John White (2008) Development & Evolution Meeting "Cell Fate: Embryonic"

John White

[Development & Evolution Meeting, 2008]

No abstract submitted.

White JG et al. (2000) Midwest Worm Meeting "4D Software"

White JG, Eliceiri KW, Thomas CF

[Midwest Worm Meeting, 2000]

Jamie White et al. (2005) International Worm Meeting "Gender-specific social behaviors"

Eliott Davidson, Jamie White, Erik M Jorgensen, Thomas Nicholas

[International Worm Meeting, 2005]

C. elegans sense and respond to the presence of other individuals in a gender-specific manner: males are attracted to hermaphrodites, but hermaphrodites avoid one another. Male attraction appears to be a mate-finding behavior, because males initiate steps of the mating motor program upon locating a source of hermaphrodite-conditioned media. Avoidance could function to disperse hermaphrodites within the available food. The gender-specific response could arise from activation of gender-speci?c signal-transduction pathways, from sexually dimorphic neural circuitry, or from a combination of these mechanisms. Given the morphological similarities between the male and hermaphrodite nervous systems, these sexually dimorphic responses should provide an opportunity to relate discrete differences in nervous system structure to differences in behavior. We are interested in determining how sensory signal transduction pathways and neural circuitry generate attraction and avoidance behaviors in a gender-specific manner. We are taking the following approaches to these questions: (1) candidate gene analysis, (2) forward genetics, (3) analysis of natural variation in the behaviors, (4) cell-specific rescue of neural function (5) neuron ablations, and (6) chemical purification of the attraction and avoidance factor(s). Results from three approaches are presented here. Candidate gene analysis indicates that attraction and avoidance behaviors use different sensory signal transduction pathways. Hermaphrodite avoidance requires a cGMP-gated channel encoded by tax-2 and tax-4, and partially depends on the DAF-11 guanylate cyclase. Additionally, avoidance requires DAF-7/TGF- and a TGF- receptor encoded by daf-1 and daf-4, perhaps for the proper expression of a chemoreceptor that detects the avoidance signal. Male attraction requires a transient receptor potential channel encoded by osm-9, but not any of the molecules required for avoidance. Forward genetics: An F2 clonal screen in him backgrounds has identified strains mutant for attraction and avoidance behavior. A screen of 800 haploid genomes for each behavior isolated 4 strains strongly mutant for avoidance, 3 strongly mutant for attraction, and 1 strain that was partially defective for both behaviors. These strains have intact chemosensory neurons as indicated by dye-filling. Chemical purification of hermaphrodite factors: After solid-phase extraction on a C18 cartridge, attraction and avoidance activities are found in different fractions, indicating that hermaphrodites release separate signals to elicit attraction and avoidance behavior.

White I et al. (2000) East Coast Worm Meeting "Screening for new alleles of gon-11"

Ginsburg MA, White I, Lambie EJ

[East Coast Worm Meeting, 2000]

gon-11 is defined by a single temperature sensitive allele, dx5. At restrictive temperature, dx5 homozygotes derived from a heterozygous mother exhibit an incompletely penetrant proximal germline proliferation phenotype. We suspect that this is due to minor defects in gonadogenesis that permit signals from the anchor cell to reach the germ cells during L2 (1). dx5 homozygotes that are derived from a homozygous mother show an incompletely penetrant Gon phenotype that resembles that seen in gon-2 mutants (2). Early divisions of the gonadal precursors and their immediate descendants are delayed, incomplete or altogether absent, resulting in very small gonad size. We are currently searching for additional (stronger!) alleles of gon-11, with the hope that they will facilitate mapping and provide us with a better understanding of the function of this gene. Since dx5/Df animals produce Gon progeny at high frequency, we have been able to establish an efficient noncomplementation screen that should enable the isolation of an allelic series. The mechanics of this screen and a progress report will be presented. 1. Seydoux, Schedl and Greenwald, 1990. Cell 61:939 2. Sun and Lambie, 1997. Genetics 147:1077 This work is supported by NIH grant GM49785

White JG et al. (1981) International C. elegans Meeting "the nervous system of C elegans."

Thomson JN, Southgate E, White JG

[International C. elegans Meeting, 1981]

White JG et al. (1983) International C. elegans Meeting "the nervous system of C elegans."

Southgate E, Brenner S, Thomson JN, White JG

[International C. elegans Meeting, 1983]

White JG et al. (1991) International C. elegans Meeting "THE STRUCTURE OF THE L4 HERMAPHRODITE GONAD."

White JG, Southgate E, Kershaw D

[International C. elegans Meeting, 1991]

We have been reconstructing the hermaphrodite gonad from electron micrographs of serial sections. This structure has a two-fold axis of symmetry centred about the vulva. There are 8 distinct regions in the somatic gonad: the connection to the vulva, the connection to the seam cells, the uterus, the spermathecal valve, the spermatheca, the oviduct, the ovary sheath and the distal tip. Starting at the vulva there are a group of three sets of two mononucleate cells (uv1-3) that form the connection of the uterus to the vulva; there is also a single dorsal uterine cell (du) with four nuclei opposite the ventral vulval/uterine junction in this region. The uterus is attached to the seam cells laterally in the vicinity of the vulva by a single 'H' shaped cell containing 9 nuclei (use). Next there is a sequence of four multinucleate toroidal uterine cells (ut1-4); these are followed by a toroidal spermathecal valve cell containing four nuclei which has a ring of microfilaments that wrap around the inside face of the torus and presumably acts as a sphincter to close the valve in the adult. The lumen of the valve cell is blocked by a bi-nucleate plug cell in the L4; presumably this gets expelled from the gonad when eggs pass through the spermathecal valve. Distal to the spermathecal valve are the cells of the spermatheca. In the L4 these are organised as an extended tube made up of 28 individual, mononuclate cells. In the proximal regions these cells are arranged as four cells surrounding the central lumen, whereas there are only two cells surrounding the lumen in more distal regions. The spermathecal cells are connected by characteristic electron dense junctions and seem to be in the process of telescoping together in the L4 to form the more compact adult structure. The oviduct is made up of two sets of two mononuclear cells which contain prominent assemblies of myofilaments. This structure is highly motile and seems to be used for picking an oocyte from the syncytial mass of germ cells and delivering it to the spermatheca where it is fertilised. Distal to the oviduct is a single binucleate toroidal cell that surrounds the germ cells. In the L4s these are primary spermatocytes. The gonad no longer has a continuous sheath of somatic cells beyond this region. It is, however, partially ensheathed by 6 cells and completely surrounded by a basal lamina. The distal tip cell, as its name implies, is situated at the distal extremity of each arm of the gonad. We hope that a more detailed appreciation of the anatomical organisation of the gonad will enable a more precise description of the phenotype of sterile or intersexual mutations to be made and thereby facilitate studies of the genetic basis of organogenesis.

White JG et al. (1991) International C. elegans Meeting "ULTRASTRUCTURAL STUDIES OF THE DEVELOPING VULVA"

White JG, Kershaw D, Southgate E

[International C. elegans Meeting, 1991]

The L4 vulval primordium consists of a tube made up of a stack of seven toroidal, multinucleate epithelial cells. We have been studying the developmental events that lead to the generation of this organ from the three progenitor ventral epithelial cells. The seven vulval cells have been designated A, B1, B2, C, D, E & F. Cell A is attached to the syncytial hypodermis (hyp-7) and F is attached to the the uv1 cells of the uterus. In addition, E is attached to the seam cells laterally. Vulval cells are polarised such that their apical surfaces are situated at the inside of the toroid. Belt desmosomes are seen at the attachment points between adjacent cells and demarcate the apical from the basolateral domain within a cell. The ventral epithelial cells of the vulval equivalence group that do not normally contribute to the vulva (i.e. P3p, P4p & P8p) fuse soon after they divide (indeed, in one reconstruction, P4pa & P4pp had fused before P6p had completed cell division). Interactions from the anchor cell designate P5p, P6p and P7p as vulval precursors and these cells undergo two rounds of division without any overt signs of differentiation. At this stage the vulval primordium consists of a linear sequence of 12 epithelial cells and has started to buckle inwards. The first sign of organogenesis occurs when P6ppp and P6paa divide transversely. The daughters of these two divisions move ventrally and laterally towards the centre line of the vulva where they connect to form a ring of cells. When the ring has formed it appears as if it contracts forming an internal mound which enlarges dorsally. We are currently reconstructing a later stage, lineaged animal which should reveal how the other toroids are formed and how the connection with the uterus is made.

Jamie White et al. (2007) International Worm Meeting "Genes required for sex-specific pheromone responses."

Jamie White, Erik M. Jorgensen, Eliott R. Davidson, Jeff Gritton

[International Worm Meeting, 2007]

C. elegans males and hermaphrodites respond differently to the presence of nearby hermaphrodites. Males are attracted to hermaphrodites, and hermaphrodites avoid one another. We would like to find out what differences between the male and female nervous systems underlie these gender-specific behaviors. To determine the genetic basis of attraction and avoidance, we screened 1,000 clonal F2 lines for mutants specifically defective in one behavior or the other, but not both. We isolated several lines that were specifically defective for attraction or avoidance. To verify that we had not simply isolated general sensory mutants, candidate mutant strains were screened for Cu2+ avoidance, osmotic avoidance, and proper dye-filling of sensory neurons. We are currently focused two mutant lines: one that is specifically impaired for hermaphrodite avoidance (ox341), and the other for male attraction (ox349). After outcrossing (4x to 8x), both lines dye-fill normally and avoid Cu2+. ox341 is defective in avoiding high osmolarity, and ox349 mildly so. Both mutations were mapped to a chromosome by testing linkage to known GFP insertions and by bulk-segregant SNP mapping: ox341 is on III and ox349 on X. Further SNP mapping has isolated the ox341 avoidance mutantion to III between -22.4 and -24.92. There are approximately 28 predicted genes in this region; none are known to be required for detection of high osmolarity. Cosmid coverage in this region is incomplete, so we are proceeding to identify the mutation by rescuing the ox341 avoidance phenotype with PCR products of candidate genes, followed by sequencing of ox341. Mapping of the ox349 male attraction mutation is complicated by an enhancer on III and an oddly wide linkage area on the left arm of X. To overcome these difficulties, we have identified the genotype of 1,000 ox341 N2/CB4856 hybrid F2 lines by qPCR-SNP analysis prior to characterizing their behavioral phenotype. Interesting lines - those homozygous on III and with a crossover on the left arm of X - are then assayed for attraction behavior. The initial genotyping should save time by restricting the relatively laborious behavioral analysis to potentially informative lines.

Jamie White et al. (2007) International Worm Meeting "Sex-specific pheromone responses in C. elegans."

Eliott R. Davidson, Long Truong, Thomas J. Nicholas, Jamie White, Erik M. Jorgensen

[International Worm Meeting, 2007]

C. elegans senses and responds to other individuals in their environment via pheromones released by hermaphrodites. The response is sex-specific: males are attracted to the pheromones and hermaphrodites avoid them. The male and hermaphrodite nervous systems are highly similar—the sex-specific circuitry can be thought of as additional modules wired on to a common core nervous system—and the stimulus detected by each is the same—hermaphrodite-derived signals—but the response is opposite. What are the neural and molecular differences that account for these sex-specific behaviors? To answer this, we are using mutant analysis, neuron-specific rescue, and laser ablation. In males, attraction behavior requires a TRPV channel encoded by the osm-9, ocr-1, and ocr-2 genes. Cell-specific rescue of osm-9 shows that three sets of neurons must be active for a full behavioral response: the AWA and AWC olfactory neuron pairs, present in both hermaphrodites and males, and the four male-specific CEM neurons. When any one set of these neurons is removed early in development, either by laser ablation or by using genetic mutants, attraction behavior is unimpaired. However, when any one set is ablated late in development, or if all three sets are ablated simultaneously, attraction behavior is severely impaired. Thus, the AWA, AWC and CEM neurons compensate for one another if any one set is missing early in development. Furthermore, because the AWA and AWC neurons are able to mediate attraction in the absence of the sex-specific CEM neurons, there must be subtle sex-specific differences in the core nervous system. In hermaphrodites, avoidance behavior requires a cGMP-gated channel encoded by the tax-2 and tax-4 genes. Cell-specific rescue of tax-4 indicates that one or more of the ASI, ASJ and ASK sensory neuron pairs are sufficient. Laser ablation experiments will determine if they are also necessary. Our results show that each sex uses distinct sensory signal-transduction pathways and neurons to detect hermaphrodite pheromones. To determine whether attraction and avoidance require only differences in sensory neurons, or if interneurons and motor neurons also must be different, we have manipulated the somatic sex-determination pathway to switch only the sex of the nervous system. Transsexual animals have both the general locomotory behaviours and pheromone responses of the overtly opposite sex. We are currently focused on using cell-specific promoters to switch the sex of specific circuits.