Cassandra G. Extavour
Assistant Professor of Organismic & Evolutionary Biology
Phone: 617-496-1935
E-mail:
Office: 4th Floor, BioLabs, 16 Divinity Ave
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. Therefore, to understand the mechanisms that specify germ cells is a central challenge in developmental and evolutionary biology.
Data from model organisms show that germ cells can be specified either by maternally inherited determinants (preformation) or by inductive signals (epigenesis). Although preformation is seen in most model organisms, it is actually the less prevalent mode of germ cell specification, and that epigenetic 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 D. melanogaster, germ line precursors form as pole cells at the posterior end of the embryo very early in development. However, it is not clear whether early germ cell precursor specification is widespread among, or representative of, all arthropods. My interests are the evolution and development of arthropod reproductive systems, and specifically, the mechanisms of initial specification of primordial germ cells. By using molecular markers and histological analysis throughout the embryonic development of arthropods from several different subphyla and orders within subphyla, I 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
Voronina, E., Lopez, M., Song, J., Extavour, C., Gustafson, E., George, S., Ransick, A., Oliveri, P., Davison, E., 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 (in press) (2007).
Extavour, C. Evolution of the bilaterian germ line: lineage origin and modulation of specification mechanisms. Integrative and Comparative Biology. 47 (5): 770-785 (2007).
Extavour, C. 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., 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. 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. 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. Not just a tasty snack: review of Evolutionary Developmental Biology of Crustacea, ed. G. Scholtz. BioEssays 26(11): 1256-1258 (2004).
Extavour, C. and Akam, M. Mechanisms of germ cell specification across the metazoans: epigenesis and preformation. Development 130(24): 5869-5884 (2003). (invited review)
Extavour, C. 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
Extavour, C. Urbilaterian Reproduction: the evolution of metazoan germ cell specification mechanisms. Evolutionary Developmental Biology. Cambridge University Press. (2007) (in press).
News Features
Travis, J. A Close Look at Urbisexuality. Science 316: 391-391 (2007).
