Darwinism: All of Us (Including Nematodes) Share a Common Ancestor

Charles Darwin (1809-1882), a British naturalist, started his historical five-years voyage on HMS Beagle in 1831 along the coastline of South America, comparing thousands living things (a variety of animals and plants) to find both their similarity and difference.

His classic 1859 book "On the Origin of Species" established evolution by common descent as the dominant scientific explanation of diversification in nature. Since then Darwin became the champion of "lateral thinking" who broke the pre-existing "artificial" wall in our mind (which was a mere "prejudice") dividing human beings and the rest of living things on this earth.

In fact the DNA sequence data in 20th century confirmed his revolutionary insight: human beings and monkey share more than 99% sequence identity in almost all genes. For instance the proto-onco protein RAS is 100% identical among all mammals from mouse to human. All of us are closely related to each other at the molecular levels!

Similarity and difference among living things
However, we should point out that there is a huge difference between bacteria and eukaryotes (organisms carrying nucleus, from yeasts to human beings or plants). Unlike all eukaryotes including yeasts, no bacteria has RAS gene.

Also there is a substantial (fundamental) difference between bacteria and viruses. Unlike bacteria or eukaryotes, no virus can propagate itself. Each virus needs either bacteria or other organisms as a host to replicate itself.

Thus, biomedically the Darwnism should be applied only among all eukaryotes in terms of their similarity (closeness). In other words, yeasts could be used as a model of human beings to study a variety of biological phenomena at the molecular levels. For instance, activation of RAS gene renders both yeasts and human beings to be very sensitive (intolerant) to heat shock treatment.

The main reason is that RAS activates another enzyme called PAK that in turn suppresses the production of a heat shock protein called Hsp16 that is responsible for heat resistance and longevity. Thus, eukaryotes with the lower RAS or PAK activity can handle much better the "global warming" to live much longer. In other words the pressure of "natural selection" would work in favor of lower RAS/PAK eukaryotes when the temperature of this earth keeps rising.

However, there is a fundamental difference between yeasts and plants or mammals including human beings. Yeasts are mono-cellular organisms, while mammals and plants are multi-cellular organism in which the cell-cell interaction plays an important role for the regulation of their growth and differentiation.

Of course, animals and plants differ significantly in terms of their behavior. Unlike animals which have both muscle and nerve, plants have no neuro-muscular systems by which they can move from one spot to another when they sense that their environment turns out to be unfavorable for their life. Interestingly, however, plants in particular trees such as Bristlecone Pines in California can live far longer than animals such as human beings in general, probably because the former could save a lot of energy that the latter have to use for hunting around and digesting foods.

In vivo (the whole animal) models

Conventionally, when we find a new chemical compound or natural product which selectively kills cancer cells, but not normal cells in vitro, we have to test its therapeutic effect in vivo, on human cancer xenografts in nude/scid mice, before we shall start its time-consuming clinical trials for cancer patients to test both its safety and efficacy, in an attempt to obtain the approval from FDA for its future marketing/ commercialization.

The main reason is that mouse (weighing around 20 g) is the smallest among mammals, and unlike "heterogeneous" human individuals, cloned mice such as nude (immuno-deficient) mice are genetically identical ("homogeneous") and accept tumors even from foreign species such as human beings. However, nude mice are very expensive (costing $50 per mouse) and each test using xenograft in mice often takes several months, depending on the growth rate of each tumor.

For these reasons, more than a decade ago, a group of progressive molecular biologists started studying the behavior of tiny short-lived animals (invertebrates) such as fruit flies (Drosophila) and nematodes (C. elegans) as an in vivo model of human beings for establishing a quick and inexpensive drug screening system to develop/identify a variety of synthetic or natural products which are potentially useful for the therapy of cancers and other formidable diseases.

Like mouse, these tiny animals also have both oncogenic RAS (GTPase) and PAK1 (kinase) as well as their down-stream targets such as tumor suppressors FOXO and Hsp16. The oncogenic RAS/PAK1 signaling pathways inactivate these tumor suppressors in both mammals and these tiny creatures, causing a variety of tumors and premature death (shortening their life-span). In other words, using these tiny invertebrates, we can screen for drugs that block selectively the function of either RAS or PAK1 in vivo.

For instance blocking PAK1 in nematodes of only 1 mm long leads to a drastic reduction of litter size (number of eggs they lay is reduced to almost 10%). Just like anti-PAK1 drugs, ivermectin dramatically reduces the litter size at sublethal concentrations, hinting that this drug also blocks PAK1. Further, to automate this nematode drug screening system, we are taking a unique approach to quantify the kinase activity of PAK1 in this transparent worm.

Reporter "GFP" Expression for Drug Screening
For instance, there is a transgenic worm called CL2070 which produces the fluorescent protein "GFP" under the control of the Hsp16 promoter. Since PAK1 inactivates the transcription factor FOXO which normally activates Hsp16 promoter, PAK1 normally silences (suppresses) the production of GFP in CL2070. However, when this worm is treated overnight by anti-PAK1 drugs such as CAPE (caffeic acid phenethy ester) and ARC (artepillin C) from propolis, the whole worm becomes intensively fluorescent, due to the massive production of GFP. In other words the most potent anti-PAK1 drug would produce the strongest fluorescence in this worm.

Using FK228, the so far most potent PAK1 blocker, and a few other anti-PAK drugs, it has recently been established that PAK1 is essential not only for the growth of more than 70% of all human cancers (including breast and prostate cancers) and NF tumors, but also for the progression of several other diseases such as Alzheimer's, AIDS (HIV infection), arthritis, asthma, epilepsy, an autism called Fragile X syndrome, and malaria.

Thus, these tiny invertebrates such as nematodes could serve the powerful (quick and inexpensive) automated screening system for identifying a new generation of anti-PAK1 drugs which would be useful for the treatment of these PAK1-dependent diseases in the future. Unlike mammals, these invertebrate models clearly lack both bone and blood circulation system as well as immune system. However, so far there is no evidence suggesting that these anti-PAK1 drugs have any side effect on these "vertebrate" systems in either mice or human beings, except for angiogenesis (blood vessel formation) which is required for both the rapid growth of solid tumors and the development of embryos in mothers' womb.

The "Darwinism" born almost 150 years ago is now about to open a new era for the automation of drug screening based on the unique signal transduction system which is shared by these tiny creatures and us (human beings).

To be continued.