Cassandra G. Extavour
Professor of Organismic and Evolutionary Biology
Professor of Molecular and Cellular Biology
Office: Biological Labs, Rm 4103
16 Divinity Ave
Lab Website: http://www.extavourlab.com
Germ cells play a unique role in gamete production, heredity and evolution. Germ cells are likely also the closest wild type in vivo equivalent to laboratory-maintained stem cells. To understand the mechanisms that specify germ cells is therefore a central challenge in developmental and evolutionary biology.
Data from model organisms show that germ cells can be specified either by maternally inherited determinants or by inductive signals. Although the inheritance mode is seen in most model organisms, it is actually likely to be the less prevalent mode of germ cell specification, and inductive germ cell specification may be ancestral to the Metazoa.
Among the invertebrates, the only arthropod in which the germ line has been studied in detail is the dipteran Drosophila melanogaster. In this fruit fly, germ line precursors form as pole cells at the posterior end of the embryo very early in development. However, it is not clear whether this mechanism of germ cell specification is widespread among, or representative of, all arthropods. Moreover, there is great variation in the time and place of germ cell specification across all multicellular animals. My interests are the evolution and development of reproductive systems, and specifically, the mechanisms of initial specification of primordial germ cells. By using molecular markers, functional genetic analysis, and cellular analysis to study the embryonic development and reproductive systems of multiple emerging arthropod laboratory systems (spiders, crickets, milkweed bugs, amphipods and fruit flies), we hope to add to our understanding of which mechanisms may have been basal to arthropods, and ultimately to metazoans, in the specification of the germline.
Modrell, M.S., Price, A. L., Havemann, J., Extavour, C.G., Gerberding, M. and Patel, N.H. Germline replacement following ablation of the primordial germ cells in Parhyale hawaiensis. (in revision)
Sharma, P.P., Tarazona, O.A., Lopez, D.H., Schwager, E.E., Cohn, M.J., Wheeler, W.C. and Extavour, C.G. A conserved genetic mechanism specifies deutocerebral appendage identity in insects and arachnids. Proceedings of the Royal Society B: Biological Sciences (in press) (2015).
Donoughe, S. and Extavour, C.G. Embryonic development of the cricket Gryllus bimaculatus. Developmental Biology (in press) (2015) PubMed.
Moczek, A., Sears, K., Stollewerk, A., Wittkopp, P., Diggle, P., Dworkin, I., Ledon-Rettig, C., Matus, D., Roth, S., Abouheif, E., Brown, F., Chiu, C.-H., Cohen, C.S., De Tomaso, T., Gilbert, S., Hall, B., Love, A., Lyons, D., Sanger, T., Smith, J., Spect, C., Vallejo-Marin, M. and Extavour, C.G. The significance and scope of evolutionary developmental biology: a vision for the 21st centure. Evolution and Development (in press) (2015).
Sarikaya, D.P. and Extavour, C.G. The Hippo pathway regulates homeostatic growth of stem cell niche precursors in the Drosophila ovary. PLoS Genetics 11(2): e1004962 (2015) * Cover Article * Read more in Biology of Reproduction * PDF PubMed
Chipman, A.D., Ferrier, D.E.K and the Strigamia maritima sequencing and annotation consortium (105 authors, including C. G. Extavour (#26) and T. Jones (#49)). The first myriapod genome sequence reveals conservative arthropod gene content and genome organisation in the centipede Strigamia maritima. PLoS Biology 12(11): e1002005 (2014) *Read more in PLoS Biology, NBC News, Tech Times, International Business Times,Astrobiology Magazine, Sci-News, Genome Web, UK Daily Mail, Nature World News, and Reuters PDF PubMed
Schwager, E.E., Meng, Y. and Extavour, C.G. vasa and piwi are required for mitotic integrity in early embryogenesis in the spider Parasteatoda tepidariorum. Developmental Biology doi: 10.1016/j.ydbio.2014.08.032 (2014) PDF of corrected proof PubMed
Sharma, P.P., Schwager, E.E., Extavour, C.G. and Wheeler, W.C. Hox gene duplications correlate with posterior heteronomy in scorpions. Proceedings of the Royal Society B: Biological Sciences 281: 20140661 (2014) PDFPubMed
Posnien, N., Zeng V., Schwager, E.E., Pechmann, M., Hilbrant, M., Keefe, J., Damen, W.G.M., Prpic-Schaper, N., McGregor, A.P. and Extavour, C.G. A comprehensive reference transcriptome resource for the common house spiderParasteatoda tepidariorum. PLoS ONE 9(8): e104885. doi:10.1371/journal.pone.0104885 (2014) PDF PubMed
Donoughe, S., Nakamura, T., Ewen-Campen, B., Green II, D.A., Henderson, L. and Extavour, C.G. BMP signaling is required for generation of primordial germ cells in an insect. Proceedings of the National Academy of Sciences of the USA 111(11): 4133-4138 (2014) PDF PubMed
Green II, D.A. and Extavour, C.G. Insulin Signaling Underlies Both Plasticity and Divergence of a Reproductive Trait in Drosophila. Proceedings of the Royal Society B: Biological Sciences 281(1779): 20132673 (2014) *Read more in the Harvard Gazette PDF PubMed
Ahuja, A. and Extavour, C.G. Patterns of molecular evolution of the germ line specification gene oskar suggest that a
novel domain may contribute to functional divergence in Drosophila. Development, Genes and Evolution 224(2): 65-77 (2014) PDF PubMed
Nast, A. R. and Extavour, C.G. Ablation of a single cell from eight-cell embryos of the amphipod crustacean Parhyale hawaiensis. Journal of Visualized Experiments (in press) doi:10.3791/51073 (2014) [PDF of accepted MS]
Sharma, P.P., Schwager, E.E., Giribet, G.G., Jockusch, E. and Extavour, C. Distal-less and dachshund pattern both plesiomorphic and derived structures in chelicerates: RNA interference in the harvestman Phalangium opilio (Opiliones). Evolution and Development 15(4): 228-242 (2013). * Cover Article * PDF
Ewen-Campen, B., Donoughe, S., Clarke, D.N., and Extavour, C.G. Germ Cell Specification Requires Zygotic Mechanisms Rather Than Germ Plasm in a Basally Branching Insect. Current Biology 23(10): 835-842 (2013) PDFPubMed
Zeng, V. Ewen-Campen, B., Horch, H.W., Roth, S., Mito, T., and Extavour, C.G. Developmental Gene Discovery in a Hemimetabolous Insect: De Novo Annotation and Assembly of a Transcriptome for the Cricket Gryllus bimaculatus.PLoS ONE 8(5): e61479 (2013) PDF PubMed
Ewen-Campen, B.*, Jones, T.E.*., and Extavour, C.G. Evidence against a germ plasm in the milkweed bugOncopeltus fasciatus, a hemimetabolous insect. Biology Open (Company of Biologists) 2(6):556-568 (2013) (* equal author contribution) PDF PubMed
Sharma, P.P., Schwager, E.E., Giribet, G.G., Jockusch, E. and Extavour, C.G. Distal-less and dachshund pattern both plesiomorphic and derived structures in chelicerates: RNA interference in the harvestman Phalangium opilio(Opiliones) Evolution and Development 15(4): 228-242 (2013)* Cover Article * PDF PubMed
Ewen-Campen, B., Srouji, J.R., Schwager, E.E. and Extavour, C.G. oskar Predates the Evolution of Germ Plasm in Insects. Current Biology 22(23): 2278-2283 (2012) *Read more in the Harvard Gazette and a Dispatch in Current Biology * Recommended by the Faculty of 1000 * PDF PubMed
Sharma, P.P., Schwager, E.E., Extavour, C. G. and Giribet, G. Evolution of the chelicera: a dachshund domain is retained in the deutocerebral appendage of Opiliones (Arthropoda, Chelicerata). Evolution and Development 14(6): 522-533 (2012)* Recommended by the Faculty of 1000 * PDF PubMed
Sharma, P.P., Schwager, E.E., Extavour, C. G. and Giribet, G. Hox gene expression in the harvestman Phalangium opilio reveals divergent patterning of the chelicerate opisthosoma. Evolution and Development 14(5): 450-463 (2012)PDF PubMed
Sarikaya, D.P., Belay, A.A., Ahuja, A., Green II, D.A., Dorta, A. and Extavour, C.G. The roles of cell size and cell number in determining ovariole number in Drosophila. Developmental Biology 363(1): 279-289 (2012) PDF PubMed
Zeng, V., Villanueva, K.E., Ewen-Campen, B., Alwes, F., Browne, W.E. and Extavour, C.G. De novo assembly and characterization of a maternal and developmental transcriptome for the emerging model crustacean Parhyale hawaiensis. BMC Genomics 12(1): 581 (2011) PDF PubMed
Kainz, F., Ewen-Campen, B., Akam, M. and Extavour, C.G. Notch/Delta signalling is not required for segment generation in the basally branching insect Gryllus bimaculatus. Development 138(22): 5015-5026 (2011) PDF PubMed
Alwes, F., Hinchen, B. and Extavour, C G. Patterns of cell lineage, movement, and migration from germ layer specification to gastrulation in the amphipod crustacean Parhyale hawaiensis. Developmental Biology 359(1): 110-123 (2011) PDF PubMed
Ewen-Campen, B., Shaner, N., Panfilio, K., Suzuki, Y., Roth, S. and Extavour, C.G. The maternal and early embryonic transcriptome of the milkweed bug Oncopeltus fasciatus. BMC Genomics 12(1): 61 (2011)* Highly Accessed * PDF PubMed
Abzhanov, A., Extavour, C.G., Groover, A., Hodges, S., Hoekstra, H., Kramer, E M., Monteiro, A. Are We There Yet? Tracking the Development of New Model Systems. Trends in Genetics 24(7): 353-360 (2008) PDF PubMed
Voronina, E., Lopez, M., Juliano, C. E., Gustafson, E., Song, J. L., Extavour, C.G., George, S., Oliveri, P., McClay, D., and Wessel, G. Vasa protein expression is restricted to the small micromeres of the sea urchin, but is inducible in other lineages early in development. Developmental Biology 314(2): 276-286 (2008) PDF PubMed
Extavour, C.G., Pang, K., Matus, D. Q. & Martindale, M. Q. vasa and nanos expression patterns in a sea anemone and the evolution of bilaterian germ cell specification mechanisms Evolution and Development 7(3): 201-215 (2005) * Nominated as a "must read" by the Faculty of 1000 * PDF PubMed
Extavour, C.G. Not just a tasty snack (review of "Evolutionary Developmental Biology of Crustacea", ed. G. Scholtz.) BioEssays 26(11): 1256-1258 (2004). PDF
Books and Book Chapters
Srouji, J. R. and Extavour, C. Redefining stem cells and assembling germ plasm: key transitions in the evoution of the germ line. Chapter 16, pp. 360-397 in Key Transitions in Animal Evolution, eds. R. DeSalle and B. Schierwater. CRC Press, Taylor & Francis Group; Science Publishers (2010)
Extavour, C. Urbilaterian Reproduction: the evolution of metazoan germ cell specification mechanisms. Chapter 17, pp. 321-342 in Evolving Pathways: Key Themes in Evolutionary Developmental Biology. Alessandro Minelli and Giuseppe Fusco, eds. Cambridge University Press (2008).
Reuell, P. Key connection: Biologists zero in on role of plasticity in evolution. Harvard Gazette, March 10 (2014) [pdf]
Byrne, P. Debate on Evolution of Multicellular Organisms Starts to Gain Focus. Scientific American, September 30 (2013). Original article published as " Debating the Evolution of Multicellularity" in Quanta Magazine, September 25 (2013)
Biological Time. Exhibit by the Ernst Mayr Library, July 2013 - present.
Smith, D. Cooperating to study Cooperation. The Scientist, February 20 (2013)
Maxmen, A. Transcriptomics for the Animal Kingdom: Using RNA-Seq to study nonmodel organisms. The Scientist, July 1 (2013)
Abouheif, E. Evolution: oskar Reveals Missing Link in Co-optive Evolution Current Biology 23(1): R24-R25 (2013).
Bondar, C . and Extavour, C. Nerd Corner Podcast Interview for Carin Bondar's Biology Blog. (2010).
Schaffer, L. Shooting Stars: Check out these faculty ballers! The Harvard Crimson Fifteen Minutes Magazine April 30 (2009).
Dolgin, E. Management for Beginners: So you’re a princial investigator – now what? The Scientist 22 (7): 75-77 (2008).
Bjorn, G. Ready, Set, Hire. Nature 451: 740-741 (2008).
Travis, J. A Close Look at Urbisexuality. Science 316: 391-391 (2007).
Hines, P. J. and Kadereit, S. Topic of the Month: Asymmetric Cell Division. International Society for Stem Cell Research. January 2004: 1-3 (2004).
MCB 291. Genetics, Genomics and Evolutionary Biology
OEB 51. The Biology and Evolution of Invertebrate Animals