An image of one of the mosaic brains of mouse embryos created at the TIFR, Mumbai

New Delhi, Jan. 20: Indian and US research teams have pinpointed a gene that creates the cerebral cortex, the part of the brain involved in higher functions like language, complex thinking and memory.

The scientists at the Tata Institute of Fundamental Research (TIFR), Mumbai, and the University of California, Irvine, have also provided the first clues to the genetic machinery that gives rise to the hippocampus — the brain’s memory centre.

In experiments on mouse embryos, the researchers have shown that a gene named Lhx2 nudges embryonic brain cells to turn into the cerebral cortex.

“It’s humbling to see how the enormous complexity of the cerebral cortex arises from such a simple step,” said Shuba Tole, the head of the team at the TIFR.

In their experiments, the TIFR researchers created mouse embryos with mosaic brains — containing some cells with Lhx2 gene turned on and some cells in which it is off.

They found that embryonic brain cells with Lhx2 turned on transformed into the cerebral cortex. And the cells with Lhx2 turned off secreted molecular signals that prompted their neighbouring cells to turn into the hippocampus, the structure that records all memories — from faces of friends to ice cream flavours.

Although the TIFR team and the California university researchers worked independently, they decided to merge their findings and present them to the world in a joint paper that appeared in the journal Science on Friday.

In the mosaic brains, islands of hippocampus grew next to the clusters of cells in which Lhx2 was turned off. While a normal brain has two hippocampi — one in each half of the brain — some embryos ended up with five hippocampi.

Tole cautioned that more hippocampi did not necessarily mean greater memory potential. “The extra hippocampi are probably created at the expense of cerebral cortex tissue that would have otherwise handled functions such as perception, decision-making or learning,” she said.

In any case, the mosaic brain embryos do not last the full term.

Although the experiments deal with the basic biology of brain formation, the researchers believe it could have spinoffs in medicine, specifically in understanding better brain disorders involving the hippocampus.

“The new understanding of Lhx2’s role can potentially be used in stem cell research to grow new cortical neurons that can replace damaged ones in the brain,” said Ed Monuci, the team leader at Irvine.

Monuci’s team showed that Lhx2 activity was critical only during the stage when the developing cortex is made up of stem cells — neither before nor after.