gon-4, a cell lineage regulator required for gonadogenesis in Caenorhabditis elegans

The gon-4 gene is required for gonadogenesis in the nematode Caenorhabditis elegans. Normally, two precursor cells, Z1 and Z4, follow a reproducible pattern of cell divisions to generate the mature somatic gonadal structures (e.g., uterus in hermaphrodites, vas deferens in males). In contrast, in gon-4 mutants, the Z1/Z4 cell lineages are variably aborted in both hermaphrodites and males: Z1 and Z4 divide much later than normal and subsequent divisions are either absent or severely delayed. In gon-4 adults, normal somatic gonadal structures are never observed, and germ-line and vulval tissues, which depend on somatic gonadal cues for their development, are also aberrant. In contrast, nongonadal tissues and the timing of other developmental events (e.g., molts) appear to be normal in gon-4 mutants. The gon-4 alleles are predicted to be strong loss-of-function or null alleles by both genetic and molecular criteria. We have cloned gon-4 in an attempt to learn how it regulates gonadogenesis. The gon-4 gene encodes a novel, acidic protein. A GON-4::GFP fusion protein, which rescues a gon-4 mutant to fertility, is expressed in somatic gonadal cells during early gonadal development. Furthermore, this fusion protein is nuclear. We conclude that gon-4 is a regulator of the early lineage of Z1 and Z4 and suggest that it is a part of a genetic program common to the regulation of both hermaphrodite and male gonadogenesis.     

Gon-2, a Gene Required for Gonadogenesis in Caenorhabditis Elegans

The gonad of the Caenorhabditis elegans hermaphrodite is generated by the postembryonic divisions of two somatic precursors, Z1 and Z4, and two germline precursors, Z2 and Z3. These cells begin division midway through the first larval stage. By the end of the fourth larval stage, Z1 and Z4 produce 143 descendants, while Z2 and Z3 give rise to ~1000 descendants. The divisions of Z2 and Z3 are dependent on signals produced by Z1 and Z4, but not vice versa. We have characterized the properties of five loss-of-function alleles of a newly described gene, which we call gon-2. In gon-2 mutants, gonadogenesis is severely impaired; in some animals, none of the gonad progenitors undergo any postembryonic divisions. Mutations in gon-2 have a partial maternal effect: either maternal or zygotic expression is sufficient to prevent the severe gonadogenesis defects. By cell lineage analysis, we found that the primary defect in gon-2 mutants is a delay (sometimes a complete block) in the onset and continuation of gonadal divisions. The results of upshift experiments using a temperature-sensitive allele suggest that zygotic expression of gon-2 begins early in embryogenesis, before the birth of Z1 and Z4. The results of downshift experiments suggest that Z1 and Z4 can generate the full complement of gonadal tissues even when gon-2 function is inhibited until the end of the second larval stage. Thus, gon-2 activity is probably not required for the specification of gonadal cell fates, but appears to be generally required for gonadal cell divisions.     

gon-14 functions with class B and class C synthetic multivulva genes to control larval growth in Caenorhabditis elegans

Previous work showed that C. elegans gon-14 is required for gonadogenesis. Here we report that gon-14 encodes a protein with similarity to LIN-15B, a class B synMuv protein. An extensive region of GON-14 contains blocks of sequence similarity to transposases of the hAT superfamily, but key residues are not conserved, suggesting a distant relationship. GON-14 also contains a putative THAP DNA-binding domain. A rescuing gon-14::GON-14::VENUS reporter is broadly expressed during development and localizes to the nucleus. Strong loss-of-function and predicted null gon-14 alleles have pleiotropic defects, including multivulval (Muv) defects and temperature-sensitive larval arrest. Although the gon-14 Muv defect is not enhanced by synMuv mutations, gon-14 interacts genetically with class B and class C synMuv genes, including lin-35/Rb, let-418/Mi-2beta, and trr-1/TRRAP. The gon-14; synMuv double mutants arrest as larvae when grown under conditions supporting development to adulthood for the respective single mutants. The gon-14 larval arrest is suppressed by loss of mes-2/E(Z), mes-6/ESC, or mes-4, which encodes a SET domain protein. Additionally, gon-14 affects expression of pgl-1 and lag-2, two genes regulated by the synMuv genes. We suggest that gon-14 functions with class B and class C synMuv genes to promote larval growth, in part by antagonizing MES-2,3,6/ESC-E(z) and MES-4.     

Tissue architecture in the Caenorhabditis elegans gonad depends on interactions among fibulin-1, type IV collagen and the ADAMTS extracellular protease

Molecules in the extracellular matrix (ECM) regulate cellular behavior in both development and pathology. Fibulin-1 is a conserved ECM protein. The Caenorhabditis elegans ortholog, FBL-1, regulates gonad-arm elongation and expansion by acting antagonistically to GON-1, an ADAMTS (a disintegrin and metalloprotease with thrombospondin motifs) family protease. The elongation of gonad arms is directed by gonadal distal tip cells (DTCs). Here we report that a dominant mutation in the EMB-9/type IV collagen α1 subunit can compensate for loss of FBL-1 activity in gonadogenesis. A specific amino acid substitution in the noncollagenous 1 (NC1) domain of EMB-9 suppressed the fbl-1 null mutant. FBL-1 was required to maintain wild-type EMB-9 in the basement membrane (BM), whereas mutant EMB-9 was retained in the absence of FBL-1. EMB-9 (either wild type or mutant) localization in the BM enhanced PAT-3/β-integrin expression in DTCs. In addition, overexpression of PAT-3 partially rescued the DTC migration defects in fbl-1 mutants, suggesting that EMB-9 acts in part through PAT-3 to control DTC migration. In contrast to the suppression of fbl-1(tk45), mutant EMB-9 enhanced the gonadal defects of gon-1(e1254), suggesting that it gained a function similar to that of wild-type FBL-1, which promotes DTC migration by inhibiting GON-1. We propose that FBL-1 and GON-1 control EMB-9 accumulation in the BM and promote PAT-3 expression to control DTC migration.     

OSM-11 facilitates LIN-12 Notch signaling during Caenorhabditis elegans vulval development

Notch signaling is critical for cell fate decisions during development. Caenorhabditis elegans and vertebrate Notch ligands are more diverse than classical Drosophila Notch ligands, suggesting possible functional complexities. Here, we describe a developmental role in Notch signaling for OSM-11, which has been previously implicated in defecation and osmotic resistance in C. elegans. We find that complete loss of OSM-11 causes defects in vulval precursor cell (VPC) fate specification during vulval development consistent with decreased Notch signaling. OSM-11 is a secreted, diffusible protein that, like previously described C. elegans Delta, Serrate, and LAG-2 (DSL) ligands, can interact with the lineage defective-12 (LIN-12) Notch receptor extracellular domain. Additionally, OSM-11 and similar C. elegans proteins share a common motif with Notch ligands from other species in a sequence defined here as the Delta and OSM-11 (DOS) motif. osm-11 loss-of-function defects in vulval development are exacerbated by loss of other DOS-motif genes or by loss of the Notch ligand DSL-1, suggesting that DOS-motif and DSL proteins act together to activate Notch signaling in vivo. The mammalian DOS-motif protein Deltalike1 (DLK1) can substitute for OSM-11 in C. elegans development, suggesting that DOS-motif function is conserved across species. We hypothesize that C. elegans OSM-11 and homologous proteins act as coactivators for Notch receptors, allowing precise regulation of Notch receptor signaling in developmental programs in both vertebrates and invertebrates.     

Tissue-specific regulation of the LIM homeobox gene lin-11 during development of the Caenorhabditis elegans egg-laying system

The egg-laying system of Caenorhabditis elegans hermaphrodites requires development of the vulva and its precise connection with the uterus. This process is regulated by LET-23-mediated epidermal growth factor signaling and LIN-12-mediated lateral signaling pathways. Among the nuclear factors that act downstream of these pathways, the LIM homeobox gene lin-11 plays a major role. lin-11 mutant animals are egg-laying defective because of the abnormalities in vulval lineage and uterine seam-cell formation. However, the mechanisms providing specificity to lin-11 function are not understood. Here, we examine the regulation of lin-11 during development of the egg-laying system. Our results demonstrate that the tissue-specific expression of lin-11 is controlled by two distinct regulatory elements that function as independent modules and together specify a wild-type egg-laying system. A uterine pi lineage module depends on the LIN-12/Notch signaling, while a vulval module depends on the LIN-17-mediated Wnt signaling. These results provide a unique example of the tissue-specific regulation of a LIM homeobox gene by two evolutionarily conserved signaling pathways. Finally, we provide evidence that the regulation of lin-11 by LIN-12/Notch signaling is directly mediated by the Su(H)/CBF1 family member LAG-1.     

EGF signaling overcomes a uterine cell death associated with temporal mis-coordination of organogenesis within the C. elegans egg-laying apparatus

We isolated cog-3(ku212) as a C. elegans egg-laying defective mutant that is associated with a connection-of-gonad defective phenotype. cog-3(ku212) mutants appear to have no connection between the vulval and the uterine lumens at the appropriate stage because the uterine lumen develops with a temporal delay relative to the vulva and, thus, is not present when the connection normally forms. The lack of temporal synchronization between the vulva and the uterus is not due to precocious or accelerated vulval development. Instead, global gonadogenesis is mildly delayed relative to development of extra-gonadal tissue. cog-3(ku212) mutants also have a specific uterine fate defect. Normally, four cells of the uterine pi lineage respond via their LET-23 epidermal growth factor-like receptors to a vulval-derived LIN-3 EGF signal and adopt the uterine vulval 1 (uv1) fate. In cog-3(ku212) mutants, these four pi progeny cells are set aside as a pre-uv1 population but undergo necrosis prior to full differentiation. A gain-of-function mutation in LET-23 EGF receptor and ectopic expression of LIN-3 EGF within the proper temporal constraints can rescue the uv1 defect, suggesting that a signaling defect, perhaps due to the temporal delay, is at fault. In support of this model, we demonstrate that lack of vulval-uterine coordination due to precocious vulval development also leads to uv1 cell differentiation defects.