Genetic and cytological investigation of Nucleostemin-1 in Drosophila melanogaster

Mammalian nucleostemin (NS) is a nucleolar GTP-binding protein implicated in cell cycle progression, stem cell proliferation, and ribosome assembly. Drosophila melanogaster contains a four-member nucleostemin family (NS1-4). Nucleostemin 1 (NS1) is the closest orthologue to human NS; it shares 33% identity and 67% similarity with human NS. We show that NS1 has intrinsic GTPase and ATPase activity, and that it is present within nucleoli of most larval and adult cells. Endogenous NS1 and lightly expressed GFP-NS1 enrich within the nucleolar granular regions as expected, while over-expressed GFP-NS1 localizes throughout the nucleolus and nucleoplasm, and to several transcriptionally active inter-bands of polytene chromosomes. Over-expression caused melanotic tumors and larval and pupal lethality. RNAi depletion of NS1 caused a loss of imaginal (precursor) cells in the larval midgut, and an apparent block in the nucleolar release of large ribosomal subunits in the terminally differentiated larval midgut polyploid cells. Depletion of 60% of NS1 transcripts lead to larval and pupal lethality. Ultra-structural examination of highly differentiated larval Malpighian tubule cells depleted for NS1 showed a loss of cytoplasmic ribosomes with a concomitant appearance of cytoplasmic pre-autophagosomes. We interpret the appearance of these structures as indicators of cell stress response.

Name thesis:degree_name

Doctor of Philosophy (PhD)

Level thesis:degree_level

Dissertation

Grantor

Biological Sciences

Year dc:date.available

2010

Author dc:creator

• Rosby, Raphyel Ojomo

• nucleostemin
• ribosomes
• large subunit
• granular component
• rRNA
• nucleolus
• NS-1
• autophagy

Statement dc:rights

• unrestricted
• Release the entire work immediately for access worldwide.

Identifier

etd-01232010-063910
https://repository.lsu.edu/gradschool_dissertations/981

OAI identifier oai:identifier

oai:repository.lsu.edu:gradschool_dissertations-1980