Why my father's brain is like a silkworm pupa

Last February, my father went into a coma for several hours as the result of a stroke. He was not expected to survive and I had to say good-bye to him over the phone. Then, the next morning, as we were on our way to see him, my brother rang me on my mobile. 'He's a little better.' he said.

When we arrived at the hospital we were surprised to be shown into the main ward, and even more surprised when a voice called out to us. My father was sitting up in bed - a bit confused but perfectly lucid. Over the next few days he recovered completely. In fact he seemed to me to have more than recovered, he seemed to be more alert and more fluent than he had been before. 'Better than ever.' I'd tell people, but not really believe it, but it really did seem that my father's brain had somehow been rejuvenated by the stroke.

Recently I read that this could be true. When the brain is damaged by a stroke there is evidence that stem cells are produced and these differentiate into the types of cells required to repair the damage. The way this might happen is for 'mature' cells (which have long been differentiated into specialised brain cells like neurons) revert back to unspecialised stem cells that can change into anything that is required.

A similar discovery was found in insect pupa which was reported in this paper in Nature in August last year. When a larva (like a silkworm) changes into a pupa most of its cells die and inside the shell of the pupa is a sort of 'gloop' with islands of special sorts of cells called imaginal cells.

Until last year it was thought that the adult insect (in this case, the moth) is formed from clumps of imaginal cells, which like stem cells can turn into anything that is required. These imaginal cells are inactive in the grub but become activated when the larva is turning into a pupa, and then again when the pupa is turning into the adult insect. However this paper reports that scientists in Stanford (Molly Weaver and Mark Krasnow) have found that it is not just the imaginal cells which turn into the components of the adult insect. In fact other cells - old specialised cells that had survived from the larva - also form part of the adult. They do this by reverting back to a less specialised state and then turn into differently specialised cells in the developing adult.

So, by looking at what happens in something as lowly as a silkworm scientists have discovered why exactly my father's brain may have recovered from his stroke. It always amazes me how the most disparate things often turn out to be connected.

Into the moult

Silkworms, I have noticed, seem to have two sets of legs: six insect legs on their front segments and then eight, more-rudimentary ones on the segments further back. (Added later: I have since discovered that the legs on the front are thoracic ('real' insect legs) on the thorax; while the ones at the back are prolegs ending in suction caps called crochets. These are on the abdomen).

I clean them out every day, removing their tiny black walnut-shaped droppings and the food they haven't deigned to eat. This is to prevent mould, which is dangerous to silkworms.

Their food comes in plastic tubs and has the consistency of butter. It is supposed to be grated into their home, but really it is too soft for that. I usually end up with a few small pieces and hope that will do. I think it does, because if I listen carefully I can hear my silkworms eating. It is a contented munching sort of sound - and I think that if I could amplify this it would be quite relaxing.

Quite often they stop moving altogether and sit with their heads in the air. They are the texture of a creamy limestone and look so much like statues of themselves that I have been tempted to prod them to make sure they are not dead. However, I have just read on a website that this means they are getting ready to moult. One of them - the small pale one in the centre right of this picture is doing that now. His head seems to have changed a little too - his eyes are protruding and yellow. At least I assume they are eyes. (Added later: these are fake eyes. The real eyes are smaller and below the fake eyes).

Now a moulting silkworm should not be touched and I feel I am a little like a midwife or an expectant father, wondering what will happen next. I suppose, like all metamorphosing creatures, the silkworm is bristling with stem cells. Somewhere, perhaps on the inner layers of the old skin, there are cells reproducing and becoming something else as they mature and are bombarded with chemical messages: a part of a wrinkle or pigment, grow a bristle or a pore. After a few days a new silk worm will appear - his skin a little tender and vulnerable but otherwise just as perfect as he used to be - part of the series of little miracles which turns the egg into the moth.