Creationism in Crisis - Evidence of Common Origins Found in Microscopic Sea Creatures

Confocal microscopy image of nuclei, coloured by depth, of Trichoplax sp. H2, one of the four species of placozoan for which the authors of the study created a cell atlas for.

Credit: Sebastian R. Najle

Trichoplax adhaerens.

Eitel M, Osigus H-J, DeSalle R, Schierwater B (2013)
Global Diversity of the Placozoa.
PLoS ONE 8(4): e57131, doi:10.1371/journal.pone.0057131

Tiny sea creatures reveal the ancient origins of neurons | Centre for Genomic Regulation (CGR)

Sad news today for any creationist trying desperately to cling to the childish notion that humans were created by magic without ancestors just a few thousand years ago and so are a special form of life, not related to any other.

It comes in the form of an open access paper in the online journal Cell announcing that researchers at the Centre for Genomic Regulation (CRG), Barcelona Institute of Science and Technology (BIST), Barcelona, Spain have found evidence of the ancient origins of neurons in microscopic sea creatures, the placozoans, the size of a grain of sand.

These simple, multicellular creatures are in many ways transitional between single-celled and multicellular organisms.

Placozoans are simple, enigmatic, and incredibly tiny marine organisms that belong to the phylum Placozoa. They are among the simplest known multicellular animals and have been the subject of scientific curiosity since their discovery in the late 19th century. Here's an overview of their biology, lifecycle, and other relevant information:

1. Morphology:
   • Placozoans are flat, disc-shaped animals with a thickness of just a few millimeters.
   • They lack specialized organs, tissues, and body symmetry. Instead, they consist of only a few cell layers.
   • The body is composed of a dorsal epithelium, ventral epithelium, and a jelly-like layer called the mesenchyme sandwiched between them.
   • They have a simple digestive system consisting of a ventral mouth-like opening and a network of cells that help to engulf and digest food particles.
2. Reproduction:
   • Placozoans can reproduce both sexually and asexually.
   • Asexual reproduction involves simple fragmentation, where a piece of the animal can regenerate into a new individual.
   • In sexual reproduction, placozoans can produce eggs and sperm. Once fertilization occurs, a larval stage is formed, which eventually settles and develops into a new placozoan.
3. Feeding:
   • Placozoans are filter feeders that primarily consume microorganisms such as algae, bacteria, and small organic particles.
   • They use their ventral surface to glide along substrates, capturing food particles with the help of specialized cells.
4. Habitat:
   • Placozoans are exclusively marine animals and are found in various coastal environments around the world.
   • They typically inhabit areas with a lot of organic material for food, such as the intertidal zone and seafloor sediments.
5. Behavior and Locomotion:
   • Placozoans exhibit simple behaviors, including moving in response to light and touch.
   • They are capable of limited gliding movement over surfaces, which is thought to be driven by cilia and muscle-like cells in the ventral epithelium.
6. Phylogenetic Position:
   • Placozoans are considered one of the earliest branches on the animal tree of life.
   • Their simple body plan and lack of specialized structures make them valuable subjects for studying the origins of multicellularity and the evolution of animals.
7. Research and Significance:
   • Placozoans have long fascinated scientists due to their simplicity and phylogenetic position.
   • They are also of interest for their potential to shed light on the early evolution of animals and the transition from single-celled organisms to multicellular animals.

In summary, placozoans are tiny, simple marine animals with minimal body structure. Their unique characteristics make them valuable subjects for research into early animal evolution and the development of multicellular organisms. While they remain relatively mysterious, ongoing studies continue to reveal insights into their biology and evolutionary significance.

Information about the research and is significance for evolutionary biology is given in the CRG press release:

The sea creatures coordinate their behaviour thanks to peptidergic cells, special types of cells that release small peptides that can direct the animal’s movement or feeding. Driven by the intrigue of the origin of these cells, the authors of the study employed an array of molecular techniques and computational models to understand how placozoan cell types evolved and piece together how our ancient ancestors might have looked and functioned.

Reconstructing ancient cell types

The researchers first made a map of all the different placozoan cell types, annotating their characteristics across four different species. Each cell type has a specialised role which comes from certain sets of genes. The maps or ‘cell atlases’ allowed researchers to chart clusters or ‘modules’ of these genes. They then created a map of the regulatory regions in DNA that control these gene modules, revealing a clear picture about what each cell does and how they work together. Finally, they carried out cross-species comparisons to reconstruct how the cell types evolved.

The research showed that the main nine cell types in placozoans appear to be connected by many "in-between" cell types that change from one type to another. The cells grow and divide, maintaining the delicate balance of cell types required for the animal to move and eat. The researchers also found fourteen different types of peptidergic cells, but these were different to all other cells, showing no in-between types or any signs of growth or division. Surprisingly, the peptidergic cells shared many similarities to neurons – a cell type which didn’t appear until many millions of years later in more advanced animals such as and Bilateria. Cross-species analyses revealed these similarities are unique to placozoans and do not appear in other early-branching animals such as sponges or comb jellies (ctenophores).

Evolutionary stepping stones

The similarities between peptidergic cells and neurons were threefold. First, the researchers found that these placozoan cells differentiate from a population of progenitor epithelial cells via developmental signals that resemble neurogenesis, the process by which new neurons are formed, in Cnidaria and Bilateria.

Second, they found that peptidergic cells have many gene modules required to build the part of a neuron which can send out a message (the pre-synaptic scaffold). However, these cells are far from being a true neuron, as they lack the components for the receiving end of a neuronal message (post-synaptic) or the components required for conducting electrical signals.

Finally, the authors used deep learning techniques to show that placozoan cell types communicate with each other using a system in cells where specific proteins, called GPCRs (G-protein coupled receptors), detect outside signals and start a series of reactions inside the cell. These outside signals are mediated by neuropeptides, chemical messengers used by neurons in many different physiological processes.

We were astounded by the parallels. The placozoan peptidergic cells have many similarities to primitive neuronal cells, even if they aren't quite there yet. It's like looking at an evolutionary stepping stone.

Dr. Sebastián R. Najle, co-first author Centre for Genomic Regulation
Barcelona Institute of Science and Technology (BIST), Barcelona, Spain

The dawn of the neuron

Placozoans lack neurons, but we’ve now found striking molecular similarities with our neural cells. Ctenophores have neural nets, with key differences and similarities with our own. Did neurons evolve once and then diverge, or more than once, in parallel? Are they a mosaic, where each piece has a different origin? These are open questions that remain to be addressed.

Dr. Xavier Grau-Bové, co-first author
Centre for Genomic Regulation. Barcelona Institute of Science and Technology (BIST), Barcelona, Spain

The study demonstrates that the building blocks of the neuron were forming 800 million years ago in ancestral animals grazing inconspicuously in the shallow seas of ancient Earth. From an evolutionary point of view, early neurons might have started as something like the peptidergic secretory cells of today’s placozoans. These cells communicated using neuropeptides, but eventually gained new gene modules which enabled cells to create post-synaptic scaffolds, form axons and dendrites and create ion channels that generate fast electrical signals – innovations which were critical for the dawn of the neuron around one hundred million years after the ancestors of placozoans first appeared on Earth.

Cells are the fundamental units of life, so understanding how they come into being or change over time is key to explain the evolutionary story of life. Placozoans, ctenophores, sponges and other non-traditional model animals harbour secrets that we are only just beginning to unlock.

Professor Arnau Sebé-Pedros, corresponding author Centre for Genomic Regulation.
Barcelona Institute of Science and Technology (BIST), Barcelona, Spain

However, the complete evolutionary story of nerve systems is still to be told. The first modern neuron is thought to have originated in the common ancestor of cnidarians and bilaterians around 650 million years ago. And yet, neuronal-like cells exist in ctenophores, although they have important structural differences and lack the expression of most genes found in modern neurons. The presence of some of these neuronal genes in the cells of placozoans and their absence in ctenophores raises fresh questions about the evolutionary trajectory of neurons.

The authors of the study believe that, as researchers around the world continue to sequence high-quality genomes from diverse species, the origins of neurons and the evolution of other cell types will become increasingly clear.

The study was led by the Sebe-Pedrós Lab with the collaboration of Luis Serrano’s lab (CRG), the Schierwater lab (Hannover University) and the Gruber-Vodicka lab (Kiel University), and with the support of the Proteomics Unit and the Advanced Light Microscopy Unit at the Centre for Genomic Regulation.

Creationists trying to convince themselves that mainstream biologists are abandoning the Theory of Evolution in favour of their childish notion involving magic and unproven supernatural entities will also be disappointed by the abstract to the paper in Cell, which shows no evidence of any such trend and every indication of quite the opposite. The finding only makes sense within an evolutionary framework:

Highlights

1. Comparative single-cell genomics reveals cell type diversity in the phylum Placozoa
2. Fourteen placozoan peptidergic cell types expressing neuronal genes
3. Post-translationally modified neuropeptides define elaborate cell signaling network
4. Peptidergic progenitors with neurogenesis-like differentiation from epithelial cells

Summary

The assembly of the neuronal and other major cell type programs occurred early in animal evolution. We can reconstruct this process by studying non-bilaterians like placozoans. These small disc-shaped animals not only have nine morphologically described cell types and no neurons but also show coordinated behaviors triggered by peptide-secreting cells. We investigated possible neuronal affinities of these peptidergic cells using phylogenetics, chromatin profiling, and comparative single-cell genomics in four placozoans. We found conserved cell type expression programs across placozoans, including populations of transdifferentiating and cycling cells, suggestive of active cell type homeostasis. We also uncovered fourteen peptidergic cell types expressing neuronal-associated components like the pre-synaptic scaffold that derive from progenitor cells with neurogenesis signatures. In contrast, earlier-branching animals like sponges and ctenophores lacked this conserved expression. Our findings indicate that key neuronal developmental and effector gene modules evolved before the advent of cnidarian/bilaterian neurons in the context of paracrine cell signaling.

Graphical Abstract

Najle, Sebastián R.; Grau-Bové, Xavier; Elek, et al (2023)
Stepwise emergence of the neuronal gene expression program in early animal evolution
Cell; DOI: 10.1016/j.cell.2023.08.027

Copyright: © 2023 The authors.
Published by Elsevier Inc. Open access.
Reprinted under a Creative Commons Attribution 4.0 International license (CC BY 4.0)

To summarise then, we have yet more evidence that creationism is a counter-factual delusion and of the credulity of creationists with evidence of:

1. The common origin of nerve cells or neurons in the very earliest forms of multicellularity.
2. The gullibility of believing the lie that mainstream biologists no longer accept the Theory of Evolution and instead are turning to a Bronze Age magical superstition for answers.
3. Evidence of the evolutionary transition from single-celled to multicellular organisms.

How much longer will it be before creationists realise that their cult is submerged beneath a growing flood of real-world evidence such as these almost daily science papers demonstrating the truth of evolution and the lie of creationism?

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