How does a fertilized 1-cell egg become a complex organism with billions of different cells (like us)?
Human egg cell (not to scale)
human body as drawn by Leonardo Da vinci
Recipe to make an animal from a fertilized egg: 1. Make more cells (cell division) 2. Make many KINDS of cells starting from 1 cell (differentiate - nerve cell, blood cell, skin cell, hair cell, muscle cell etc.) 3. Make the cells form tissues and organs at the right time and place (morphogenesis, organogenesis) 4. Make the various tissues and organs connect and function together in synergy to make a living animal !
How do we study these questions? We use “Model Organisms” such as the worm, C. elegans or the common aquarium fish, zebrafish.
Why do we use “model organisms”? Because they are simple, grow fast in laboratory conditions, and are easy to manipulate and observe. Its easy to do experiments with them (especially if they don’t talk back to you !)
What kinds of experiments can you do with these animals? -You can study the functions of genes: genetics and genomics -You can observe cells and tissues form as they happen in real time in a living animal, especially if parts are “labeled” with a visible marker, which emits light of a certain wavelength: cell & developmental biology -You can manipulate them in various ways: treat with specific substances (chemicals or mutagens): chemical genetics -You can physically manipulate them and see the outcome: mechanobiology -You can see how cells or tissues grow back after injury: Stem cells & regeneration Worm facts: Grows on compost has ~ 1000 cells, 1 mm long as adult, small C. elegans larva genome size (1/30 of humans), takes 3-4 days to
become an adult . Clear body, easy to see cells.
brain Fish facts: freshwater fish, vertebrate like blood humans, 70% genes similar to humans; 1 mm diameter egg, 3 months to become adult, rudiments of all organs in place by 24 hours ! Clear body for first day or so.
Normal zebrafish heart embryo at 24 h
What will you see today?
1) We did an experiment to determine the effect of alcohol on developing fish embryos. We treated eggs at 4 hours after fertilization with 2.4 % alcohol for 3 hours, and then removed the alcohol and grew the embryos in normal egg water (water with some salts). As controls we left the embryo in egg water throughout.
Which panel has the treated fish? Spot the differences and tell us.
2) Worms with neurons labeled with a green fluorescent protein. We will visualize different tissues/organs such as neurons in living animals with a powerful technique of genetic engineering that utilizes a green fluorescent protein (GFP) that was originally discovered in a jellyfish.