dc.contributor.author
Marczenke, Maike
dc.date.accessioned
2022-05-09T09:45:18Z
dc.date.available
2022-05-09T09:45:18Z
dc.identifier.uri
https://refubium.fu-berlin.de/handle/fub188/34800
dc.identifier.uri
http://dx.doi.org/10.17169/refubium-34519
dc.description.abstract
The morphogen sonic hedgehog (SHH) regulates central patterning processes along the
dorsoventral axis of the emerging forebrain. Secreted from the prechordal plate (PrCP), SHH
targets neuroepithelial cells of the overlying forebrain organizer region in the rostral
diencephalon ventral midline (RDVM), to establish and further specify ventral identity of the
forebrain. Defects in this pathway result in severe developmental forebrain defects including
holoprosencephaly (HPE). Besides the canonical SHH receptor patched 1 (PTCH1), several
additional cell surface proteins have been identified as being essential for SHH signaling in the
neuroepithelium. Jointly, they are referred to as the SHH receptorsome and include LRP2 and
GAS1. Mutations in these co-receptors are the cause of familial forms of HPE and related
phenotypes, such as in Donnai-Barrow syndrome (DBS), corroborating their importance for
SHH-dependent forebrain development in humans. Intriguingly, the structure of SHH coreceptors
is highly diverse and they show spatial and temporal differences in expression
pattern, arguing for distinct functions of each receptor in SHH-dependent developmental
processes. In this thesis, I used human induced pluripotent stem cell (iPSC)-based cell models
to recapitulate early steps in neuroepithelial patterning and to elucidate unique roles for LRP2
and GAS1 in these processes. In the first project, I studied a unique missense mutation in
LRP2 in two siblings with DBS. To do so, I differentiated patient-derived iPSCs into neural
progenitor cells (NPCs) and studied the impact of this mutation on receptor handling of SHH.
I demonstrated that the mutant receptor was unable to discharge its ligand SHH, leading to
enhanced lysosomal degradation of the mutant receptor bound to its ligand. These studies
showed that ligand-induced decay of LRP2 is responsible for the disease phenotype in this
family with DBS. Additionally, the results of this study verified the molecular function of LRP2
as SHH co-receptor as it mediates endocytosis and trafficking of the morphogen in forebrain
neuroepithelial cells, a process essential for SHH signal reception in this cell type. In the
second project, I uncovered a novel function for GAS1 in integrating SHH and NOTCH
signaling during early forebrain development. Performing comparative analyses in GAS1-
deficient mice and genetically engineered GAS1 knockout (KO) iPSC-derived NPCs, I showed
that loss of GAS1 impairs NOTCH-dependent facilitation of SHH signaling and results in a
failure to maintain the SHH activity domain in the rostral ventral neuroepithelium. Thus, besides
its known function as SHH co-receptor, GAS1 also acts as co-receptor for NOTCH1,
enhancing pathway activation which, in turn, promotes maintenance of SHH signaling in the
rostral ventral neuroepithelium during forebrain development.
en
dc.format.extent
XI, 161 Seiten
dc.rights.uri
https://creativecommons.org/licenses/by/4.0/
dc.subject
Neurodevelopment
en
dc.subject
Disease modeling
en
dc.subject
Sonic hedgehog
en
dc.subject
Holoprosencephaly
en
dc.subject.ddc
500 Naturwissenschaften und Mathematik::570 Biowissenschaften; Biologie::570 Biowissenschaften; Biologie
dc.title
FUNCTIONAL CHARACTERIZATION OF THE SHH RECEPTORSOME USING HUMAN INDUCED PLURIPOTENT STEM CELL MODELS
dc.contributor.gender
female
dc.contributor.firstReferee
Koch, Ursula
dc.contributor.furtherReferee
Willnow, Thomas E.
dc.date.accepted
2022-04-12
dc.identifier.urn
urn:nbn:de:kobv:188-refubium-34800-9
refubium.affiliation
Biologie, Chemie, Pharmazie
dcterms.accessRights.dnb
free
dcterms.accessRights.openaire
open access