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Supervisors: Erwin Pauws, Tengyang Qiu
Project Description:
Background:
The skull base is the central bone of the cranium, creating a platform for craniofacial growth[1]. The skull base is made of the frontal, ethmoid, sphenoid and occipital bone. The skull base bones connect via cartilage structures known as synchondroses. There are two synchondroses in the skull base: the spheno-occipital synchondrosis (SOS) and the inter-sphenoidal synchondrosis (ISS).
Most craniofacial bones are made of intramembranous bone, whereas the skull base is entirely formed of endochondral bone. The cartilaginous synchondroses act as growth plates and facilitate bi-directional, longitudinal bone growth. The cranial synchondroses are made of well-organized chondrocyte cell columns. These consist of a central resting zone containing precursor (stem) cells, flanked by proliferation zones that give rise to the outside hypertrophic zones[2].
Aims/Objectives
Recent research in our laboratory has identified skull base defects in a mouse model for Crouzon syndrome[3]. Subsequently, we performed a comparative study using Crouzon, Apert and Saethre-Chotzen syndrome model mice, all of which are caused by mutations in FGF signalling pathway genes like FGFR2[4]. These studies have shown that skull base defects are the primary cause of the midfacial hypoplasia phenotype associated with syndromic craniosynostosis. This work was done at postnatal stages of development. To expand this work and study the prenatal, fetal development of the skull base, this PhD project will:
- Characterise skull base development during normal fetal stages in wild-type mice.
- Investigate abnormal skull base development in a mouse model for Crouzon syndrome.
- Determine the molecular mechanism that underpins the skull base defects.
Together, these objectives will address the lack of data that currently prevents a good understanding of the development of the skull base and its contributions to abnormal skull size and shape.
Methods
To study the development of the skull base in more detail, we will harvest mouse fetuses from E15.5 to E18.5 and postnatal mice from P7 to P21. Skulls will be dissected if appropriate and analysed as follows:
• microCT scanning
Whole embryos or mouse heads will be scanned and this data will be used to assess the skull base phenotype at the macro level and perform morphometrical analysis by quantifying several skull base size and shape parameters using established landmarks. This analysis will answer two questions: 1) how the skull base develops at fetal stages and when synchondroses form and fuse normally; 2) when and where does the skull base phenotype first appear?
• Histological analysis
After microCT scanning, samples will be sectioned and stained, initially by H&E, but also by more specific staining, e.g. Alcian Blue to study chondrocytic development. Qualitative and quantitative analysis will be performed to assess the phenotypic characteristics of the chondrocyte organisation within the synchondrosis. This analysis will describe the precise cellular events that precede synchondrosis failure.
• Gene/protein expression analysis
To identify genes and pathways that are involved in the molecular mechanism, relevant candidates will be analysed using immunohistochemistry and/or RNAScope. The selection of candidate genes is supported by a previously performed, unpublished RNAseq analysis that identified downstream targets of the FGFR2 mutation.
In addition, proliferation will be assessed by phoshohistone-3 immunohistochemistry (ex vivo) and BrdU/EdU (in vivo) labelling to establish if abnormal proliferation of chondrocytes in the proliferative zone causes premature fusion.
References
1. Nie, X., Acta Odontol Scand, 2005. 63(3): p. 127-35.
2. Rengasamy Venugopalan, S. and E. Van Otterloo, J Dev Biol, 2021. 9(1).
3. Peskett, E., et al., Biol Open, 2017. 6(2): p. 223-231.
4. Hoshino, Y., et al., J Anat, 2023. 242(3): p. 387-401.