Cassandra G. Extavour

Cassandra G. Extavour

Professor of Organismic and Evolutionary Biology and of Molecular and Cellular Biology
Cassandra G. Extavour

Faculty Support: Rosa Capellan

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 inParhyale hawaiensis. (in revision)

Iyer, H., Issigonis, M., Sharma, P.P., Extavour, C.G. and Newmark, P.A. A novel pre-meiotic function for boule in the planarian Schmidtea mediterraneaPNAS (in press) (2016)

Whittle, C.A. and Extavour, C.G. Expression-linked patterns of codon usage, amino acid frequency and protein length in the basally branching arthropod Parasteatoda tepidariorumGenome Biology and Evolution (in press) (2016) 

Nakamura, T. and Extavour, C.G.The transcriptional repressor Blimp-1 acts downstream of BMP signaling to generate primordial germ cells in the cricket Gryllus bimaculatus. Development 143(2): 255-263 (2016) 

Whittle, C.A. and Extavour, C.G. Codon and amino acid usage are shaped by selection across divergent model organisms of the Pancrustacea. G3: Genes, Genomes, Genetics 5(11): 2307-2321 (2015) 

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 282: 20150698 (2015) 

Courses Taught

OEB 51 Biology and Evolution of Invertebrate Animals
OEB 371 Comparative and Evolutionary Invertebrate Developmental Biology


Contact Information

Biological Labs, Rm. 2087
16 Divinity Ave
Cambridge, MA 02138
p: 617-496-1935



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