egl-17 encodes an invertebrate fibroblast growth factor family member required specifically for sex myoblast migration in Caenorhabditis elegans

Receptor tyrosine phosphatases: the worm clears the picture

Recent work on the Caenorhabditis elegans clr-1 gene shows that the receptor tyrosine phosphatase that it encodes negatively regulates a receptor tyrosine kinase related to mammalian fibroblast growth factor receptors. This opens up a promising system for investigating receptor tyrosine phosphatase function.

Fibroblast growth factors as multifunctional signaling factors

The fibroblast growth factor (FGF) family consists of at least 15 structurally related polypeptide growth factors. Their expression is controlled at the levels of transcription, mRNA stability, and translation. The bioavailability of FGFs is further modulated by posttranslational processing and regulated protein trafficking. FGFs bind to receptor tyrosine kinases (FGFRs), heparan sulfate proteoglycans (HSPG), and a cysteine-rich FGF receptor (CFR). FGFRs are required for most biological activities of FGFs. HSPGs alter FGF-FGFR interactions and CFR participates in FGF intracellular transport. FGF signaling pathways are intricate and are intertwined with insulin-like growth factor, transforming growth factor-beta, bone morphogenetic protein, and vertebrate homologs of Drosophila wingless activated pathways. FGFs are major regulators of embryonic development: They influence the formation of the primary body axis, neural axis, limbs, and other structures. The activities of FGFs depend on their coordination of fundamental cellular functions, such as survival, replication, differentiation, adhesion, and motility, through effects on gene expression and the cytoskeleton.

LIN-12 protein expression and localization during vulval development in C. elegans

We have used a LIN-12::GFP fusion protein to examine LIN-12 accumulation during cell fate decisions important for vulval development. During the naturally variable anchor cell (AC)/ventral uterine precursor cell (VU) decision of the somatic gonad, a transcription-based feedback mechanism biases two equivalent cells so that one becomes the AC while the other becomes a VU. LIN-12::GFP accumulation reflects lin-12 transcription: LIN-12::GFP is initially present in both cells, but disappears from the presumptive AC and becomes restricted to the presumptive VU. During vulval precursor cell (VPC) fate determination, six equipotential cells uniformly transcribe lin-12 and have invariant fates that are specified by multiple cell-cell interactions. The pattern of LIN-12::GFP accumulation in VPCs and in the VPC lineages is dynamic and does not always reflect lin-12 transcription. In particular, LIN-12::GFP is expressed initially in all six VPCs, but appears to be reduced specifically in P6.p as a consequence of the activation of the Ras pathway by an EGF-like inductive signal from the AC. We propose that downregulation of LIN-12 stability or translation in response to inductive signalling helps impose a bias on lateral signalling and contributes to the invariant pattern of VPC fates.

Understanding cell migration guidance: lessons from sex myoblast migration in C. elegans

Studies of sex myoblast (SM) migration in the nematode Caenorhabditis elegans have shown that multiple guidance mechanisms cooperate to ensure the accurate and reproducible targeting of the SMs. Many issues arise in the analysis of SM migration, including the action of multiple guidance mechanisms, redundant sources of guidance information, the multiple uses of molecular components, and whether factors affect cell fate determination events or the guidance mechanisms themselves. These issues are common to many cell migration events and make the analysis of SM migration instructive to our general understanding of how cell migrations are controlled.

Primary structure of ovine fibroblast growth factor-1 deduced by protein and cDNA analysis

The amino acid sequence of full-length ovine fibroblast growth factor-1 (FGF-1) was determined by a combination of protein and cDNA sequencing. FGF-1 cDNA analysis indicated that ovine kidney cells express mRNAs encoding both full-length FGF-1 and a truncated FGF-1 variant. An overall comparison of the ovine FGF-1 primary sequence to the eight species studied to date revealed a high degree of conservation, with ovine FGF-1 sharing 90 and 95% sequence identity with human FGF-1 and bovine FGF-1, respectively. Additionally, the FGF-1 proteins from the various species have conserved cysteine residues at positions 30 and 97 and contain acetylated amino-terminal alanine residues. Mass spectrometry analysis confirmed that the blocking group of ovine FGF-1 is also consistent with that of an acetyl-moiety. In contrast to the other FGF-1 proteins, the 154 residue primary sequence of ovine FGF-1 contains three unique amino acid differences: Arg9, Arg44, and Ile123. Ovine FGF-1, unlike human FGF-1, is a potent mitogenic factor for NIH 3T3 fibroblasts in the absence of heparin. In the presence of exogenous heparin, the mitogenic activity of ovine FGF-1 is potentiated slightly.

EGL-17(FGF) expression coordinates the attraction of the migrating sex myoblasts with vulval induction in C. elegans

During the development of the egg-laying system in Caenorhabditis elegans hermaphrodites, central gonadal cells organize the alignment of the vulva with the sex myoblasts, the progenitors of the egg-laying muscles. A fibroblast growth factor [EGL-17(FGF)] and an FGF receptor [EGL-15(FGFR)] are involved in the gonadal signals that guide the migrations of the sex myoblasts. Here we show that EGL-17(FGF) can act as an instructive guidance cue to direct the sex myoblasts to their final destinations. We find that egl-17 reporter constructs are expressed in the primary vulval cell and that EGL-17(FGF) expression in this cell correlates with the precise positioning of the sex myoblasts. We postulate that EGL-17(FGF) helps to coordinate the development of a functional egg-laying system, linking vulval induction with proper sex myoblast migration.