Life Lines by Dr. Dolittle

Sponsored by the American Physiological Society

Hagfish 101: How to eat a whale from the inside out

The Dr. Dolittle award is given to outstanding graduate students or postdoctoral fellows who are conducting comparative physiology research that they are presenting at the annual Experimental Biology conference. Applicants for the award are asked to submit guest blog posts describing their research. I am very pleased to share this guest blog post from this year’s Dr. Dolittle travel award recipient, Alyssa Weinrauch. Alyssa presented her research today the Experimental Biology conference in San Diego, CA.

By: Alyssa Weinrauch

Chances are if you’ve heard of hagfish you’ll know one of two things: 1) They
produce oodles of slime as a defense against predators 2) They burrow into
carcasses and eat their way out – for the visual folks, it’s not unlike that classic
scene in Alien.

Both are not the most appealing of traits but show some of the
intriguing aspects of these ancient fish. Ancient indeed! Hagfish are considered
the living descendants of the first vertebrates and swam in the oceans relatively
unchanged for the last 550 million years, through the coming and going of the
dinosaurs, to the present day. They have a simple digestive system that lacks a
stomach and instead, have a straight intestinal tube filled with cells for both
lubrication and absorption. Examining nutrient uptake in this primitive system can
give researchers (such as myself) a peek into the past and understand how
digestive systems evolved. With many millions of years of evolution between
hagfish and humans, how similar can these digestive systems really be? Could
we too digest a whale from the inside out? We set out to answer such questions
in a study that examines how nutrients are acquired in hagfish and how that
relates to studies already conducted in other vertebrates including fish and
mammals. In short, we are not so different from our hagfish counterparts in terms
of how we get nutrients into our body. The following three easy steps can be
used by anyone who wishes to digest a whale from the inside out. Please use at
your own discretion.

Step 1. Prepare for anything. Whales are big and complex, composed of many
different delicious nutrients. That means machinery is required to acquire each of
the macronutrients: carbohydrates (ex. glucose), fats (ex. oleic acid) and proteins
(ex. Alanyl-alanine). Research shows that hagfish regulate the movement of
each of these nutrients across the intestine using similar mechanisms to higher
vertebrates such as mammals. How can you tell? Basically, if you fill yourself at
an all-you-can-eat buffet (we’re talking whaley big amounts of food here) at some
point there will be more nutrients than each intestinal cell can acquire. This
results in constant transport rates because the transporters are always in use
with a steady supply of nutrients.

Step 2. Mobilize your intestinal army. Now that nutrients are in your intestine, its
time to regulate the transporters; for instance, you may want to increase their numbers to get the most out of the whale buffet. One such regulator is the well-known glucose regulator, insulin. Interestingly, insulin-containing islet cells appear to emerge with the primitive hagfish and so again hagfish are useful models to study the early actions of insulin. Insulin can also regulate the amount of fatty acid transporters available for a cell to use in specific mammalian tissues. While mammalian insulin incites classic metabolic responses in hagfish such as the lowering of blood glucose shown in this study, there was no change in the rate of fatty acid uptake. Fear not, you may still be able to digest a whale despite this apparent difference! Intestinal fatty acid transport in mammals is also unaffected by insulin, perhaps to ensure these particular nutrients can always be acquired. The primitive hagfish do not have as many variants of fatty acid transporter as higher vertebrates and it is possible insulin regulation came about later on in evolution. Only time and research $$ will tell.

Step 3. Sit back, digest and regress. Now that the whale has been thoroughly
digested, it’s time to enter a period of fasting. Hagfish can live upwards of 11
months (yes nearly a year!) without eating another meal. Much like binge-eating
snakes, the hagfish use specific tactics to decrease energy use and that includes
regression of intestinal tissue. Since the energetically expensive intestine will not
be in use, these animals decrease the cell size and absorptive villi lengths, along
with the number of costly transport proteins, leading to reduced rates of nutrient
uptake.

And there you have it. Hagfish are capable of consuming all kinds of prey using
machinery much like that found in higher vertebrates. Most surprising perhaps,
are the conserved mechanisms of regulation that may have been part of the
vertebrate lineage for millions of year, making you more like a hagfish than you
might think (or want)!

Categories: Comparative Physiology

Tags: , , , , ,

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