Ferreira, Helder C. et al. (2013) International Worm Meeting "Developmental regulation of telomere anchoring in C. elegans."

Jegou, Thibaud, Ferreira, Helder C., Gasser, Susan M., Towbin, Benjamin

[International Worm Meeting, 2013]

Telomeres are specialized protein-DNA structures that protect chromosome ends. In lower eukaryotes, such as budding yeast, telomeres show a distinct nuclear organization, being bound to the nuclear periphery. By imaging telomere position in the metazoan C. elegans, we find that, here too, telomeres are preferentially located near the nuclear envelope. Peripheral telomere localization increases during embryogenesis and persists in later larval stages. We show that in early embryogenesis telomere position is independent of the Ku complex and of H3 K9 methylation but instead is regulated by the PIAS-like SUMO E3 ligase gei-17 and the nuclear envelope protein SUN-1. Moreover, we find that the shelterin component POT-1 but not POT-2 is required to maintain telomeres at the nuclear periphery. Interestingly, POT-1 inhibits recombination mediated telomere maintenance. To our knowledge, this is the first description of telomere position in C. elegans.

Yu, Xupeng et al. (2021) International Worm Meeting "Characterising single-stranded telomere binding proteins in C. elegans"

Ferreira, Helder, Gray, Sean, Yu, Xupeng

[International Worm Meeting, 2021]

Telomeres are nucleoprotein complexes that protect the ends of linear chromosomes. Loss of telomere capping activates the DNA damage response, normally resulting in senescence or apoptosis. C. elegans telomeres are unusual in that they end in C-rich single-stranded DNA overhangs as well as the more common G-rich single-stranded DNA overhangs. Distinct proteins, namely POT-1 and POT-2, bind these different overhangs. However, neither of these proteins are essential, which suggests that there may be other telomeric single-stranded DNA binding proteins in worms. We characterise POT-3 as a single OB-fold containing protein that specifically binds the G-rich telomere strand with remarkable selectivity and affinity. We map its minimal DNA recognition sequence to a 6nt GCTTAG sequence. Strikingly, POT-3 and POT-2 bind precisely the same minimal nucleotide sequence but POT-3 has higher selectivity when the GCTTAG recognition sequence is at the extreme 3' hydroxyl end. We believe that POT-3's ability to cap the terminal end of the G-overhang mediates a unique telomeric function.

Lisa Girard et al. (2001) International C. elegans Meeting "Role of egl-5 in EGF/Wnt signal integration in the specification of P12 fate"

Scott Emmons, Paul Sternberg, Henrique B Ferreira, Lisa Girard

[International C. elegans Meeting, 2001]

The C. elegans Hox gene egl-5 is most similar, based on sequence analysis, to Abdominal-B . Consistent with its assignment into this paralog group, egl-5 is expressed in the posterior region of the worm. Immuno-staining results have shown that in the hermaphrodite, egl-5 is expressed in the hermaphrodite specific neuron, body wall muscle, posterior lateral microtubule neuron, PVC interneuron, the rectal epithelial cells K, F, B, U and the P12 neuroectoblast cell. 1 The two most posterior P cells are P11 and P12. The anterior products of their first division are both neuroblasts. P11.p fuses with the epidermal syncytium and P12.p divides again during late L1. The anterior division products, the epidermal cells P12.pa and P11.p are distinguishable by their distinct nuclear morphologies and positions. Previous genetic analysis indicates that P12 fate specification requires the synergistic action of the EGF and the Wnt signaling pathways. Reduction - or loss of function mutations in components of the EGF or the Wnt pathway result in partially penetrant P12 to P11 or P11 to P12 transformations. Double mutants of EGF and Wnt pathway components significantly enhance the frequency of transformation. P12 is not specified in an egl-5(lf) mutant and overexpression of egl-5 can rescue the loss of P12 specification phenotype of let-23 mutants. 2 In order to understand how information from the EGF and Wnt pathway are integrated at a cis -regulatory level, we have undertaken an analysis of the egl-5 promoter in collaboration with Scott Emmons to determine elements required for egl-5 expression in P12. 3 Do the two pathways converge on the egl-5 promoter or upstream of it? Beginning with a large promoter construct provided by Ferreira and Emmons, we have identified an approximately 1.3 kb. fragment of egl-5 promoter sufficient to drive expression of a heterologous promoter in P12. This 1.3 kb fragment contains six sites of approximately 20-40 bp each which are conserved between C. elegans and C. briggsae . Specific deletion of at least two of these sites in certain combinations eliminates expression in P12, suggesting that these sites might represent P12 enhancers. Complementary to our cis regulatory analysis, we have been using EMS screens to identify, and are currently characterizing, potential trans-acting factors as well as other genes which may participate in signal integration. Ferreira et al .(1999) Dev. Biol. 207:215-228 Jiang and Sternberg (1998) Development 125:2337-2347

Hannes E Buelow et al. (2005) International Worm Meeting "HOX genes define position-specific projection patterns of ventral nerve cord motor neurons"

Oliver Hobert, Hannes E Buelow, Nartono Tjoe

[International Worm Meeting, 2005]

The developing nervous system of all animals consists of a multitude of neuronal cell types with characteristic position-specific projection and innervation patterns. In the developing spinal cord of vertebrates recent work has shown that homeodomain-containing transcription factors of the Hox-c class are sequentially expressed in overlapping domains along the anterior-posterior (ap) axis and thereby determine distinct neuronal cell fates (1). However, little is known about how neuronal fate and cell position is translated into the specific neuronal trajectories that are characteristic for their respective position along the ap axis. The cluster of Hox genes in C. elegans consists of at least four genes ceh-13, lin-39, mab-5, and egl-5 which have been studied widely for their role in different cell fate decisions along the ap axis (2). Furthermore, Hox genes in C.elegans have been shown to define the migratory behavior of neuroblasts along the ap axis, yet few if any axonal phenotypes have been reported for these mutants (3). We show here that in C. elegans mutations in Hox genes lead to homeotic transformations in neuronal cell fates of motor neurons in the ventral nerve cord where specific neurons at specific positions along the ap axis adopt fates of adjacent neurons. These transformations are evidenced by changes in axonal projection patterns of motor neurons along the ap axis and will allow to dissect how cell fate/position is linked to axonal projection patterns. We are currently working on two basic questions relating to the observed axonal phenotypes. Specifically we are asking whether (a) Hox genes act cell-autonomously in neurons to determine position-specific axonal projection patterns and (b) which guidance factors may be under (direct or indirect control) of the Hox genes to determine the axonal trajectories. We are using a combination of expression analyses and cell-specific rescue experiments to address the first question. To answer the second question we are employing a candidate gene approach to identify guidance cues which may be responsible for specific axonal projection patterns. For these experiments we are using both gfp reporters for various guidance cues to determine whether these reporters are under control of Hox genes as well as double mutant analyses. (1) Dasen JS et al., Nature. 2003;425: 926-33. (2) Wang BB et al., Cell. 1993;74(1): 29-42.; Clark, S. et al. Cell. 1993;74(1)43-55. Costa M, et al. Cell. 1988; 55(5):747-56.; Ferreira HB et al., Dev. Biol. 1999; 207: 215-228; Brunschwig K et al., Development. 1999;126(7): 1537-46. (3) Desai C et al. Nature. 1988; 336:638-46.