Functional study of AVE secreted genes during mouse embryogenesis: insights on the role of mADTK1

Silva, Lisa Gonçalves Dias da

http://hdl.handle.net/10400.1/728

Use this identifier to reference this record.

Name:	Description:	Size:	Format:
PhD Lisa Goncalves Dias da Silva.pdf		7.48 MB	Adobe PDF	Download

Send Feedback

Authors

Silva, Lisa Gonçalves Dias da

Advisor(s)

Belo, José António

Abstract(s)

The vertebrate organisms are characterized by being asymmetrically organized in three different axes, it is important to study the onset of these axes. Several pathways are involved in this crucial event, among them is Transforming Growth Factor-β (TGF-β) superfamily which comprises several key molecules as Nodal and Bone Morphogenetic Proteins (BMP). The Anterior Visceral Endoderm (AVE) is a very important structure during mouse embryonic development, where first asymmetries start to show and axes start to be established. Several genes such as mouse cerberus-like, a member of the TGF-β superfamily, and a Nodal and BMP antagonist, are expressed in this tissue and are of major importance for correct development of the embryo. cerl-1 is a critical player in the Nodal signaling pathway, which is of major importance during gastrulation and the onset of axes establishment. Interestingly, the analysis of potential interactions between Cer-l and Nodal co-receptor Cripto, suggested the possibility of a Cripto independent Nodal signaling pathway, in establishing the anterior-posterior (A-P) and dorso-ventral (D-V) axes during embryonic development. In an attempt to further study the AVE a pool of novel genes upregulated in this tissue was discovered by a differential screening. Among these were found shisa and ADTK1. Previous work in Xenopus has shown that Shisa-1 inhibits both FGF and Wnt signaling pathways, by regulating the maturation of their receptors. Downregulation of Shisa-1 leads to defects in anterior structures. In the lab, it was demonstrated that Shisa-2 is involved in the correct development of somites. During this work, it was performed an exhaustive comparative analysis of shisa expression patterns in mouse and chick. Cross-species comparison showed that the expression pattern is conserved in mouse and chick, indicating that the Shisa family genes are typically expressed in tissues known to require the modulation of Wnt and FGF signaling, such as somites, eye and limbs. The largest part of this work consisted of the analysis of ADTK1 role in mouse. A detailed analysis of its expression pattern was performed, indicating several processes in which this gene might be involved in, such as the formation of anterior structures, limb and heart development and neurulation. This hypothesis was consistent with data from Xenopus and chick orthologs, where downregulation of ADTK1 leads to defects in neural tube closure and heart development, respectively. XV In order to evaluate ADTK1 biological function, a targeted inactivation was performed. Although the majority of ADTK1 null mutants presented no visible phenotype, some presented defects in the eye and ear. Skeletal analysis of ADTK1 null mutants demonstrated defects in bone length; these mutants present shorter limbs than their wild-type littermates. Regarding the internal organs, defects in kidney development were detected in all analyzed mutants. ADTK1 mutant kidneys were larger and had a reddish color, comparing to the wild-type littermates. Furthermore, preliminary histological analysis suggests that the kidney medullar region is affected, and that glomerular structures are diminished, when comparing to the wild type. The process of kidney development is a complex one, not yet fully understood. Several signaling pathways, such as Wnts, Shh, BMPs and FGFs, are involved in the process of nephrogenesis. Once again, as it happens with so many genes, ADTK1 null mutants don‟t mimic the defects presented by downregulation in Xenopus and chick orthologs. It is possible that the lack of striking phenotype can be accounted for the fact that, in mammals, there are several genes with redundant activity, preventing, this way, potential anomalies, and overcoming defects that could lead to embryonic development arrest.