Figure 4. Extending MIMS to Drosophila and human metabolism.

1. Drosophila anterior midgut enterocytes (gut, left panels) accumulate more ¹³C from 24hr exposure to dietary ¹³C-palmitate than adipocytes (fat body cells; fb, right panels). Lipid droplets (arrows) have low nitrogen content and so appear dark in ¹⁴N images (top panels). The ¹³C/¹²C HSI images reveal ¹³C incorporation into lipid droplets. Scale bars=10µm.
2. Timecourse of ¹³C accumulation in Drosophila lipid droplets of anterior midgut enterocytes (Gut) and adipocytes (Fat body) over 24hr of larval exposure to dietary ¹³C-palmitate. Initial rates of ¹³C-incorporation in the lipid droplets were 9.7%/hr (Gut) and 1.16%/hr (Fat body) with the first timepoint after pulse taken at 1hr.
3. Rapid lipid turnover in Drosophila anterior midgut enterocytes (gut) after larval dietary ¹³C-palmitate pulse-chase. Upper panels show ¹⁴N images and lower panels show corresponding ¹³C/¹²C HSI images, indicating strong ¹³C incorporation at the end of the pulse (bottom left) and rapid elimination during a 4 hr chase (bottom right). Scale bar=5µm.
4. ¹³C tracer dilution in the lipid droplets of anterior midgut enterocytes during a label-free chase fits an exponential decay curve (R²=0.90, half-life=9.1 h).
5. ¹⁵N-thymidine administered for 48hrs: no labeled WBC were found. After a 4 wk chase we found few labeled lymphocytes. Top: unlabeled polymorphonuclear leukocyte (PMN) with multi-lobed nucleus. Bottom: ¹⁵N-labeled lymphocyte after chase. The round nucleus seen in the ³¹P image occupies the majority of the cell, as is typical for lymphocytes. Scale bars=3µm.