Bombyxin: The Silkworm's Insulin

An Insect With Insulin

Bombyxin is a family of insulin-like peptides produced mainly in the brain of the silk moth — and the resemblance to vertebrate insulin is not a loose analogy. It is a structurally related molecule doing a structurally related job.

Nearly forty genes encoding bombyxin have been identified in the Bombyx mori genome, which is a lot for one peptide family and suggests it does more than one thing.

What It Does

Bombyxins are secreted by brain neurosecretory cells and regulate nutrient-dependent growth and metabolism. In practice that means linking how much the animal has eaten to how much it grows — the same fundamental problem insulin solves in us.

One demonstrated effect: bombyxin increases the respiration rate by facilitating carbohydrate breakdown. Signal arrives, metabolism speeds up, sugar gets used.

Why It Was Found Here

Because the silkworm was already the animal in which brain secretory peptides were being characterised. PTTH, the hormone that triggers moulting, came out of the same body of work — researchers going through silk moth brains looking for what they secrete.

Bombyxin was in fact first encountered during that search, which is a reminder of how these things go: you look for one hormone and find a second doing something else entirely.

Why It Matters Beyond Insects

Insulin-like signalling turns out to be deeply conserved, running from insects to mammals and governing growth, metabolism and lifespan across enormous evolutionary distance. Finding a working insulin-like system in a moth was part of establishing that.

There is also a practical afterlife: the bombyxin signal peptide — the molecular tag that tells a cell to secrete a protein — is used in biotechnology to get other proteins secreted correctly, which ties directly to using silkworms as protein factories.

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