JP Jan 14 16
Notes on 1995 ADAPTIVE RESPONSES TO FEEDING IN BURMESE PYTHONS: PAY BEFORE PUMPING
Stephen M. Secor and Jared Diamond
"Three factors combine to make the metabolic response to feeding so large in pythons compared with that in mammals: the pythons’ much larger meal size; their gut atrophy during their long fasts, requiring a high investment in rebuilding the atrophied gut; and their much lower basal metabolic rates, constituting the low baseline from which oxygen consumption rises during digestion" (1321).
"The first organs to respond with significant increases in wet mass (within 6 h of the snake’s consuming a meal) are the stomach and small intestine, the organs most immediately involved in digesting the meal" (1323).
"typical responses to feeding include intestinal hypertrophy and up-regulation of intestinal nutrient transporters and hydrolytic enzymes (Karasov and Diamond, 1987; Toloza et al. 1991)*" (1313).
- Track this* research down, look for specific proteins in order to find the responsible genes.
"Most of the increase in anterior small intestinal mass resulted from the mass increase of its mucosal layer" (1320).
6 & 12 hours; our experiment started the first 30 mins. At what point did the clock start?
Figure 2 suggests that the mass of the food is being liquefied in the stomach; not much solid mass reaches the small intestine; small intestine = absorption, not digestion.
Figure 3: absorption of the amino acids and sugar peaks early (< 10 days post feeding) in the small intestine. Suggests a transport mechanism (intestinal nutrient transporters) active in the small intestine during digestion. How is the genome responding to the feeding with the rapid uptake? Making new proteins - increased transcription? Post translational modifications -> increased uptake? *we won't be able to see this. Increased translation? *we can't see this either.
- All we can see would be increased transcription. Need to find the ortholog name of the transporters so as to find in Python.
Possible that the outer serosa layer stays the same, and the intestinal brush border expands inward causing an increase in mass.
Figure 5: there are sodium dependent and independent components of uptake; transport proteins can use a sodium gradient to drive uptake. High Na+ concentration location depends on transporter. (sim v anti porter)
- Take note on Na+ dependence or independence. What options are there to bring amino acids into cells?
- Make a catalog on amino acids and glucose import proteins, then we find the genes.
Figure 7: everything in this figure must have transporters! Elevation in blood plasma means they must have been absorbed from the food.
Figure 10: liver mass increases.
Can't thaw the organs as we would lose the RNA. However, if the intestine was wadded up and only the serosa was sampled, we may have missed the mRNA. Is it legitimate to throw out a snake if it was all serosa? What if only one subset of snakes got their brush border sampled?
A vertebrate model of extreme physiological regulation
Stephen M. Secor & Jared Diamond
"The small intestine doubles in wet and dry mass within 1 day, largely as a result of a sixfold increase in microvillus length and a doubling of mucosal enterocyte volume" (660).
"Molecular mechanisms of regulation of the glucose transporter SGLT1 are being studied in pythons" (662).
- look at this gene: SGLT1
Need to find:
Housekeeping genes? Which are specific to intestines.
Do the cells get bigger (how?) or are there more cells being made?
Track down the transport proteins