Recently while reading about circadian biology in my model organism (Neurospora crassa), I came across something so fantastical that it seems to border on science fiction and makes you see the “super-powers” life seems to possess. There is a class of flavoproteins known as Cryptochromes, also meaning hidden color and they are sensitive to blue light. Besides, there is something so special about the wavelength for blue light (475 nm), which makes it such a startling characteristic of almost every living creature’s day-to-day life on this planet. But that’s a topic for another day.
So crytochromes (CRY) have been shown to have a significant role in circadian biology, where they tend to act as blue-light photoreceptors. For example, in the fruit fly, Drosophila sp., these proteins directly control input of light into the circadian clock machinery [REF], while in mammals these act as transcription repressors (prevent RNA synthesis from DNA) for the clock machinery [REF]. What’s even more revealing is that some insects such as the monarch butterfly, have a medley of mammal-like and Drosophila-like versions of CRY proteins [REF]. So once again you see evolution rears its amazing head! There must have been a more ancient mechanism sensing both light and repressing transcription with regards to regulation of the clock.
The last mentions I would like to put forward regarding these amazing cryptochromes is – magnetoreception. Yes, you read that right. In a number of species, these CRY proteins can regulate how the organism can sense the earth’s magnetic field lines! For example, in birds, CRY proteins in the photoreceptor neurons in the eye can regulate magnetic orientation during migration [REF]. These same proteins can help fruit flies sense the magnetic fields while growth of the model plant Arabidopsis is affected by magnetic fields in presence of blue light [REF]. Ever wondered whether biology can marry quantum physics? Well this is it – Klaus Schulten and Thorsten Ritz had suggested that when a cryptochrome is struck with blue light, it would transfer one electron to another partner called FAD (flavin adenine dinucleotide) [REF]. So now both have one electron and become what is known as a “radical pair”. In this pair, the spins of the two “lone” electrons are linked and so they can spin together or even in opposite directions. Also these two states would have different chemical properties and the radical pair can flip between each other – influenced by the Earth’s magnetic field. This is in turn influences the speed/ outcome of the chemical reactions involving the pair, for e.g. the circadian clocks or firing of neurons. So is it possible that even you and me can sense magnetic field lines of the earth? When lost in pitch black and a cloudy night can you find your way back home, blindfolded? Well, it turns out human cryptochromes are least understood and behaviourial neuroscience has time and again failed to answer this question and even led to fierce controversies in this field [REF1, REF2]. But yes, what we do not understand - we seem to fantasize about? After all isn’t it all about human nature?
So crytochromes (CRY) have been shown to have a significant role in circadian biology, where they tend to act as blue-light photoreceptors. For example, in the fruit fly, Drosophila sp., these proteins directly control input of light into the circadian clock machinery [REF], while in mammals these act as transcription repressors (prevent RNA synthesis from DNA) for the clock machinery [REF]. What’s even more revealing is that some insects such as the monarch butterfly, have a medley of mammal-like and Drosophila-like versions of CRY proteins [REF]. So once again you see evolution rears its amazing head! There must have been a more ancient mechanism sensing both light and repressing transcription with regards to regulation of the clock.
The last mentions I would like to put forward regarding these amazing cryptochromes is – magnetoreception. Yes, you read that right. In a number of species, these CRY proteins can regulate how the organism can sense the earth’s magnetic field lines! For example, in birds, CRY proteins in the photoreceptor neurons in the eye can regulate magnetic orientation during migration [REF]. These same proteins can help fruit flies sense the magnetic fields while growth of the model plant Arabidopsis is affected by magnetic fields in presence of blue light [REF]. Ever wondered whether biology can marry quantum physics? Well this is it – Klaus Schulten and Thorsten Ritz had suggested that when a cryptochrome is struck with blue light, it would transfer one electron to another partner called FAD (flavin adenine dinucleotide) [REF]. So now both have one electron and become what is known as a “radical pair”. In this pair, the spins of the two “lone” electrons are linked and so they can spin together or even in opposite directions. Also these two states would have different chemical properties and the radical pair can flip between each other – influenced by the Earth’s magnetic field. This is in turn influences the speed/ outcome of the chemical reactions involving the pair, for e.g. the circadian clocks or firing of neurons. So is it possible that even you and me can sense magnetic field lines of the earth? When lost in pitch black and a cloudy night can you find your way back home, blindfolded? Well, it turns out human cryptochromes are least understood and behaviourial neuroscience has time and again failed to answer this question and even led to fierce controversies in this field [REF1, REF2]. But yes, what we do not understand - we seem to fantasize about? After all isn’t it all about human nature?