Cassandra G. Extavour
Associate Professor of Organismic & Evolutionary Biology
Phone: 617-496-1935
E-mail:
Office: 4103, BioLabs, 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.
Recent Publications
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).
Sarikaya, D.P., Belay, A.A., Ahuja,A. Green, D.A. Dorta, A. and Extavour, C.G. The roles of cell size and cell number in determining ovariole number in Drosophila. Developmental Biology Epub Dec 19 (2011).
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).
Kainz, F., Ewen-Campen, B., Akam, M. and Extavour, C. G. Delta/Notch signaling is not required for segment generation in the basally branching insect Gryllus bimaculatus. Development 138(22): 5015-5026 (2011).
Alwes, D., 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 139(1): 110-123 (2011).
Extavour, C.G. Long-Lost Relative Claims Orphan Gene: oskar in a Wasp. PLoS Genetics Epub April 28. doi/10.1371/journal.pgen.1002045 (2011).
Green, D.A., Sarikaya, D.P. and Extavour, C.G. Counting in oogenesis. Cell and Tissue Research 344 (2): 207-212 (2011).
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: 61 (2011).
Ewen-Campen, B., Schwager, E.E., and Extavour, C.G. The molecular machinery of germ line specification. Molecular Reproduction and Development. 77 (1): 3-18 (2010).
Extavour, C.G. Oogenesis: Making the Mos of Meiosis. Current Biology 19 (2): R489-R491 (2009).
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).
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).
Extavour, C.G. Evolution of the bilaterian germ line: lineage origin and modulation of specification mechanisms. Integrative and Comparative Biology. 47 (5): 770-785 (2007).
Extavour, C.G. Gray Anatomy: phylogenetic patterns of somatic gonad structures and reproductive strategies across the Bilateria. Integrative and Comparative Biology 47 (3): 420-426 (2007).
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).
Extavour, C.G. The fate of isolated blastomeres and formation of germ cells in the amphipod crustacean Parhyale hawaiensis. Developmental Biology 277 (2): 387-402 (2005).
Extavour, C.G. Hold the germ cells, I’m on duty (on germ cell specification and caste determination in a polyembryonic wasp). BioEssays 26 (12): 1263-1267 (2004). (invited review)
Extavour, C.G. Not just a tasty snack (review of "Evolutionary Developmental Biology of Crustacea", ed. G. Scholtz.) BioEssays 26 (11): 1256-1258 (2004).
Extavour, C.G. and Akam, M. Mechanisms of germ cell specification across the metazoans: epigenesis and preformation. Development 130 (24): 5869-5884 (2003). (invited review)
Extavour, C.G. and García-Bellido, A. Germ cell selection in genetic mosaics in Drosophila melanogaster. P.N.A.S. 98 (20): 11341-11346 (2001).
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).
News Features
Bondar, C . and Extavour, C. Nerd Corner Podcast Interview for Carin Bondar's Biology Blog. (2010).
Tintori, S. and Extavour, C. CreatureCast Episode 2 "Why Cells Cooperate" about the evolution and development of multicellular organisms and germ cells. NPR's Science Friday. (2009).
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).
Courses Taught
MCB 291. Genetics, Genomics and Evolutionary Biology
OEB 51. The Biology and Evolution of Invertebrate Animals
