Figure 1. Pathobiology of aging C. elegans tissues.

(A) Tissue sections stained with pararosaniline and methylene blue from equivalent regions of a 4-day-old and 20-day-old wild-type worm. Top is a schematic of the lateral view of a wild-type worm showing pharynx (purple), intestine (yellow), and gonad (red). The regions shown in the below sections are represented by gray boxes. The middle row is the 4-day-old worm and the bottom row is the 20-day-old worm. Left to right, the regions are the head containing the pharynx, the region immediately posterior to the pharynx, the midbody containing the distal and proximal gonad arms, the midbody containing the uterus, and the rectum. Body wall muscle (bwm), intestine (int), distal gonad arm (dga), proximal gonad arm (pga), oocytes (ooc), embryos (emb), uterus (ut), anal dilator (ad), pharyngeal muscle (pm4), bacteria (bac), and yolk particles (y) are labelled. The intestine is barely visible as a thin pink wedge in the fourth section from the 20-day-old worm. Scale bar is 10 μm.

(B) Representative transmission electron micrographs from 18-day-old wild-type worms showing the pharynx, the region immediately posterior to the pharynx, and the rectum. Zoomed regions below their respective images are indicated by dotted lines of the bacterial packing in the intestine and the rectum. The intestinal lumen in a Class “C” animal shows no microvilli facing the clustered bacteria and the intestinal cytoplasm is dominated by empty vacuoles and a lack of ground substance. Other organelles are profoundly diminished. Pharynx and rectum TEMs come from Class “B” animals.