MESODERMAL ORGANS- Coelomocyte System

General description -Embryonic development -Structure and function -Cell list - Back to Contents

General Description

In C. elegans hermaphrodite, there are six coelomocytes (cc's) which are oblong cells residing as 3 pairs (ventral anterior, ventral posterior and dorsal) in the pseudocoelomic cavity adjacent to the somatic musculature (ccFIG1, ccFIG3, ccFIG4 and ccFIG5). Four of these cc's are present at hatching and two are generated in the first larval stage (ccFIG2). Because of their ability to take up a variety of molecules from the body cavity fluid these cells have been suggested to act as scavenger cells (Fares H. and Grant B., 2002).

Embryonic development

The ventral four cc's, the two anterior and the two posterior pairs, are derived from the embryonic MS lineage and are generated symmetrically (ccFIG6)(Sulston J. E. et al, 1986). The MS lineage also gives rise to the the postembryonic M mesoblast which later generates the two dorsal cc's. The M mesoblast is born in the embryo and then migrates to the posterior of the animal. Here, several consecutive divisions give rise to 14 body wall (striated) muscles, 2 dorsal coelomocytes, and 2 sex (non-striated) muscle progenitor cells which later migrate toward the center of the gonad and proliferate to give rise to 8 vulval muscles and 8 uterine muscles (see M lineage). In males, the M lineage gives rise to a single dorsal coelomocyte so that the total number of cc's in males is 5 instead of 6. Also in L1 males, one of the ventral left side cc's is located posterior to the gonad primordium rather than anterior as in L1 hermaphrodite (See Fig 5 in Sulston J. E. and Horvitz H. R., 1977)

Similar to the intestine and gonad, locations of the coelomocytes reveal the dextral handedness of the animal grown at 20°C; the ventral anterior pair is located on the right side and the ventral posterior pair on the left (Wood W. B. et al, 1996). When animals are cultivated at 10°C this handedness is reversed.

Structure and Function

The nucleus of each cc is rather large, and the cytoplasm is characterized by a large swollen (distended) RER and several large membrane-bound vacuoles ccFIG7). When viewed by DIC optics, the cells are distinctive in containing both pale vacuoles and highly refractile inclusions(ccFIG8) (cf. Sulston J. E. and Horvitz H. R., 1977). Each cell is covered by its own basal lamina. Some portions of the plasma membrane show active endocytosis, with multiple “omega-figures” lying in close proximity to one another (ccFIG7). This active endocytosis may be essential for a scavenging behavior. In C. elegans, cc's have been shown to uptake fluid-phase markers such as india ink, rhodamine-dextran, fluorescein isothiocyanate (FITC)-BSA and FITC-lipopolysaccharide from S. typhimurium from the pseudocoelom (Fares H. and Greenwald I., 2001). In ccFIG9 red fluorescent protein secreted by myocytes into the body cavity is shown to be accumulated in the two pairs of cc's. Although they do not normally take up yolk particles from the pseudocoelom, coelomocytes can be induced to take up GFP-tagged yolk particles, apparently due to the presence of the GFP moiety (Paupard M. C. et al., 2001). It is hypothesized that this scavenging behavior may allow for a primitive immune surveillance function. This function does not seem to be essential for the animal's survival or fertility, however, since animals in which cc's are toxin-ablated continue to grow and bear progeny (Fares H. and Greenwald I., 2001).

In some other species cc's sometimes adopt a stellate shape. Coelomocytes in larger species have also been shown to take up india ink, some dyes (methylene blue, crystal violet) and even injected bacilli and invading organisms (Chitwood and Chitwood, 1950, Bolla R.I. et al, 1972). The inclusions and/or vacuoles will easily stain with dyes such as methylene blue, neutral red, and neutral violet, sometimes appearing to collect these dyes in high concentrations.

Cell List

i.Ventral anterior (R side) pair coelomocytes

ccAR
ccPR

ii. Ventral posterior (L side) pair coelomocytes

ccAL
ccPL

ii. Dorsal coelomocytes

ccDL (only in hermaphrodite)
ccDR (only in hermaphrodite)
cc_male_D (only in male)


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