No food, yet larvae reach within and develop

Dr. Gaiti Hasan (right) and Dr. Megha observed that when even when starved of food, fruit fly larvae managed to develop into pupae  

Seeking to understand the development of young ones in nutrition-starved conditions, Dr. Gaiti Hasan and Dr. Megha of National Centre for Biological Sciences (NCBS), Bengaluru, have studied fruit flies (Drosophila melanogaster) and discovered a very interesting phenomenon. Brain development in Drosophila larvae under conditions of starvation is supported, in the absence of adequate supply of nutrients, by an alternate “pathway.” The results will soon be published in the journal Development. In their experiments, the researchers focussed on neuroendocrine cells (NE cells). These are neurons, or brain cells, that secrete certain hormones that activate other cells to produce proteins that govern vital function. They observed that when developing larvae of Drosophila were starved, they continued to proliferate. This led them to question whether Drosophila possessed alternate ways of ‘weathering” this nutrient-deficient stress.

“How a developing animal deals with nutritional loss is an interesting question academically as well as from a public health perspective — poor maternal nutrition [implies] a growing foetus gets less nutrition,” says Dr. Megha the lead author of the paper in an email to this correspondent. In fact, there is a phenomenon, known as brain sparing that is taking place here. This has been known since the 1970s — while reduced nutrition during pregnancy results in overall smaller-sized babies, the brain’s development is not compromised to that extent. While this makes sense, as the brain is needed to help the organism as a whole survive, why this happens is not understood.

“Our work is a small contribution to understanding this process [how the brain develops in these conditions in Drosophila], and it is hoped that it might inform human developmental studies,” says Dr. Megha.The research shows that there exists an alternative to the “pathway” that triggers protein production in the cells. A pathway is a series of steps that allow cells to convert external information into internal action. It typically acts to amplify a specific signal.

Two pathways

In this case, the researchers found two pathways: In the first case, nutrients, such as amino acids and sugars, are the external signal that is sensed by the insulin receptor (InR) and then conveyed by various steps along the pathway, to finally tell the cell to make more protein. In the second pathway, small molecules bind a cell surface protein called G-protein coupled receptor. One of the pathways activated by this is the IP3R (Inositol1,4,5-trisphosphate receptor) Ca2+ signalling pathway. IP3R acts by releasing calcium ions from the endoplasmic reticulum within the cell. This takes the level of calcium ions in the cells much above normal levels: “Calcium ion concentration in the cytosol is kept deliberately very low. So, when calcium ions are released, many enzymes in the cytosol, which were hitherto inactive, become activated and can now further potentiate the change by affecting other proteins,” she explains. That IP3R can stimulate protein synthesis is itself a new finding from this research. Also, the finding that when the cell gets enough nutrition, this pathway is turned off and becomes active only when needed. Thirdly, it also shows that the effect of IP3R on neuroendocrine cell protein synthesis affects the protein metabolism at the level of the whole organism.

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Printable version | Oct 16, 2021 1:03:40 AM |

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