Bachelor of Arts
Laura A. Katz
Foraminifera, Life cycles, Transcriptomics, Single cell, Flourescence microscopy
Foraminifera are single-celled rhizarian amoebae that build shells called tests, and while they are best known for their extensive fossil record, far less known about their biology and genomes. Past biological research suggests that foraminifera have some of the most complex life cycles and genomic processes of any eukaryotic lineage, but knowledge on this topic is greatly limited by our inability to culture most taxa. Many species, for which the life cycles are known, undergo an alternation of asexual and sexual generations, that are characterized by variations in ploidy, number and size of nuclei and cell size. In addition, some species exhibit test dimorphism, with test morphology differing between life cycle stages. In my research, I chose to focus on members of the genus Ammonia, which exhibits test dimorphism through changes in the prolocular (i.e. first chamber) size: the gamont, or sexual stage, has a large proloculus while the agamont, or asexual stage, has a small one. This allowed me to identify the two generations morphologically, without observing a full life cycle in culture. In this thesis, I explored the nuclear and genome changes that occur between these two life cycle stages. In order to achieve this, I performed whole transcriptome amplifications on individuals from both generations to explore the expression of life cycle related genes. I approached these data in two ways. First, through gene tree analysis of meiosis-specific genes to analyze the distribution of these genes across the tree of life, as well as across foraminifera. I found many of these meiotic genes across Rhizaria and Foraminifera. Second, I looked at the function of genes present in one life cycle stage but not the other using BLAST2GO. I found one gene family (OG5_140136) that is associated with “mitotic chromosomal condensation,” which is likely to be associated with nuclear replication (either mitotic or meiotic). In addition to molecular work, I developed a protocol to use 4′,6-diamidino-2-phenylindole (DAPI) staining to visualize the diversity of nuclear morphologies in Ammonia. I found both uninucleate and multinucleate individuals, suggesting that both life cycle stages were present in my samples. This project scratches the surface of the life cycle dynamics of foraminifera and through further research, gaining a better understanding of the life cycles of these microbes could provide a more complete picture of the diversity and evolution of sex and other life history strategies.
©2019 Eleanor Goetz. Access limited to the Smith College community and other researchers while on campus. Smith College community members also may access from off-campus using a Smith College log-in. Other off-campus researchers may request a copy through Interlibrary Loan for personal use.
Goetz, Eleanor, "Genome dynamics and nuclear changes throughout the life cycles of foraminifera" (2019). Honors Project, Smith College, Northampton, MA.
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