic creation without ancestors is actually what happens, or at least what evolutionary biologists think happens. So, they imagine explaining how the first chicken hatched from the first egg before there was a chicken to lay it, is an insurmountable problem.
In fact, of course there never was a first chicken just as there never was a first human, and eggs are simply a phase in the life cycle of, in this case, chickens, so hens' eggs are chickens just as much so as adult hens are. The ancestral species that the Southeast Asian jungle fowl evolved from had been laying eggs ever since they diverged from the egg-laying avian dinosaurs that had evolved from the egg-laying theropod dinosaurs, etc, etc, back to the egg-laying tunicates and chordates in the Cambrian and their egg-laying ancestors...
What information do you have on the micro-organism, Chromosphaera perkinsii? Chromosphaera perkinsii is an interesting microorganism that belongs to the Ichthyosporea, a small group of protists closely related to animals. These single-celled organisms are significant in evolutionary studies because they diverged from animals over a billion years ago, making them valuable for understanding the origins of multicellular development and cell division mechanisms.And now scientists at the Univerité de Genève, Switzerland, believe they have discovered the earliest single-celled organism, Chromosphaera perkinsii, that, although it is a single-celled eukaryote spends part of its life cycle as a multi-cellular ball of cells resembling the first stages of the development of an embryo from the single-celled zygote.
One unique aspect of C. perkinsii is its developmental process. Researchers have observed that it undergoes symmetry breaking and cleavage divisions, leading to organized multicellular colonies with distinct cell types, resembling some early stages of animal embryogenesis. This developmental pattern suggests that multicellular organization could have origins predating animals or evolved independently in these organisms.
Additionally, C. perkinsii primarily uses open mitosis, where the nuclear envelope breaks down during cell division, contrasting with some ichthyosporean relatives that use closed mitosis (a trait more typical of fungi). This has provided insight into how different cell division methods might have evolved across various lineages, helping scientists map key transitions in early eukaryotic evolution.
For more technical details, studies on C. perkinsii highlight how it serves as a model for understanding the diversity of life cycles and cellular adaptations across eukaryotes.
Can you elaborate on those 'more technical details', please.
Chromosphaera perkinsii presents a fascinating case for studying eukaryotic cell biology and development. Here are some of the more technical insights about its life cycle and cellular mechanisms:These insights not only reveal the complexity within this single-celled organism but also emphasize its potential as a model for studying early evolutionary transitions that led to animal multicellularity. This work also underscores the importance of studying diverse organisms to uncover the origins and diversification of life on Earth.
- Multicellular Development and Symmetry Breaking: Unlike typical single-celled organisms, C. perkinsii demonstrates a form of early multicellular organization by producing colonies with distinct cell types through a process called symmetry breaking. This process involves directional cell divisions where cells establish polarity, an essential step for forming organized multicellular structures. In C. perkinsii, these steps hint at mechanisms foundational to early multicellular development in animals.
- Cleavage Division Patterns: During colony formation, C. perkinsii uses cleavage divisions to produce separate, spatially organized cell types within a single colony. This pattern resembles some embryonic stages in animal development, where specific cleavage sequences determine body patterning. The discovery of these coordinated divisions in a protist suggests that some of the cellular mechanisms underpinning animal development might predate animals themselves.
- Open Mitosis: In open mitosis, the nuclear envelope disintegrates, allowing the chromosomes to separate without the constraint of a surrounding membrane. This is different from closed mitosis (where the nuclear envelope remains intact) and aligns with the mitotic process in animals, further underscoring its relevance to understanding animal evolution. Studying C. perkinsii thus provides insights into how and why open mitosis might have evolved in eukaryotes, shedding light on a possible ancestral mechanism.
- Comparative Phylogenetics and Genomics: Genetic studies on C. perkinsii involve comparative analyses to identify genes and proteins similar to those in animals, revealing potential genetic innovations that led to the evolution of multicellularity. For instance, researchers use advanced imaging and genomic analysis to understand its cell division machinery, tracing similarities with animals and highlighting unique adaptations in ichthyosporeans.
- Ultrastructure Expansion Microscopy: In a recent approach, scientists used ultrastructure expansion microscopy (U-ExM) to study the cytoskeletal elements and internal structures in C. perkinsii. This technique involves expanding biological samples within a transparent gel, which greatly enhances visualization of cellular components. U-ExM revealed intricate details of C. perkinsii's cellular architecture, crucial for understanding its cell biology at a near-molecular level.
References:
- Burns, J., Dudin, O., et al. (2024). "A multicellular developmental program in a close animal relative." bioRxiv. This preprint details the processes of symmetry breaking and cleavage division in C. perkinsii, exploring how these mechanisms resemble early animal development.
- Shah, H., Dey, G., et al. (2024). "Life-cycle-coupled evolution of mitosis in close relatives of animals." Nature. This study contrasts the open and closed mitosis in ichthyosporeans, including C. perkinsii, to explain cell division evolution across eukaryotes.
- "A Billion-Year Evolutionary Tale – Biologists Trace Cell Division Back to Its Roots." (2024). SciTechDaily. This article discusses C. perkinsii's cellular mechanisms and its use as a model for understanding the evolution of open mitosis in animal lineages.
They have published their findings, open access, in Nature and explained it in a press release from Univerité de Genève:
The egg or the chicken? An ancient unicellular says egg!
A cell division resembling that of an animal embryo has been observed in a prehistoric unicellular organism, suggesting that embryonic development might have existed prior to the evolution of animals.
Chromosphaera perkinsii is a single-celled species discovered in 2017 in marine sediments around Hawaii. The first signs of its presence on Earth have been dated at over a billion years, well before the appearance of the first animals. A team from the University of Geneva (UNIGE) has observed that this species forms multicellular structures that bear striking similarities to animal embryos. These observations suggest that the genetic programs responsible for embryonic development were already present before the emergence of animal life, or that C. perkinsii evolved independently to develop similar processes. Nature would therefore have possessed the genetic tools to “create eggs” long before it “invented chickens”. This study is published in the journal Nature.
The first life forms to appear on Earth were unicellular, i.e. composed of a single cell, such as yeast or bacteria. Later, animals - multicellular organisms - evolved, developing from a single cell, the egg cell, to form complex beings. This embryonic development follows precise stages that are remarkably similar between animal species and could date back to a period well before the appearance of animals. However, the transition from unicellular species to multicellular organisms is still very poorly understood.
These cells divide without growing any further, forming multicellular colonies resembling the early stages of animal embryonic development.
Recently appointed as an assistant professor at the Department of Biochemistry in the UNIGE Faculty of Science, and formerly an SNSF Ambizione researcher at EPFL, Omaya Dudin and his team have focused on Chromosphaera perkinsii, or C. perkinsii, an ancestral species of protist. This unicellular organism separated from the animal evolutionary line more than a billion years ago, offering valuable insight into the mechanisms that may have led to the transition to multicellularity.
By observing C. perkinsii, the scientists discovered that these cells, once they have reached their maximum size, divide without growing any further, forming multicellular colonies resembling the early stages of animal embryonic development. Unprecedentedly, these colonies persist for around a third of their life cycle and comprise at least two distinct cell types, a surprising phenomenon for this type of organism.
Images of the multicellular development of the ichthyosporean Chromosphaera perkinsii, a close cousin of animals. In red we can see the membranes and in blue the nuclei with their DNA. The image was obtained using expansion microscopy.© O. Dudin, UNIGEAlthough C. perkinsii is a unicellular species, this behaviour shows that multicellular coordination and differentiation processes are already present in the species, well before the first animals appeared on Earth.
Omaya Dudin, co-corresponding author
Swiss Institute for Experimental Cancer Research
School of Life Sciences
Swiss Federal Institute of Technology (EPFL), Lausanne, Switzerland.
Even more surprisingly, the way these cells divide and the three-dimensional structure they adopt are strikingly reminiscent of the early stages of embryonic development in animals. In collaboration with Dr John Burns (Bigelow Laboratory for Ocean Sciences), analysis of the genetic activity within these colonies revealed intriguing similarities with that observed in animal embryos, suggesting that the genetic programmes governing complex multicellular development were already present over a billion years ago.
It’s fascinating, a species discovered very recently allows us to go back in time more than a billion years.
Marine Olivetta, co-author
Swiss Institute for Experimental Cancer Research
School of Life Sciences
Swiss Federal Institute of Technology (EPFL), Lausanne, Switzerland.
In fact, the study shows that either the principle of embryonic development existed before animals, or multicellular development mechanisms evolved separately in C. perkinsii.
This discovery could also shed new light on a long-standing scientific debate concerning 600 million-year-old fossils that resemble embryos, and could challenge certain traditional conceptions of multicellularity.
AbstractThis article will probably come as a big disappointment to creationists because not only does it answer one of their more childish 'gotcha!' questions, it also shows what living organisms were doing a billion years before their mythical 'Creation Week' when some of the basic processes of modern life were being established in the early complex cells, before multicellularity got going.
Eukaryotes have evolved towards one of two extremes along a spectrum of strategies for remodelling the nuclear envelope during cell division: disassembling the nuclear envelope in an open mitosis or constructing an intranuclear spindle in a closed mitosis1,2. Both classes of mitotic remodelling involve key differences in the core division machinery but the evolutionary reasons for adopting a specific mechanism are unclear. Here we use an integrated comparative genomics and ultrastructural imaging approach to investigate mitotic strategies in Ichthyosporea, close relatives of animals and fungi. We show that species in this clade have diverged towards either a fungal-like closed mitosis or an animal-like open mitosis, probably to support distinct multinucleated or uninucleated states. Our results indicate that multinucleated life cycles favour the evolution of closed mitosis.
Main
Eukaryotic mitosis relies on a tight coordination between chromosome segregation and the remodelling of the nuclear compartment to ensure the fidelity of nuclear division and genome inheritance2,3. Two classes of nuclear remodelling have been widely investigated: open mitosis4, in which the nuclear envelope (NE) is disassembled at mitotic entry and reassembled following chromosome segregation; and closed mitosis5,6,7, in which the nuclear compartment retains its identity throughout division (Extended Data Fig. 1). Although open and closed mitosis have each probably evolved independently several times in different branches of the eukaryotic tree8,9, with many unique lineage-specific adaptations resulting in a broad distribution of intermediates from fully open to fully closed1,2, the evolutionary pressures which drive species towards the extremes of either mitotic strategy are not well understood. Studies, primarily in mammalian and yeast models, suggest that open and closed mitosis require distinct adaptations in key structural components of the division machinery1, including the microtubule organizing centre (MTOC)10, the spindle11, the NE12,13 and the kinetochore14. For example, building an intranuclear spindle in closed mitosis must be accompanied by NE fenestration to allow insertion of the MTOC15. On the other hand, open mitosis requires distinct interphase and postmitotic mechanisms for the insertion of new nuclear pore complexes (NPCs) into the NE16. These significant differences in the core division machinery imply that certain molecular signatures of the mode of mitosis may be encoded in the genome, enabling the use of comparative genomics to identify new cases of probable divergence between related species outside traditional model systems. We can then combine phylogenetic inference with the targeted experimental investigation of mitotic dynamics in these lineages to ask whether constraints imposed by ecological niche and life cycle could drive species towards either open or closed mitosis.
The Opisthokonta, a principal eukaryotic group which includes animals, fungi and their deep-branching relatives, with the Amoebozoa as a close outgroup, present an ideal context for such an evolutionary cell biology analysis, with species in the clade exhibiting a broad range of genome organization modes, physiology and ecology17,18,19. Importantly, either open or closed mitosis is dominant in the main animal and fungal lineages, respectively2,3. We know little about mitosis in the deep-branching opisthokonts which lie between animals and fungi, including the Choanoflagellatea, Filasterea, Ichthyosporea and Corallochytrea (Fig. 1a,b)17,20. Among these, Ichthyosporea, consisting of two main lineages, Dermocystida and Ichthyophonida, exhibit diverse life cycles (Fig. 1a) featuring a mixture of fungal-like traits and transient multicellular stages reminiscent of early animal development17,21,22. Most Ichthyosporea proliferate as coenocytes, multinucleated cells formed through sequential rounds of mitosis without cytokinesis, which eventually complete their life cycle through coordinated cellularization21. However, a few understudied species undergo nuclear division with coupled cell cleavages (palintomic division)23,24, providing a unique opportunity to assess if and how mitotic strategies in a group of related species might be coupled to distinct uninucleated or multinucleated life cycles (Fig. 1a).
Fig. 1: Divergence of mitotic machinery in the Ichthyosporea with different life cycles.
a, Differences in life cycles and the uninucleated and multinucleated states of dermocystid C. perkinsii (Cper), ichthyophonids A. appalachense (Aapp), S. arctica (Sarc), C. fragrantissima (Cfra) and corallochytrean C. limacisporum (Clim), respectively. Ihof, Ichthyophonus hofleri. Representative image single-slice images through cells labelled for cell membranes with FM4-64 (magenta) and DNA (grey). b, Cladogram of opisthokonts, highlighting the position of Ichthyosporea between well-studied animal, fungal and amoebozoan model systems. Phylogenetic profiles of selected proteins involved in mitosis (complete profiles in Extended Data Fig. 1). Filled and empty circles or pie charts indicate the presence and absence of proteins, respectively (Methods). In addition to Ichthyosporea (Sarc and Cper) and Corallochytrea (Clim), profiles of key species are represented, including Homo sapiens (Hsap), Drosophila melanogaster (Dmel), S. pombe (Spom), the choanoflagellate Salpingoeca rosetta (Sros), the early-branching chytrid fungus Spizellomyces punctatus (Spun) and amoebozoa Dictyostelium discoideum (Ddis) and P. polycephalum (Ppol). The mitotic strategies, open (white), intermediate (grey squares) or closed (dark grey squares), of the represented opisthokont and amoebozoan species are indicated at the end of each profile, KT (kinetochore). c, C. perkinsii has a centriolar MTOC. Single slices from TEM tomography of C. perkinsii cells showing top and side views through centrioles. d, S. arctica has an acentriolar MTOC. Single slice from TEM tomography of S. arctica interphase nucleus. Side and top views of segmentation of S. arctica MTOC from an interphase nucleus. Scale bars, 2 μm (a), 200 nm (c), 500 nm (d).
Some of those processes were so fundamental to all multicellular species, plants, animals and fungi, that it leaves little room for doubt that these organisms were close to the LUCA (last common ancestor of all living things).
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