COLOR CODE
lin6-1 (B55)
e1466 (this gene is now called mcm-4)
May 24, 2012; interpretation by DHH
This L4 larval mutant animal was reconstructed in the RVG and anterior ventral cord, and in the dorsal cord. Prominent ventral cord axons were reconstructed using a red and green color code. I have not found any documents that explain them so have made a few conservative guesses here to decode a few cell IDs below.
The B55 allele was originally isolated by John Sulston in a search for lineage defective mutants, and may have been propagated as a balanced strain with dpy-5 (e61) and/or unc-35 (e259), now known as tln-1 (see Horvitz and Sulston, 1980; Sulston and Horvitz, 1981). LIN-6 was recently renamed MCM-4 (Korzelius et al., 2011).
In this lin-6 allele, embryonic ventral cord motor neurons can continue to undergo cell divisions and cell morphogenesis despite a block in DNA replication. Eventually some neurons may die in place. Daughters from P cells fail to be born or enter the ventral cord during larval development, so the final mixture of neurons within older lin-6 nerve cords still lacks VA, VB, VC, VD and AS cells. Other members within the nerve cords may be somewhat out of their normal positions.
This TEM series was used to look for evidence of cell pathology and potential changes in synaptic wiring as the larval animal developed. On the dorsal side, it appears that DD neurons fail to switch polarity in their connections to bodywall muscles; see White, Albertson and Anness, 1978, for details. While many neuromuscular junctions and chemical synapses remain looking healthy in both nerve cords, several neuron cell bodies appear to be in distress. Their nuclei remain full size and virtually unchanged in appearance, but the nearby RER (connected to the nuclear membrane) or Golgi bodies are often grossly swollen, and some mitochondria within the cell body also appear swollen or vacuolated. In the case of one neuron (green 6), one portion of the cell process (ventral cord prints 218-234) not far from the cell body is also grossly swollen and the cytoplasm appears almost empty there. In the case of green 17, its axon shows empty cytoplasm in the vicinity of presumed NMJs (see ventral cord prints 60-68), which might reflect poor synaptic maintenance, or an aborted attempt to specifically change connectivity during late larval development (see White, Albertson and Anness, 1978).
Print #10 in the dorsal cord series is shown as Figure 4A, and print #46 in the dorsal cord series as Figure 4B in White, Albertson and Anness (1978).
References:
White, Albertson and Anness (1978) Nature 271: 764-6. “Connectivity changes in a class of motoneurone during the development of a nematode”
Horvitz and Sulston (1980) Genetics 96: 435-54. “Isolation and genetic characterization of cell-lineage mutants of the nematode Caenorhabditis elegans”
Sulston and Horvitz (1981) Dev. Biol. 82: 41-55.“Abnormal cell lineages in mutants of the nematode Caenorhabditis elegans”
Korzelius, The, Ruijtenberg, Portegijs, Xu, Horvitz and van
den Heuvel (2011) Dev. Biol. 350: 358-369.
“C. elegans MCM-4 is a general DNA replication and checkpoint component with an
epidermis-specific requirement for growth and viability”
18
22 DD1
1 AVAR
2 AVBL
3 AVBR
4 AVAL
5
6
7
8
9
10 DA1?
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17 DB2?
18
19
20