An Update on the Development of Killfish as a Model Organism in Aging Research

Researchers have in recent years made inroads into the infrastructure and knowledge needed to investigate the molecular biology of aging in killifish. The various species of killifish occupy a good compromise position between short length of life and the degree to which their biochemistry is relevant to human aging. As an added bonus, there is a fair degree of variation in life span between different killifish species, allowing for comparative investigations of their genetics and cellular biology. Short-lived animals mean faster studies, more research conducted for any given amount of funding, but the further removed from humans the species is, the more likely it is that the output of any given study provides no useful insight to direct the study of aging in mammals. As in all things, there are trade-offs involved.

A favourite of fish hobbyists since the 1970s, killifish are gaining popularity among scientists who study ageing, and dozens of labs now house them. Elderly killifish - a couple of months old - show hallmarks of ageing. Their bright scales fade and their cognition wavers; many develop tumours. Lifespan-altering experiments that take years in mice and decades in primates can be over in months in killifish, which are also more closely related to humans than are fruit flies, nematodes and other short-lived lab organisms popular in ageing research. "It turns out to be the shortest-lived vertebrate that can be raised in captivity."

The turquoise killifish genome contains several clues to its peculiar, fleeting life. Valenzano and his colleagues found that variations in genes involved in nutrient sensing, DNA repair and ageing have been selected for during its evolutionary history. Such genes might prove instructive for ageing in longer-lived animals. One such is IGF1R, which has been linked to extreme longevity in bowhead whales, naked mole-rats and Brandt's bat. Genes linked to IGF1R vary between an extremely short-lived killifish lab strain and a wild variety that can live for twice as long. A similar difference between short-lived and longer-lived strains was also seen in a gene that has been linked to dementia in humans. "Maybe these genes are central hubs for regulating survival. In some species they can accelerate ageing, and in some they can slow it down."

Genetic-engineering experiments - such as creating knock-out fish that lack particular genes - are needed to confirm whether the genes pinpointed in these studies truly influence ageing. These tests are already under way. Earlier this year a team used CRISPR-Cas9 genome editing in 'proof-of-principle' experiments to alter several ageing-related genes in killifish. "We are excited at trying to make it live longer." The team is also screening drugs in killifish to see if any lengthen its lifespan or slow tissue degeneration.



Summary : IGF1r is responsible and IGF/GH are bad in GHKO mouse and other growth hormone deprived *mouse* specie...not humans who benefit in a controlled dosage (in the brain. centenarians have higher IGF/r in brain, those with dementia (who die younger) have low brain IGFr). Killifish just helps kill this
hormones good/bad doubt.

"Maybe these genes are central hubs for regulating survival.
In some species they can accelerate ageing, and in some they can slow it down."

He nailed it there. IGF1 receptors orchestrate so many survival neuroendrocrinal growth hormone signal effects depending on the specie and its evolutionnary survival context/blueprint (speed of metabolism, energy resource utilization vs conservation vs damage accumulation vs specie survival, rate of procreation and sexual maturation, transfer of sexual energy resources towards cellular energy repair gene systems maintenance in long-lived and vice versa in short-lived specie, colonization formation for specie survival). Again, this shows why studies in mice, killifish and other small short-lived animals don't have much repeatability or translatabiliy in humans (or very weak one) when these species differ in their survival master plan/evolution survival context; and they differ in age by an order of magnitude (thus differ in their gene pathways activation by evolution's longevity gene selection pression for long-lived ones and selection pression for sexual genes in short-lived ones; all upstream of the endrocine sexual hormonal systems via IGF receptors in the brain and the hormones modulating them (testosterone, Human Growth Hormone, estrogen, tryptophan, melatonin, pituatry hormones, thyroiid T3 T4 etc,....).
The fact we hit puberty late is one reason we live long. When puberty is shortened, life is dramatically shortened too (Bowhead whales, A.Islandinc, giant turtles, and what not other extreme lifespan animal, are late late late in the sexual puberty, protracted period of Growth to become 'grown' sexually capable adult (puberty) is ultra extended).
Studies in naked mole rat NMR have shown that the period of sexual maturation of NMR is close to that of a human and the brain neuron/sunapse/plasticity of NMR retains juvenile charateristics (of young adolescents or children, neotony) while growing up; which means their stage to become a grown adult is delated immensely compared to a mouse. This protracted development coincides with extreme lifespan, the longer to puberty period the longer the MLSP. IGF1r and hormones endocrine growth control all behind this. Let's remember that so many studies touched IGF1/IGF1r/IGF/DAF-2/DAF-16/SIRTUINS/PIP3/MEK/ERK/HISTONE/FOXO-3/Foxos, it is a interconnected pathway that dictates the growth of an animal, energy utilsation and damage accrual. Insulin (growth) and glycemia/energy utilisation control is at the top of this mega chain.

Protracted brain development in a rodent model of extreme longevity.

Here, we provide evidence that the naked mole rat brain undergoes prolonged postnatal development, including biophysical, molecular, and structural measures of maturation, but not including postnatal neurogenesis15,17,18. First, we studied the size and positioning of adult-born neuronal contingents in olfactory areas and hippocampus throughout the life-span of naked mole rats, cautioning that brain size and neuronal numbers are regulated by **sexual activity in this eusocial animal15.**

We found significantly reduced rates of neurogenesis in adult naked mole rats in comparison to adult mouse levels. Despite this reduced neurogenesis, naked mole rat brains continue to grow for at least one year postnatally. We demonstrate the continued and **slowed acquisition of mature** neuronal morphology, lasting up to **at least 10 years postnatally, **
to build brain volume and neuronal circuits. This is supported by i) the presence of axonal pathways,
**fetal-like guide scaffolds and neurochemical arrangements known to dominate in mouse fetuses**

ii) continued morphogenesis of hippocampal neurons and iii)** incomplete synapse segregation** in the hippocampus, including mixed subcellular targeting of glutamatergic and GABAergic terminals along the somatodendritic axis of principal neurons.

These mechanisms diminish by the **second decade** of life.

In sum, our data identify that developmental processes occurring at the **hour-to-day scale in mouse** are prolonged along **months-to-years time scales in naked mole rats**, highlighting that **neoteny** is a **successful evolutionary strategy to enhance the capacity of the central nervous system for successful environmental adaptation to extreme longevity.**

Neoteny/Juvenilization, central nervous system (IGFr control of growth via central nervous system to brain and metabolism).

''In neoteny, the physiological (or somatic) development of an animal or organism is slowed or delayed.''
''neoteny. (nē-ŏt'n-ē) The retention of juvenile characteristics in the adults of a species''
Basically very late bloomer/late puberty.


Posted by: CANanonymity at December 4th, 2015 12:15 PM

I've got to wonder why Killifish haven't really been used much until now. A quick search turns up this 2005 Fightaging! article but there don't seem to have been a lot of aging experiments involving Killifish since then.

What are the obstacles and have they since been overcome?

Posted by: Jim at December 5th, 2015 8:15 AM


Hi Jim,

That's a very good question, indeed ! I don't know...Just my opinion, I feel it's a mix of things : mouse models have high popularity and availability/methods of captivity/lab research convenience/lots of backed research/ ''tried and tested'' research proof (what does killifish have? it's been ignored so no results) (and thank lord for these mouse acting guineapigs for their service (life sacrifice) in the name of science advancement, what would we do without them ! Insects (flies, worms) studies got us this far, it's mouse and rat (and now naked mole rats and other rodent models) that helped us get much farther), yeast, flies, bees, worms and other insect or bacterial wannabe models are very important and great too; but nowhere near a full animal with resembling organs like a mouse.
Killifish ressemble that too, I guess it's more having to do with an animal found in water (other environment) and not as available or maintainable/studyable so well. Fish studies are very important too, but not always so translatable in humans, we don't even live in same environment (us in air out of water, them below in water, so different oxygen availability and different adaptation of system than out-of-water ground animals). I guess it's also kind of the 'black sheep' of the models, it's just not studied enough, unavailable or not seeked, like forgotten for simply that no one is studying them; so it remains obscure. It may be more difficult to research its gene pathways too than say in a mouse. One more thing, the house mouse and rat (mus musculus/rattus) rodents are mammal like us (lung breathing), this gives it a compatibility/human mammal translatability edge over the non-mammal (gill breathing) killifish.There may be also cost/housing/studying/breeding reasons (cheap to get mouse and get results fast that you can compare in databanks, it's now overused, price dropped, killifish is rare studied specie, higher price; harder to get from the ocean, you can get and (in)breed mice like easy, again with lab model convenience). Mouse the more hip popular, killifish the unpopular outcast.

With a unusual name like killifish you would think it would help, it's possibly not helping its cause, perhaps it was named in such honor ('' who wants to study a Killi fish, right? it's no kill for sure, this fish is killed dead already, by its name, and my level of optimism specie... '').

Maybe it's time to recall killifish,

: P

Posted by: CANanonymity at December 5th, 2015 12:55 PM

@Jim, @CANanonymity: I suspect this is just a matter of adoption time for a new method of doing things in a largely grant-based system, while the old methods are still good enough for most labs and don't require new expenditure, retraining, etc.

Posted by: Reason at December 5th, 2015 1:16 PM

Putting up front my complete ignorance of this particular organism, my own overarching objection to doing much with the killfish is the simple fact that it's a fish, and not a mammal. They're cold-blooded, you can slow down the aging of fish by simply lowering the temperature of the water they're kept in, which fails almost entirely in mammals. They also have a completely different solution to gravity, which means that their bodies (most obviously their skeletal systems, but also their vasculature and muscles) are facing quite different forces and challenges over a lifetime.

And, there are other advantages built into using mice and rats in particular, inasmuch as their use for many decades in biomedical research generally and biogerontology in particular means that their genetics, physiology, nutritional needs, endemic infections, and aging are very well-characterized: every time you introduce a new model organism, you have to build up the basic biology and a model of "normal" aging from scratch. It's easy to dismiss an enormous number of bogus claims of life extension in mice because we can see that the control group deviates in the shape or length of the survival curve from what can be done under good laboratory conditions; until you have multiple labs having raised killfish under different laboratory conditions for many generations (and different strains of killfish), you won't even know if your control group is any good.

And even with all of what we do know about the mouse model from those many decades of use, we're still learning about new problems with them as models for human aging and disease: critical differences in mice's inflammatory response to sepsis and trauma, for instances, or in the regulation and behavior of mouse vs. human microglia. How long is it going to take to uncover such experimental confounders and model-generated artifacts when starting from scratch on a new organism?

Posted by: Michael at December 5th, 2015 2:28 PM

@Reason @Michael

Excellent comments on killifish model study/usage motives.

This one is long (like an epiphany): Summary : Cellular Reorganization correlates to MLSP.

In bringing attention to IGF1-r (Insulin Growth Factor-1 Receptor) from this killifish study finding to the Naked Mole Rat's (NMR) development (an extremely short-lived model (killifish) vs an extremely long-lived model (NMR)); I made a second realization :

The last study cited has so much meaning when explored more deeply.

''Protracted brain development in a rodent model of extreme longevity.''

NMRs have extremely lenghtened/slow/late period of child-to-adult transition growth to become a fully sexually capable (sexual maturation); just like us humans. What more is that
Neoteny/Juvenilization IS Rejuvenation in a sense (Juvenil in Juvenilization prefix, (re)Juven(ation) Juven prefix in reJuvenation), Rejuvenation intends to Reverse aging to a Biologically younger age Phenotype.

Cellular reorganisation or Cellular remodelling may be the key element of reprogrammation that allows immortal life in certain cancer cells who remodel/reorganize many elements such as the ECM and whatnot genetic pathways. This clearly means organ tissue plasticity (reorganization) is altered by cancer cells.

''These data, supported by the loss of these structural plasticity markers in the olfactory bulb by 10 years of age (Supplementary Fig. 4j,h) suggest prolonged cellular reorganization as a means to retain neuroadaptation in the olfactory system, including primary cortical areas, of naked mole rats.''

Centenarians and mice who lose their capability to discriminate between certain repulsive odors and smells, show that their olfactory bulbs and cells/neurons are damaged and this is in correlation with the biological age.
Meaning these senses (smell, eyesight, touch, taste) all have connection to the different senses' brain regions via CNS (central nervous system) signals/stimuli. The fact that the NMR has celllular reorganisation/remodelling in the olfactory bulb as it ages shows that reorganisation is a special feature of Neoteny and Extreme lifespan too.
Cellular reorganisation or remodellin would equald to reprogrammation in a sense, and this way possible allow to avoid irreversilibity of certain damages accumulation (crosslink and ceroid, liposcins granules). I am beting that the proteasome, autophagosome and lysosome are reorganized too with age. If reorganization is Plasticity, then if we lose Plasticity (cellular reorganization/remodellin) capability than we age dramatically.
Telomerase is capable of rejuvenation and increases telomeres, plus in the brain telomerase activation in mice Increases their brain weight/size/volume/mass; showing that humans lose GM WM (grey matter, white matter volume) in the brain as they age. Alzheimer's shows dramatic loss of GM in the brain. Alzheimer's lose about 80% of synaptic Plasticity proteins (this is a proof that plasticity or cellular reorganization is critical for extreme longevtiy and protection against oxidative insults),

''The brain continues to slowly lose volume through neuron shrinkage''
''As reported in the Journal of Neuroscience, Fjell and colleagues studied 132 elderly adults who took part in the Alzheimer's Disease Neuroimaging Initiative (ADNI) (see ARF related news story). The investigators used a variety of measures, including memory tests, cerebrospinal fluid markers of amyloid pathology, and ApoE4 status to identify participants at very low risk of developing AD. Magnetic resonance imaging (MRI) scans showed that over a year, these seemingly healthy elders lost, on average, 0.44 percent of whole brain volume. Most areas of the brain were affected, with the hippocampus and amygdala losing about 1 percent and cortical regions about 0.5 percent.''

Alzheimer's lose up from 5 to 9 times more brain mass when going from slightly demented to fully demented and alzheimer's advanced state. Plus, they all show dramatic loss of plasticity (thus loss of synpase/neuron reorganization/remodelling).

''Meditation found to increase brain size | Harvard Gazette
Feb 2, 2006 - Brain scans they conducted reveal that experienced meditators ... “Our data suggest that meditation practice can promote cortical plasticity in ...
4-OHT treatment helps increase telomerase in mouse:

''Furthermore, a 4-OHT treatment course of only 4 weeks is sufficient to cause significant partial reversion of the brain size defect, with G4TERT-ER brain weights increasing from 77.3±3.3% of G0TERT-ER brain weights in the vehicle group to 89.7±4.0% in the 4-OHT group (Figures 5a,b). Importantly, telomere elongation can be detected in the CC after 4 weeks of telomerase reactivation (Figure S3c). Thus, endogenous telomerase reactivation exerts a swift impact on oligodendrocyte proliferation and differentiation, and promotes repopulation of white matter structures with mature oligodendrocytes and active myelin deposition.
Figure 5
Myelination, brain size, and olfactory function [increased] following telomerase reactivation

That also means, brain has a MLSP of 120 years if in normal aging, it loses 0.5-1% per year for a full life.
Jeanne Calment the eldest woman human recorded ever at 122 years old, was very lucid, was visited at
119 years old before death and received a CAT MRI scan, it revealed that her brain was deterioated everwhere but her prefrontal cortex was solid and still kept (meaning the cortex is very important for communication, thinking and regular motor-speech capacatiies).

''Neuroplasticity or brain plasticity refers to the brain's ability to CHANGE throughout life. The brain has the amazing ability to reorganize itself by forming ...

Loss of proteins regulating synaptic plasticity in normal aging of the human brain and in Alzheimer disease.
Hatanpää K1, Isaacs KR, Shirao T, Brady DR, Rapoport SI.
Alzheimer disease, the most common cause of dementia in the elderly, was associated with an additional 81% decrease in levels of drebrin, a protein regulating postsynaptic plasticity. Disturbed mechanisms of plasticity may contribute to cognitive dysfunction during aging and in Alzheimer disease

''indeed, based on findings from nonhuman animal studies, it is suggested that the hormonal events of puberty trigger a second period of structural reorganization and plasticity in the brain [Sisk and Foster, 2004].''

''A clear association was found between higher fitness levels and greater hippocampal volume, but importantly, greater hippocampal volume also mediated the fitness-memory association. This result suggests that greater hippocampal volume is not just a meaningless by-product of more vascularization, but rather has a meaningful impact on memory function in late life
the causal nature of physical activity on brain plasticity.''

''the brain is a plastic organ capable of remodeling itself in adulthood, even in old age''

''Plasticity of Mammary Cell Boundaries Governed by EGF''

BDNF, EGF, IGF, FGF, TGF, HGH, GHRH, T3, T4, Testosterone, Estrogen, LRH Luteinizing hormones, SHGB,...
epithelial growth factor, insulin growth factor (receptors), fibroblast growth factor, transforming growth factor and other growth factors, ALL act in the brain to increase neuron and tissue plasticity/reorganization through endrocrinal hormones working on them.
Hormones through Growth Factor Receptors Control Cellular Remodeling/Reorganization (especially TGF, with a name like Transformation growth factor, this one is very implicated in cancers).

If telomerase can rejuvenate and increases brain volume, increases testicule volume and ovary output (by increases sex hormones), than there is a sexual hormones axis (testerone can be converted to estrogen via aromatase and estrogen receptors activate Telomerase; that's why women suffer greatly after menopause, their estrogen loss equals to telomerase loss from reduced estrogenic receptors sendin signals to telomerase to slow bp loss in telomeres). IGF communicate with testosterone and estrogen; they communicate with cellular reorganization and remodelling proteins in the brain that reorganize brain tissue to withstand aging.
Remember demented people have low IGF, IGF is a compensating survival signal to protect neurons and increase neurogenesis. Not only that, it rebuild skeletal muscle and dictates glycemia, metabolism (growth) and energy use. I don't need to tell all that DAF/IGF/Nrf2 iare conserved signals we now know that governs metabolism, antioxidants, Cellular Reorganization and aging.

In the future we will have to increase this period of plasticity and cellular reorganization to live long lives and make entire body rejuvenation.
I'm not saying we have to increase our peroid of puberty but in a sense I am...the later we hit puberty the Longer our cellular plasticity maturation process is extended, we have to be 'continously' be in this sort 'of cell morphing (adolescent juvenile -not yet an adult)' state where our cells and organ tissues continue to Replasticize, Rebuild, Remodel, Reorganize, Retransform, Remorph, Remutate themselves day in day out to a youth state (Reorganization IS a youth state Rejuvenation, pre-puberty and neoteny show that), so we avoid any damage residue retention.The danger will be excess transformation and tumorigenic neoplasticity following cancer formation and tissue damage.


Posted by: CANanonymity at December 7th, 2015 3:39 PM

Relevant to the discussion is this testimony, which was featured in a news article on a potential chronic pain treatment, that Reason pointed in his latest post:

“Our results reaffirm the clinical relevance of transgenic mouse models for human diseases,” says Professor Wood. “Studying the mice showed us what was going on in the nervous system that led to painlessness and our findings were directly translatable to humans, as confirmed by the painless patient. Without the work in transgenic mice, none of this would have been possible and we still wouldn’t know how to replicate the effects to help people suffering from chronic pain.”


My guess is that the professor specifically underlined the importance of using mice in this study, because as I recall, there has been a recent surge in questionning (yet another time?) the use of mice for experiments.

Posted by: Nico at December 7th, 2015 5:46 PM

Nico: Maybe it's due to the GMOphobia that is so pervasive in the lay people these days, particularly in Europe.

Posted by: Antonio at December 8th, 2015 12:49 AM

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