Characterization and physiological role of 17 [alpha], 20 [beta]-dihydroxy-4-pregnen-3-one steroid receptor activity in the cytosolic and zona radiata membrane fraction of the ovarian follicles of brook trout salvelinus fontinalis during the terminal stages of oocyte maturation

Maneckjee, Aspi (1989) Characterization and physiological role of 17 [alpha], 20 [beta]-dihydroxy-4-pregnen-3-one steroid receptor activity in the cytosolic and zona radiata membrane fraction of the ovarian follicles of brook trout salvelinus fontinalis during the terminal stages of oocyte maturation. Doctoral (PhD) thesis, Memorial University of Newfoundland.

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Abstract

Cardiomyocytes and hematopoietic blood cells are closely associated during zebrafish development, as they are both derived from the lateral plate mesoderm. The heart also helps circulate blood cells throughout the developing tissues of the embryo. Proper cardiac function is required to ensure blood circulation. Shear stress at the atrioventricular canal (AVC) from blood flow has been implicated in valvulogenesis in zebrafish. In this dissertation, we present a study that defines the role of zebrafish alpha cardiac actin (actc1a) during early heart development and endocardial cushion morphogenesis (ECs), a step in valve formation. Mutations in cardiac actin (ACTC) have been associated with different cardiac abnormalities in humans including dilated cardiomyopathy and septal defects. However, it is still poorly understood how altered ACTC structure affects cardiovascular physiology and results in the development of distinct congenital disorders. A zebrafish mutant (s434) was identified that demonstrates heart-specific defects, such as heart dilation and failure to generate ECs. We identified the mutation as a Y169S amino acid substitution, located within the W-loop of actin, which has been implicated in nucleotide sensing and proper actin polymerization. This mutation affects actin polymerization and stability of actin filaments and produces defects in heart function. Characterization of this mutant has led to the identification of a role for actc1a during zebrafish valvulogenesis, which is needed to produce proper shear stress at the AVC to form ECs. -- Zebrafish hematopoietic cells formed in primitive hematopoiesis include erythrocytes, macrophages and neutrophils. The first myeloid cells to emerge in the zebrafish posterior lateral plate mesoderm (PLPM) are neutrophils, and the genetic pathways that direct differentiation of myeloid precursors into neutrophils are not well understood. Neutrophils are an important component of the innate immune systems in vertebrates and can be identified in zebrafish based on myeloperoxidase (mpx) gene expression. Ets-1 related protein (Etsrp/Etv2), an ETS-family transcription factor required for vascular development, has been shown to be important for myeloid cell development in the zebrafish. In this dissertation, we report findings of an investigation of Etv2's role during neutrophil development, and reveal an early cell-autonomous requirement for Etv2 during primitive neutropoiesis. It was also found that Gata1, an erythroid master regulator gene, is required for neutrophil formation during primitive hematopoiesis in the zebrafish. These roles for Etv2 and Gata1 during primitive hematopoiesis provide further insight into how progenitor cells make the fate decision to differentiate into neutrophils. -- In summary, these results underscore the importance of the W-loop for actin functionality and will help us to understand structural and physiological consequences of ACTC mutations in human congenital disorders. The findings from the hematopoietic study help to expand our understanding of the intricate processes and genetic regulation guiding the process of hematopoiesis.

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