Most cells in our bodies contain 46 separate long DNA strings that spend most of their time in what appears to be a tangled mess – in a sort of round shape we know as the nucleus. Then lo and behold, these long strings fold up and become chromosomes. Why do they do that?
Bill Earnshaw’s lab at Edinburgh University does some amazing work with chromosomes and cell division. He can explain very elegantly why we need chromosomes.
The DNA makes a copy of itself before the cell divides into two. The chromosomes help make sure each new daughter cell gets an identical copy of this DNA. It’s easier to divide tangled strings into two if you untangle them and roll them up into balls first
Here are some photos from the Earnshaw lab of the chromosomes during cell division.
In the photo above the chromosomes are lining up along the middle of the dividing cell (the “equator” or “metaphase plate”). When they’re all lined up correctly (this stage is “metaphase”) the next stage can start:
The photo above shows the blue chromosome halves (after the doubled-up chromosomes have split in two) separating along the green spindle fibres (this stage is “anaphase”). Each set of chromosomes will belong to one of the two new daughter cells. If this happens correctly both new cells have identical sets of DNA. This whole cycle of chromosome growth and division is called “mitosis”.
DNA carries genes that make up the blueprint that’s responsible for making every cell, every tissue, every organ work correctly. So it’s important we have the right set of genes.
Cells divide a lot – millions of our cells divide every minute so it’s important that the DNA is shared precisely each time. Mistakes can cause the new daughter cells to misfunction. These cells can become cancerous or produce babies with genetic disease. Usually the cell watches out for these mistakes and self-destructs. But not always. Research helps us understand these processes, how they can go wrong, and work out ways to prevent or fix these mistakes.
Cross-posted to Fireside Science at SciFund Challenge.
Carl Sagan was an astronomer and academic, best known for popularising astronomy. He hosted and co-produced the original hugely popular series Cosmos: A Personal Voyage. Its sequel Cosmos: A Spacetime Odyssey was released this year. Even though I’m a biologist at heart I was fascinated by the original Cosmos.
Sagan was diagnosed with a myelodysplastic syndrome (MDS) and died at the age of 62, in 1996. In interviews near the end of his life he discussed myelodysplasia and said he was hopeful he’d been cured. He died at the Fred Hutchinson Cancer Research Center of pneumonia after his third bone marrow transplant, a complication of this illness.
Most people with a diagnosis of MDS won’t have heard of it before. MDS is a group of bone marrow diseases. It’s at least as common as or more common than leukaemia but older people have a higher risk – perhaps one in 2,000 over the age of 60. A third of people with MDS will develop leukaemia. The 14th July, 2014, is the Leukaemia Foundation of Australia‘s second National MDS Day . One of the aims of MDS Day is to raise awareness of MDS.
Sagan’s illness was an opportunity to popularise MDS, but look how the cause of his death was described in these TV news reports.
In these news stories he was said to have died from a complication of “a rare blood disorder that led to cancer”, or “a blood disease”, “a bone marrow disease”, and even a” bone cancer” – the name of his disease was avoided.
Myelodysplasia literally means abnormal bone marrow cells. Blood cells are made in the bone marrow. In MDS the immature bone marow cells are abnormal and don’t mature properly. So the blood doesn’t have enough normal blood cells to do its job effectively. The blood is made of a number of different types of cells and the different types of MDS relate to the type of abnormal cell. MDS is often associated with a recognised chromosome abnormality, and identifying these chromosome abnormalities can help with diagnosis, treatment and prognosis. Therapy-related MDS is a specific type of MDS caused by treatment for a previous unrelated cancer and it usually has a poor outcome and very abnormal chromosomes.
MDS research has been neglected but has picked up recently. Some of the recent progress includes work by Carl Walkley and Louise Purton at St Vincent’s Institute in Melbourne, Australia.
MDS has had a history of name changes that seems to have made the meaning of its name less clear, except to medically trained people. This hasn’t helped improve public awareness of MDS. It was first named Di Guglielmo Syndrome in 1923 after its discoverer, then became refractory anaemia, then preleukaemic anaemia, preleukaemic acute human leukaemia, preleukaemia, and finally in 1976 the French-American-British Co-Operative Group of haematologists named it myelodysplastic syndromes. This recognised that it’s a group of related diseases and that not all cases will go on to develop into leukaemia.
Pathologist Ed Uthman, thinks Sagan’s Disease would be a better name for myelodysplastic syndromes – both as a tribute to Carl Sagan and a name that would mean more to most people than myelodysplastic syndromes. Maybe he has something. Plenty of syndromes and diseases are named after people who studied them. Down Syndrome would have to be the best known example. Have you heard of amyotrophic lateral sclerosis? Motor neurone disease? Lou Gehrig’s disease? The first name is probably a nice technical description of the disease, but I’m guessing you’re more likely to have an idea of what the disease is from one of the last two names, because they’re used in popular media and are connected in the public eye with famous sufferers – Stephen Hawking and Lou Gehrig. (Ed Uthman also think’s Lou Gehrig’s Disease should be “Hawking’s Disease”.)
I’ll let Carl Sagan have the last words on popular (mis)understanding of science (extract from Wikiquote).
We live in a society absolutely dependent on science and technology and yet have cleverly arranged things so that almost no one understands science and technology. That’s a clear prescription for disaster.
Every kid starts out as a natural-born scientist, and then we beat it out of them. A few trickle through the system with their wonder and enthusiasm for science intact.
This is the opening title of Paper Thin. Yesterday was the last day of filming and I got a look at some of the Director/Producer Elizabeth Duong‘s work. It’s exciting – this will be a touching but beautiful film. It’s based on a true story of a girl called Sadako who developed leukaemia after exposure to radiation in Hiroshima.
One of the hallmarks of leukaemia that’s caused by radiation or toxic chemicals is very rearranged chromosomes. I’m working on unravelling the patterns and causes of the very disorganised genetics of this type of leukaemia (known as therapy-related acute myeloid leukaemia).
Sadako hoped for a cure. My hope is that with the help of this film this research can continue and realise her dream for future leukaemia patients. A big thank-you to Elizabeth and all her helpers, who have given their time freely. A special mention also to Daniel Hernandez who composed the original soundtrack. It’s awesome. Here we have Essendon Symphony playing the opening theme and I think that’s Daniel playing over the stings.
Chromosomes and Cancer 