Bioengineering laboratory

Lab head: Munira Xaymardan
Location: Bioengineering laboratory, Dental School. Westmead Hospital, Westmead, NSW 2145

Congenital malformation, injury, infection and tumour removal surgeries can inflict defects on the facial region that result in diminished oral health and life quality of the patients. For example, tongue squamous cell carcinoma is one of the most prevalent malignant tumours of the head and neck region with surgical management remaining as the principle treatment. After lesions excision, many patients are left with functional impairment of gustation, mastication and phonetic articulations that cannot be fully restored by current reconstructive treatments. Stem and progenitor cells can provide novel strategies for repair of the damaged tissue. However, harnessing the full potential of the stem cells will require understanding of the regulatory mechanisms that control tongue and facial tissue during morphogenesis.

In our laboratory, we found that contrary to thecurrent concept that the tongue muscle originate from paraxial mesoderm similar to those of the limb and trunk muscles originate from a pool of cardiac progenitors bearing the cardiac TF Nkx2-5, which was accompanied by further expressions of the cardiac markers Tbx1, Isl-1, MEF2C and to a lesser extent, GATA4. Additionally, we have found that these cardiac markers co-localise with the skeletal myocyte markers MYF5, MYOGENIN and MYOD starting from the embryonic day 12.5 in mouse. Supporting a hypothesis that the tongue muscle progenitors originate from the heart field muscle stem cell pool, ingress through pharyngeal arches to found the orofacial muscle primordia. These primary muscle cells carrying cardiac genes would later adopt number of skeletal TFs to develop into a hybrid muscle phenotype, perhaps an adaption necessary for functional integrity of the regional tissues.

To further our understanding of the molecular mechanism of the tongue myogenesis, we propose to use a human pluripotent stem cell (hPSC) line to generate the tongue muscle cells with cardiac-skeletal hybrid muscle characteristics in vitro. By careful literature analysis and in reference to our own preliminary experiments, we have identified that the mechanisms responsible for this “hybrid” characteristic in the orofacial muscles may be due to the dual modulation of Wnt and notch pathways. The cell differentiation assays are currently being performed and the honours project will involve in the assistance with cell culture, PCR and immunohistochmical characterisation of myogenic markers.

Funding: University Internal Funding, ADRF
Research approach equipment: Embryonic stem cell culture; Cell differentiation; PCR, Immunohistochemistry

Role of Transcription Factor Nkx2-5 in Orofacial Muscle Development

Primary supervisor: Munira Xaymardan

Developmental process of mammalians including humans is complex process. Each organ system has its unique developmental network; yet, they also share many common mechanisms that facilitate coordinated effort to ensure integrated function of the body. We found that the development of the tongue, provides an excellent example for such a “molecular sharing” process, in which both heart muscle and skeletal (such as muscle of the limb) developmental processes are involved in development of the tissue. It is interesting that the tongue muscle has more similarity to the heart muscle than to skeletal muscles of the limb and truck.

This highlights that studying tongue muscle in this context may provide opportunities for finding an additional source of stem cells that can be used to repair and renew heart tissue after a heart attack. To be able to best utilized these cells, we need to first understand how these cells are originate and differentiate during the embryonic and developmental processes.

Our preliminary data indicated that the orofacial region is the largest extra-cardiac expression for the cardinal cardiac transcription factor Nkx2-5. However, the function of which in the development of facial muscle is unknown, mostly because full deletion of Nkx2-5 arrests heart formation and causes early embryonic lethality.

 

This study will use a hypomorphic strategy to bypass early embryonic lethality and specifically address the role of Nkx2-5 in facial development. Briefly, the hypomorphic Nkx2-5 condition is achieved by crossing a Nkx2-5-cre males to Nkx2-5-GFP female to generation embryos that have a “null or deleted” allele and a 50% functioning allele. The net expression of the Nkx2-5 will be reduced to a 25% of the “normal level”. These embryos survive till day 14.5 in utero which will cover the major developmental stages of the tongue formation.

Methodology used in this project will involve in generation of hypomorphic embryos via time mating by crossing the Nkx2-5GFP and Nkx2-5Cre mice lines. The embryos will be collected at the embryonic days of 11.5 to 14.5. These embryos will be analyzed morphologically in comparison to the wild-type siblings. Histological and molecular signature alteration of the hypomorphic embryos will be analyzed using PCR and immunohistochemistry methods.


Discipline: Applied Medical Sciences, Westmead
Co-supervisors: Elizabeth Kelly
Keywords: Stem and cancer cell biology, Embryology, Oral Biology
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