Expression Pattern And Function Of Drosophila Heixuedian (Heix) Gene In Hematopoiesis

The Drosophila heixuedian (heix) gene encodes a potential prenyltransferase, which bearing a high sequence identity with human UBIAD1protein. UBIAD1gene is responsable for SCCD (Schnyder crystalline corneal dystrophy) disease, which is characterized by abnormal deposition of cholesterol and phospholipids in the cornea resulting in progressive corneal opacification and visual loss. In addition, loss of function of UBIAD1tends to cause the progression of certain types of cancers such as bladder carcinoma and prostate carcinoma. Interestingly, UBIAD1/Heix was identified as a vitamin K2biosynthetic enzyme. As a mitochondrial electron carrier, vitamin K2could be related to blood coagulation and Parkinson’s disease. UBIAD1has also been reported as a non-mitochondrial CoQ10-forming enzyme with a specific function of antioxidant in cardiovascular system.UBIAD1exhibits a wide range of subcellular localization in various cell lines, such as ER (endoplasmic reticulum), Golgi and mitochondria.As the ortholog of UBIAD1, heix was previously reported to be related to the hematopoiesis. However, the temporal-spacial expression pattern and function of heix have not been studied in Drosophila. The hematopoietic system plays a pivotal role in immunity for both human and Drosophila. Genes and genetic pathways controlling hematopoiesis are highly conserved between insects and vertebrates. The Drosophila hematopoiesis, which supplies mature circulating hemocytes, initiates in two distinct waves. The first population of hemocytes, originated from the procephalic mesoderm, is restricted to the anterior region with70%to80%egg length and gives rise to two types of blood cells:plasmatocytes (embryonic macrophages) which regulate apoptosis with the phagocytic function, and crystal cells which still have unknown function in the embryo. The second population of hemocytes, which is restricted to the larval development in a specialized hematopoietic organ, lymph gland, is differentiated into three different types of hemocytes:plasmatocyte (phagocytosis), crystal cell (melanization) and lamellocyte (with giant and flat morphology, encapsulation of parasites). Besides, the Drosophila fat body releases antimicrobial peptides under immune challenge and has a crucial role in the innate immunity. In this thesis, we mainly used immunohistochemical staining and Real-time quantitative PCR analysis to demonstrate the expression pattern and function of Heix in Drosophila hematopoetic system. The results indicated that Drosophila Heix is specifically highly expressed in Srp-expressing hemocyte progenitors on head mesoderm in embryos as well as in the crystal cells within cortical zone of the lymph gland primary lobes in the third instar larvae. Moreover, in the third instar larvae, Heix is partially localized to the ER of different tissues such as lymph gland. Only a small portion of Heix appeared in the mitochondria of the third instar larval fat body. Furthermore, this protein encodes an eight-transmembrane protein and belongs to the prenyltransferase family. Loss of function of heix results in lymph gland hypertrophy, overproliferation of hemocyte, aberrant differentiation of lamellocyte and formation of melanotic tumor. Using qRT-PCR analysis, a loss of function of heix induces aberrant activation of multiple hemocyte proliferation-related as well as immune-related pathways, including JAK/STAT pathway, Ras/MAPK pathway, IMD pathway and Toll pathway. These data suggest that heix is a potential blood tumor suppressor gene and plays a pivotal role in both hemocyte proliferation/differentiation and innate immunity of Drosophila.