US researchers have identified the gene, Atoh1, as vital in mice for their ability to recognise dangerous levels of carbon dioxide in the bloodstream. This study may provide clues to the genes involved in neonatal Sudden Infant Death Syndrome (SIDS) in humans, also known as cot death.
Professor Huda Zoghbi of the Baylor College of Medicine, Texas, USA, who led the study said: 'The death of mice [lacking Atoh1] at birth clued us in that Atoh1 must be needed for the function of some neurons critical for neonatal breathing, so we set out to define these neurons'.
The findings, published in the journal Neuron, showed deletion of the gene Atoh1 in mice from a subset of neurons called the retrotrapezoid nucleus (RTN) neurons, results in an impaired response to levels of carbon dioxide in the blood.
'This population of neurons resides in the ventral brainstem. When there is a change in the makeup of the blood, lack of oxygen or build-up of carbon dioxide, the RTN neurons sense that and tell the body to change the way it breathes', said Mr Wei-Hsiang Huang, a graduate student working on the project with Professor Zoghbi.
RTN neurons, located in the posterior part of the brain called the brainstem, respond to high carbon dioxide levels by sending a message to the respiratory centre of the brain. This triggers an increase in the rate of ventilation, which helps to flush out the excess carbon dioxide and increase levels of oxygen in the blood.
Using gene knockout studies in mice, researchers removed the Atoh gene in increasingly narrow regions of the brain, until they eventually identified the subset of neurons that had the most pronounced effect on the survival rates of young mice. Almost 50 percent of young mice born without the Atoh1 gene in their RTN neurons died at birth.
Their research showed that the protein produced by the Atoh
1 gene was vital in helping the RTN neurons orient themselves in the brainstem during
early development. This is critical to establishing a link with a part of the brainstem
known as pre-Bötzinger complex (preBötC), which is responsible for establishing a breathing rhythm in response to fluctuating levels of oxygen and
carbon dioxide in the blood, to ensure tissues receive sufficient oxygen.
'Without Atoh1 the mice have significant breathing problems because they do not automatically adjust their breathing to decrease carbon dioxide and oxygenate the blood', said Mr Huang.
Another recent study, led by Professor Lavezzi at the Lino University of Milan, Italy, investigating neonatal and prenatal infant deaths found defective RTN neurons in 71 percent of infants that died either of SIDS or sudden intrauterine unexplained death. These two studies, in combination, may offer insights to the genetic factors responsible for SIDS.