Worm Breeder's Gazette 13(4): 45 (October 1, 1994)
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.
MRC-LMB, Hills Road, Cambridge CB2 2QH, England
The duplications eDp26 ('xol brother') and mnDp73 together define a region of the
X chromosome, between lin-32 and unc-2 ,which is likely to contain a major
numerator site for the assessment of X:A ratio, and hence for primary sex
determination. As previously described, (WBG 13(2): 43,1994), we have identified a
locus on the physical map that may correspond to this numerator. Transgenic him-8
animals carrying extrachromosomal arrays of certain cosmids, marked with the
dominant Rol plasmid pRF4 ,segregate wildtype hermaphrodites and wildtype males,
numerous Rol hermaphrodites but almost no Rol males. Subsequent experiments
have demonstrated that these arrays exert a dominant Xol (XO lethal) effect, feminize
2X:3A triploids, and have genetic properties consistent with increased numerator
activity. The locus responsible has been termed 324 fox-1 ',for 'Feminizing site On X'.
Further delimitation of fox-1 was carried out by testing each of six cosmids in the
region (see figure), as well as various derived plasmids. R04B3 , F16E1 ,and F53B5 all
exert a strong (99-100%) Xol effect. T13H8 is wholly negative and turns out to be
wrongly assigned to this part of the physical map. F33H6 exerts a weak Xol effect, and
T07D1 is consistently negative, but coinjection of F33H6 and T07D1 leads to an array
with a strong Xol effect. Together these results suggest that the overlap between F33H6
and T07D1 contains an essential part of fox-1 .
A cDNA hybridizing across part of this overlap has been obtained, from the
embryonic cDNA library constructed by Pete Okkema et al. This cDNA has been
sequenced, and contains one long ORF of 401 amino acids. The predicted protein
includes an excellent match to the 90 aa RNP consensus, the best characterized of
RNA-binding domains. At present, there is no proof that the Fox effect arises from
overexpression of this particular transcript, though this hypothesis can obviously be
tested. However, the circumstantial evidence is suggestive, and the possibility that an
RNA-binding protein is involved in primary sex determination in C. elegans is
definitely thought-provoking. (see figure)