Human beings can never truly be alone. Even when apart from other humans, we still share our body with trillions of microorganisms. In fact, there are likely more non-human cells in your body than there are human cells; the most recent estimates of that ratio approximate that you have three non-human cells in our body for every human cell. This complex system of microbial organisms living inside us is referred to as the microbiome. Some of these bacteria live in your mouth or on your skin, but a majority of them (around 100 trillion or so) live in the gastrointestinal tract. Most of these are beneficial, and include bacteria such as Bacteroides fragilis, Helicobacter pylori, Lactobacillus casei, and Lactobacillus reuteri. This gut microbiome can have far reaching impacts on the human body. Imbalances in the composition of the gut microbiome, or “flora,” have been shown to impact the immune system, metabolism, digestion, and even brain function. This means that, in addition to obvious things like intestinal diseases and infections (such as CDI, or Clostridium difficile infection, which can occur when overuse of antibiotics kills off so much beneficial gut bacteria that the toxic C. difficile can spread rampantly), imbalances in gut flora can also lead to things like depression.
In the 1960’s, two researchers in London were investigating why diseases like scrapie and Creutzfeldt–Jakob disease (CJD) resisted ionizing radiation. What they hypothesized was that these diseases were caused by proteins, rather than a biological agent. However, it wasn’t until the 1980’s that these hypothetical proteins, dubbed prions, were isolated and purified. Prions are proteins that can fold in multiple structurally distinct ways. These folds can be transferred to other prion proteins, and this propagation results in diseases similar to bacterial infections. In addition to scrapie and CJD (a human disease that causes brain tissue to rapidly decay, leaving the brain with a sponge-like texture), prions are also suspected as the cause of bovine spongiform encephalopathy (BSE, a.k.a. “mad cow disease”).
Currently, all of the known prion diseases in mammals target either the brain or neural tissue. Since prion proteins are able to transfer their folded state to normal versions of the protein, treatment methods for prion disease would involve denaturing the proteins: un-twisting them back into their natural state so that they are no longer able to induce folding of other proteins. However, a practical method to do this doesn’t currently exist, so prion diseases are untreatable – and always fatal.
In 1963, Dr. Sydney Brenner, a South African biologist, went looking for a model organism to advance the study of biological development, specifically targeting the nervous system. What he found was Caenorhabditis elegans, or C. elegans for short. C. elegans is a small, free-living (i.e. non-parasitic) roundworm. Dr. Brenner chose C. elegans to be the model organism since it is one of the simplest organisms with a nervous system. The nervous system of every C. elegans specimen contains exactly 302 neurons, and this consistency between individuals makes them perfect for study. Studies with C. elegans have also branched out to include other fields such as embryogenesis, sex determination, and larval development. Research using C. elegans has led to discoveries in areas such as programmed cell death (a.k.a. apoptosis, which is an important process in the study of diseases like Leukemia), RNA interference, nicotine addiction (worms respond to nicotine similarly to the way mammals do), ageing research, and space research including zero gravity effects on development, muscle atrophy, etc.
C. elegans has a lot of characteristics that make it desirable for research in general. The specimens are small; they measure about 1 millimeter in length. They eat bacteria (such as E. coli), so they can be easily grown on agar plates with up to 10,000 worms on a single petri dish. Most adult C. elegans specimens are hermaphroditic, and each hermaphroditic worm can produce 300-350 offspring, so breeding for specific mutations can be done relatively easily. They also have short development times (3 days from egg to adult) and life spans (2-3 weeks), so studying genetic effects across generations is possible over short time periods. C. elegans can also survive while frozen in liquid nitrogen, making long-term storage of specific mutations possible for future studies.
Many rodents are nocturnal. However, even rodents that are active during the day tend to prefer darker areas. Most rats, for example, have adapted to be accustomed to spending daylight hours largely sheltered from light sources. This makes lighting control in habitats used for rodent research an important variable to be considered. However, lighting control encompasses more than just light intensity. Things like the duration of exposure, pigmentation of the animal, age, species, and sex of the animal are just some of the other factors that need to be considered. Additionally, many rodents used in research applications are albino, which makes them more susceptible to light than other varieties. Because of this, albino rodents have been used in establishing baselines for illumination levels.
So what light levels are appropriate for housing rodents? According to the US National Research Council’s Guide for the Care and Use of Laboratory Animals, the light experience of each animal can affect its light sensitivity, but in normal cases light intensity at the cage level should be between 12 and 30 foot candles (130-325 lux). The normal fluorescent bulbs in our Rodent Incubators produce light intensity between 80-100 foot candles (860-1080 lux) at the cage, which is quite strong. A glass door in the incubator (with no timed light control) could allow the room lighting to provide the correct illumination, but we wanted to provide a better option for researchers looking for less intense, and timed, lighting within the chamber. Powers Scientific now offers dimmable light covers on our Rodent Incubators. These light covers are plastic bulb sleeves with graded black striping to block some of the light emitted. The striping changes in density around the cover so that as the covers are rotated around the bulb, more or less of the light is blocked depending on the direction you twist it. With the light covers mounted, light intensity inside the chamber is reduced to 10-40 foot candles (105-430 lux), depending on how the covers are oriented. With these light covers, our chambers are capable of providing low-intensity lighting conditions for many applications.
“Complexity that works is built up out of modules that work perfectly, layered one over the other.”
– Kevin Kelly
Living creatures are almost incomprehensibly complex. Take the human body, which is made up of trillions of cells creating thousands of different parts. Our mass of interconnected systems, and indeed the complex biological systems of many members of the animal kingdom, have slowly built up over the course of millions of years as life forms have grown in complexity and adapted to become more specialized. One of the reasons that these forms of life have been able to become so elaborate is that their cells are capable of determining their location and orientation within the body. This ability for cells to know where they are in the body leads to an evolutionary advantage: it allows for the creation of elaborate, non-symmetrical systems.
While the details of living organisms have changed massively in the past half-billion years, one thing common to most of them hasn’t changed very much at all: the genetics that control the process of orienting cells in consistent directions within the body. In March 2016, Scientific American ran an article discussing how scientists are experimenting to determine how these genes work. These “polarity genes” originally evolved five hundred million years ago and haven’t changed much in the interim. They cause certain proteins in cells to work a lot like magnets. Within each cell, these proteins push each other apart to opposite ends of the cell. Between the cells, the same proteins that repel each other within a cell experience an attraction, pulling the opposite protein from adjacent cells towards them. The ultimate effect of this is that, locally, the cells become oriented with all the proteins of one type lined up on one side of the cell, and all proteins of the other type lined up on the opposite side. This effectively creates a sort of compass for the cells and allows the establishment of a common directionality.