Draper BW et al. (1993) International C. elegans Meeting "Muscle lineage specification in the C. elegans embryo."

Mello CC, Draper BW, Priess JR

[International C. elegans Meeting, 1993]

Draper BW et al. (1995) International C. elegans Meeting "mex-3 AND MATERNAL CONTROL OF MUSCLE DEVELOPMENT IN THE EARLY C. ELEGANS EMBRYO"

Priess JR, Draper BW, Mello CC

[International C. elegans Meeting, 1995]

The first division of the nematode zygote creates two blastomeres, called AB and P1, that differ in their autonomous ability to produce muscle; P1 can produce muscle cells when cultured in isolation but AB cannot. We have previously reported that in mex-3 mutant embryos, both AB and P1 have the autonomous ability to produce muscle cells. In contrast to mex-1 and par-1 mutant embryos, the AB blastomere in mex-3 mutants does not require skn-1(+) activity to produce muscle cells. Our results thus suggest that a factor other than SKN-1 is inappropriately expressed in the AB blastomeres in mex-3 mutants and that the expression of this factor leads to muscle cell development. We have cloned the mex-3 gene and shown that it encodes a novel, but highly conserved, cytoplasmic protein with two potential RNA-binding motifs called KH domains. We have sequenced three mex-3 alleles that result in mutant phenotypes indistinguishable from null alleles yet produce the wild-type amount of protein. We have found that these mutations are changes in highly conserved residues in the second KH domain, indicating that the KH domains are required for mex-3(+) activity. We find that mex-3 mRNA accumulates predominately at the anterior pole of the zygote following fertilization and that MEX-3 protein is abundant in oocytes and early embryos. We propose that mex-3(+) activity contributes to the very different muscle-forming abilities of the early blastomeres by regulating the expression of maternal mRNA(s).

Draper BW et al. (1991) International C. elegans Meeting "MATERNAL GENES WHICH AFFECT THE DEVELOPMENT OF BODY WALL MUSCLE IN C. ELEGANS"

Priess JR, Mello CC, Krause MW, Weintraub H, Draper BW

[International C. elegans Meeting, 1991]

A homolog of the mouse skeletal muscle-specific master regulatory gene MyoD-l (called CeMyoD) has recently been identified in C. elegans, and its pattern of embryonic expression make it a likely candidate for being a regulator of nematode myogenesis (see abstract by Krause). We have screened for maternal-effect lethal mutations which alter the number of body wall muscles to identify genes that may be involved in the early regulation of CeMyoD expression. Thus far we have identified five mutations which define three loci. All of these alleles cause excess muscle to be produced and we call them mex-l (Jl), mex-2 (II) and mex-3 (I) for muscle excess. mex-l and 2 mutant embryos can have as many as twice the normal number of CeMyoD positive cells. The temporal pattern of expression of CeMyoD appears altered in the mex mutant embryos such that expression begins early and in an abnormal number of cells. A wildtype AB blastomere does not produce any muscle or pharyngeal cells if its sister blastomere Pl is ablated with a laser microbeam. In contrast, a mex-l mutant AB blastomere produces both body wall muscle and pharyngeal cell when Pl is destroyed.

Mello CC et al. (1991) International C. elegans Meeting "THE MATERNALLY EXPRESSED GENE pie-1 IS REQUIRED FOR THE SPECIFICATION OF THE EMBRYONIC BLASTOMERE P2."

Krause MW, Draper BW, Priess JR, Mello CC

[International C. elegans Meeting, 1991]

We have identified maternal effect mutations that alter the number or types of differentiated cells produced by specific early blastomeres. Among these we are particularly interested in genes whose products regulate the commitment of cells to pharyngeal development. The first two cells, AB and Pl, both produce pharyngeal cells in normal development and we have identified a number of mutants that affect pharyngeal development in each of these blastomeres. The product of the gene glp-l is required for AB to produce pharyngeal cells. We have found 8 new alleles of glp-l as well as two alleles of a second gene in which mutations cause an embryonic defect indistinguishable from glp-l. We have identified six mutations that appear to result in an absence of pharynx and intestine. Three of these are new alleles of the gene skn-l (described by Bruce Bowerman, this meeting) and three define a new complementation group. We have identified 3 loci defined by five mutations which appear to affect both pharyngeal development and the commitment of blastomeres to produce muscle cells (described in an abstract by Draper et al). Finally, we have found 3 genes in which mutations cause embryos to produce an excess of pharynx and intestine. Among the most interesting in this class is a gene (pie-l, pharynx and intestine excess) defined by two alleles. The pie-l mutant embryos have as many as twice the normal number of intestinal cells and often have two distinct pharynges. A series of laser ablation experiments were performed on early embryos in order to define the source of the extra cells. In wild-type development, the early blastomere EMS, produces an intestine and part of the pharynx. When all blastomeres except EMS are killed in a wild-type or pie-l mutant embryo EMS produces the normal complement of intestinal and pharyngeal cells. In wild-type development P2, the sister of EMS, produces muscle and hypodermis even after all other early blastomeres are killed by laser ablation. Strikingly, in pie-l embryos, P2 instead produces an intestine and pharynx. Further ablation experiments suggest that the daughters of P2, C and P3, develop like the daughters of EMS, MS (pharyngeal and muscle precursor) and E (intestinal precursor), respectively. Thus in the pie-l mutant embryo, both daughters of Pl, P2 and EMS, appear to develop like a wild-type EMS. The pie-l gene may be required for the specification of the P2 cell fate. Alternatively the product of pie-l may be required to partition an EMS determinant, present in Pl, into EMS. In an effort to distinguish these models we are making a double mutant with the gene skn-l which appears be required for the wild type program of EMS development. The gene pie-l maps to the right of dpy-18 on chromosome three.

Mello CC et al. (1993) International C. elegans Meeting "Analysis of maternal-effect lethal mutations that result in a hyper-induction of pharyngeal cells."

Priess JR, Draper BW, Mello CC

[International C. elegans Meeting, 1993]

Kemphues KJ et al. (1993) International C. elegans Meeting "Mutator-induced par alleles, a new par gene and gutless embryos."

Priess JR, Mello CC, Draper BW, Kemphues KJ

[International C. elegans Meeting, 1993]

Bowerman BA et al. (1993) International C. elegans Meeting "The maternal gene skn-1 encodes a protein that is distributed unequally in early C. elegans embryos."

Priess JR, Draper BW, Bowerman BA, Mello CC

[International C. elegans Meeting, 1993]

Pagano, John M et al. (2009) International Worm Meeting "RNA recognition by the cell fate determinant MEX-3."

Pagano, John M, Ryder, Sean P

[International Worm Meeting, 2009]

Post-transcriptional regulation of gene expression governs the development of the Caenorhabditis elegans germline and early embryo. The putative RNA binding protein MEX-3 is essential for maintaining totipotency of germline stem cells and for specification of the anterior founder cell (AB) during embryogenesis. mex-3 mutants are maternal effect lethal with a terminal phenotype that includes posterior muscle proliferating into the anterior (1). In addition, worms that are deficient in MEX-3 and a second RNA binding protein, GLD-1, are sterile and form transdifferentiated germline tumors (2). Genetic studies reveal that two genes involved in early development, pal-1 and nos-2, are dependent upon mex-3 for their protein expression pattern (1, 3). MEX-3 contains two conserved KH domains and is thought to control mRNA stability, translation efficiency, and/or mRNA localization through specific interactions with target maternal mRNAs. However, the RNA binding specificity and network of regulatory targets have not been determined. Here, we used in vitro selection (SELEX) and quantitative biochemical methods to define the consensus MEX-3 recognition element (MRE). We demonstrate that MEX-3 binds specifically to a bipartite element consisting of two four-nucleotide elements with variable spacing between each half-site. The putative mRNA targets pal-1 and nos-2 each contain two MREs in their 3''UTR. Furthermore, the transcript nos-2 has an MRE within a critical cis-regulatory element required to repress NOS-2 expression in early embryos (4). Our results show that MEX-3 binds specifically to this element. The MRE is present in several other genes that are required for germline development and embryogenesis. Candidate regulatory targets include a number of RNA binding proteins (mex-1, gld-1, spn-4, puf-6, puf-7) and membrane proteins (glp-1, ooc-3). Target prediction based on the MRE will be used to further elucidate the role of MEX-3 in early development. 1. Draper BW, et al. (1996) Cell 87, 205-216 2. Ciosk R, et al. (2006) Science 311, 851-853 3. Jadhav S, et al. (2008) Development 135, 1803-1812 4. D''Agostino I, et al. (2006) Dev. Biol. 292, 244-252.

Lin R et al. (1993) International C. elegans Meeting "Specification of the MS and E blastomeres in C. elegans."

Draper BW, Bowerman BA, Priess JR, Mello CC, Lin R

[International C. elegans Meeting, 1993]

Mello CC et al. (1995) International C. elegans Meeting "PIE-1 PROTEIN LOCALIZATION CORRELATES WITH THE GERM CELL FATE DURING EARLY C. ELEGANS EMBRYOGENESIS"

Zhang W, Lobel R, Priess JR, Schubert CM, Mello CC, Draper BW

[International C. elegans Meeting, 1995]

The maternally expressed gene pie-1 is required for germline specification in the early C. elegans embryo. In pie-1 single mutants and in all double mutant combinations analyzed, the germ cell precursors adopt somatic cell fates, in addition, pie-1 mutations exhibit a synthetic dominant maternal effect sterile phenotype in specific genetic backgrounds (see abstracts by Flanagan and Rocheleau). Recent findings suggest that pie-1 may suppress somatic development in the germ lineage by acting as a general transcriptional repressor (see abstracts by Batchelder and Seydoux).