Worm Breeder's Gazette 10(2): 109

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.

Positioning the Ray/Alae Border

Lisa Wrischnik and Cynthia Kenyon

We are interested in understanding the mechanism by which antero-
posterior differences in body pattern arise after hatching.  A 
striking example of antero-posterior patterning takes place among the 
V cells, which lie along the lateral margin of the animal.  Initially 
these cells appear uniform, but subsequently anterior V cells generate 
seam cells that make alae, while posterior V cells instead produce 
neuroblasts that make sensory rays.
Two genes are known to influence the 'ray/alae' decision.  mab-5 
null mutations cause all V cells to generate lineages characteristic 
of V(1-4) and to produce alae but no rays.  Recessive lin-22 mutations 
(Horvitz, et al., CSHSQB 43:453) cause certain cells produced by V(2-4)
, and sometimes V1, to generate rays instead of the alae they would 
normally produce.  Thus, in a lin-22 mutant, alae is located near the 
head and the body is lined with ray papillae.  The phenotypes of these 
mutants indicate that in wild type males, mab-5 + is required for ray 
production by V cells, and lin-22 is required to produce alae (at 
least as far anteriorly as V2).
We have found that Bill Fixsen's lin-22 allele n372 is temperature 
sensitive for ray production.  This suggested that either the n372 
product is thermolabile, or else that this mutation reveals an 
intrinsic temperature dependence of the ray/alae decision.  In our 
efforts to define the Lin-22 null phenotype, we have isolated two new 
alleles, mu2 and mu5.  Like n372, both are temperature sensitive.  
n372 and mu2 have similar phenotypes, while mu5 appears to be a weaker 
allele because it results in the formation of approximately twice as 
much alae as n372 and mu2 at 16 C, 20 C and 25 C.  The fact that all 
alleles are temperature sensitive supports the notion of an intrinsic 
temperature-dependence of the ray/alae decision such that ray 
production is favored at high temperature.  The transformation of V 
cells is variable in all three alleles, so there are often patches of 
alae interspersed with ray cells.  However, in general, alae appear to 
be made preferentially in the anterior, and are progressively lost 
from posterior regions as the temperature is increased from 16 C to 25 
C.  In other words, changes in temperature have the effect of shifting 
the ray/alae boundary along the body axis, as if there is a graded 
anterior-posterior difference in the response of these cells to 
Previously, we showed that as the mab-5+ gene dosage is increased in 
a lin-22 mutant, cells located progressively more anteriorly will 
produce rays (Kenyon, Cell 46:477).  Thus, mab-5 activity may play a 
role in the important process of determining the position of the 
ray/alae boundary.  To test whether lin-22 activity could also be 
involved in positioning the boundary, we lowered lin-22 dosage in a 
mab-5 mutant.  At 20 C, 0/50 mab-5 (e1239 
n372 1+; 
e1490 males produced extra rays.  However, we had determined that the 
formation of rays is favored at high temperature, so we examined the 
animals at 25 C.  At this temperature an extra ray was present in the 
fan of 13/50 animals (one side scored) and 1/50 animals had two extra 
rays ( 0/64 e1239; e1490 males had extra rays at 25 C).  Thus, like 
mab-5,  can also influence the position of 
the ray/alae boundary.  The fact that lin-22 and mab-5 activities 
shift the boundary in opposite directions suggests that in the wild 
type the boundary may be positioned by the lin-22/mab-5 ratio.