COLOR CODE FOR dpy-1; unc-7

                                                                                                Aug. 2, 2012

                                                                                                DHH interpretation

 

This mutant adult hermaphrodite dpy-1 (e1); unc-7 (e5) was originally called strain “D2”.  It was one of the first double mutants created by Sydney Brenner as a proof of principle that C. elegans could be useful for genetic manipulations. We suspect that the mutant genes were chosen because they offered two easily visible recessive phenotypes could be followed by eye during genetic crosses.

 

Why this individual animal was chosen for serial section study at the EM level is unclear. The posterior ventral cord was reconstructed over almost 500 serial images (perhaps 1000 thin sections) and the principal motor neuron somata were annotated. At the time the work was done, there was no available information on what these genes encoded - a collagen gene and an innexin (gap junction) gene.

 

Several unusual anatomical phenotypes can be noted, and their relation to the two genetic mutations is not entirely clear.  First, the ventral bodywall muscle quadrants are unequal, with a broader left quadrant and a thin right quadrant (a rarity in our experience).  Second, the pattern of L/R commissures of the motor neurons is disturbed, with too many processes going leftwards rather than rightwards (not uncommon in developmental mutants). Third, the neuron processes seem somewhat defasciculated, not tightly bound to their neighbors.  Fourth, not only are most ventral cord gap junctions missing (as expected), but most chemical synapses are also missing, despite a good quality fixation.

 

Based upon this last finding, we presume that this individual animal may have been paralysed, and perhaps that is how it got chosen for EM analysis.

 

Interestingly, a milder effect on chemical synapse formation has been noted in other unc-7 alleles by Yeh et al. (2009) J Neurosci. 29(16):5207. Perhaps the combination of unc-7 and dpy-1 is causing a synthetic enhancement of the disruption in chemical synapse formation.

 

Interneurons (based on MRC notes) – but these were not traced

1          AVBR

2          AVBL

 

Motor Neurons 

1         

2                      has L comm at #81

3          AS       has R comm at 121

4                      has R comm at 320

5         

6         

7          DA?    has L comm at 320

8         

9          DB?    has R comm at 421

10