Worm Breeder's Gazette 7(2): 45

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unc-86 Affects Developmental Decisions that Do Not Involve Cell Division

M. Finney, B. Horvitz

Figure 1

The gene unc-86 III is known to affect specific developmental 
decisions involving cell division: unc-86 mutants undergo posterior 
parental reiterations in the postembryonic cell lineages of three 
neuroblasts (Chalfie, Horvitz and Sulston, Cell, 24, 59, 1981).  We 
have continued genetic studies of unc-86, including the generation of 
new unc-86 alleles and the characterization of the unc-86 region.  A 
revised map of a portion of LGIII is shown below.  We have isolated 
five new unc-86 alleles by complementation screening: EMS-mutagenized 
dpy-19 males were mated with marked unc-86 hermaphrodites and F1 Unc-
86 cross progeny were picked.  None of these nine alleles was 
suppressed by the amber suppressor sup-7 X.
In addition, an EMS-induced temperature-sensitive (ts) unc-86 allele,
n848, was isolated by Nancy Tsung in a screen for animals abnormal in 
dopaminergic or serotonergic neurons.  At 20 C, n848 animals have the 
supernumerary dopaminergic neurons characteristic of unc-86 mutants, 
but appear wild-type in the dissecting microscope; at 25 C, n848 
animals are Mec and Egl.  We have investigated the temperature-
sensitive period (tsp) for the Mec and Egl phenotypes of n848.  The 
tsp for Mec is embryonic, as is the generation of the mechanosensory 
neurons.  In contrast, the tsp for Egl is in the L4, considerably 
after all neurons in the hermaphrodite have been generated.  Thus, the 
Egl phenotype of unc-86 does not result from a lineage defect.
Several lines of evidence indicate that unc-86 animals are Egl 
because they fail in the differentiation of the hermaphrodite-specific 
neurons (HSN's).  1) unc-86 animals have the Egl phenotype 
characteristic of HSN-deficient animals (see Trent, Tsung and Horvitz, 
this Newsletter).  2) unc-86 adults have missing, displaced or 
abnormal HSN's.  3) unc-86 L1 hermaphrodites contain undifferentiated 
HSN's that are normal by three criteria: first, they are capable of 
forming a functional HSN in n848 animals grown at 25 C if the 
temperature is shifted down in the L4, the normal time of HSN 
differentiation; second, egl-1(n487), which appears to induce 
specifically the programmed deaths of the HSN's in wild type (see 
Ellis and Horvitz, this Newsletter), also induces the deaths of these 
putative HSN's in unc-86 animals; third, these putative HSN's are 
normal in lineage history, migration and appearance (John Sulston, 
personal communication).
Thus, the wild-type function of unc-86, which is necessary for the 
correct execution of several developmental decisions involving cell 
division, is also necessary for the execution of a developmental 
decision not involving cell division.  This observation indicates that 
developmental decisions can occur independently of cell division and 
that unc-86 controls at least one such decision.
[See Figure 1]
Approximate length of region shown is 0.6 map units.  EMS-induced 
lethals were generated linked to dpy-19.  deficiencies were generated 
with gamma rays.  lin(n758) and lin(n766) , which are synthetic 
multivulva mutations (see Ferguson and Horvitz, this Newsletter), were 
mapped by Chip Ferguson.  n709, which causes VC neurons to undergo 
programmed cell death, was generated and mapped by Hilary Ellis (see 
Newsletter, Vol.  7, Mo.  1).  Alleles of sup-18, which are 
suppressors of unc-93(e1500), were isolated and mapped by Iva 

Figure 1