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Vikki M Weake

Biochemistry 

  • Assistant Professor of Biochemistry
765.496.1730
BCHM Room 320A

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Weake Lab

Area of Expertise: Chromatin modifying complexes in Drosophila development as a model for neurodegenerative disease and cancer

 

               

Figure captions:

1.    Histones were extracted from SAGA mutant third instar larvae and probed with antibodies against histones H2B, monoubiquitylated histone H2B (ubH2B), H3 and acetylated Lys-9 H3 (H3K9ac). The H2B antibody also recognizes ubH2B (upper band). Mutations in nonstop and sgf11 result in a global increase in ubH2B but do not affect acetylated Lys-9 H3 levels. Conversely, mutation of the SAGA subunit ada2b reduces acetylated Lys-9 H3 but does not result in an increase in ubH2B (Weake et al. 2008 EMBO J.).

2.    In third instar larvae, photoreceptor cells from the eye disc extend axons through the optic stalk (os) into the optic lobe. The projection of R2 - R5 axons was visualized in wild type and sgf11 larval optic lobes using the ro-tlacZ marker (red). R1 – R6 axons terminate in the lamina (dotted lines) in wild type within a triple layer of glial cells, visualized using anti-repo (green). In sgf11 optic lobes, R2 – R5 axons project through the lamina into the medulla (me) and an increased number of glial cells accumulate at the edges of the lamina (arrowheads) while fewer glial cells are present along the lamina (Weake et al. 2008 EMBO J.).



In eukaryotes, such as yeast, flies and humans, our DNA is compacted into a nucleoprotein structure known as chromatin. The histone proteins that wrap around the DNA to form chromatin can be modified by the addition of small chemical and protein molecules, and these modifications are important for regulating both gene expression and genomic integrity. In our lab, we study the SAGA chromatin modifying complex using the fruitfly, Drosophila melanogaster, as a model system. SAGA is a large multi-subunit complex and has two distinct histone modifying activities. It is both a histone acetyltransferase and a histone deubiquitylating enzyme. Intriguingly, the two activities of the complex can be separated using mutations in different subunits. Mutations that disrupt the histone acetyltransferase activity of SAGA such as ada2b reduce global levels of acetylated Lys-9 on histone H3 (Figure 1). In contrast, mutations that affect the histone deubiquitylase function of SAGA such as sgf11 or nonstop increase global levels of monoubiquitylated histone H2B (Figure 1). However, mutations in ada2b do not affect levels of monoubiquitylated histone H2B. Furthermore, mutations in sgf11 or nonstop do not affect acetylation of histone H3 at Lys-9. We are interested in understanding how the different activities of the SAGA complex function mechanistically to regulate transcription and gene expression in specific cell types. Misregulation of SAGA subunits is associated with poor prognosis in specific types of cancer, and we hypothesize that specific activities of SAGA are required in particular cell types for proper regulation of gene expression and cell division.  Why do we think SAGA has tissue-specific functions? Our previous work has identified a role for SAGA in regulating neuronal connectivity in the developing fly eye. Mutations in sgf11 or nonstop disrupt targeting of photoreceptors from the eye imaginal disc into the optic lobe (Figure 2). Previous studies indicate that SAGA is required in glial cells rather than neurons for proper photoreceptor axon targeting. We are interested in finding out why SAGA is required for axon targeting by identifying genes that are regulated by SAGA in glial cells, and by searching for potential non-histone targets of SAGA in the brain. This work might provide insights into human neurodegenerative disease because a hereditary human neurodegenerative disorder, spinocerebellar ataxia 7, results from mutation of a SAGA subunit also involved in histone deubiquitylation. Furthermore, this ataxia is associated with retinal degeneration and blindness, suggesting that SAGA could also play an important role in eye development and function in humans.

Awards & Honors

(2002) Massey Scholarship.

(2002) NZ Federation of Graduate Women Manawatu Branch Scholarship. Hildegard Gabriel Scholar (Predoctoral).

(2005) Top Achiever Doctoral Scholarship. Foundation for Research, Science & Technology.

(2010) Winner of Postdoctoral Oral Presentation. Stowers Institute for Medical Research, Crossroads Postdoctoral and Student Association Research Day..

Selected Publications

Stephenson, R., Hosler, M., Gavande, N., Ghosh, A., & Weake, V. (2015). Characterization of a Drosophila ortholog of the Cdc7 kinase: A role for Cdc7 in endoreplication independent of Chiffon. J. Biol. Chem, doi:10.1074/jbc.M114.597948. Retrieved from http://www.jbc.org/content/290/3/1332.full.pdf+html

Ma, J., & Weake, V. (2014). Affinity-based isolation of tagged nuclei from Drosophila tissues for gene expression analysis. J. Vis. Exp, 85, e51418. Retrieved from http://www.jove.com/pdf/51418/jove-protocol-51418-affinity-based-isolation-tagged-nuclei-from-drosophila-tissues-for

Mohan, R., Dialynas, G., Weake, V., Liu, J., Martin-Brown, S., Florens, L., Washburn, M., . . . Abmayr, S. (2014). Loss of Drosophila Ataxin-7, a SAGA subunit, reduces H2B ubiquitination and leads to neural and retinal degeneration. Genes Dev, 28, 259-272. Retrieved from http://genesdev.cshlp.org/content/28/3/259.long