It's probably the first thing you ever did by yourself, but how did you know what to do? It's long been a mystery how newborn mammals draw their first breath after life in a fluid-filled womb – and more importantly why this mechanism fatally fails in some individuals.
Xavier Caubit from CNRS (National Centre for Scientific Research) in Marseille, France, and colleagues knew that mice that don't have the Teashirt 3 gene (Tshz3) fail to breathe at birth and so die.
"Initially we suspected that the Tshz3 mutant embryos might have some defects in lung smooth muscle," says co-author Laurent Fasano, also from CNRS. But the researchers soon realised the problems in fact lie in the brain cells that tell muscles involved in breathing what to do.
There are two areas in the brain known to be key for breathing. The first is a set of cells responsible for controlling muscles that open the airways and move chest muscles. The second is the respiratory rhythm generator (RRG) – a kind of pacemaker that produces an oscillating rhythm in the brainstem and controls autonomous breathing.
To test what happens to these brain areas in Tshz3 mutant mice, Caubit and his team examined the brains of mouse embryos lacking the gene at the later stages of development to see whether they were developing normally.
"We expected that some neurons could be missing," says Fassano. In fact, the RRG neurons were present, but hadn't developed properly.
"That absence of rhythmic activity [due to the faulty RRG neurons] correlates with inability to breath at birth," says Fassano. What's more, without Tshz3, brain cells responsible for the control of the upper airways were being killed off in the days before birth.
"The really interesting thing about this research is that a single gene seems to be essential for a key component of the complex neural networks that regulate breathing," says Jeremy Ward, a respiratory cell physiologist from Kings College London who wasn't involved in the research. But can this help us to understand breathing defects in people better?
Fasano hopes so, because humans have Teashirt 3 too. This optimism is shared by paediatrician Aaron Hamvas, of Washington University in St Louis, Missouri. "Disturbances in respiratory patterns, predominantly in the form of apnoea, are seen in most premature babies and some full-term babies. Knowing the genetic basis for these types of problems will permit development of diagnostic tests and ultimately therapeutic interventions."
Journal reference: The Journal of Neuroscience, DOI: 10.1523/jneurosci.1765-10.2010
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