Type II collagen is the major extracellular matrix (ECM) protein present in
cartilage and is detected in non-chondrogenic tissues such as the heart and the
neural tube during developmental stages involving rapid tissue morphogenesis
indicating an active role played by the collagen in embryogenesis. Type II
collagen is synthesized as a procollagen precursor which has amino- and
carboxyl-terminal globular extensions (N- and C-propeptides) flanking a central
triple helical domain. Two isoforms of type II procollagen are generated by
alternative mRNA splicing of the exon 2: IIA and IIB. Sequence present in the
N-propeptide of IIA, translated from the spliced-in exon 2, encodes a von
Willebrand factor-like C cysteine rich (CR) domain. This domain is homologous
to those present in regulators of the bone morphogenetic protein (BMP) signaling
such as chordin (Chd), twisted gastrulation (Tsg) and crossveinless (Cv).
Previous in vitro binding assays and overexpression studies in frog embryo
suggest that the CR domain of IIA antagonized BMP signaling. In order to give
a better understanding of the function of IIA in embryonic development and
cellular signaling, several approaches including expression pattern analyses,
phenotypic analyses of null mutant and gain of function studies are employed in
this study. Expression studies of IIA mRNA in early postimplantation mouse
embryos find that it is present in the axial mesendoderm (including the anterior
definitive endoderm [ADE] and the prechordal plate) which is a critical head
organizer at neural plate (E7.5) and head process (E8.0) stages. Characterization
of the IIA deficient mice (IIA-/-), constructed by removing exon 2 from type II
collagen (Col2a1) gene by homologous recombination, indeed reveals that the
anterior-most neural tissue is deficient at early somitogenesis denoted by
reduction/loss of the forebrain/optic cup markers. Marker studies indicate that
the ADE may already be affected at the neural plate stage in IIA-/-. The neural
phenotype of IIA-/- displays significant similarities with mutants deficient in BMP
pathway components such as Chd-/-;Nog+/-, Tsg-/- and Tsg-/-;BMP4+/- suggesting
that IIA plays a role in maintaining the specification and/or regulating the
signaling properties of the anterior midline tissue which involves regulation of
BMP signaling. Results of ectopic expression of IIA in Xenopus laevis embryos
suggest that IIA regulate BMP and the related Nodal signaling pathways in a
context dependent manner which has significant implications in normal anterior
neural plate development. Based on the work described in this thesis and the
body of existing evidence, a model is presented which suggests that IIA
promote/maintain anterior neural plate development by regulating the range and
extent of BMP signaling in the anterior neural plate. This study sheds light on
the role of an ECM component in regulating tissue patterning and cellular
signaling during early mouse development and also provides putative function for
the CR domain of other fibrillar procollagens including type I, III and V which is
poorly understood currently. This work will provide the framework for the
design of subsequent studies in re-examining the role of these fibrillar
procollagens in embryogenesis. / published_or_final_version / Biochemistry / Doctoral / Doctor of Philosophy
| Identifer | oai:union.ndltd.org:HKU/oai:hub.hku.hk:10722/159140 |
| Date | January 2006 |
| Creators | Leung, Wai-lun, Alan., 梁瑋倫. |
| Publisher | The University of Hong Kong (Pokfulam, Hong Kong) |
| Source Sets | Hong Kong University Theses |
| Language | English |
| Detected Language | English |
| Type | PG_Thesis |
| Source | http://hub.hku.hk/bib/B4501548X |
| Rights | The author retains all proprietary rights, (such as patent rights) and the right to use in future works., Creative Commons: Attribution 3.0 Hong Kong License |
| Relation | HKU Theses Online (HKUTO) |
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