942 research outputs found
Aquaporins in kidney development and disease
No full textpublished_or_final_versionabstracttocSurgeryMasterMaster of Philosoph
Expression of sphingosine-1-phosphate receptor in abdominal aortic aneurysm
No full textpublished_or_final_versionSurgeryMasterMaster of Philosoph
Expression analysis of Hoxb5 in enteric neurons and generation of Tamoxifen inducible Cre mice for neuronal Hoxb5 signalingperturbation
No full textpublished_or_final_versionSurgeryMasterMaster of Philosoph
Chloride channel in glioma cell invasion
No full textpublished_or_final_versionSurgeryMasterMaster of Philosoph
Identification and characterization of a biliary atresia hepatic progenitor pool from an organoid-transcriptomic approach
No full textBiliary atresia (BA) is the commonest cause of paediatric liver transplantation (>50%).
Kasai hepatoportoenterostomy (HPE) is a universal surgical treatment when a diagnosis
is made early. Yet, the disease continues to progress, leading to a series of complications
and need of liver transplantation in 60% of patients.
Clinical research on BA investigated into the clinical variants of BA, age of performing
HPE for better success, neonatal hepatobiliary biochemical profiles and the effect of
using post-HPE adjuvant steroid therapy on clinical outcome.
While clinical research shed insights on the clinical features, course and outcome of BA,
basic research is critical to uncovering the underlying pathogenic mechanisms based on
which new intervention can be proposed to improve the dismal outlook of BA. Rhesus
rotavirus-induced BA mouse model, animal outbreak of BA, zebrafish-biliatresone model,
induced pluripotent stem cells (iPSCs), genetics studies and pathological human tissue
immunohistochemistry analyses were used to suggest hypotheses of BA pathogenesis,
including viral, environmental toxin, developmental immaturity, genetic predisposition,
immune dysregulation and fibrogenic ductular reaction.
Discrepancies exist between human and animal models. Questions remain regarding
how close animal models are recapitulating the actual human pathology. For example,
multiple viruses and inconsistencies were identified on human tissue and BA epidemic
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has not been observed in humans. While iPSCs studies rely on genetic manipulation and
access to human biliary material for cell culture studies is limited due to the lack of cell
ability to proliferate, there is a gap between basic research and their reflection on human
BA pathology.
A key and interesting question to a paediatric surgeon and the patients' family is: Is the
palliative biliary fibrosis outcome preventable at the time of Kasai HPE?
This thesis details a novel approach-combining human liver biopsy-derived diseased
organoids-in-the-dish and transcriptomic analyses-addressing the first step of this
question. It identified and characterized a group of aberrant hepatic progenitors in
paediatric BA livers at the time of Kasai HPE. The attempt made use of an optimized
biliary organoid culture protocol and a series of next-generation sequencing
(transcriptomics) analyses to identify an aberrant group of hepatocytes with progenitor
properties that are non-existent in non-BA human livers. At the end, a long-overlooked
perspective on the hepatocyte populations in the context of BA-a biliary disease, was
revisited and suggested as a modern research direction.
Such finding opens two key possibilities: first, human biliary cells from diseased tissue
are not available in abundance to support further basic research into the pathogenic
mechanisms; second, the same approach could be utilized on diseased tissues of
different ethnicities, clinical background and disease stages in future to capture the
distinctions among them.published_or_final_versionSurgeryDoctoralDoctor of Philosoph
Fenestrated endovascular aortic repair (FEVAR) for complex abdominal aortic aneurysm (AAA) : a morphologic and hemodynamic study
No full textpublished_or_final_versionSurgeryDoctoralDoctor of Philosoph
Wnt inhibitory factor 1 (Wif-1) coordinates Shh and Wnt signaling activities in urorectal development
No full textIn vertebrates, the urogenital sinus and the hindgut are connected at a hollow region called cloaca. A midline mesenchymal structure known as urorectal septum (urs) descends from the ventral body wall to separate the urogenital sinus from the hindgut before the formation of an anal opening. Subsequent cloaca membrane regression at the ventral midline of the genital tubercle (GT) is crucial for the formation of an anal opening. These two events are important during cloaca septation in urorectal development.
Mice with defective Shh or Wnt signaling displayed similar urorectal defects such as GT agenesis, un-partitioned cloaca (persistent cloaca) and proximal urethral opening that are attributable to increased cell apoptosis. Furthermore, Shh and Wnt signal transduction coordinate with each other and regulate cell survival of the developing urorectum. However, the molecular mechanisms by which these two signaling pathways coordinate in urorectal development remain unclear.
We previously identified Wnt inhibitory factor1 (Wif1) from Affymetrix array analysis for genes/pathways that is implicated in urorectal development. Wif1 is a secreted protein that binds directly to Wnt ligands preventing Wnts from binding to receptors. This leads to -catenin degradation and thereby inhibits their activities. It is known that Wif1 binds to Wnt3a and Wnt5a with high affinity and deletion of Wnt3a, Wnt5a and -catenin in mice caused GT agenesis, persistent cloaca and proximal hypospadias. Using ETU-induced anorectal malformations model, I found out that Wif1 is ectopically expressed in the un-tubularized and un-septated urorectum. Wif1 is mainly expressed at the fusing endoderm that associates with programmed cell death during cloaca septation. Exogenous addition of Wif1 protein in urorectum culture also caused cloaca membrane disintegration, and proximal urethral opening that may be due to aberrant apoptosis.
Shh and Wif1 are differentially expressed at the cloaca endoderm. In normal mice, Shh is highly expressed at the cloaca endoderm except those Wif1-expressing endodermal cells. Blockage of Shh pathway by cyclopamine in urorectum culture induced ectopic expression of Wif1, concomitant with genital tubercle hypoplasia and un-septated cloaca. More importantly, deletion of Shh in mice hastened Wif1 expression at the cloaca membrane endoderm and elicited increased cell death in the
Wif1 expressing endoderm. Wif1-/- embryos display urorectal defects including delayed genital outgrowth and proximal hypospadias. Therefore, disruption of spatiotemporal expression of Wif1 could lead to defective Wnt signaling and contributes to abnormal urorectal development in Shh-/- mutant.
Current study revealed that Wif1 is involved in urorectal development and is implicated in urorectal defects. It may function as a pro-apoptotic factor to regulate endodermal cell death which is essential for the septation process. Its specific expression is restricted at the midline cloaca endoderm by Shh signaling to inhibit local Wnt--catenin activities during cloaca septation. I proposed novel hypothetical models to explain (1) the significance of the tempo-spatial expression of Wif1; (2) the significance of cell death; and (3) the molecular mechanism that Shh signaling regulates Wnt signaling activities through Wif1 in urorectal development.published_or_final_versionSurgeryDoctoralDoctor of Philosoph
Studying the roles of conserved domains of the transcription factor Sox10 in neural crest development
No full textpublished_or_final_versionBiochemistryMasterMaster of Philosoph
Differential expression of Wnt inhibitors Dickkopf-1 (Dkk-1) and Wnt inhibitory factor-1 (Wif1) in the regulation of urorectal development
No full textIn mammals, the external genitalia, urinary tract and anorectal tract are developed from a common embryonic primordium, the urorectum. Cloaca is the hollow space inside the urorectum that connects the hindgut and the urogenital sinus. During the urorectal development, the external genitalia is formed from the outgrowth of genital tubercle (GT) protruding from the urorectum, while the future urinary tract and anorectal tract are formed by the partition of cloaca during cloacal septation. GT outgrowth and cloacal septation are important developmental events for the formation of genitourinary and anorectal system. In human, dysregulation of these developmental events results in congenital anorectal malformations (ARM).
Wnt signaling is one of the key signaling pathways that regulates urorectal development. The activity of Wnt signaling is initiated by the binding of Wnt ligands to cell surface receptors, which can be antagonized by secretory Wnt inhibitors. Dickkopf1 (Dkk1) and Wnt inhibitory factor 1 (Wif1) are secretory Wnt inhibitors implicated in urorectal development. However, the functions of other secretory Wnt inhibitors during urorectal developments remain to be elucidated.
In this study, expression analyses showed that Dkk1, Dickkopf2 (Dkk2), Dickkopf4 (Dkk4), Secreted Frizzled-related Protein 1 (Sfrp1) and Wif1 were expressed in the developing urorectum. The dynamic, overlapping and restricted expression patterns of these Wnt inhibitors were closely associated with the GT outgrowth and the cloacal septation events, implying that these Wnt inhibitors functioned in a coordinated manner in defining the field of Wnt signaling activities in the developing urorectum.
Wif1 knockout mice (〖Wif1〗^(-/-)) was used as the model to investigate the functions of and the interplay between secretory Wnt inhibitors in urorectal development. GT outgrowth and cloacal septation defects were observed in 〖Wif1〗^(-/-) embryos. Most of the 〖Wif1〗^(-/-) embryos displayed varying degrees of GT outgrowth defects, while septation defects were only occasionally observed. This suggested that GT outgrowth and cloacal septation were regulated by Wif1 via different regulatory mechanisms.
In the urorectum of 〖Wif1〗^(-/-) embryos, Dkk1 was significantly upregulated in the peri-cloacal mesenchyme. Further expression analysis suggested that Dkk1 was sufficient to rescue cloacal septation defects but not GT outgrowth defects in 〖Wif1〗^(-/-)embryos. In the 〖Wif1〗^(-/-) embryos with severe GT outgrowth defects, the Fgf8-expressing distal urethral epithelium, the signaling center in the urorectum, was absent, suggesting that the GT outgrowth defects could be contributed by the loss of dUE-expressing signals such as Fgf8.
This study demonstrated the importance of secretory Wnt inhibitors in the GT outgrowth and cloacal septation and suggested that secretory Wnt inhibitors played partially overlapping roles in urorectal development. A rescue mechanism for cloacal septation performed by Dkk1 upon Wif1 deletion was proposed. Such auto-regulatory mechanism within the Wnt signaling pathway indicated that Wnt inhibitors play essential regulatory roles in the urorectal development and a balanced Wnt signaling activity modulated by Wnt inhibitors is crucial to the development of urorectum.published_or_final_versionSurgeryMasterMaster of Philosoph
The Ret gene in the enteric nervous system: expression analysis and generation of ret deficient mice
No full textpublished_or_final_versionabstractSurgeryDoctoralDoctor of Philosoph
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