On the tracks of Systems Biology: An interim look

Abstract  Systems biology is a potential new branch of biology with roots in many other fields such as biology, physics, mathematics, and computer science. Accordingly, this is a manifestation of mathematical biology and endeavors to understand complex systems, such as networks of genes, as interacting systems’ components.  In this paper, we analyze the field from a literature review framework; the author is passive in the review. Further, we conclude that systems biology is a potential field for contributing to the new horizons of science, especially biomedical sciences; also the weakness of systems biology is that it is not commonly mentioned in traditional books in biology, even recently published. Nonetheless, as the literature claims, this field might be the bridge for making biology, especially genetics, a source of ideas and principles for other fields, such as biomechanics; and simultaneously an example for other fields of biomedical sciences that mathematics, physics and other branch indeed can enhance those with new insights and methods.  


Keywords—Systems Biology; Biological Systems; Biological Networks; Gene sharing; 


I.           Introduction

‘The all is more than the sum of the parts.’ This sentence might be tricky for some not endowed with the right thinking. One might figure it out that some phenomena cannot be overcome, such as in quantum mechanics (Heisenberg Principle), or some cannot be modeled, such as the prediction of the sides of a coin in a sequence of tosses, due to not being feasible. The observation that possibly some phenomena cannot be always put under the ‘law of action and reaction’ was warmly discussed in one of the Einstein’s scientific life [1] where he has asked if it is always possible to predict the outputs of physical systems if one models every part of this phenomena accurately. Nonetheless, in some cases, not completely new in science, but neglected intentionally for past scientists under names such as ‘vital forces’, is the fact that some systems just can be interpreted properly if it is looked from ‘above.’ This was defended firmly by Capra ([2], [3]); this is sometimes referred as ‘holistic’ view against ‘reductionism.’ Therefore, the observation that some systems cannot be tore up for being studied is not a matter of ‘human limitations’, but rather a question of workings of the systems. Some properties, termed widely emergent properties, can be just seen with the system ‘at work;’ they disappear when one ‘turns off’ or change the state of some system’s component.

Regarding the matter of the workings of complex systems, in biology it has recently formally given this task to a new branch named Systems Biology (approximately documented in the literature about 2000 with [26], which claims to be the first formal publication, book, in systems biology; however, the principles is not new). This paper intends to shed some light on the issue. The current manuscript intends to be a map on the theme, a short-hand writing in which one can encounter a list of references for starting out in the theme or even increasing their knowledge; the topic discussed and references left represents the current author’s points of view and literature. The paper is far away from exhaustive, but rather informative. Systems biology is a ‘hot’-scientific field, as points out [26], any attempts might get obsolete fast. The most notable changes might come into the application; nonetheless, the principles have been conserved. Systems biology has emerged as a formal and important field from the necessity to understand interactions of genes-genes and proteins-proteins; the question is how it comes out “strange” observations, such as ‘conscious’ in the mind or even the cyclic beating of the heart from movements of ions. With the explosion of data coming from the project for mapping the genome, some information was observed to be missing and this was interaction, the potential last step in the complete understanding of life from the gene-level podium.    
Control Systems Theory (CST) [5] attempts to understand each part of a plant for controlling; this theory is highly-dependent on differential equations theory. This is assumed that any input will trigger some output by interaction between the parts. Moreover, this is widely applied to complex systems composed of machines, for example; each part is a complex system by its own, but they are regarded as ‘black box’, it does not matter how they are inside, but rather how they ‘act’; this is an ‘engineering look of complex systems.’ See that this is a recursive action, start from a complex problem as start ‘calling’ for the response of other complex systems inside it until you get some ‘basal’ response; this is possible because all parts are connected. Further, this is termed up-bottom approach.

In mathematics, complex systems are analyzed by Bifurcation Theory (BT) [13]. It was observed, in some simple cases created models, that complex systems might exhibit two or more behavior depending on the state of the components; the system changes its behavior in some cases completely different from the previous. The parameters under which it happens are called bifurcation parameters. Some model cases for bifurcations was identified and documented in the literature [28]. A system can change from stable to unstable or from equilibrium as a point to as a cycle, for example. This can be shown that even negative autoregulation in gene expression can display those behaviors; negative autoregulation is the simplest network motif in the theory of transcription network in systems biology analysis [10].

Systems biology is strongly rooted in network theory for making sense of the all based upon the components integrated, however it cannot be said that networks makes up the field. Network flows from optimization theory [16] is strongly dependent on networks, nonetheless, they work on static networks, which is simpler than the kind of networks under analysis by systems biology; in systems biology, they are dynamical networks, with phase portraits; they can be unstable; they can exhibit complex behaviors, such as bifurcations.  

In spite of the fact that little books in systems biology leave it clear, systems biology just could be possible due to efforts coming from the long past; works from previous scientists. The question constantly posed was the applicability of the laws of physics to living matter [12]; they used to believe that ‘not’, it gave space for concept such as ‘vital force,’ some just existing in living matter. Nonetheless, this started to be questioned with creation of simple ‘living’ systems in laboratory via inorganic matter [4]. This would prove that life is not more than the laws of physics under certain conditions; this opened space for an explosion of ‘artificial life’ creation; as points out [4], biologists did not get happy in the first attempts following successive failures.

Some might say, based upon the following excerpt [27] that systems biology is just physiology renewed; in some sense it is, but one needs to be careful with this assumption. Physiology is the study of living organisms work. Further, it includes the study of proteins, such as how the shape and electrical properties of proteins allow it to work as sodium channel for moving ions in and out of the cell; at the other end, it is concerned with complex processes that depend on the interplay of many widely separated works in the body. What makes physiology unique among biologists is that they are always interested in functions and integration; systems biology takes the word ‘integration’ to the extreme sense of the word. Further, in physiology, many areas are still poorly understood, such as ‘mind’ coming from the brain; approaches from systems biology might give us some insights into the answer. Making use of this passage, D. Noble [8] trained in physiology has worked a bio-process in the heart for creating the pulses for heartbeats; in the times when the reductionism was the state of the art, the author highlights the problems to convince the scientists of his scientific realm on the validity of the model presented; this was a practice of systems biology, emergent properties from the integration of proteins.

One quite interesting application of systems biology is ‘gene sharing’ [6], termed coined by the author [6]. Some proteins might execute more than one function depending on its current concentration (gene expression); [6] cites the example that gave rise to the book in which the same protein from the lens of the eye of birds is expressed in lower rate in the same organism working as enzyme in biochemical reactions. Another example is given regarding a second protein working as receptor in the cell membrane and transcription factors in the nucleus of the same cell. See that transcription factor is left by the author as ‘ambiguous’ case; some transcription factor might activate and repress depending in the environment conditions. This is any example of bifurcation, once the proteins interact for changing their molecular-function; this interaction makes the systems a N-dimensional dynamical system, where N is the number of proteins.

Bifurcations in biological systems are not new at all. In [14] it is studied bifurcations in neurons; as claims the author, the literature has given too much attention to neurons in networks and neglecting the specificity of neurons individually, this potential pitfall is not done in systems biology. It was observed that neurons anatomically identical might act differently and neurons different in anatomy might act equally; this is due to bifurcation of the emergent states of the neurons. Note that the biochemical process that starts with the application of an input current in neurons and culminate with the spikes of the neuron is protein-dependent.

Another interesting study of systems biology is given in [30], by the author of this paper. As defends [29], much has been discovered in the nature of matter, such as genes and interactions between proteins, one must take it into account in new theories for biomechanics. [29] uses the name continuum biomechanics, also used by  [31].  Systems biology looks upon protein interaction for creating the all, whereas continuum biomechanics looks upon the response of living matter (the all) for creating properties of the biomaterial under analysis; this studies also the element until the point it is necessary. They are dual problems: one sees matter from above while the other from the bottom. 


Fig. 1.    The two antagonistic, but complementary ways, of studying living matter [30]. (The letters means: on systems biology box “G- gene; P – protein; C – Cell”; and on the biomechanics box “M – matter; S – Structure; C – Components”)

Systems biology is a manifestation of mathematical biology. Mathematical biology is the application of mathematical modeling to problems coming from biological sciences, see for example ([20]. [21]). As defends [20], mathematical biology tries to exploit the trivial synergy between biology and mathematics; biology offers difficult problems to mathematics, mathematics offers solutions via models, and biology offers the place for testing the models.  Mathematics was not accepted in biology easily [4]; much attempted has failed for establishing what we see nowadays. As [4] points out that the biggest problems came from biologists that insisted in not believing in the power of mathematics; hidden was the concept that biology is somehow too different from other existences for being modeled via mathematics, concepts such as ‘vital forces’ gained place.

Minsky [7] has pointed out the fact that some systems cannot be understood unless one takes into account the entire working system. In neuron science [15], it has emergent properties in the neuronal networks, quite similar to those of genes; neuronal network is also treated by textbooks in systems biology [10]. This must be noted that the complexity encountered in biological system is not new, but avoided by previous scientists; this is seen in the work of the quantum mechanics scientist Schrödinger [9] by highlighting the potential difficult of reducing complex systems such as living matter to the simple laws of physics, as it has been done for centuries in physics. When looking in the genome, systems biology is not concerned in a single gene, which is the concern of bioinformatics, but rather in thousands of genes working simultaneously; this creates quite complex dynamical networks. Emergent properties in neuronal systems are widely studies in the physics of neural networks ([22], [23], [24]). The most important in gene expression via networks, as one of the most common application of systems biology, is the fact that the study of genes as nucleic acid sequences, as it is done in bioinformatics practices, just provides us with which protein is expressed, but it gives rises to non information regarding quantity, place and period of time [32]. This is interesting noting that every cell contains the same genetic code, but the question is how they are different and the answer is on the expression patterns. As [4] presents, this dilemma of gene expression by different cells puzzled scientists for a quite long time; the second puzzle came from cellular differentiation, with the ‘French flag’ model dominating; how ‘gene’ knows where they are.  

The concept of emergent property is quite important for systems biology; this is what really gives systems biology a specific and remarkable place in biomathematics. In Neural networks, this is widely applied for calculation in computer science [25]; this is hardly seen some concerned about how it works, it just works. In the body this is similar, but we have not just networks of neurons, but also proteins for executing similar tasks [10]; ‘learn’ is not something just from ‘neurons,’ this is in every piece of our body. In the literature, the concepts of systems biology has been absorbed via new names, such as systems biomedicine [18] and system bioinformatics [17]. This is in some sense positive, once results might be migrated without prejudices, as discussed by [4] potential barrier for migrating mathematical biology to biomedical sciences.

In the remaining part of the paper, the author will dissert on some topics. The selection is merely for opening scientific view, the reader is invited to consult the references left in the end of the current work for broadening idea or some specific point. The first set of topics regards the dimensions of systems biology, this is meant, the scientific field that contributes for the existence of systems biology as an independent and promising field. As one will likely conclude, the multidisciplinary nature of systems biology will give it a place in the scientific realm. The next set of topics is regarded networks of genes, the most popular documentation of systems biology applications. This might be explained keeping in mind the high-connectivity in the genetic code, which makes reductionism impracticable for interesting results. The next is gene sharing, a recent documented application of systems biological principles; proteins changing their function based upon concentration or interaction with the environment; permanent-multifunctional genes. The next section discusses modular look, this is a guiding principle from systems biology, one ‘neglects’ the nature of small-systems, one application is the use of network motifs for understanding complex transcriptional networks. The next is mathematical computational models in systems biology. Systems biology is highly dependent in computational practices for getting some results; such as algorithms for simulating networks of expressing genes, set of nonlinear differential equations. Finally one reaches the conclusions and final remarks.

    

  II.          The dimensions of Systems Biology

This is presented a scheme below, fig. 2, with the ‘dimensions’ of systems biology; this is meant the fields that borrow principles and tools for the existence of systems biology as a well-established field. 

Fig. 2.    The related fields to systems biology. (Note that some circles might be claimed as dependent, but this is separated for highlighting their importance. The dashed circle intends to pinpoint the synergic existence of the fields by their own)

The boxes are explained below.
  • Computer Science: the theories from systems biology is connected to complex systems, such as graph theory and nonlinear dynamical systems; analysis of bifurcation theory and simulation-modeling of complex systems. Those cannot be successfully inferred with simple models solved by hand for hypothetical cases. Further, it is desirable the analysis of parameters;

  • Bioinformatics: One might claim that bioinformatics is just a sub-area of computer science, but it is not; in spite of the fact it has some dependence. Bioinformatics has concerns on laboratorial experiments and translation to common use. The place of systems biology is to make sense of those data in ‘on-working’; not a single gene, even thousands, see microarrays analysis for example;

  • Mathematics: Mathematics nowadays has rooted in almost all fields of sciences and biology is not different. One of those manifestations comes out in systems biology. For examples, gene can have their expression patterns analyzed using nonlinear differential equation. The ‘French flag’ model is the diffusion equation (a partial differential equation, pde). Gene expression is in general noisy (stochastic differential equation);

  • Biology: Besides one can claim that biology is the mother of systems biology, this claim might be dangerous; this is the target of systems biology and main body; nonetheless, the principles can be migrated to other fields such as graph theory;

  • Physics: Physics goes into systems biology through mainly philosophical principles: the chase of generalization always present in physics. Also as a example of successful case of mathematical exportation, mathematical physics. The instruments for measurement might be applications of physics;

  • Chemistry: the nature of controlling networks is mainly chemical; important phenomena such as inclusion of chemicals for changing molecular properties are strongly chemistry in action. See for example chemotaxis;
  • Artificial Intelligence: Artificial intelligence offers methods not encountered in pure mathematics, such as neural networks or optimization programming. Further, systems biology might contribute to artificial intelligence;

  • Engineering sciences: The concern on understanding to design is also part of systems biology, such as how to recreate the studied phenomena in the hope to prove that they can be reproduced in laboratory.

     

III.          Feedbacks in biological systems

As presents [4], feedbacks in biological systems might happens in many levels, such as gene-proteins or organism-gene; see scheme in fig. 3. Feedbacks is something important for systems biology once the second step in the development of the ideas coming from the revolution triggered by the gene discover was the inclusion of feedbacks in the genetic circuits as idea models.
In system control theory [5], feedbacks is a way for making systems robust; they might adapt based upon the current states for future states. This is used for training neural network, in which the feedback is given by an error function, for example. In biological systems this was proposed and verified. As points out [8], this increased the role of the environment in biological systems. The genes does not have all information, some is adapted to the environment condition via controlling systems endowed with feedbacks, see fig. 3. This suggested [8] the gene-environment paradigm. As noted by Savageau [10], not only the gene information is under selection, also the controlling patterns; repression or activation, as model controlling patterns.


Fig. 3.     The new approach proposed by systems biology (second scheme) and the first thinking proposed by first genetic-based scientists. (Inspired by [8], scheme used in paper proposed to the same scientific meeting).       




 IV.          Networks of genes

When ‘someone’ is ‘hot’, they sweat; the question is how this happens. Bearing in mind that every process in the body is directly or indirectly a function of protein production and protein is produced from gene information; one might ask how that is done. Systems biology has worked on this kind of questions. Those networks are called Sensory Transcription Networks; they ‘sense’ environmental demands and trigger some internal transcription networks. See scheme following, fig. 4. 



Fig 4. Transcription networks and the environmental. (The signal are external “forces” such as glucose starvation or light presence. “X” are transcription factors, special set of proteins used for communicating genes. The arrows are flux of something, such as information. Source: inspired [10]).

 
The most remarkable observation is that those responses are carried out in networks; genes communicating for some final task. Transcription networks are networks of genes that control gene expression; in general, genes might repress or activate others. In addition, networks touch a second important observed-peculiarity of biological systems: redundancy.   


V.          Gene Sharing


Gene sharing [6] is a quite interesting manifestation of the ideas defended by systems biology; the correlations between elements of a system might create different properties even the system being the same. It was observed that structural proteins, called crystallins, responsible for transparent and refractive properties of the cellular lens in the eye also perform nonrefractive stress-related or metabolic functions (enzymatic) in other tissues. The difference is in the level of expression of the protein; in the lens they are expressed in a relative-high level, whereas in the tissue they are expressed in a low-level. As claims [6], this is not a special case. A second example is a polypeptide that works as ligand when it is in the cellular membrane or transcription factor when it migrates to the center of the cell. The author claims that the examples presented are not special cases. The author [6] attempts to clarify the meaning of gene sharing. For example, the changing of amino acid sequence is not gene sharing; even if this changes the function of the final molecular system. Further, in general gene sharing happens in bifurcation style; the molecular system keeps multifunction being ‘turned off’ under certain environmental conditions, such as high expression in the case of the crystallins. Moreover, gene sharing maintains the same gene as root for the molecular system and in general the primary structure of the molecular system (sequence of amino acid) is not affected; however, not always this means gene sharing; splicing and pos-editing of mRNA will not always culminate in gene sharing.

Gene sharing is a quite good example that emergent properties exist and that the environment plays central role in the protein workings. This is possible to demonstrate using simple numerical simulations at home that simple network motifs such as negative autoregulation or positive regulation can generate those bifurcation points depending on parameters values or concentrations; those simulations impose non-protein property assumptions, just concentration and parameters. Negative autoregulation is a network motif where a gene represses itself whereas positive regulation is a network where a gene activates another.

   VI.         Module look


The brain is a highly-layered system [33]. This was observed that the brain is a set of specialized compartment connected to each other. The most interesting is that those parts are highly connected [15]; some has tried to destroy one part in the hope to affect just some isolated part, but the whole brain is affected [15]. Further, tasks such as ‘thinking’ about works, highly abstracted, requires the activation of most of all the cortex cerebral, see fig. 5. This is not peculiar from the brain. Genes have showed similar behavior; this is seen in the attempt to treat one disease and appearing the well-known side-effects. See scheme following, fig. 6. In gene expression networks, those elements of the system are called network motifs; highly specialized sub-graphs of genes. In studies, [10] has demonstrated that complex networks can be successfully decomposed into those simpler graphs called network motifs.

VII. .       Mathematical-computational models in systems biology


The meaning of model is not a commonplace for biology and mathematics [4]. In fact, in mathematics this is a set of principles and formulae; while in biology this is a model organism used to make studies, such as the bacteria C. Coli. Therefore, this was the first problem encountered by mathematical biologist [4]. But, with the efforts of some scientists, they have achieved some agreements and today mathematical models are an important part of biological sciences. Since biological systems are complex systems, the old ‘pen and paper’ mathematics cannot be applied successfully, computer is of high-priority. The main reason is the problem of finding analytical solution for most of the problems treated in the literature in a feasible time. Design and application of algorithms are part of systems biology practices ([19]. [26]). The most promising models are from computational intelligence ([30], [34]) due to their nonparametric nature. Another set of models comes from systems control theory [35]. This is chased parameter approximation via technique from systems control theory. Numerical simulations, such as Molecular Dynamics and numerical methods for differential equations are quite important models for systems biology [30].



Fig 5. The highly interconnected processing of the brain. (Sourceadapted from [15])


Fig 6. Organism, scheme (Each irregular shape intends to represent a component, whereas the arrow stands for connections between those components. The dashed arrows are internal connection while the other are external (coming in and out.  source: from paper by the author submitted to the same scientific meeting).
    


        VIII.          Conclusions and final remarks

It was surveyed systems biology in the literature; a passive analysis. Thus, systems biology is a relatively recent field with roots in physics, biology, mathematics, computer science, and other fields that endeavors to understand biological systems as small parts interacting for creating what we ‘see’ and ‘feel’. Further, this is claimed that some important properties cannot be ‘seen’ unless the entire system under work is analyzed; all the elements working simultaneously. In addition, it was discussed some case-examples, such as gene sharing, which is an example encountered in the literature of proteins that have multifunction depending on the environment states; this is a bifurcation case. It was discussed as well in the demand for mathematical-computational models and some principles for systems biology. Furthermore, models from computational intelligence are promising models as well numerical methods for differential equations.  

Perhaps the world we leave in is a proof that emergent properties exist and are effective. This might be found out on the problems encountered by physicists to unite quantum mechanics and classical mechanics. Non one can say for sure the numerical value for what the classical mechanical world disappears (the collapse of the wave function) or for which the quantum mechanical world starts and finishes out. The difficult to explain the macro-world (classical mechanics) based upon the micro-world (quantum mechanics) might be because the macro-world is itself an emergent property of the micro-world. Another supporting point might be for example the nature of light as posed by Clerk Maxwell [11], light just exists in a definite speed and interchanges of electric and magnetic fields; light itself is a emergent property, light disappears if one stops it. Nonetheless, those are just enforcing point, not representing practices of systems biology.  

Regarding the complexity from biological systems, the author in a paper submitted to the same scientific meeting has written “…one always needs to be recollected on the difficult to capture biological laws with the current state of the art of applied sciences, it cannot be an obstacle, but the reason for improving. Systems biology has taken this task……..” and this could a guiding principle. Additionally, the potential weakness of systems biology is that it is still not part of classical textbooks books in genetics ([36], [37], [38], [39]); this is rarely encountered mathematical terms such as ‘noise’ in textbook of traditional biology, even recently written books.

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Systems Biology and Machine Learning

Systems Biology and Machine Learning