Date of Award
Doctor of Philosophy (PhD)
Heart development and the genetic pathways underlying it are highly conserved among vertebrates. During heart development, an embryo must induce mesoderm formation, pattern the mesoderm, specify cardiomyocytes, increase the population of cardiomyocytes through proliferation, and pattern the cardiac chambers. It is becoming increasingly clear that chromatin modifications help mediate the complex processes of heart development by providing spatiotemporal regulation of gene expression. My thesis work focuses on characterizing functions of the chromatin factor Gonad-4-like (Gon4l), encoded by the gene ugly duckling (udu), in zebrafish heart development. Previous works established a requirement for Gon4l in the formation of many mesoderm derivatives including somites and blood. My studies define novel roles for maternal and zygotic Gon4l function in zebrafish heart development. Embryos lacking both maternal and zygotic udu (MZudu) expression have perturbations in the formation of all three germ layers, but this thesis focused on the disruptions in mesoderm development. MZudu-/- embryos have abnormal mesoderm patterning that results in defects in the development of mesoderm derived tissues and organs. MZudu mutant embryos present an almost complete loss of anterior lateral plate mesoderm formation, and subsequently heart development. RNA-sequencing performed on MZudu /- embryos uncovered broad misregulation of genes including morphogens and transcription factors. Cell autonomy transplants indicated that Gon4l has both cell-autonomous and non-cell-autonomous functions in heart development, which suggests that disruption of multiple signaling pathways contributes to the defects in heart development. In addition, this work establishes separate zygotic functions for Gon4l in cardiomyocyte proliferation and maintenance of ventricular identity. Notably, these deficiencies in heart development are not due to increased expression of tp53, unlike the hematopoiesis defects in zygotic udu (Zudu) mutant embryos. Cardiomyocyte proliferation is reduced in Zudu-/- embryos. Differential expression of ccnd3 and ccne2 and evidence that Gon4l associates with regulatory regions of these cyclins posits that Gon4l may be required for progression through the G1/S cell cycle checkpoint. Analysis of nkx2.5;udu compound mutant phenotypes revealed that nkx2.5 and udu genetically interact in the maintenance of ventricular identity. However, ectopic expression of nkx2.5 failed to restore ventricular patterning in udu-/- embryos, which indicates that Gon4l could regulate multiple pathways to maintain ventricular identity. Altogether my work establishes novel roles for Gon4l in regulating mesoderm patterning, cardiomyocyte proliferation, and maintenance of ventricular identity during vertebrate heart development.
Chair and Committee
Kristin Kroll, Patrick Jay, Stacey Rentschler, Andrew Yoo,
Budine, Terin Elise, "The Essential Roles of the Chromatin Factor Gon4l in Heart Development" (2018). Arts & Sciences Electronic Theses and Dissertations. 1689.