Scientists at the University of Innsbruck, Austria have explained an important developmental mechanism - the reason why the right hand's thumb grows on the left hand side, and vice versa.
Lead researcher Pia Aanstad, a molecular biologist at the university, this process depends upon the concentration of a signalling molecule called Hedgehog.
The researcher points out that this molecule controls the development of the extremities, the central nervous system, the teeth, eyes, hair, lung and the gastrointestinal tract.
"What is most remarkable: The cells are told what to do not only because the molecule is present but also by the different concentrations of the molecules in the tissue. The concentration of Hedgehog makes the thumb of the right hand grow on the left hand side and the thumb of the left hand grow on the right hand side," says Aanstad.
Considering the functions of Hedgehog, the scientists define it as a morphogen-a signal that is concentration-dependent and controls the pattern formation of an organism.
They say that a mutation in this signalling pathway induces dramatic and embryonically lethal malformations in the early developmental stage, such as the formation of just one central eye.
According to them, defects in the Hedgehog signalling pathway in humans are a cause for one of the most common birth defects-holoprosencephaly.
"Hedgehog genes are not new in evolution and the signaling pathway functions in the fly, mouse, fish and in humans similarly", says Aanstad.
She focuses on the zebra danio or zebra fish for her research work because their short developmental cycle enables her to observe the development of the small tropic fish in fast motion.
"We want to better understand how the cells process the signals of the signalling molecules and how they react," she said.
A research article on the current study has been published in the journal Current Biology.