Identifying embryonic mechanisms that induce a germ cell fate in sea stars

Fresques, Tara

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Year:: 2017
Contributor:: Fresques, Tara (creator); Wessel, Gary (Advisor); Creton, Robbert (Reader); Freiman, Richard (Reader); Dunn, Casey (Reader); Wharton, Kristi (Reader); Extavour, Cassandra (Reader); Brown University. Department of Molecular Biology, Cell Biology and Biochemistry (sponsor)
Genre:: theses
Subject:: Developmental biology; Echinodermata; Germ cells; Reproduction
Extent:: xvi, 269 p.
DOI: https://doi.org/10.7301/Z0Z31X3P

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Abstract:: Germ cell specification is required for reproduction in all sexually reproducing animals. During animal development, animals can specify their germ cells through inheritance of maternal molecules or through induction by cell-cell signaling events. Although the ancestral mode of germ cell specification appears to occur by inductive mechanisms it is still not clear how signals selectively induce a germ cell fate. I use the sea star as a model to determine how signaling mechanisms direct germ cell formation. First I use RNA in situ hybridizations to identify when genes associated with germ cell formation are expressed during sea star embryogenesis. I find that the conserved germ cell factors Nanos, Vasa, and Piwi all localize in a germ cell pouch at the larva stage. In addition, Nanos and Vasa mRNA appear to be serially restricted into smaller and smaller embryonic domains during early embryogenesis. One of these restriction events involves Left/Right asymmetry because the germ cell pouch forms on the left side of the embryo. Since Nodal is conserved and required for specification of the Left/Right axis I use a gene perturbation strategy, primarily by injecting a translation blocking morpholino into sea star oocytes, to determine the role that the Nodal signal has on germ cell specification. My results show that Nodal inhibits retention of Nanos and Vasa mRNA in the ventral and right sides of the embryo by inhibiting transcription and by stimulating RNA degradation. In addition, my work suggests that Nodal also inhibits cell morphogenetic events in the ventral and right sides of the embryo required for germ cell pouch morphogenesis. Finally, I use RNA in situ hybridizations to determine when Nanos accumulates in diverse echinoderm species to determine how germ cell specification mechanisms have changed during evolution. My results support the growing consensus that germ cell specification by induction in sea stars represents the ancestral state in echinoderms. Lastly, I speculate which developmental phenomena may be repeatedly required for the evolution of an inherited germ cell specification in all animals.
Notes:: Thesis (Ph. D.)--Brown University, 2017

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Rights: In Copyright
Restrictions on Use: Collection is open for research.

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Fresques, Tara, "Identifying embryonic mechanisms that induce a germ cell fate in sea stars" (2017). Molecular Biology, Cell Biology, and Biochemistry Theses and Dissertations. Brown Digital Repository. Brown University Library. https://doi.org/10.7301/Z0Z31X3P

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Molecular Biology, Cell Biology, and Biochemistry Theses and Dissertations

Theses and Dissertations for the Molecular Biology, Cell Biology, and Biochemistry department.
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