Lesch BJ et al. (2012) Nat Rev Genet "Genetics of germ cell development."

Page DC, Lesch BJ

[Nat Rev Genet, 2012]

The germ line represents a continuous cellular link between generations and between species, but the germ cells themselves develop in a specialized, organism-specific context. The model organisms Caenorhabditis elegans, Drosophila melanogaster and the mouse display striking similarities, as well as major differences, in the means by which they control germ cell development. Recent developments in genetic technologies allow a more detailed comparison of the germ cells of these three organisms than has previously been possible, shedding light not only on universal aspects of germline regulation, but also on the control of the pluripotent state in vivo and on the earliest steps of embryogenesis. Here, we highlight themes from the comparison of these three alternative strategies for navigating the fundamental cycle of sexual reproduction.

Lesch BJ et al. (2009) Genes Dev "Transcriptional regulation and stabilization of left-right neuronal identity in C. elegans."

Gehrke AR, Lesch BJ, Bargmann CI, Bulyk ML

[Genes Dev, 2009]

At discrete points in development, transient signals are transformed into long-lasting cell fates. For example, the asymmetric identities of two Caenorhabditis elegans olfactory neurons called AWC(ON) and AWC(OFF) are specified by an embryonic signaling pathway, but maintained throughout the life of an animal. Here we show that the DNA-binding protein NSY-7 acts to convert a transient, partially differentiated state into a stable AWC(ON) identity. Expression of an AWC(ON) marker is initiated in nsy-7 loss-of-function mutants, but subsequently lost, so that most adult animals have two AWC(OFF) neurons and no AWC(ON) neurons. nsy-7 encodes a protein with distant similarity to a homeodomain. It is expressed in AWC(ON), and is an early transcriptional target of the embryonic signaling pathway that specifies AWC(ON) and AWC(OFF); its expression anticipates future AWC asymmetry. The NSY-7 protein binds a specific optimal DNA sequence that was identified through a complete biochemical survey of 8-mer DNA sequences. This sequence is present in the promoter of an AWC(OFF) marker and essential for its asymmetric expression. An 11-base-pair (bp) sequence required for AWC(OFF) expression has two activities: One region activates expression in both AWCs, and the overlapping NSY-7-binding site inhibits expression in AWC(ON). Our results suggest that NSY-7 responds to transient embryonic signaling by repressing AWC(OFF) genes in AWC(ON), thus acting as a transcriptional selector for a randomly specified neuronal identity.

Lesch BJ et al. (2010) Genes Dev "The homeodomain protein hmbx-1 maintains asymmetric gene expression in adult C. elegans olfactory neurons."

Lesch BJ, Bargmann CI

[Genes Dev, 2010]

Differentiated neurons balance the need to maintain a stable identity with their flexible responses to dynamic environmental inputs. Here we characterize these opposing influences on gene expression in Caenorhabditis elegans olfactory neurons. Using transcriptional reporters that are expressed differentially in two olfactory neurons, AWC(ON) and AWC(OFF), we identify mutations that affect the long-term maintenance of appropriate chemoreceptor expression. A newly identified gene from this screen, the conserved transcription factor hmbx-1, stabilizes AWC gene expression in adult animals through dosage-sensitive interactions with its transcriptional targets. The late action of hmbx-1 complements the early role of the transcriptional repressor gene nsy-7: Both repress expression of multiple AWC(OFF) genes in AWC(ON) neurons, but they act at different developmental stages. Environmental signals are superimposed onto this stable cell identity through at least two different transcriptional pathways that regulate individual chemoreceptor genes: a cGMP pathway regulated by sensory activity, and a daf-7 (TGF-beta)/daf-3 (SMAD repressor) pathway regulated by specific components of the density-dependent C. elegans dauer pheromone.

Alqadah, A. et al. (2017) International Worm Meeting "An importin protein controls asymmetric olfactory neuron differentiation by mediating nuclear transport of a homoeodomain transcription factor for sox-2 expression."

Chuang, C.-F., Hsieh, Y.-W., Alqadah, A., Lesch, B.J.

[International Worm Meeting, 2017]

Defects in brain laterality are associated with several neurological diseases. Left-right asymmetry in the nervous system is observed in many species; however, the mechanisms used to establish brain lateralization are not well understood. The pair of AWC olfactory neurons displays molecular and functional left-right asymmetry in the nematode C. elegans. The neurons are differentiated into the AWCOFF and AWCON subtypes that express different sets of genes and have unique functions. The AWC neurons display stochastic asymmetry, such that either subtype has equal probability of residing on the left or right side of the animal. This asymmetry is established using a calcium-triggered signaling pathway consisting of voltage-gated calcium channels, CaMKII, TIR-1 (Sarm1) adaptor protein, and a MAP kinase cascade to promote the default AWCOFF identity. The contralateral neuron represses the calcium signaling pathway through NSY-5 gap junctions and downstream redundant SLO-1/SLO-2 BK potassium channels to induce the AWCON cell identity. It is unknown what molecules function downstream of the SLO-1 and SLO-2 potassium channels to induce AWCON. To address this question, we performed a forward genetic screen to discover suppressors of slo-1(gf) mutants that act as modifiers of K+ channels (mok genes). Out of 6,000 genomes screened, we identified 16 mok mutants. Using whole genome sequencing (kindly performed by Oliver Hobert's lab), we found that the mok-5 gene encodes a highly conserved importin protein. A vy10 missense mutation in the mok-5 importin gene results in a 2AWCOFF phenotype, suggesting an essential role of mok-5 in promoting the AWCON subtype. Double mutant analysis places mok-5 downstream of the calcium-triggered MAP kinase cascade to promote the AWCON subtype. Consistent with the genetic data, mok-5 importin is asymmetrically expressed in the AWCON neuron and acts cell autonomously to specify the AWCON subtype. Furthermore, we show that mok-5 importin functions to mediate transport of a homeodomain transcription factor required for AWCON subtype specification into the nucleus of AWC neurons. Lastly, we show that the homeodomain transcription factor regulates the expression of HMG transcription factor sox-2 by direct binding to the sox-2 promoter to promote the AWCON identity. To the best of our knowledge, this is the first study to implicate an importin protein in the development of left-right asymmetry in the nervous system.

Vasiliauskas D et al. (2009) Genes Dev "Maintaining a stochastic neuronal cell fate decision."

Johnston R, Desplan C, Vasiliauskas D

[Genes Dev, 2009]

Sensory systems generally contain a number of neuronal subtypes that express distinct sensory receptor proteins. This diversity is generated through deterministic and stochastic cell fate choices, while maintaining the subtype often requires a distinct mechanism. In a study published in the February 1, 2009, issue of Genes & Development, Lesch and colleagues (pp. 345-358) describe a new transcription factor, NSY-7, that acts to stabilize a stochastic subtype choice in AWC chemosensory neurons in Caenorhabditis elegans.

H Pamjav et al. (1999) International C. elegans Meeting "Phylogenetic analysis of entomopathogenic nematode / bacterium symbiotic complexes by using PhastSystem PAGE PCR-RFLP of rDNA spacer sequences"

D Triga, A Fodor, H Pamjav, Z Buzas, E Szallas

[International C. elegans Meeting, 1999]

Entomopathogenic nematode (EPN)species belonging to the Steinernema and Heterorhabditis genera are closely related to C. elegans (Blaxter et al., 1998). They form an intimate symbiotic complex with bacteria Xenorhabdus spp. and Photorhabdus spp., respectively, which are closely related to E. coli . The symbiosis is developmentally regulated: there is a direct cell-cell contact between the gut cell of the (infective) dauerlarva and the primary phase variant of the symbiotic bacteria. The symbiosis is taxon specific. Individual Xenorhabdus species used as symbionts by each Steinernema species and individual strains of Photorhabdus luminescens used as symbionts by each Heterorhabditis strains belonging to different species. The phylogenetic relations between species and strains have been analysed by RFLP of the internally transcribed spacer region of the respective rRNA operon. The PCR-amplified DNAs were digested by different restriction enzymes and the restriction patterns obtained by PhastSystem PAGE were compared. On the basis of the comparative analysis of the ITS1 - ITS2 patterns nematodes could be identified at species level. Xenorhabdus species could also be identified on the basis of the comparative analysis of the spacer region of the 16S - 23S rRNA operon. P. luminescens strains, belonging to different subclusters (Szallas et al., 1997) could be separated on the basis of the RFLP pattern of the spacer region of the 16S - 23S rRNA operon. Adams, B.J. (1998). Species conception and the evolutionary paradigm in modern nematology. J. nematol. 30, 1-21. Adams, B.J., Burnell, A.M. @ Powers,T.O. (1998). A phylogenetic analysis of Heterorhabditis based on ITS 1 DNA sequence data. J. nematol. 30, 22-39. Blaxter,R. et al.(1998).Molecular evolutionary framework for Phylum nematoda. Nature 392,71-75. Szallas E., Koch, H., Fodor,A.,Szentirmai, A., Nealson,K.H. Stackebrandt, E.(1997).Phylogenetic evidence for taxonomic heterogeneity of P.luminescens. IJSB 47, 402-407.

Chin Yee Loh et al. (2001) International C. elegans Meeting "The nuclear receptor SEX-1 in C. eleganssex determination"

Barbara J Meyer, Chin Yee Loh

[International C. elegans Meeting, 2001]

In C. elegans , the primary sex determination signal that specifies the two sexes, XO males and XX hermaphrodites, is the number of X chromosomes relative to the sets of autosomes. The X-signal elements located on the X chromosome function cumulatively to repress the sex determination and dosage compensation switch gene xol-1 , whose level of expression sets the sexual fates. The X-signal element, sex-1 , encodes a nuclear receptor that transcriptionally regulates xol-1. Previously, we have identified a 2.8 kb region of the xol-1 promoter that binds SEX-1 in vivo (Carmi, 1998). A GFP reporter fused to this 2.8 kb promoter region is derepressed in a sex-1(gm41) mutant background, further suggesting that SEX-1 regulatory regions might be contained within this fragment of the xol-1 promoter. To determine whether SEX-1 binds directly to the xol-1 promoter, we are undertaking in vitro binding experiments with a partially-purified DNA-binding domain of SEX-1 and fragments of the xol-1 promoter. In these experiments, we are also interested in investigating whether SEX-1 functions as a monomer or dimer. Carmi I., Kopczynski J.B., and Meyer B.J. (1998). The nuclear hormone receptor SEX-1 is an X-chromosome signal that determines nematode sex. Nature 396 , 168-73.

Rauthan, M. et al. (2017) International Worm Meeting "MicroRNA regulation of nicotine-dependent behavior in C. elegans."

Rauthan, M., Ronan, E.A., Gong, J., Xu, X.Z.S., Liu, J., Wescott, S.

[International Worm Meeting, 2017]

Tobacco smoking is the leading cause of preventable death in developed nations. Nicotine is the principle addictive substance in cigarettes. Chronic exposure to nicotine up-regulates nAChRs and is thought to play a critical role in the primary steps of nicotine dependence, but the underlying mechanisms are not well understood. We have previously developed a C. elegans model of nicotine dependent behavior, and shown that the nAChR gene acr-15 is required for acute response to nicotine (Feng et al., 2006). Here we identify a key role for microRNA in regulating nicotine-dependent behavior by modulating nAChR expression in C. elegans. Specifically, we show that chronic nicotine treatment down-regulates microRNA machinery, leading to up-regulation of another nAChR gene that is specifically required for nicotine withdrawal behavior. This effect is mediated by a microRNA that recognizes the 3'UTR of nAChR transcripts. These observations uncover an interesting phenomenon that different nAChRs mediate distinct aspects of nicotine dependence in C. elegans. Our results reveal a functional link between nicotine, microRNA, nAChRs, and nicotine-dependent behavior. Reference(s): 1. Feng, Z., Li, W., Ward, A., Piggott, B.J., Larkspur, E., Sternberg, P.W., and Xu, X.Z.S. (2006). A C. elegans model of nicotine-dependent behavior: regulation by TRP family channels. Cell 127, 621-633.

Patel M et al. (2024) ACS Chem Neurosci "Amyloidogenic Propensity of Metabolites in the Uric Acid Pathway and Urea Cycle Critically Impacts the Etiology of Metabolic Disorders."

Nazir A, Tripathi A, Naseer A, Pandey MK, Kautu A, Gupta S, Joshi A, Gour N, Patel M, Joshi KB, Jaiswal A, Verma S, Dubey KD, Kumar R, Minocha T

[ACS Chem Neurosci, 2024]

Novel insights into the etiology of metabolic disorders have recently been uncovered through the study of metabolite amyloids. In particular, inborn errors of metabolism (IEMs), including gout, Lesch-Nyhan syndrome (LNS), xanthinuria, citrullinemia, and hyperornithinemia-hyperammonemia-homocitrullinuria (HHH) syndrome, are attributed to the dysfunction of the urea cycle and uric acid pathway. In this study, we endeavored to understand and mechanistically characterize the aggregative property exhibited by the principal metabolites of the urea cycle and uric acid pathway, specifically hypoxanthine, xanthine, citrulline, and ornithine. Employing scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM), we studied the aggregation profiles of the metabolites. Insights obtained through molecular dynamics (MD) simulation underscore the vital roles of &#x3c0;-&#x3c0; stacking and hydrogen bonding interactions in the self-assembly process, and thioflavin T (ThT) assays further corroborate the amyloid nature of these metabolites. The <i>in vitro</i> MTT assay revealed the cytotoxic trait of these assemblies, a finding that was substantiated by <i>in vivo</i> assays employing the <i>Caenorhabditis elegans</i> (<i>C. elegans</i>) model, which revealed that the toxic effects were more pronounced and dose-specific in the case of metabolites that had aged via longer preincubation. We hence report a compelling phenomenon wherein these metabolites not only aggregate but transform into a soft, ordered assembly over time, eventually crystallizing upon extended incubation, leading to pathological implications. Our study suggests that the amyloidogenic nature of the involved metabolites could be a common etiological link in IEMs, potentially providing a unified perspective to study their pathophysiology, thus offering exciting insights into the development of targeted interventions for these metabolic disorders.

Erich M Schwarz et al. (2003) International Worm Meeting "Comparative analysis of cis-regulatory sequences using four Caenorhabditis species."

Nora Mullaney, Erich M Schwarz, Tristan De Buysscher, Paul W Sternberg, Barbara J Wold, John A DeModena, Eunpyo Moon, Hiroaki Shizuya

[International Worm Meeting, 2003]

Comparing homologous cis-regulatory DNA sequences from three or more genomes has advantages over pairwise comparison of only two. Cis-regulatory sequences are short (6-20 bp) and tolerate substantial variation. Purely random pairing of unrelated 100-bp DNA segments is expected to yield two perfect 6 bp matches. Alignment of a third or fourth sequence should greatly lower the frequency of false positive regions, allowing small but real cis-regulatory sequences to be efficiently detected. This increased resolution should also allow direct comparison between phylogenetically conserved sequences and statistically overrepresented sequences, which may yield complementary views of regulatory elements. In the Caenorhabditis genus, C. remanei appears to be most closely related to C. briggsae; two other species, CB5161 and PS1010, comprise the two closest known and culturable Caenorhabditis species outside the elegans-briggsae group (Fitch, 2000). CB5161 is closest to C. elegans, and PS1010 the next most divergent; these two species thus provide an evolutionarily graded series. We have constructed fosmid libraries from CB5161 and PS1010, and begun sequencing individual fosmids for comparative analysis of genes involved in vulval or sensory neuron development. At the same time, we have devised the Mussa software package to adapt the algorithms of Davidson and coworkers (Brown et al., 2002) to multiple sequence analysis. At this writing, we have sequence data from the egl-30, lin-11, and mab-5 loci of both CB5161 and PS1010. Initial results of sequencing and comparative sequence analysis will be presented. References: Brown, C.T., Rust, A.G., Clarke, P.J., Pan, Z., Schilstra, M.J., De Buysscher, T., Griffin, G., Wold, B.J., Cameron, R.A., Davidson, E.H., and Bolouri, H. (2002). New computational approaches for analysis of cis-regulatory networks. Dev. Biol. 246, 86-102; Fitch, D.H.A. (2000). Evolution of Rhabditidae and the male tail. J. Nematol. 32, 235-244.