Worm Breeder's Gazette 9(3): 54

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More About tra Genes

J. Hodgkin

1. Intragenic mapping of tra-1In order to determine the relative 
location of recessive (masculinizing) and dominant (feminizing) 
mutations of the sex determining gene tra-1 III, I have carried out a 
variety of intragenic recombination experiments. One protocol utilizes 
alleles that were generated by reverting the dominant allele e1575. 
This was first partly reverted to a weaker dominant e1575e1816, and 
recessive mutations were then introduced in cis by selecting for loss 
of the dominant feminization phenotype. Some of the resulting triple 
mutants contain an amber mutation, e.g. the leaky amber e1825. 
Heterozygotes with flanking markers were constructed (genotype vab-7 + 
dpy-18/+ 75e1816e1825)+), and their progeny were 
screened for female recombinants. Screening was facilitated by 
introducing a homozygous unc-32 marker, because females are 
conspicuous in starved Unc-32 populations. Out of a total of 18 
intragenic recombinants, all had the genotype vab-7 
75).    Thus, the order must be e1825 - e1575, with 
the modifying mutation e1816 either left of e1825 or very close to it. 
The distance between e1825 and e1575 is ca. 0.2 map units, which is 
very large. Either tra-1 is a huge gene, or it experiences map 
expansion (since tra-1 is not in the LGIII cluster). Another amber 
allele, e1828, is much more tightly linked to e1575, ca. 0.02 map 
Using other protocols, e1099 (the reference non-amber null) W25 
found to map ca. 0.03 map units to the left of e1575; also, several 
different tra-1(d) alleles were all found to map to the right of e1099 
(and in one case to the right of e1575). Thus far, all dominants 
tested map to the right of all recessives.
. The gene tra-3 can be expressed in an XO 
The gene tra-3 is required for hermaphrodite sex determination, but 
is not required in males, because null mutations of tra-3 cause 
partial masculinization of XX animals and have no effect on XO animals.
The gene also shows a strong maternal effect: tra-3/tra-3 XX 
daughters of tra-3/+ hermaphrodites are normal hermaphrodites, and the 
masculinization is only seen in the next generation of self-progeny. 
However, there is no paternal rescue: mating tra-3 hermaphrodites with 
tra-3/+ XO males gives rise to tra-3/tra-3 XX cross progeny which are 
just as masculinized as their self-progeny sisters. The absence of 
paternal rescue could be explained by l) lack of tra-3 expression in 
XO animals, or 2) the small size of the sperm, which probably 
contributes little more than a genome to the zygote. Tests for tra-3 
expression in XO animals were carried out using feminizing mutations 
of fem-l and tra-1, which are believed to act downstream of tra-3 in 
the sex determination pathway, and therefore should not affect tra-3 
expression. Females of genotype fem-l -1 + XO , and 
tra-1(d)/+; constructed and crossed with tra-
3 XO males. Both crosses yielded several XX animals which were fully 
fertile hermaphrodites of normal appearance, but whose progeny were 
all Tra-3 abnormal males. Therefore, in the XO parents of these 
animals, tra-3(+) must have been expressed, at least in the germline. 
This result lends support to the notion that the tra-3 gene or gene 
product is not regulated, but is a necessary cofactor for the action 
of another gene, tra-2 (which probably is regulated; see Hodgkin, 
Genetics 96; Doniach, Genetics 114).