Worm Breeder's Gazette 15(1): 69 (October 1, 1997)
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IS MUT-7 TEMPERATURE SENSITIVE?
Rene F. Ketting,
Henri G.A.M. van Luenen,
Ronald H.A. Plasterk
Division of Molecular Biology, Netherlands Cancer Institute, Plesmanlaan 121, 1066 CX Amsterdam, The Netherlands.We have previously reported the isolation of the mut-7(pk204) allele in an EMS mutagenesis screen for transposition proficient mutants (Worm Breeder's Gazette 14(2):24). Next to activating transposons in the germ line, this allele also confers a Him phenotype. Here we describe a temperature sensitive phenotype of the mut-7 strain NL917.
When L1 larvae are grown at 20C and are shifted to 25C they mainly lay dead eggs. We have not analysed these eggs extensively but they appear to be early embryonic arrests. However, when worms are grown to L4 at 20C and are then shifted to 25C the progeny does develop into adults. These results are preliminary and are not quantified yet, but it is clear that NL917 worms cannot be grown at 25C. The strain does grow at 23C, but its brood size appears to decrease each generation. Worms grown at 20, 18 and 15C do not show this effect. This temperature sensitive lethal effect is still present in a mut-7 strain which is four times outcrossed and in which the regions flanking mut-7 have been replaced with "clean" Bristol sequences (using visible markers).
Also the Him phenotype appears to be temperature sensitive: 4.5(+/-0.9)% males at 23C and 1.0(+/-0.6)% at 15C (average of three experiments). We are currently investigating whether transposition frequencies are also affected by temperature. A first experiment addressing the transposition frequency at various temperatures did suggest that the transposition frequency is higher at elevated temperatures: after approximately 10 generations we detected 8 transposition events at 15C versus 25 at 20C .
All these results together suggest that it is the mut-7 allele itself that is temperature sensitive and not some other mutation that was introduced by the EMS mutagenesis. This may provide us with a very convenient phenotype for rescue experiments, aimed at the identification of the mut-7 gene.