Abstract
How cell and tissue interactions lead to complex structures and differentiated
cell types during organogenesis is still one of the most fundermental questions
in modern molecular biology. Laminin appears to have a role in branching
morphogenesis during organ development. Laminin5 (α3β3γ2) is an
epithelium-specific isoform of laminin and previous report has shown that two
alternative transcripts for the γ2 chain, the longer γ2 and the shorter
γ2*, result from alternative use of the last exon in the human
LAMC2 gene. But the transcription of murine laminin γ2
and γ2* and their biological significance have remained unclear. Type XVIII
collagen is a newly identified member of the collagen family. It may be involved
in the Wnt signaling pathway, since its longest N-terminal variant contains a
frizzled domain, which is part of the Wnt receptor and could antagonize Wnt
signaling when secreted. Wnt2b is a new member of the Wnt family. Also its
function in organogenesis is unknown. In this study, we have investigated the
expressions of laminin γ2 and
γ2*, type XVIII collagen and
Wnt2b during mouse organogenesis. The function of type XVIII
collagen in developing lung, kidney and a recombination of ureteric bud and lung
mesenchyme tissue and the function of the Wnt-2b gene during
kidney organogenesis were studied by using the combined methods of traditional
experimental embryology and modern molecular biology.
Two alternative laminin γ2 transcripts were demonstrated in mouse. In the
developing kidney, the shorter γ2* form was localized in the mesenchyme,
whereas the longer γ2 form was only present in the epithelium of the
Wolffian duct and in the ureteric bud, indicating different functions for the
γ2 variants. Type XVIII collagen was expressed throughout the respective
epithelial bud at the initiation of lung and kidney organogenesis. It becomed
localized to the epithelial tips in the early-stage lung, while it was confined
to the epithelial stalk region and was absent from the nearly formed ureteric
tips in the kidney. In recombinants of ureteric bud and lung mesenchyme, the type
XVIII collagen expression pattern in the ureteric bud shifted from the kidney to
the lung type, accompanied by a shift in epithelial Sonic
Hedgehog expression. The lung mesenchyme was also sufficient to induce
ectopic lung Surfactant Protein C expression in the ureteric
bud. A blocking antibody for the type XVIII collagen reduced the number of
epithelial tips in the lung and completely blocked ureteric development with lung
mesenchyme, which was associated with a notable reduction in the expression of
Wnt2. The shift in type XVIII collagen expression in
ureteric bud and lung mesenchyme tissue recombinant was also accompanied by the
significant morphological changes in the branching pattern in ureteric bud
development. Wnt2b was expressed in numerous developing
organs in the mouse embryo, but it was typically localized in the perinephric
mesenchymal cells in the region that partly overlaps the presumptive renal stroma
at E11.5. Functional studies of the kidney demonstrated that 3T3 cells expressing
Wnt2b were not capable of inducing tubule formation but rather stimulated
ureteric development. Recombination of ureteric bud treated with cells expressing
Wnt2b and isolated kidney mesenchyme resulted in recovery of the expression of
epithelial marker genes and better reconstituted organogenesis. Lithium, a known
activator of Wnt signaling, was also sufficient to promote ureteric branching in
reconstituted kidney in a manner comparable to Wnt2b signaling.
Our data suggest that different organ morphogenesis is regulated by an intraorgan
patterning process that involves coordination between inductive signals and
matrix molecules, such as type XVIII collagen. In the mouse kidney,
Wnt2b may act as an early mesenchymal signal controlling
morphogenesis of epithelial tissue, and the Wnt pathway may regulate ureteric
branching directly.
| Identifer | oai:union.ndltd.org:oulo.fi/oai:oulu.fi:isbn951-42-6566-1 |
| Date | 15 November 2001 |
| Creators | Lin, Y. (Yanfeng) |
| Publisher | University of Oulu |
| Source Sets | University of Oulu |
| Language | English |
| Detected Language | English |
| Type | info:eu-repo/semantics/doctoralThesis, info:eu-repo/semantics/publishedVersion |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess, © University of Oulu, 2001 |
| Relation | info:eu-repo/semantics/altIdentifier/pissn/0355-3221, info:eu-repo/semantics/altIdentifier/eissn/1796-2234 |
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