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The Looptail mutation promotes a defect in apical morphology in the dorsal midline primordium of the early mouse embryo
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Mice carrying the homozygous Looptail (Lp) mutation, affecting the Vangl2 gene – a core element of
the Wnt-PCP pathway – are known to develop craniorachischisis, a rare and severe neural tube defect.
This derives from an impairment of convergent extensions cellular movements at the neural plate
midline level, resulting in a broad floor plate and failure of the initiation of Closure 1 of the neural tube.
Neurulation in an important developmental step that is strongly linked to node regression and the
establishment of the notochord, both of which appear to be affected by the Lp mutation. Studies on the
mouse embryonic node have focused mostly on its ventral component, as this is the one thought to
contain all the properties of the organizer. Because the dorsal component of the node – or the dorsal
midline primordium (DMP) – has been treated, over the years, as an extension of the epiblast, little is
known about the cellular behaviour of this layer. Some evidence suggests that DMP cells may participate
in notochordal formation, raising the question of whether or not the DMP contributes to cell intercalation
at midline level and overall node regression. Following this hypothesis, and since (ventral) node
morphology and midline formation have been shown to be affected in Vangl2Lp/Lp embryos, it is possible
that the Lp mutation may also promote defects in the DMP.
The main objective of the present work is to shed some light on how DMP cells behave during node
regression, and how this process may affect neural plate midline establishment, later on in development.
For this purpose, i) apical morphology and cells dynamics in the Vangl2+/+ DMP were characterized ii)
and compared to that found in Vangl2Lp/Lp embryos; iii) the parameters found altered in the Vangl2Lp/Lp
DMP were also assessed in the Vangl2+/Lp embryo; iv) possible changes at the apical level of the DMP,
through its development, were assessed in different genotypes.
Through whole mount immunohistochemistry and the use of an antibody against the zonula occludens
1 (ZO1) protein, it was possible to label the apical domain of DMP cells. This, coupled with image
segmentation techniques, allowed a cell-by-cell approach which focused, solely, on this dorsal
component of the embryonic node. Furthermore, the use of the Lp mouse strain helped to inquire how
the Wnt/PCP pathway may act in the context of DMP development.
The results reported here suggest an active contribution of the DMP for midline formation and that the
Wnt/PCP pathway may be required for proper apical morphology within the DMP. Furthermore, the
results suggest that a single copy of the Lp mutation may be sufficient to promote a defect in cell division
orientation, and that this, coupled with a partial defect in apical constriction, may be a driver for the
failure of Closure 1 in the NT of Vangl2Lp/Lp mice.
Descrição
Tese de mestrado, Biologia Evolutiva e do Desenvolvimento, Universidade de Lisboa, Faculdade de Ciências, 2022
Palavras-chave
Vangl2 intercalação celular nó dorsal orientação da divisão celular defeitos do tubo neural Teses de mestrado - 2022