Miniscule monsters

by Tyler Shendruk

Published: Feb 9

The problem
Genomicists have a serious bias toward “model” organisms. Model organisms are species that have historically been well studied. Fruit flies, yeast, zebrafish, and mice are examples of model organisms. So are humans.
But these model organisms are each just some leaf on a random twig of the tree of life. Scientists are only beginning to realize the true extent of biodiversity and the staggering variety of differing genes and structures that make up genomes.

The researcher
Nicolas Corradi studies comparative genomics, which means that he sequences organisms’ genomes and then compares their genes and structure to those of other species. Corradi’s lab in the biology department at the University of Ottawa focuses on unicellular eukaryotes, single-celled micro-organisms that harbour curious genomes in their nuclei.

The project
Corradi’s favourite eukaryotes are microsporidia, parasitic unicellular fungi. These little monsters are highly adapted for infecting host cells. They are opportunistic bugs that steal everything they need to survive from their host. In fact, the only time microsporidia spend outside of a host cell is as spores, scouring to invade other cells.

The key
Corradi sequenced the genome of the microsporidia Encephalitozoon intestinalis. This particular microsporidia has the smallest nuclear genome of any known organism. It is made of only 1,800 genes (1,500 times smaller than the human genome and 20 per cent smaller than the next smallest genome ever sequenced).
Why do they have such small genomes? Because these microsporidia are marauding picaroons. They don’t do anything they don’t have to. They steal so much from their hosts that they have shed every gene but the bare minimum needed to function.
Evolutionarily speaking, it is easier to lose genes than to gain them, so these microsporidia are extremely adapted for their parasitic lifestyle. Their genome is so compact that Corradi believes it may represent the limit for a fully functional genome.

Fishy neurons

by Tyler Shendruk

Published: 10/6/10

The problem
PARKINSON’S DISEASE (PD) deteriorates a patient’s central nervous system and debilitates motor skills. Doctors don’t know the cause of 90 per cent of PD cases, but better understand the source of the other 10 per cent. Heredity and genetics are the culprits in this type, called early-onset PD.
Surprisingly, the genes associated with PD are found in all kinds of life forms, including mice, yeast, and zebrafish. These genes play an important role in the special cells that control body motion and make dopamine, an indispensable chemical needed to transmit signals between neurons—these cells are called dopaminergic neurons.

The researcher
Marc Ekker, a biology professor at the U of O, works in the Center for Advanced Research in Environmental Genomics to better understand the genetics of PD. Ekker genetically alters zebrafish, whose genes are simpler than those of humans and can be associated with the disease, in order to further study the causes of PD.

The project
Since zebrafish are transparent, Ekker is able to genetically alter their neurons to fluorescent, enabling him to watch the destruction and regeneration of the dopaminergic neurons in the fishes’ brains while they are alive. He can therefore destroy individual neurons with a laser blast, poison, or alternatively, he can genetically block the gene altogether, making it inactive for the fishes’ entire life—essentially giving the zebrafish PD.

The key
Ekker looks at the genetically altered neurons in the brain and studies what they are doing to the fishes’ motion. Fish larva whose dopaminergic neurons are destroyed have very limited motor skills, and young fish without dopaminergic neurons will not respond with evasive motion when gently poked. Ekker’s zebrafish share the same symptoms as PD patients. Zebrafish, however, can regenerate the neurons. We can’t.
They can do this because of stem cells. Stem cells are different from common cells because they aren’t committed to becoming any one type such as a blood cell or a neuron. While humans have only a limited number of stem cells, zebrafish make stem cells throughout their entire life. The fish can draw on their bank of stem cells to replace the neurons.
Lucky fish.