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Researchers found in studies with mice, that the cells lining our middle ear cavity
originated from two different tissue types – 'endoderm' and 'neural crest' cells.
The part of the lining that originated from the endoderm is covered in cilia (hairs) that
help clear debris from the ear. But, the lining made from neural crest cells has no cilia,
making that part less efficient at cleaning itself, and susceptible to infection.
The process of the middle ear transforming into an air-filled space during development is different in birds and reptiles, which have just one little ear bone. Mammals may have evolved this new air-filled space to house our additional bones.
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'Evolutionary glitch' possible cause of childhood ear infections
Researchers at King's College London have uncovered how the human ear is formed, giving clues as to why children are susceptible to infections such as 'glue ear' or build-up of fluid in the middle ear chamber.
Researchers at King's College London have uncovered how the human ear is formed, giving clues as to why children are susceptible to infections such as glue ear. The work was funded by the UK Medical Research Council and published today in the journal Science.
It is estimated that one in five children around the age
of two will be affected by glue ear, a build-up of fluid
in the middle ear chamber.
This part of the ear contains three tiny bones that carry
sound vibrations from the eardrum to the inner ear.
When fluid builds up in the chamber, this prevents the
three bones from moving freely so they cannot pass sound
vibrations to the inner ear, causing temporary hearing loss.
Until now, little was known about why some children appear
much more prone than others to developing chronic ear
problems, with repeated bouts of 'glue' ear.
Carrying out studies in mice, scientists have discovered the cells that line the middle ear cavity originate from two different tissue types – 'endoderm' and 'neural crest' cells. The part of the lining that originates from the endoderm is covered in a lawn of cilia (hairs) that help to clear debris from the ear, but the lining derived from neural crest cells do not have cilia. This makes that part of the middle ear less efficient at cleaning itself, leaving it susceptible to infection.
Interestingly, the process of the middle ear transforming into an air-filled space during development appears to be different in birds and reptiles, which have just one little ear bone. Mammals may have evolved this new mechanism for creating an air-filled space to house the additional bones. This indicates that the process of two distinct cell types to create the lining of the middle ear cavity may be linked to the evolution of the three tiny sound-conducting bones.
"Our study has uncovered a new mechanism for how the
middle ear develops, identifying a possible
reason for why it is prone to infection.
The process of neural crest cells making up part of the
middle ear appears fundamentally flawed as these cells are
not capable of clearing the ear effectively.
While this process may have evolved in order to create
space in the ear for the three little bones essential for
hearing, the same process has left mammals prone
to infection – it's an evolutionary glitch.
These findings are contrary to everything we thought we
knew about the development of the ear – in all the
textbooks it describes that the lining of the middle ear
is made of endodermal cells and formed from an extension
of another part of the middle ear – the Eustachian tube.
The textbooks will need to be re-written!"
Dr Abigail Tucker
Department of Craniofacial Development
King's College London's Dental Institute
King's College London
King's College London is one of the top 30 universities in the world (2011/12 QS World University Rankings), and the fourth oldest in England. A research-led university based in the heart of London, King's has more than 25,000 students (of whom more than 10,000 are graduate students) from nearly 140 countries, and some 6,500 employees. King's is in the second phase of a £1 billion redevelopment programme which is transforming its estate.
King's has a particularly distinguished reputation in the humanities, law, the sciences (including a wide range of health areas such as psychiatry, medicine, nursing and dentistry) and social sciences including international affairs. It has played a major role in many of the advances that have shaped modern life, such as the discovery of the structure of DNA and research that led to the development of radio, television, mobile phones and radar. It is the largest centre for the education of healthcare professionals in Europe; no university has more Medical Research Council Centres.
The Medical Research Council has been at the forefront of scientific discovery to improve human health. Founded in 1913 to tackle tuberculosis, the MRC now invests taxpayers' money in some of the best medical research in the world across every area of health. Twenty-nine MRC-funded researchers have won Nobel prizes in a wide range of disciplines, and MRC scientists have been behind such diverse discoveries as vitamins, the structure of DNA and the link between smoking and cancer, as well as achievements such as pioneering the use of randomised controlled trials, the invention of MRI scanning, and the development of a group of antibodies used in the making of some of the most successful drugs ever developed. Today, MRC-funded scientists tackle some of the greatest health problems facing humanity in the 21st century, from the rising tide of chronic diseases associated with ageing to the threats posed by rapidly mutating micro-organisms. http://www.mrc.ac.uk
The MRC Centenary Timeline chronicles 100 years of life-changing discoveries and shows how our research has had a lasting influence on healthcare and wellbeing in the UK and globally, right up to the present day. http://www.centenary.mrc.ac.uk
Original article: http://www.eurekalert.org/pub_releases/2013-03/kcl-gp032013.php
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