By IANS,
New York : A new study has found why birds lack a heat-generating tissue present in mammals – and concludes that the absence of this tissue may have led to the extinction of dinosaurs.
All mammals have two kinds of adipose tissue — white and brown fat. White fat is used for storing energy-rich fuels, while brown fat generates heat.
For instance, hibernating bears and human infants have a lot of brown fat relative to their body size. This allows bears to sleep for six months and protects infants from hypothermia.
Clinicians would like to find ways of making adult white fat behave more like brown fat so that we could burn, rather than store, energy.
While most mammals have a key gene called UCP1, which is responsible for the heat-generation function of brown fat, birds do not.
Researchers at New York Medical College found they could induce a specific type of stem cell in chicken embryos to produce differentiated cells that are structured and behave like brown fat.
These chicken cells could even activate a UCP1 gene if presented with one from a mouse.
The ability to produce brown fat evolved in a common ancestor of birds and mammals, but the ability to generate heat was lost in the group that gave rise to birds and lizards after it separated from the mammalian lineage.
This strongly implies that dinosaurs, which diverged from birds even later than lizards, also lacked brown fat.
The paper titled ‘The brown adipocyte differentiation pathway in birds: an evolutionary road not taken’ has been published in the latest issue of the journal BMC Biology.