January 19, 2011 | David F. Coppedge

Molecules as Traffic Cops

One of the cutting-edge developments in cell biology and genetics is the realization that there are networks of molecules that are regulated by other molecules.  Some molecules stimulate growth while others repress it.  The dynamic interplay between signals, hormones, repressors and other processes somehow leads to “homeostasis” – a dynamic balance that is responsive to the environment and able to adapt to changing needs.
    Three papers in PNAS this week discuss these dynamic networks that are only slowly being understood. 

  • Plant growth:  High school biology students may have learned about auxins and gibberelins, plant hormones that students can observe affecting growth of roots and shoots in the lab.  Two papers in PNAS discussed gibberelins this week, teasing apart some of the complex interactions of genes and hormones that affect each other.  Zhang et al1 found that genes called DELLA act as repressors for growth-promoting gibberelins (GA), but are themselves repressed by another gene, SCL3.  “Our data further show that SCL3 and DELLA antagonize each other in controlling both downstream GA responses and upstream GA biosynthetic genes,” they said.  That means the two antagonists can not only affect the response of cells that get the gibberelins, but can turn up or down the upstream spigot – the genes that create the gibberelins.  “This work is beginning to shed light on how this complex regulatory network achieves GA homeostasis and controls GA-mediated growth and development in the plant.”
        Working with the same genes and hormones, Heo et al learned a little more about how GA, DELLA and SCL3 work in root elongation and stem elongation in Arabidopsis plants.2  They noted that because plants cannot move, proper signaling is vital: “During plant development, because no cell movement takes place, control of the timing and extent of cell division and coordination of the direction and extent of cell expansion are particularly important for growth and development,” they began.  “The plant hormone gibberellins (Gas) play key roles in the control of these developmental processes.”
  • Sense organ growth:  Signalling is important in animals, too.  Complex interplays of molecules and genes are involved in the formation of the complex structures of the inner ear.  It was only recently that molecular biologists noticed that scads of RNA pieces called micro-RNAs are involved in regulating genes.  Kuhn et al found that a micro-RNA acts like a traffic cop as the cochlea develops.3  Mutating one in particular, named miR-96, causes “widespread changes in the expression of many genes.”
        Parents who’ve held a newborn may want to reflect on the complexity of processes working in harmony to perfect a baby’s inner ears:

We found that the physiological development of mutant sensory hair cells is arrested at around the day of birth, before their biophysical differentiation into inner and outer hair cells.  Moreover, maturation of the hair cell stereocilia bundle and remodelling of auditory nerve connections within the cochlea fail to occur in miR- 96 mutants.  We conclude that miR-96 regulates the progression of the physiological and morphological differentiation of cochlear hair cells and, as such, coordinates one of the most distinctive functional refinements of the mammalian auditory system.

None of these papers mentioned evolution.


1.  Zhang et al, “SCARECROW-LIKE 3 promotes gibberellin signaling by antagonizing master growth repressor DELLA in Arabidopsis,” Proceedings of the National Academy of Sciences, published online before print January 18, 2011, doi: 10.1073/pnas.1012232108.
2.  Heo et al, “Funneling of gibberellin signaling by the GRAS transcription regulator SCARECROW-LIKE 3 in the Arabidopsis root,” Proceedings of the National Academy of Sciences, published online before print January 18, 2011, doi: 10.1073/pnas.1012215108.
3.  Kuhn et al, “miR-96 regulates the progression of differentiation in mammalian cochlear inner and outer hair cells,” Proceedings of the National Academy of Sciences, published online before print January 18, 2011, doi: 10.1073/pnas.1016646108.

These papers are mentioned briefly for the sake of readers who would like to delve further into the details.  If nothing makes sense except in the light of evolution, why wouldn’t the scientists saturate their papers with Darwinspeak?  Networks and signals are concepts of intelligent design, not evolution.  These are exciting times when scientists can begin to look into the black box and see elaborate interactions between molecules acting for all the world like robots or a well-organized city with security and traffic control.  The new paradigm should be, “Nothing in biology makes sense except in the light of information technology.”
    Whittaker Chambers, the ex-communist spy who testified against high-level Russian spy Alger Hiss, explained in his book Witness one of the things that began turning his mind away from atheist materialism and toward faith.  He was watching his baby daughter eat, and took note of her “intricate, perfect ears.”  “The thought passed through my mind: ‘No, those ears were not created by any chance coming together of atoms in nature (the Communist view),” he said in the foreword to his book.  “They could have been created only by immense design.’” (see full quote at Creation Tips).  What if he had learned about miR-96, too?  That would have been overkill against any materialist ideology.

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