Functions of Notch and Neuralized in Drosophila hematopoiesis

Title

Identifier

d_2009_2013:c1fb238a6625:10936

identifier

11055

Creator

Small, Chiyedza,

Contributor

Shubha Govind

Date

2011

Language

English

Publisher

City University of New York.

Subject

Abstract

In vertebrates, hematopoiesis is commonly divided into two temporal phases, primitive (embryonic) and definitive (adult). Genetic studies in zebrafish and mice have implicated signaling pathways and molecular networks of transcription factors in the control of primitive and definitive hematopoietic programs. Notch signaling is essential for the proper execution of a wide array of cell fate decisions and developmental processes, including hematopoiesis. Many of these same signaling and transcriptional mechanisms also control hematopoiesis in simpler animals, such as the fruit fly Drosophila melanogaster . Because of its simple organization and genetic accessibility, Drosophila hematopoiesis has recently gained attention.;Drosophila larvae produce three cell types: plasmatocytes, crystal cells and lamellocytes. While plasmatocytes and crystal cells arise in embryonic stages, lamellocytes do not. In fact very few lamellocytes are typically found in healthy third instar larvae. However, their differentiation is induced in large numbers upon oviposition by parasitic wasps. Circulating blood cells divide continuously as the animal grows in size. In addition, a small hematopoietic organ flanking the dorsal vessel supports the growth and development of blood cells.;In larval stages, the Notch pathway regulates the differentiation of crystal cells: loss or reduction of Notch signaling results in the reduction of crystal cells while an increase in Notch signaling leads to the expansion of the crystal cells population in circulation and in the lymph gland (Duvic et al., 2002; Lebestky et al., 2003). Notch encodes the receptor/transcription factor that mediates short range cell-cell signaling. Notch ligand Serrate is expressed in the niche of the lymph gland. Serrate activates Notch in the pro-crystal cells and promotes commitment of the crystal cell fate. This step requires the functions of transcription factor Suppressor of Hairless (Lebestky et al., 2003).;Duvic et al. (2002) also reported that Notch function is essential for lamellocyte differentiation, although how this occurs was not explored in the Duvic study. The goal of this work was to analyze the contributions of Notch and Neuralized in lamellocyte differentiation. Neuralized encodes an E3 ligase for ubiquitination of Notch ligands, and its role in hematopoiesis remains unexplored.;The thesis contains three chapters. In Chapter 1, I report the expression of Notch in the lymph gland and circulating blood cells. Using RNA interference and clonal analysis, I show that Notch maintains lamellocytes in their progenitor state. This requirement is non cell-autonomous. Lamellocytes induced by loss of Notch appear mostly in the peripheral cortical zone of the anterior lobes, that houses both mature cells and progenitors. Notch target genes are expressed in most anterior lobe cells.;In Chapters 2 and 3, the functions of Neuralized are explored in three ways: RNA interference, clonal analysis (Chapter 2), and using putative alleles of neuralized, l(3)hem1 and l(3)hem 2 (Chapter 3). These studies show that Neuralized function is essential in maintaining hematopoietic stem-like progenitors in their undifferentiated state. In the medullary zone, where these undifferentiated progenitors reside, Neuralized plays an essential role in cell division and differentiation. Further, like Notch, it provides an inhibitory non cell-autonomous influence on pro-lamellocytes in the cortical zone, and keeps them from differentiating in the absence of infection.;In chapter 3, I characterize a classical hematopoietic mutation, l(3)hem1, a putative weak allele of neur . The lymph glands and blood cells of this homozygous mutant are severely affected, with multiple defects in cell division and differentiation. These studies support the three functions of Neuralized uncovered in Chapter 2.;Our studies provide novel insights into hematopoieitic stem/progenitor division and differentiation. Notch signaling plays an essential role in mammalian hematopoiesis. Misregulation of the Notch pathway leads to hematopoietic malignancies in humans. Because of the high molecular conservation between flies and mammals, understanding the regulation of Notch signaling in Drosophila hematopoiesis will yield insights into its role in mammalian hematopoiesis and potentially in developing therapies for treatment of human malignancies.

Type

dissertation

Source

2009_2013.csv

degree

Ph.D.

Program

Biology

Item