Worm Breeder's Gazette 12(2): 87 (January 1, 1992)
These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.
When a worm eats, the three main sections of the pharynx, the corpus, isthmus, and terminal bulb, contract together. Since the pharyngeal nervous system is not required for this synchronization (Neuron 3: 473), a good guess is that pharyngeal muscles are coupled by gap junctions. I have been trying to test this guess in two ways: by studying a mutant, eat-5 ( ad464 ),in which the corpus and terminal bulb don't contract together, and by testing whether fluorescent dye can diffuse from one pharyngeal muscle to another.
eat-5 has not yet been informative. I mapped it between let-75 and unc-13 I. Since let-75 is likely to be an alias for myo-1 (Waterston, personal communication), this placed eat-5 within a 180 kb region of the physical map. 3-point interpolation suggested that the cosmid B0332 would contain eat-5 ,and in fact B0332 as well as the overlapping cosmid T21B9 rescue eat-5 in transgenic worms. I am now subcloning. Dye injection has been more helpful. The pharynx can be exposed by cutting an L4 through just behind the pharynx. In C a2 +containing buffers, the cuticle shrinks up (presumably because the underlying body muscles contract), exposing the pharynx from the back of the corpus to the terminal bulb in the best dissections. These exposed pharynxes pump normally in egg salts, in some cases for as long as two hours. The results of carboxyfluorescein injections into wild-type and unc-31 ,or eat-5 pharynxes are shown below. Dye almost always diffuses into one adjacent section of the pharynx, but seldom lights up the entire pharynx. The pharynxes die within a few minutes after injection, and dye never diffuses from one muscle cell to another in a dead pharynx, observations I believe account for the usual failure to label all the muscles. I hope to overcome this problem by using a gentler injection technique. I am certain the dye was not injected into the pharyngeal lumen, because when I inject into the lumen the location of the fluorescence is obviously different. Furthermore, in one case I was able to look at focal cross-sections through the isthmus of a pharynx injected in the terminal bulb, and could unambiguously identify the fluorescent cells as m5 isthmus muscle. eat-5 pharynxes were dye-coupled as well as wild-type. Although a disappointment, this is not a great surprise. I have only one allele of eat-5 ,and it is impenetrant in older larvae and adults. Even before dye injections, I suspected eat-5 weakened but did not eliminate pharyngeal muscle coupling.
[See Figure 1]