This seems to me to be an important result:
What do you think?
This seems to me to be an important result:
What do you think?
Thanks for sharing this paper - seems like a great example of gain of a critical and completely new protein function by only single amino acid changes. I wonder if this was also claimed to be “irreducibly complex” before this paper came out.
Since this might be of interest to others, see below for eLife’s “digest” excerpt and the public abstract for the paper (it’s open access).
For billions of years, life on Earth was made up of single cells. In the lineage that led to animals – and independently in those that led to plants and to fungi – multicellular organisms evolved as cells began to specialize and arrange themselves into tissues and organs. Although the evolution of multicellularity is one of the most important events in the history of animal life, very little is known about the molecular mechanisms by which it took place.
Anderson et al. have now used a technique called ancestral protein reconstruction to investigate how this molecular complex evolved its ability to position the spindle. First, the amino acid sequences of the scaffolding protein’s ancient progenitors, which existed before the origin of the most primitive animals on Earth, were determined. Anderson et al. did this by computationally retracing the evolution of large numbers of present-day scaffolding protein sequences down the tree of life, into the deep past. Living cells were then made to produce the ancient proteins, allowing their properties to be experimentally examined.
Abstract (emphases mine):
To form and maintain organized tissues, multicellular organisms orient their mitotic spindles relative to neighboring cells. A molecular complex scaffolded by the GK protein-interaction domain (GKPID) mediates spindle orientation in diverse animal taxa by linking microtubule motor proteins to a marker protein on the cell cortex localized by external cues. Here we illuminate how this complex evolved and commandeered control of spindle orientation from a more ancient mechanism. The complex was assembled through a series of molecular exploitation events, one of which – the evolution of GKPID’s capacity to bind the cortical marker protein – can be recapitulated by reintroducing a single historical substitution into the reconstructed ancestral GKPID. This change revealed and repurposed an ancient molecular surface that previously had a radically different function. We show how the physical simplicity of this binding interface enabled the evolution of a new protein function now essential to the biological complexity of many animals.
More on this discovery.
Unicellular and multicellular Organisms are best explained through design
Proponents of evolution claim like a mantra, that micro evolution leads to macro evolution, and no barrier exists which hinders the transition from one to the other, which last not least explains our biodiversity today.
The emergence of multicellularity was supposedly, a major evolutionary leap. Indeed, most biologists consider it one of the most significant transitions in the evolutionary history of Earth’s inhabitants. “How a single cell made the leap to a complex organism is however one of life’s great mysteries.”
Macro evolutionary scenarios and changes include major transitions , that is from LUCA, the last common universal ancestor, to the congregation to yield the first prokaryotic cells, the associations of prokaryotic cells to create eukaryotic cells with organelles such as chloroplasts and mitochondria, and the establishment of cooperative societies composed of discrete multi-cellular individuals. Or in other words : The current hierarchical organization of life reflects a series of transitions in the units of evolution, such as from genes to chromosomes, from prokaryotic to eukaryotic cells, from unicellular to multi cellular individuals, and from multi-cellular organisms to societies. Each of these steps requires the overcome of huge hurdles and increase of complexity , which can only be appreciated by the ones, that have spend time to educate themselves, and gained insight of the extraordinarily complex and manifold mechanisms involved. The emergence of multi-cellularity was ostensibly a major evolutionary leap.
The switch from single-celled organisms to ones made up of many cells have supposedly evolved independently more than two dozen times. Evolution requires more than a mere augmentation of an existing system for co-ordinated multicellularity to evolve; it requires the ex nihilo creation of an entirely new system of organisation to co-ordinate cells appropriately to form a multicellular individual.
There is a level of structure found only in multi-cellular organisms: intercellular co-ordination. The organism has strategies for arranging and differentiating its cells for survival and reproduction. With this comes a communication network between the cells that regulates the positioning and abundance of each cell type for the benefit of the whole organism. A fundamental part of this organisation is cellular differentiation, which is ubiquitous in multicellular organisms. This level cannot be explained by the sum of the parts, cells, and requires co-ordination from an organisational level above what exists in individual cells. There is a 4-level hierarchy of control in multicellular organisms that constitutes a gene regulatory network. This gene regulatory network is essential for the development of the single cell zygote into a full-fledged multicellular individual.
If evolution and transition from unicellular to multi cellular life is exceedingly complex, the chance that it happened once is also exceedingly small. That it happened multiple times separately, becomes even more remotely possible. Convergent evolution of similar traits is evidence against , not for evolution. In order to infer that a proposition is true, these nuances are important to observed. The key is in the details. As Behe states : In order to say that some function is understood, every relevant step in the process must be elucidated. The relevant steps in biological processes occur ultimately at the molecular level, so a satisfactory explanation of a biological phenomenon such as the de novo make of cell communication and cell junction proteins essential for multi-cellular life must include a molecular explanation.
The cells had not only to hold together, but important mechanisms to stick the cells together had to emerge, that is, the ability of individual cells to associate in precise patterns to form tissues, organs, and organ systems requires that individual cells be able to recognize, adhere to, and communicate with each other.
Of all the social interactions between cells in a multicellular organism, the most fundamental are those that hold the cells together. The apparatus of cell junctions and the extracellular matrix is critical for every aspect of the organization, function, and dynamics of multicellular structures. Animal cells use specialized adhesion receptors to attach to one another. Many of these adhesion proteins are transmembrane proteins, which means the extracellular portion of these proteins can interact with the extracellular portion of similar proteins on the surface of a neighboring cell. Although diagrams of adhesive structures may suggest that they are static once assembled, they are anything but. Cells can dynamically assemble and disassemble adhesions in response to a variety of events. This seems to be a essential requirement for function right from the beginning of multicellularity. Many adhesion proteins are continuously recycled: Protein at the cell surface is internalized by endocytosis, and new protein is deposited at the surface via exocytosis. The molecular machines to exercise these functions therefore had to emerge together with adhesion proteins. Furthermore, cell adhesion is coordinated with other major processes, including
3.cell proliferation, and
We now know that cell-cell adhesion receptors fall into a relatively small number of classes. They include
1.immunoglobulin superfamily (IgSF) proteins,
3.selectins, and, in a few cases,
In order to explain multicellularity, its origin must be explained .
Thus, the apparatus of cell junctions and the extracellular matrix is critical for every aspect of the organization, function, and dynamics of multi cellular structures. The arise of adhesive junctions, tight junctions and gap junctions, and how they emerged is therefor a key factor to explain multi-cellular life. The cells of multi-cellular organisms detect and respond to countless internal and extracellular signals that control their growth, division, and differentiation during development, as well as their behavior in adult tissues. At the heart of all these communication systems are regulatory proteins that produce chemical signals, which are sent from one place to another in the body or within a cell, usually being processed along the way and integrated with other signals to provide clear and effective communication. The arise of these communication channels had to arise together with junction mechanisms in order to establish successful multi cellular organisms. One feature without the other would not have provided success and advantage of survival.
The ability of cells to receive and act on signals from beyond the plasma membrane is fundamental to life. This conversion of information into a chemical change, signal transduction, is a universal property of living cells. Signal transductions are remarkably specific and exquisitely sensitive. Specificity is achieved by precise molecular complementarity between the signal and receptor molecules.
Question : signal transduction had to be present in the first living cells. How could the specificity of the signal molecule , and the precise fit on its complementary receptor have evolved ? or the Amplification, or the desensitization/adaptation, where the receptor activation triggers a feedback circuit that shuts off the receptor or removes it from the cell surface, once the signal got trough ?
Three factors account for the extraordinary sensitivity of signal transducers: the high affinity of receptors for signal molecules, cooperativity (often but not always) in the ligand-receptor interaction, and amplification of the signal by enzyme cascades. The trigger for each system is different, but the general features of signal transduction are common to all: a signal interacts with a receptor; the activated receptor interacts with cellular machinery, producing a second signal or a change in the activity of a cellular protein; the metabolic activity of the target cell undergoes a change; and finally, the transduction event ends. This seems to be a irreducible system, requiring high content of pre-programming and advanced coding.
Question : how did the high affinity, cooperativity and amplification have emerged ? Is a preestablished convention not necessary, and so a mental process to yield the function ? Is trial and error or evolution not a completely incapable mechanism to get this functional information system ?
This is a important, essential and fundamental macro evolutionary change, and the explanation of macro-evolution must account for these changes, and provide feasible possible and likely ways through mutation and natural selection. Beside this, a shift on several levels of biological organization had to occur, providing a considerable advantage of survival, considering that for example one of the first cooperative steps required for the evolution of multicellularity in the volvocine algae was the development of the extracellular cell matrix from cell wall components, which can be metabolically costly to produce. But much more is required.
Ann Gauger: New genes and proteins must be invented. The cytoskeleton, Hox genes, desmosomes, cell adhesion molecules, growth factors, microtubules, microfilaments, neurotransmitters, whatever it takes to get cells to stick together, form different shapes, specialize, and communicate must all come from somewhere. Regulatory proteins and RNAs must be made to control the expression in time and space of these new proteins so that they all work together with existing pathways.In fact, in order for development to proceed in any organism, a whole cascade of coordinated genetic and biochemical events is necessary so that cells divide, change shape, migrate, and finally differentiate into many cell types, all in the right sequence at the right time and place. These cascades and the resulting cell divisions, shape changes, etc., are mutually interdependent. Interrupting one disrupts the others.
And last not least:
Like engineers carefully blowing up a bridge, cells have intricate, programmed suicide mechanisms. Without apoptosis, all multicellular life would be impossible. Good luck to proponents of evolution to explain how it emerged…
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