Dr. Hisham Bazzi

1. Research Background:

In order to understand aging and how the organism is disassembled, we need to understand how it was assembled in the first place. In general, there is a positive correlation between the time spent in development (gestation in mammals) and lifespan, and we believe that studying embryonic development will undoubtedly guide our understanding of aging and aging-associated diseases.

Cells in a developing organism or tissue are faced with multiple fate choices. However, they do adopt specific fates in a very reproducible manner. Just like a computer program initiates a sequence of events where one leads to another, cells follow a defined path to arrive at their pre-determined fates. Our main interest is to decipher part this complex cellular program with a focus on signaling pathways and cytoskeletal organization.

In order to study cell fate decisions, our lab primarily uses genetic approaches in the mouse, as a model organism. In addition, we utilize cells in vitro such as mouse embryonic stem cells (mESCs) and primary cell culture to investigate the mechanisms that are difficult to address in the mouse in vivo. Our lab employs cutting edge techniques of gene editing such as the CRISPR/Cas9 system and proteomics and transcriptomics in our studies.

Our work is mainly focused on embryonic development in the mouse which takes around 19 days. We are interested in mouse embryonic development around the beginning of gastrulation (embryonic days E6.5-E7.5) as well as skin development (E12.5-E17.5). We study the roles of signaling pathways and cytoskeletal organizers in in cell fate choices in these developmental processes.
 
1) The functions of centrosomes in mouse development

Centrosomes are major microtubule organizing centers of animal cells. During interphase or in differentiated cells, the centrosome is essential to provide the template for cilia and flagella, whereas during cell division the centrosome is required for the efficient assembly of the mitotic spindle. Using genetic mutations in the mouse, we have previously removed centrosome function in the developing mouse embryo and brain (Bazzi and Anderson, 2014; Insolera et al, 2014). The main result was the activation of a p53-dependent apoptosis pathway that was not due to the secondary loss of cilia and was linked to prolonged mitosis. We and others have shown that this novel checkpoint is also independent of DNA damage or abnormalities in chromosome segregation. Our group is using genetics and biochemistry to unravel the mechanism of this novel checkpoint in mouse embryos and mESCs. Our aim is to shed light on centrosome-related human diseases and to help find ways of treating them.

2) The functions of centrosomes in skin epithelial development

Centrosomes regulate mitotic spindle orientation which has been linked with the mode of progenitor cell division (symmetric versus asymmetric divisions). The skin epidermis is an ideal system to investigate the roles of centrosomes and cell division in determining cell fate during embryonic development and adult homeostasis. We are using genetic approaches to investigate the roles of centrosomes and cilia in cell fate specification in the skin epithelium.
  
3) The functions of the STRIPAK complex in the skin

The striatin-interacting phosphatases and kinases complex (STRIPAK) is biochemical complex that regulates the balance of the activities of the phosphatase PP2A and associated kinases. We have shown that striatin-interacting protein 1 (STRIP1), a core component of the STRIPAK, is essential for normal mesoderm formation and migration in the mouse embryo through regulation of the actin cytoskeleton organization (Bazzi et al, 2017). We are studying the roles of the STRIPAK in the skin epithelial development and differentiation.

4) Hair follicle development and patterning

The first hair follicles in mouse skin develop ~E14 through an interaction between the mesenchyme and overlying epithelium and are precisely spaced and patterned (Bazzi et al, 2007). We are using transcriptomics and genetic approaches in the mouse to study the signaling hierarchies in determining hair follicle initiation and patterning.

2. Research questions addressed by the group:

  1. How does the loss of centrosomes lead to the activation of a novel p53-dependent checkpoint?
  2. How do centrosomes regulate cell division and cell fate in the skin?
  3. How does the STRIPAK complex regulate cell adhesion and migration?
  4. How are hair follicles initiated and patterned in the skin?

3. Possible projects:

  • How is the novel p53-dependent checkpoint established during mouse development?
  • How does the STRIPAK complex regulate cell adhesion and migration in the skin epithelium?
  • How are hair follicles initiated and patterned in the skin epithelium?

4. Applied Methods and model organisms:

Our models are the mouse and mouse-derived cells: embryonic stem cells (mESCs), skin epidermal keratinocytes and fibroblasts. Methods include:

  • Generating knockout and knockins using CRISPR/Cas9
  • Live imaging of cells, embryos and skin
  • RNA-Seq, ChIP-Seq, scRNA-Seq and Mass Spec
  • Histology, immunofluorescence and immunohistochemistry
  • Transmission and scanning electron microscopy
  • Biochemical techniques (such as Western Blots and IPs)
  • Molecular cloning

5. Desirable skills and qualifications:

High interest in Developmental Genetics and willingness to learn cutting-edge technology to address biological questions.

6. References:

  • Bazzi H#, Soroka E, Alcorn H, Anderson, KV#. (2017). STRIP1, a core component of STRIPAK complexes, is essential for normal mesoderm migration in the mouse embryo. Proc Natl Acad Sci U S A, 114: E10928-E10936. #Corresponding authors.
  • Bazzi H & Anderson KV. (2014). Centrioles in the mouse: cilia and beyond. Cell Cycle, 13, 2809.
  • Insolera R*, Bazzi H*, Shao W, Shi SH, Anderson KV. (2014). Cortical neurogenesis in the absence of centrioles. Nat Neurosci, 17, 1528-35. *Equal contribution.
  • Bazzi H & Anderson KV. (2014). Acentriolar mitosis activates a p53-dependent apoptosis pathway in the mouse embryo. Proc Natl Acad Sci U S A, 111, E1491-500.
  • Bazzi H, Fantauzzo KA, Richardson GD, Jahoda CA & Christiano AM. (2007). The Wnt inhibitor, Dickkopf 4, is induced by canonical Wnt signaling during ectodermal appendage morphogenesis. Dev Biol, 305, 498-507.