Selection of the week

May 22, 2015

Violinist Hilary Hahn, who hails from Baltimore, and pianist Valentina Lisitsa, play the first movement of American composer Charles Ives’s Fourth Sonata.

Journal Club

May 20, 2015

Here’s the paper I will be covering in Journal Club tomorrow:

Neurons for hunger and thirst transmit a negative-valence teaching signal

Abstract

Homeostasis is a biological principle for regulation of essential physiological parameters within a set range. Behavioural responses due to deviation from homeostasis are critical for survival, but motivational processes engaged by physiological need states are incompletely understood. We examined motivational characteristics of two separate neuron populations that regulate energy and fluid homeostasis by using cell-type-specific activity manipulations in mice. We found that starvation-sensitive AGRP neurons exhibit properties consistent with a negative-valence teaching signal. Mice avoided activation of AGRP neurons, indicating that AGRP neuron activity has negative valence. AGRP neuron inhibition conditioned preference for flavours and places. Correspondingly, deep-brain calcium imaging revealed that AGRP neuron activity rapidly reduced in response to food-related cues. Complementary experiments activating thirst-promoting neurons also conditioned avoidance. Therefore, these need-sensing neurons condition preference for environmental cues associated with nutrient or water ingestion, which is learned through reduction of negative-valence signals during restoration of homeostasis.

New paper on steroid-regulated gene expression

May 19, 2015

I am extremely pleased that the third leg of our theory on steroid-regulated gene expression is finally published.

Theory of partial agonist activity of steroid hormones
Abstract: The different amounts of residual partial agonist activity (PAA) of antisteroids under assorted conditions have long been useful in clinical applications but remain largely unexplained. Not only does a given antagonist often afford unequal induction for multiple genes in the same cell but also the activity of the same antisteroid with the same gene changes with variations in concentration of numerous cofactors. Using glucocorticoid receptors as a model system, we have recently succeeded in constructing from first principles a theory that accurately describes how cofactors can modulate the ability of agonist steroids to regulate both gene induction and gene repression. We now extend this framework to the actions of antisteroids in gene induction. The theory shows why changes in PAA cannot be explained simply by differences in ligand affinity for receptor and requires action at a second step or site in the overall sequence of reactions. The theory also provides a method for locating the position of this second site, relative to a concentration limited step (CLS), which is a previously identified step in glucocorticoid-regulated transactivation that always occurs at the same position in the overall sequence of events of gene induction. Finally, the theory predicts that classes of antagonist ligands may be grouped on the basis of their maximal PAA with excess added cofactor and that the members of each class differ by how they act at the same step in the overall gene induction process. Thus, this theory now makes it possible to predict how different cofactors modulate antisteroid PAA, which should be invaluable in developing more selective antagonists.

Steroids are crucial hormones in the body, which are involved in development and homeostasis. They regulate gene expression by first binding to nuclear receptors that freely float in the cytosol. The receptor-steroid complex is activated somehow and transported to the nucleus, where it binds to a hormone response element and initiates transcription. Steroids can either induce or repress genes in a dose dependent way and the dose-response function is generally a linear-fractional function. In our work, we modeled the whole sequence of events as a complex-building biochemical reaction sequence and showed that a linear-fractional dose response could only arise under some specific but biophysically plausible conditions. See herehere, and here for more background.

Given the importance of steroids and hormones, several important drugs target these receptors. They include tamoxifen and raloxifene, and RU486. These drugs are partial agonists in that bind to nuclear receptors and either, block, reduce, or even increase gene expression. However, it was not really known how partial agonists or antagonists work. In this paper, we show that they work by altering the affinity of some reaction downstream of receptor-ligand binding and thus they can do this in a gene specific way. We show that the activity of a given partial agonist can be reversed by some other downstream transcription factor provided it act after this reaction. The theory also explains why receptor-ligand binding affinity has no affect on the partial agonist activity. The theory makes specific predictions on the mechanisms of partial agonists based on how the maximal activity and the EC50 of the dose response change as you add various transcription factors.

The big problem with these drugs is that nuclear receptors act all over the body and thus the possibility of side effects is high. I think our theory could be used as a guide for developing new drugs or combinations of drugs that can target specific genes and reduce side effects.

Selection of the week

May 15, 2015

Mozart’s String Quartet No. 14 in G minor, K. 387, nicknamed “Spring”, the First Movement, played by the Gewandhaus Quartet.

Here’s the whole thing played by the Hagen Quartet

Selection of the week

May 8, 2015

Two of the greatest violinists ever, Yehudi Menuhin and David Oistrakh, play my favourite piece, the Double Violin Concerto in D minor, BWV 1043, by JS Bach.  I believe this is a performance from 1958 in Paris in the Salle de Pleyal with the RTF Chamber Orchestra conducted by Pierre Capdevielle.

The hazards of rounding

May 6, 2015

I parked at a meter today where the rate was 8 minutes per 25 cents. I threw in a nickel and the meter added 1 minute. I inserted in a dime and got and an additional 3 minutes. The meter was rounding down and not even correctly. My 5 cent piece should have netted me 96 seconds and my 10 cent piece 192 seconds. Instead, one quarter, four dimes and three nickels only got me 23 minutes, where I should have received 25 and a half minutes. I believe not accepting all forms of money at face value is a Federal offense. I certainly was offended.

Selection of the week

May 1, 2015

For May Day, here is Fanfare for the Common Man by American composer Aaron Copeland performed by the New York Philharmonic conducted by James Levine.

Here is the Emerson, Lake and Palmer version from 1977 in Montreal:

Selection of the week

April 24, 2015

Songs of a Wayfarer by Gustav Mahler, sung by mezzo soprano Sarah Connolly with the BBC Symphony Orchestra.

Talk at Michigan

April 23, 2015

I gave a talk in the Department of Computational Medicine and Bioinformatics at the University of Michigan yesterday. The video of the talk is here.  The talk is similar to the one I gave at the SMB annual meeting this summer.  My slides can be found here.

Selection of the week

April 18, 2015

Bela Bartok’s Romanian Folk Dances played by the Sydney Camerata Chamber Orchestra.

The philosophy of Thomas the Tank Engine

April 16, 2015

My toddler loves to watch the television show Thomas and Friends based on the The Railway Series books by the Rev. Wilbert Audry. The show tells the story of sentient trains on a mythical island off the British coast called Sodor. Each episode is a morality play where one of the trains causes some problem because of a character flaw like arrogance or vanity that eventually comes to the attention of the avuncular head of the railroad, Sr. Topham Hatt (called The Fat Controller in the UK). He mildly chastises the train, who becomes aware of his foolishness (it’s almost always a he) and remedies the situation.

While I think the show has some educational value for small children, it also brings up some interesting ethical and metaphysical questions that could be very relevant for our near future. For one, although the trains are sentient and seem to have full control over their actions, some of them also have human drivers. What are these drivers doing? Are they simply observers or are they complicit in the ill-judged actions of the trains? Should they be held responsible for the mistakes of the train? Who has true control, the driver or the train? Can one over-ride the other? These questions will be on everyone’s minds when the first self-driving cars hit the mass market in a few years.

An even more relevant ethical dilemma regards the place the trains have in society. Are they employees or indentured servants of the railroad company? Are they free to leave the railroad if they want? Do they own possessions? When the trains break down they are taken to the steam works, which is run by a train named Victor. However, humans effect the repairs. Do they take orders from Victor? Presumably, the humans get paid and are free to change jobs so is this a situation where free beings are supervised by slaves?

The highest praise a train can receive from Sir Topham Hatt is that he or she was “very useful.” This is not something one would say to a human employee in a modern corporation. You might say you were very helpful or that your action was very useful but it sounds dehumanizing to say “you are useful.” Thus, Sir Topham Hatt at least, does not seem to consider the trains to be humans. Perhaps, he considers them to be more like domesticated animals. However, these are animals that clearly have aspirations, goals, and feelings of self-worth. It seems to me that they should be afforded the full rights of any other citizen of Sodor. As machines become more and more integrated into our lives, it may well be useful to probe the philosophical quandaries of Thomas and Friends.

 

 

 

 

Selection of the week

April 10, 2015

Igor Stravinsky’s ballet Le sacre du printemps (The Rite of Spring), Part 1 with the San Francisco Symphony conducted by Michael Tilson Thomas. This piece ushered in the modern age. It cause minor rioting when first performed in Paris in 1913 but now is considered one of the masterpieces of the 20th century.

R vs Matlab

April 4, 2015

It has now been almost half a year since I switched from Matlab to open source software and I’ve been amazed at how easy the transition has been. I had planned to replace Matlab with Python, Julia, and R but I have found that R and Julia have been sufficient for my requirements. Maxima is also more than adequate to replace Mathematica. I have become particularly attached to R especially after I started to use R Studio as the interface. I had only used R before as just a statistics tool but it really is a complete programming platform like Matlab. It has very nice graphics capabilities and I find the language very nice to program in. I really like its use of lists where I can pile sets of any type and any size into one object. I also like how R Studio can save your work into Projects, which keeps the whole environment and history in one place. I can then switch between multiple projects and everything comes back. The only thing I miss from Matlab is the command completion history feature, where I could easily find a previous command by just typing the first few letters. Also, I haven’t quite figured out how to output R data into a text file seamlessly yet. I seem to always get extraneous row or column information. I use Julia when I want to write a code that needs to loop fast but for everything else I’ve been reaching for R.

Selection of the week

April 3, 2015

For Good Friday, here is the famous aria Erbarme dich from Johann Sebastian Bach’s St. Matthew Passion, with mezzosoprano Marianna Pizzolato.

If you have three spare hours, I would listen to the whole thing.  You should do this at least once in your life.

New paper on gene repression

April 2, 2015

CC Chow, KK Finn, GB Storchan, X Lu, X Sheng, SS Simons Jr., Kinetically-Defined Component Actions in Gene Repression. PLoS Comp Bio. 11:e1004122, (2015)

Abstract

Gene repression by transcription factors, and glucocorticoid receptors (GR) in particular, is a critical, but poorly understood, physiological response. Among the many unresolved questions is the difference between GR regulated induction and repression, and whether transcription cofactor action is the same in both. Because activity classifications based on changes in gene product level are mechanistically uninformative, we present a theory for gene repression in which the mechanisms of factor action are defined kinetically and are consistent for both gene repression and induction. The theory is generally applicable and amenable to predictions if the dose-response curve for gene repression is non-cooperative with a unit Hill coefficient, which is observed for GR-regulated repression of AP1LUC reporter induction by phorbol myristate acetate. The theory predicts the mechanism of GR and cofactors, and where they act with respect to each other, based on how each cofactor alters the plots of various kinetic parameters vs. cofactor. We show that the kinetically-defined mechanism of action of each of four factors (reporter gene, p160 coactivator TIF2, and two pharmaceuticals [NU6027 and phenanthroline]) is the same in GR-regulated repression and induction. What differs is the position of GR action. This insight should simplify clinical efforts to differentially modulate factor actions in gene induction vs. gene repression.

Author Summary

While the initial steps in steroid-regulated gene induction and repression are known to be identical, the same cannot be said of cofactors that modulate steroid-regulated gene activity. We describe the conditions under which a theoretical model for gene repression reveals the kinetically-defined mechanism and relative position of cofactor action. This theory has been validated by experimental results with glucocorticoid receptors. The mode and position of action of four factors is qualitatively identical in gene repression to that previously found in gene induction. What changes is the position of GR action. Therefore, we predict that the same kinetically-defined mechanism usually will be utilized by cofactors in both induction and repression pathways. This insight and simplification should facilitate clinical efforts to maximize desired outcomes in gene induction or repression.

I am so happy that this paper is finally published.  It was a two-year ordeal from the time I had the idea of what to do until it finally came out. This is the second leg of the three-legged stool for a theory of steroid-regulated gene expression. The first was developing the theory for gene induction (e.g. see here) that started over ten years ago when Stoney and I first talked about trying to understand his data and really took off when Karen Ong turned her summer internship into a two-year baccalaureate fellowship. She’s now finishing up the PhD part of her MD-PhD at the Courant Institute at NYU.

In the first leg, we showed that if the dose-response curve for steroid-regulated gene induction (i.e. gene product as a function of ligand concentration), had the form  a x/ (c+x), (which has been variously called noncooperative, Michaelis-Menten function, Hill function with Hill coefficient equal to 1, hyperbolic, first order Hill dose response curve, to give a few), then the dose-response could be written down in closed form.  The theory considers gene induction to be a sequence of complex forming reactions Y_{i-1} + X_{i} \leftrightarrow Y_i for i = 1, 2, ..., n, and the dose-response is given by [Y_n] as a function of [Y_0], which in general is a very high order polynomial which is not Michaelis-Menten. However,  when some biophysically plausible conditions on the parameters are met, the polynomial can be represented by the group of lower triangular matrices and can be solved exactly.  We can then use the formulae to make predictions for the mechanisms of various transcription factors.

However, steroids also repress genes and interestingly enough the repression curve is also noncooperative and is given by the linear fractional function a + bx/(1 + c x). The question then was how does this work. I was puzzled for a while on how to solve this but then thought that if we believe that the transcription machinery after initiation is mostly conserved then the induction theory we had previously derived should still be in place. What is different is that in repression instead of steroids initiating the cascade, there was some other agonist and steroid repressed this. In our induction theory, we included the effects of activators and inhibitors from enzyme kinetics, which we called accelerators and decelerators to avoid confusing with previously used terms. Because of the group property of the reactions, basically any function you are interested in has linear-fractional form. I thus postulated that steroids, after binding to a nuclear steroid receptor, acts like a decelerator. I then had to work out all the possible cases for where the decelerator could act and the large number of them made the calculations rather tedious. As a result, I made lots of mistakes initially and the theory just wouldn’t fit the data. I finally had a breakthrough in the fall of 2013 when I was in Taiwan for a workshop and everything started to come together. It then took another six months to work out the details and write the paper, which was then followed by several back and forth’s with the referees, a major rewriting and a final acceptance a few months ago. In the process of working on this paper, I discovered a lot of properties about the induction system that I didn’t realize. I still didn’t believe it was finished until I saw it posted on the PLoS Comp Bio website this week.

I’m currently putting on the finishing touches for revisions on the third leg of the stool now. We have even reunited the band and convinced Karen to take some time away from her thesis to help finish it. This paper is about how partial agonists or antagonists like tamoxifen work, which could have implications for drug development and avoiding side effects. Steroids are not the only ligand that can activate a steroid-regulated gene. The steroid cream that you use for rashes consists of a highly potent steroid agonist. There are also molecules that block or impede the action of steroids by binding to steroid receptors and these are called partial agonists, antagonists or antisteroids. However, steroid receptors are widely expressed and that is why when you take them they can have severe side effects. Hence, it would be nice to be able to control where they act and by how much. This third leg paper is the theory behind how to do this.

The perils of math pedagogy

March 30, 2015

It seems that the prevailing wisdom in teaching mathematics is to make abstract concepts as concrete as possible. The thinking is that if math can be related to everyday concepts or pictures then it will be more palatable and understandable. I happen to disagree. I think part of what makes math fun is the abstractness of it. You make up some rules and follow them to their logical conclusions. This is also how I see children play. They like to invent make-believe worlds and then play within them according to the rules of the world.

Usually these attempts at concreteness seem harmless enough but I have recently come up with an example where making things concrete is much more confusing than just teaching a rule. The example is in division with remainders. My third grader was asked to “draw” 7 divided by 2 in terms of items and groups. Her instinct was to draw 2 groups with three balls each with one ball remaining, like this

(x x x)

(x x x)

x

She then was supposed to write this as a mixed number, which looking at the diagram she wrote 3 1/3. When she asked me if this is correct I asked her to multiply this by 2 and see if it gets back 7 and when she got 6 2/3, she was extremely confused as to why she didn’t get the right answer. I tried to explain to her that the way she grouped things, the remainder was in terms of the fraction of the number of groups, which is very unintuitive and almost impossible to explain. It would have been even worse if the example was 8 divided by 3.

I then tried to tell her that a better way to think of division is not to ask how many elements would you get if you divided 7 into 2 groups because this amounts to begging the question (phrase used the correct way), since you need to know the answer before you can do the operation. Rather, what you really want to ask is how many groups would you have if you divided 7 items into groups of size 2 (which is a local rule), whereupon the diagram would be

( x x)

(x x)

(x x)

x

Now if you write down the mixed number you get 3 1/2, which is the correct answer. She then argued vehemently with me that this is not what the teacher taught her, which may or may not be true.

I think even most adults would get confused by this example and maybe working through it would give them a new appreciation of division. However, if you wanted children to learn to divide correctly than teaching them the rule is better. To divide 7 by 2 you find the largest integer that multiplied by 2 fits into 7 and what’s left over is divided by 2. Even better, which introduces and motivates fractions, is that you write 7 divided by 2 as 7/2 and this then becomes 3 1/2. If you learn the rule, you will never end up with 3 1/3.

Selection of the week

March 27, 2015

Leonard Bernstein conducts the “Orchestre National de France” in Hector Berlioz’s (psychedelic) Symphonie Fantastique 5th Movement:Larghetto, Allegro (Songe d’une nuit de Sabbat) in Paris, 1976.

If you have the time, here’s the whole piece played by the Chicago Symphony Orchestra conducted by Stéphane Denève.

New paper on path integrals

March 24, 2015

Carson C. Chow and Michael A. Buice. Path Integral Methods for Stochastic Differential Equations. The Journal of Mathematical Neuroscience,  5:8 2015.

Abstract: Stochastic differential equations (SDEs) have multiple applications in mathematical neuroscience and are notoriously difficult. Here, we give a self-contained pedagogical review of perturbative field theoretic and path integral methods to calculate moments of the probability density function of SDEs. The methods can be extended to high dimensional systems such as networks of coupled neurons and even deterministic systems with quenched disorder.

This paper is a modified version of our arXiv paper of the same title.  We added an example of the stochastically forced FitzHugh-Nagumo equation and fixed the typos.

Selection of the week

March 20, 2015

Vivaldi’s Spring from the Four Seasons, with Julia Fischer and the Academy of St. Martin in the Fields.

Selection of the week

March 13, 2015

The first movement of the Cello (and Piano) Sonata No.1 Op. 38 by Johannes Brahms played by Alisa Weilerstein, cello and  Ilan Rechtman, piano.

 

Here is the whole thing with Yo Yo Ma and Emanuel Ax


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