Zalevsky J et al. (1997) Worm Breeder's Gazette "Mutation via Gene Conversion"

Zalevsky J, Villeneuve AM

[Worm Breeder's Gazette, 1997]

We previously reported that the him-14 gene, which is required for the formation of meiotic crossovers, corresponds to ZK1127.11, a gene encoding a member of the MutS family of mismatch repair proteins. The genome sequencing consortium has also identified a partial duplication (termed T02G5.6) of this gene on the adjacent cosmid. Specifically, a 1.1 kb segment of genomic DNA including both exons and introns is duplicated at a position 10 kb from the intact him-14 gene; this DNA segment shares >96% sequence identity with the him-14 gene The duplicated segment duplicates nearly 30% of the him-14 coding region, but it is not expected to produce any functional protein since it not only lacks both the 5' and 3' ends, but also includes a base substitution and a base deletion that produce in frame stop codons. The presence of this gene duplication is not remarkable in and of itself, since partial gene duplications of this type are reasonably common in the C. elegans genome, as was noted in the 1994 Nature article reporting on the first 2.2 Mb of sequence. Despite their frequent occurrence in the worm genome, the origins and consequences of these duplications remain unknown. We report here that a duplicated gene segment can serve as a donor of genetic information in a gene conversion event involving the intact gene as the recipient. In the course of sequencing him-14 alleles, we found that the mutant allele it21 (isolated following EMS mutagenesis) contains numerous base changes over a 350 bp region, and that these changes all correspond to the sequence present at the T02G5.6 locus. We know that this was a gene conversion event rather than a gene fusion since the template for sequencing was a PCR product amplified using primers from the him-14 gene that flank the duplicated portion; other data confirm that the downstream region of the him-14 gene is intact in the it21 mutant. The changes incorporated result in several amino acid substitutions as well as truncation of the protein upstream of a conserved putative helix-turn-helix thought to be involved in important protein/protein interactions. We wonder how common this type of gene conversion event might be, and are interested in hearing from anyone else who has observed similar mutational events.

Zalevsky J et al. (1996) Worm Breeder's Gazette "The Role of HIM-14, a Putative MutS Homolog, in Crossover Formation During Meiosis"

Villeneuve AM, Zalevsky J

[Worm Breeder's Gazette, 1996]

Pairing and crossing over between homologous chromosomes are required to direct proper orientation of homologs on the meiosis I spindle, thereby ensuring their faithful disjunction. By screening directly for mutants with high levels of meiotic nondisjunction, we identified mutations in at least twelve genes required for normal levels of crossing over between homologs. One of these mutations is an allele of him-14, a gene initially identified in a screen for maternal-effect lethals (Kemphues et al., Genetics 120:977-86). him-14 mutants are defective for the segregation of all chromosomes, and thus produce broods consisting mainly of dead aneuploid embryos plus a few healthy, fertile adult survivors, many of which are male, that by chance received a euploid (or near euploid) chromosome complement. him-14 is required for the formation of crossovers between homologs (Duffy, Basl, and Kemphues, WBG 10(1):104; A.V.). Cytological examination reveals a high frequency of achiasmate chromosomes in him-14 oocyte nuclei at the diakinesis stage of meiotic prophase. Whereas wild-type oocytes at this stage contain six bivalents, indicative of each pair of homologs having undergone a crossover, him-14 oocytes contain up to 12 univalents, and few or no bivalents. him-14 mutants also exhibit a severe reduction in genetic recombination frequencies, indicating that the absence of chiasmata is due to failure to form crossovers rather than to a defect in chiasma maintenance. Temperature-shift experiments suggest that the him-14 gene product functions during the pachytene stage of meiotic prophase, when chromosomes are fully synapsed and recombination is taking place. We shifted young gravid him-14 (it44ts) hermaphrodites from permissive to restrictive temperature (and vice-versa), fixed batches of worms at various times following the shift, and examined DAPI-stained oocytes for the presence of achiasmate chromosomes. By estimating the rate of progression of nuclei through the gonad (based on egg-laying rates and estimates that 1/3 to 1/2 of nuclei undergo programmed cell death), we inferred the stage at the time of the shift for the oocyte being scored. These experiments show that the requirement for him-14 begins during the pachytene stage, and is complete before the end of pachytene. A pachytene requirement indicates that him-14 is not required to establish pairing or synapsis of homologous chromosomes, and suggests a more direct involvement in crossover formation. Our molecular analysis strongly suggests that him-14 encodes a member of the MutS family of mismatch repair proteins. We mapped him-14 between unc-104 and lin-26, immediately to the right of the right breakpoint of mnDf30, which we mapped to cosmid ZK1127 (between sequence coordinates 6743 and 30841) by PCR from mnDf30/mnDf30 dead eggs. By SSCP analysis and/or sequencing, we have now identified mutations in four of six him-14 alleles in the candidate gene ZK1127.11, which encodes a MutS family member most closely related to the MSH4 protein from S. cerevisiae . MutS proteins function in mismatch repair by binding directly to mismatched base pairs or insertion loops and directing the mismatch repair machinery to the site of the mismatch. In humans, homologs of MutS and other mismatch repair proteins are mutated in several types of familial cancer syndromes. Members of the MutS gene family, including MSH4, have recently been shown to play a role in meiotic recombination in yeast. Although the role of MutS proteins in mismatch repair has been well studied, how members of this family might interact with DNA to promote the formation of crossovers is not at all understood. We are attracted by the hypothesis that they may function by binding to Holliday junction recombination intermediates to influence resolution in the direction of crossovers. Our laboratory is currently testing whether HIM-14 can in fact bind Holliday junctions in vitro. We are also testing whether him-14 mutants are defective for mismatch repair.

Miller DM et al. (1992) Worm Breeder's Gazette "unc-4 LacZ Expression in A-Type Motor Neurons"

Miller DM, Niemeyer CJ

[Worm Breeder's Gazette, 1992]

unc-4 LacZ expression in A-type motor neurons David M. Miller and Charles J. Niemeyer, Dept. of Cell Biology, Duke Univ. Medical Ctr, Durham, NC 27710

Sommer RJ et al. (1994) Worm Breeder's Gazette "Evolution of Vulva-Formation: Part II: Species With a Central Vulva"

Sommer RJ, Sternberg PW

[Worm Breeder's Gazette, 1994]

Evolution of vulva-formation: Part II: Species with a central vulva Ralf J. Sommer & Paul W. Sternberg, California Institute of Technology, Division of Biology 156-29, Pasadena, CA 91125

Huang Y-J et al. (1994) Worm Breeder's Gazette "From Ascaris to C. elegans: A Way to Study Gene Structure and Function"

Tobler H, Huang Y-J, Mueller F

[Worm Breeder's Gazette, 1994]

FROM ASCARIS TO C. ELEGANS: A WAY TO STUDY GENE STRUCTURE AND FUNCTION Huang Y-J., Tobler H. and Muller F., Institute of Zoology, University of Pribourg, Perolles, CH-1700 Fribourg, Switzerland

Li WQ et al. (1992) Worm Breeder's Gazette "Characterization of the Axonal Guidance and Outgrowth gene Unc-33"

Shaw JE, Li WQ, Herman RK

[Worm Breeder's Gazette, 1992]

Characterization of the axonal guidance and outgrowth gene unc-33 W. Li, R. K. Herman and J. E. Shaw Department of Genetics and Cell biology, University of Minnesota, St Paul, MN 55108

Almeida CA et al. (1994) Worm Breeder's Gazette "Function of a Domain of the Myosin Heavy Chain Implicated in Familial Hypertrophic Cardiomyopathy"

Collins JJ, Almeida CA, Swift KE

[Worm Breeder's Gazette, 1994]

Function of a Domain of the Myosin Heavy Chain Implicated in Familial Hypertrophic Cardiomyopathy Craig A. Almeida, Kerry E. Swift and John J. Collins Department of Biochemistry and Molecular, University of New Hampshire, Durham, NH 03820

Sommer RJ et al. (1994) Worm Breeder's Gazette "Evolution of Vulva Formation: Part IV: Variation in AC Position Can Cause a Shift of Vulva Formation Towards P(4-6).p."

Sternberg PW, Sommer RJ

[Worm Breeder's Gazette, 1994]

Evolution of vulva formation: Part IV: Variation in AC position can cause a shift of vulva formation towards p(4- 6).p Ralf J. Sommer & Paul W. Sternberg, HHMI & California Institute of Technology, Division of Biology 156-29, Pasadena, CA

Bowerman BA et al. (1994) Worm Breeder's Gazette "The Maternal Gene skn-4 and the Specification of Ventral Blastomere Fates in the Early C. elegans Embryo"

Bowerman BA, Shelton CA, Thorpe CJ, Martin PR

[Worm Breeder's Gazette, 1994]

THE MATERNAL GENE SKN-4 AND THE SPECIFICATION OF VENTRAL BLASTOMERE FATES IN THE EARLY C. ELEGANS EMBRYO Bruce Bowerman, Paula R. Martin, Christopher J. Thorpe, and Christopher A. Shelton. The Institute of Molecular Biology, University of Oregon, Eugene, OR 97403.

Fields CA (1990) Worm Breeder's Gazette "An Updated Codon Usage Table"

Fields CA

[Worm Breeder's Gazette, 1990]

A number of new genes have been sequenced since worm codon usage was summarized by Emmons (Table 2 in The Genome, The Nematode Caenorhabditis ing Harbor Lab.). An updated codon usage table has been derived from the sequences of act-1, act-2, act-3, act-4 (Krause et al., J. Mol. Biol. 208 (1989) 381-392), col-1, col-2 (Kramer et al., Cell 30 (1982) 599-606), col-6, col-7, col-8, col-14, col-19 (Cox et al., Gene 76 (1989) 331-344), deb-1 (Barstead and Waterston, J. Biol. Chem. 264 (1989) 10177-10185), dpy-13 (von Mende et al., Cell 55 (1988) 567-576), glp-1 (Yochem and Greenwald, Cell 58 (1989) 553-563), lin-12 (Yochem et al., Nature 335 (1988) 547- 550), myo-1, myo-2, myo-3 (Dibb et al., J. Mol. Biol. 205 (1989) 603- 613), sqt-1 (Kramer et al., Cell 55 (1988) 555-565), unc-15 (Kagawa et al., J. Mol. Biol. 207 (1989) 311-333), unc-54 (Kam et al., Proc. Natl. Acad. Sci. USA 80 (1983) 42534257), and vit-5 (Spieth et al., Nucl. Acids Res.) [See Figure 1]