Haloupek N (2019) Genetics "Barbara J. Meyer: 2018 Thomas Hunt Morgan Medal."

Haloupek N

[Genetics, 2019]

The Genetics Society of America's (GSA) Thomas Hunt Morgan Medal honors researchers for lifetime achievement in genetics. The recipient of the 2018 Morgan Medal, Barbara J. Meyer of the Howard Hughes Medical Institute and the University of California, Berkeley, is recognized for her career-long, groundbreaking investigations of how chromosome behaviors are controlled. Meyer's work has revealed mechanisms of sex determination and dosage compensation in <i>Caenorhabditis elegans</i> that continue to serve as the foundation of diverse areas of study on chromosome structure and function today, nearly 40 years after she began her work on the topic.

Sternberg PW (1990) Adv Genet "Genetic control of cell type and pattern formation in Caenorhabditis elegans."

Sternberg PW

[Adv Genet, 1990]

As recognized by T. H. Morgan, the problems of genetics and development are interwoven. Morgan noted that understanding how the genotype of an organism specifies its phenotype would require knowing the fundamental mechanisms of gene action, how genes interact to specify the properties of cells, and how cells interact to specify each adult character. We now have a basic understanding of the primary effects of genes (to encode protein or RNA products). However, little is known about how the genes of a zygote specify a complex pattern of cell divisions, the generation of diverse cell types, and the arrangement of those cells into specific morphological structures. A "favorable material" (as Morgan put it) for investigating these problems would be a simple organism in which development could be analyzed at the level of single genes and single cells. The small free-living soil nematode Caenorhabditis elegans is such an organism...

Gerhold AR et al. (2016) Dev Cell "Bigger Isn't Always Better: Cell Size and the Spindle Assembly Checkpoint."

Maddox PS, Gerhold AR, Labbe JC

[Dev Cell, 2016]

Variation in the activity of the spindle assembly checkpoint has been observed in different cell types, yet the reason for this variability remains poorly understood. Reporting in Developmental Cell, Galli and Morgan (2016) show that checkpoint activity increases during development as cell size, and the cytoplasm-to-kinetochore ratio, decreases.

Chen X et al. (2015) Mol Neurodegener "Erratum to: Ethosuximide ameliorates neurodegenerative disease phenotypes by modulating DAF-16/FOXO target gene expression."

McCue HV, Chen X, Morgan A, Kashyap SS, Barclay JW, Kraemer BC, Burgoyne RD, Wong SQ

[Mol Neurodegener, 2015]

The original version of this article [1] unfortunately contained a mistake. The author list contained a spelling error for the author Hannah V. McCue. The original article has been corrected for this error. The corrected author list is given below:Xi Chen, Hannah V. McCue, Shi Quan Wong, Sudhanva S. Kashyap, Brian C. Kraemer, Jeff W. Barclay, Robert D. Burgoyne and Alan Morgan

Hwang HY et al. (2017) PLoS Comput Biol "Effect of mutation mechanisms on variant composition and distribution in Caenorhabditis elegans."

Wang J, Hwang HY

[PLoS Comput Biol, 2017]

Genetic diversity is maintained by continuing generation and removal of variants. While examining over 800,000 DNA variants in wild isolates of Caenorhabditis elegans, we made a discovery that the proportions of variant types are not constant across the C. elegans genome. The variant proportion is defined as the fraction of a specific variant type (e.g. single nucleotide polymorphism (SNP) or indel) within a broader set of variants (e.g. all variants or all non-SNPs). The proportions of most variant types show a correlation with the recombination rate. These correlations can be explained as a result of a concerted action of two mutation mechanisms, which we named Morgan and Sanger mechanisms. The two proposed mechanisms act according to the distinct components of recombination rate, specifically the genetic and physical distance. Regression analysis was used to explore the characteristics and contributions of the two mutation mechanisms. According to our model, ~20-40% of all mutations in C. elegans wild populations are derived from programmed meiotic double strand breaks, which precede chromosomal crossovers and thus may be the point of origin for the Morgan mechanism. A substantial part of the known correlation between the recombination rate and variant distribution appears to be caused by the mutations generated by the Morgan mechanism. Mathematically integrating the mutation model with background selection model gives a more complete depiction of how the variant landscape is shaped in C. elegans. Similar analysis should be possible in other species by examining the correlation between the recombination rate and variant landscape within the context of our mutation model.

O'Connor, Vincent et al. (2015) International Worm Meeting "Neurochip: a microfluidic device for improved throughput to translate agrochemical, pharmacological and biological potential of nematode pharyngeal function.."

Callahorro, Fernando, Hu, Chunxiao, Dillon, James, O'Connor, Vincent, Holden-Dye, Lindy, Ferreiro, Teressa, Morgan, Hywel

[International Worm Meeting, 2015]

The pharyngeal system of C.elegans provides a powerful in vivo route to investigate the biological function of a tractable neuroactive circuit. It consists of a muscular structure made up of the corpus isthmus and terminal bulb. This produces a rhythmic cycle of contraction and relaxation modulated by overriding neural activity. The pharynx expresses the major transmitter pathways and/or their cognate receptors that operate across the phyla. This makes its function sensitive to pharmacological regulation by many classes of neuroactive drugs. This includes those of general bio-medical and agrochemicals relevance and a more selective nematicidal potency. Thus, the pharynx lends it-self to use as a model for drug discovery, better mapping of mode of action and comparative approaches for selective and ecological toxicity. Measurement of pharyngeal function using extracellular measurement provides a powerful tool for the above approaches and supplements visual measurement of pumping. Microelectrode recording from intact C.elegans is a tractable route as it offers the potential to investigate chemically induced changes in the context of whole organism, to scope pharmacokinetics and comparative toxicity. The electropharyngeogram (EPG) is recorded by immobilizing the worm in glass electrode fabricated to make a tight seal around the nose of the worm. By analogy with a grease gap this allows recording of the potential difference between the two sides of the tight seal. We have adapted this principle and embedded it into microfluidic chip we have called neurochip. The central aspect of this device is the delivery of the worm into a PDMS trapping channels in which a double layer design allows the production of a compliant circular aperture that restrains the worm with a tight seal. The device has intrinsic platinum electrodes either side of the seal and when the pharynx contract a waveform with all the characteristic features of the EPG is recorded. We can record EPG in loading buffer or prime them by loading in 5-HT a potent stimulator of pumping. We have optimized a medium through put plate assays where worms are cultivated in drug overnight prior to investigation in the neurochip. This approach is particularly useful in instances where access across the cuticle is slow or mode of action of implies an important role of chronic exposure. Pre-exposure of the inhibitor with known and unknown candidates reveals a dose dependent inhibition of the EPG in which the frequency and pattern of activity are modified. A further iteration of the neurochip design incorporates supporting flow channels designed to direct efficient drug perfusion onto the pre immobilized worms. Restrictions to efficient flow in the immobilizing and recording micro channels is circumvented by incorporating perforated exit ports along the length of the trapped worm. Thus, the device and accompanied optimization of dosing regimes opens up a wide user base for previously technically challenging measurement of EPG. The format and ergonomics of loading are suited to investigation of both the chronic or acute effects of important classes of chemicals on wild type, mutant or genetically modified C.elegans sculpted to express targets of experimentally intractable nematode species. .

K Lundin et al. (1999) International C. elegans Meeting "Ethanol Tolerance in C. elegans"

K Lundin, PC Phillips

[International C. elegans Meeting, 1999]

It is thought that increased ethanol tolerance in humans leads to increased risk of alcoholism. Unfortunately, not much is known about the genetics and physiology of ethanol tolerance, and therefore we have begun a set of preliminary experiments on this topic using Caenorhabditis elegans as a model system. Individuals were tested for initial tolerance over a wide range of ethanol concentrations, yielding a determination of the lethal concentration. Initial tolerance to ethanol after five minutes of exposure was surprisingly high, with a tolerance threshold of approximately 36% with an LD50 of 19.5%. The tolerance considered here is of an extreme type (lethality) compared to an intoxication response such as lack of movement (Morgan and Sedensky 1995) or mating ability (Crowder et al. 1996), but is very straightforward to assay and is compatible with many similar studies in Drosophila. Determination of the lethal concentration of wild type worms allows for a simplified screening method for obtaining genetic mutants with higher ethanol tolerances. We are currently in the process of searching for such mutants. We also hope to study the influence of previous exposure to ethanol by contrasting tolerance of naive individuals to that of individuals exposed as larvae. Crowder, C. M., Shebester, L. D., Schedl, T. 1996. Behavioral effects of volatile anesthetics in Caenorhabditis elegans . Anesthesiology 85:901-912. Morgan, P. G., Sedensky, M. M. 1995. Mutations affecting sensitivity to ethanol in the nematode, Caenorhabditis elegans . Alcoholism: Clinical and Experimental Research 19:1423-1429.

Sternberg PW et al. (1984) Annual Review of Genetics "The genetic control of cell lineage during nematode development."

Sternberg PW, Horvitz HR

[Annual Review of Genetics, 1984]

As recognized by T. H. Morgan, the problems of genetics and development are interwoven: understanding how the genotype of an organism specifies its phenotype requires knowing the fundamental mechanism of gene action, how genes interact to specify the properties of cells, and how cells interact to specify each adult character. We now know that the primary effect of a gene is to encode a protein or RNA product. However, little is known about how the genes of a zygote specify a complex pattern of cell divisions, the generation of diverse cell types, and the arrangement of those cells into specific morphological structures. A "favorable material" (as Morgan put it) for investigating these problems would be a simple organism in which development could be analyzed at the level of single genes and single cells. The small free-living soil nematode Caenorhabditis elegans is such an organism. C. elegans is easily grown and handled in the laboratory and is well suited for both genetic and developmental studies. This nematode consists of only about 1,000 (non-germ) cells, and both its anatomy and its development are essentially invariant. The complete anatomy of C. elegans, including the "wiring diagram" of the nervous system, is known at an ultrastructural level. In addition, the developmental origin of every cell is known since the complete cell lineage from the zygote to the adult has been determined. The genetic properties of C. elegans allow researchers to combine the classical Mendelian approach of Morgan and his coworkers with the approach of modern microbial genetics: C. elegans is diploid but microscopic in size (so large numbers of animals can be handled, up to 10*5 on a single petri dish) and has a very rapid life cycle (an egg matures into a fertile adult within two to four days, depending upon temperature; this adult produces 300-400 progeny over the next few days, resulting in an effective organismal doubling time of about 15 hours). Many aspects of the biology of C. elegans have been reviewed. Here we describe how these features have led to an initial understanding of some of the issues concerning genetics and development that Morgan raised fifty years ago. We review the methods underlying and the results derived form four approaches that have been used to study the genetics of nematode development. The first approach, which takes advantage of the genetic diversity generated by evolution, is to compare the development of related species. For example, simple differences in otherwise identical cell lineages may be the result of one or a few mutational events that occurred during the divergence of two species; the nature of these differences can suggest ways in which genes may control development. The second approach is to identify a large set of mutations that affect particular cell lineages; this approach can indicate the number, types, and specificities of genes that affect particular developmental events. The third approach involves the detailed genetic analyses of genes identified by mutations that alter development; such studies can reveal the wild-type functions of those genes and thereby identify genes that play regulatory roles in development. The fourth approach is to examine the interactions among mutations using studies of extragenic suppression and epistasis; this type of analysis can suggest how genes interact during normal development to

Sorokin, Elena P. et al. (2011) International Worm Meeting "Chemically reprogramming the adult sperm/oocyte fate decision."

Morgan, Clinton T., Sorokin, Elena P., Kimble, Judith

[International Worm Meeting, 2011]

The molecular basis of germ cell specification as sperm or oocyte remains poorly understood. In most animals (nematodes, fruitflies and mice), somatic signaling controls germline sexual fate, but the regulators in germ cells that direct the sperm or oocyte fate are best understood in C. elegans. Based on that knowledge, we recently devised a method to chemically reprogram germline sex: U0126, a MEK kinase inhibitor, transforms a puf-8; lip-1 masculinized germline to produce functional oocytes instead of sperm (Morgan et al., 2010). Here we report the use of this chemical method to analyze two critical aspects of germ cell fate reprogramming. First, we mapped the reprogramming to cells at the boundary of the mitotic and transition zone, where virtually all germ cells have entered the meiotic cell cycle. Consistent with this map, active MAP kinase and the terminal sperm fate regulator FOG-1 rapidly decrease in the transition zone after U0126 treatment. Therefore, the U0126-mediated effect on the sperm/oocyte decision occurs as germ cells enter meiotic prophase. Second, we used RNA-seq to profile changes in mRNA expression after chemical reprogramming. Specifically we compared RNAs from U0126-treated puf-8; lip-1 vs U0126-treated N2s and from U0126-treated vs DMSO vehicle-treated puf-8; lip-1 over an 18-hour time course. Preliminary results reveal a highly-enriched binding motif in the promoters of mRNAs differentially expressed upon reprogramming. Moreover, RNAi against the likely transcription factor affects germline sex. This approach therefore promises to extend our molecular understanding of germ cell fate determination to a transcriptional level. We conclude that chemical reprogramming provides an invaluable tool for analyzing the sperm/oocyte decision. Morgan, C. T., Lee, M. H., Kimble, J., 2010. Chemical reprogramming of Caenorhabditis elegans germ cell fate. Nat Chem Biol 6, 102-4.

McMiller T et al. (2006) Biochem Mol Biol Educ "Middle/high school students in the research laboratory: A summer internship program emphasizing the interdisciplinary nature of biology."

McMiller T, Johnson CM, Lee T, Green T, Saroop R

[Biochem Mol Biol Educ, 2006]

We describe an eight-week summer Young Scientist in Training (YSIT) internship program involving middle and high school students. This program exposed students to current basic research in molecular genetics, while introducing or reinforcing principles of the scientific method and demonstrating the uses of mathematics and chemistry in biology. For the laboratory-based program, selected students from Baltimore City Schools working in groups of three were teamed with undergraduate research assistants at Morgan State University. Teams were assigned a project that was indirectly related to our laboratory research on the characterization of gene expression in Caenorhabditis elegans. At the end of the program, teams prepared posters detailing their accomplishments, and presented their findings to parents and faculty members during a mini-symposium. The posters were also submitted to the respective schools and the interns were offered a presentation of their research at local high school science fairs.