Yanai, Itai (2015) International Worm Meeting "The molecular signature of animal embryogenesis."

Yanai, Itai

[International Worm Meeting, 2015]

The evolution of embryogenesis is biased since many variations affect vital processes and lead to nonviable organisms. Species comparisons have enabled to evolutionary developmental biologists to characterize such constraints. For the animal embryo, it has been proposed that a stage in mid-development is conserved throughout the kingdom. As part of a consortium of ten labs, we test this hypothesis by identifying the developmental transcriptomes of ten species, each of a different animal phylum, including Nematodes, Ctenophores, Annelids, Chordates, Platyhelminthes, Tardigrades, Arthropods, Echinoderms, Cnidarians, and Poriferas. We find that animal embryonic development comprises the coupling of two conserved gene expression modules, primarily involved in proliferation and differentiation, where the switch between them occurs at the apparent phylotypic period of each phylum. Genes whose expression is coherent across the examined species are expressed in the first module, while clade specific variations occur in the second module and the transition to it. Our results are consistent with an inverse hour-glass model of animal evolution: gene expression differences across phyla are concentrated at the inter-module switch. Since, expression differences within a phylum appear to be minimal at the phylotypic stage, our work leads us to define a phylum as a collection of species where an hourglass model holds for gene expression differences. All together, we provide a map of embryology upon which ancestral constraints are mapped and distinguished from the stages in which variations are available to the agency of natural selection. [This work is a collaboration among the Arendt (Heidelberg), Rink (Dresden), Blaxter (Edinburgh), Goldstein (North Carolina), Salzberg (Haifa), deLeon (Haifa), Yaniv (Rehovot), Gat (Jerusalem), Degnan (Queensland), Martindale (Florida), and Yanai (Haifa) labs.].

Shoenfeld, Julien et al. (2011) International Worm Meeting "Determining the role of heterotrimeric G proteins in dauer entry."

Danzi, Bryan, Shoenfeld, Julien, Myers, Edith

[International Worm Meeting, 2011]

C. elegans enter dauer under conditions of limited food, high temperature, and high concentrations of dauer pheromone. Signaling through heterotrimeric G proteins regulates sensitivity to food and dauer pheromone1,2. We are interested in whether the specific G proteins, EGL-30 (Gaq) and GOA-1 (Gao) are important for sensing the environmental signals that regulate dauer entry because it has been suggested that GOA-1 may regulate dauer formation3. EGL-30 signaling antagonizes GOA-1 signaling, suggesting that EGL-30 may also somehow regulate dauer formation. By separately controlling pheromone, temperature, and food levels we have begun to study the role of EGL-30 and GOA-1 in dauer formation and recovery. We assayed dauer formation in response to different environmental cues in egl-30 and goa-1 mutants. We found that EGL-30 and GOA-1 were not necessary for normal dauer formation at 25 deg C. Because some proteins are only required for dauer entry at higher temperatures4, we wanted to assay dauer formation in egl-30 and goa-1 mutants at 27 deg C. However, animals with egl-30 and goa-1 mutations were not viable at 27 deg C, therefore we could not determine whether these proteins are necessary for dauer formation in response to high temperatures. We determined that GOA-1 and EGL-30 were required for normal sensitivity to dauer-related ascarosides. Further studies are underway to determine the role of these specific heterotrimeric G proteins in relaying food related dauer signals. 1. Dong MQ, Chase D, Patikoglou GA, Koelle MR. (2000). Genes Dev. 14(16): 2003-14. 2. Zwaal, RR, Mendel, JE, Sternberg, PW, and Plasterk, RHA. (1997). Genetics. 145: 715-727 3. Keane and Avery. (2003). Genetics. 164(1): 153-62. 4. Ailio, M and Thomas, JH. (2000). Genetics. 156: 1047-1067.

Alter JR et al. (1998) East Coast Worm Meeting "Analysis of Protein Expression in a C. elegans Model of Huntington's Disease"

Hart AC, Faber PW, MacDonald ME, Alter JR

[East Coast Worm Meeting, 1998]

We have developed a C. elegans model of Huntington's Disease (HD) and other neurodegenerative CAG repeat diseases. HD is an autosomal dominant disorder caused by the expansion of an exonic CAG repeat in the human huntingtin gene. The 350 kDa ubiquitously expressed huntingtin protein is known to be essential, yet its function remains elusive. While unaffected individuals have a range of ~20-34 CAG repeats, affected individuals have greater than 35. The mechanism by which the corresponding expanded polyglutamine tract causes neurodegeneration and eventual cell death is unknown. Recent evidence from tissue culture experiments, transgenic mouse models and human patient data indicate that the mutant huntingtin protein forms intracellular aggregates prior to symptom formation or cell death. In addition, perinuclear aggregates of the mutant protein have been associated with neurodegeneration in patient brains (reviewed in Martindale et al. 1998 Nature Genetics 18:150). However, the mechanism by which these aggregates contribute to (or are a byproduct of) neurodegeneration is unknown. We are using the osm-10 promoter to drive expression of an N-terminal fragment of the human huntingtin protein in the ASH, ASI, PHA and PHB sensory neurons of C. elegans (WBG 15(1):40). We have expressed both 2QHD and 150QHD constructs along with OSM-10::GFP to mark the cells which are affected in our transgenic animals. The results described below are exclusively from animals coexpressing the HD and GFP proteins. We find that up to 40% of the ASH neurons of 150QHD containing animals appear to die in 8 day old animals (WBG 15(1):42). We assessed cell death by the ability of the cells to fill with DiD, a fluorescent dye that fills 6 bilateral amphid neurons in the head including ASH. Defects in dye filling are usually caused by defects in the neuron's sensory cilia. ASH neurons that did not fill with dye and did not express OSM-10::GFP were considered dead in this assay. We have used immunohistochemistry to confirm that ASH cell death is age and polyglutamine dependent in this system. We stained 8 day old transgenic animals with antisera which recognize OSM-10 and GFP; failure of an individual ASH neuron to be visualized by both antibodies led us to conclude that the cell was dead. In this experiment, we confirmed that 2QHD does not cause ASH neurons to die, but that 150QHD causes cell death in old but not young animals. To determine whether our C. elegans model is consistent with human patient data and mouse models, we analysed the formation of intracellular protein aggregates in the ASH neurons of transgenic worms. We used the 3715(HP1) polyclonal huntingtin antibody, which recognizes the N-terminal fragment of the protein, to assess the expression level and subcellular localization of the various huntingtin protein fragments. While expression of all HD constructs was detected in a polyglutamine independent manner, we demonstrated a correlation between the level of 150HD accumulation and the percentage of ASH neurons affected in this system. In our transgenic animals, the N-terminal fragment of huntingtin forms cytoplasmic, axonal, dendritic and perinuclear aggregates in a time- and polyglutamine- dependent manner. Currently we are using other huntingtin antibodies, which have recognized intranuclear mutant huntingtin aggregates in human and mouse brains, to determine whether similar aggregates form in C. elegans ASH neurons expressing the mutant protein (Davies et al. 1997 Cell 90:537). The work presented here and other data (Faber et al. 1998 ECWM) suggest that the activity of mutant huntingtin is similar in our model and the human disease.