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defined culture conditions reported to be sufficient to maintain a CM phenotype
in vitro away from the niche (Brown et al. 2015 ; Tanigawa et al. 2016 ). This may be
important for the successful engineering of replacement organs from stem cells.
Almost all studies on mammalian kidney morphogenesis have been performed
using rodent models, primarily mice. While mouse is not human, it would appear
that many molecular pathways in kidney morphogenesis are conserved between
these two species based upon the similarity of phenotype between gene knockouts
in mouse and mutations identified in human patients (Olbrich et al. 2003 ; Jain 2009 ;
Chatterjee et al. 2012 ; Hynes et al. 2014 ). More recent studies have confirmed the
conserved expression of key genes during early human kidney development
(O’Brien et al. 2016 ), including the conservation of key transcription factors within
the cap mesenchyme and ureteric tip. Perhaps the most compelling evidence for a
conservation between human and mouse have been recent studies in which the
directed differentiation of hPSCs, based upon existing knowledge of mesodermal
patterning and metanephric morphogenesis in the mouse, has successfully resulted
in the generation of complex multicellular organoids containing segmenting and
functionalising nephrons within a renal interstitium (Freedman et al. 2015 ; Takasato
et al. 2015 ; Morizane et al. 2015 ). Expression profiling would suggest congruence
between gene expression in trimester 1 human foetal kidney and pluripotent stem
cell-derived kidney organoids, further supporting a conservation of key morphoge-
netic steps between these species. What we will focus on in the rest of this chapter
is our knowledge of kidney development in the mouse, how this has been harnessed
to generate kidney organoids and what applications are available using this approach.
11.2 Key Developmental Steps for Generating Kidney
Organoids from Human Pluripotent Stem Cells
During embryogenesis, the pluripotent epiblast gives rise to three germ layers, ecto-
derm, mesoderm and endoderm, from which all tissues are formed. Successful pro-
tocols for the directed differentiation of hPSCs, including both human embryonic
stem cells and induced pluripotent stem cells, attempt to recreate the induction
events that occur during embryogenesis required for the desired cell type/tissue
type, generally delivering this in a stepwise fashion via the addition or inhibition of
specific signalling pathways. For directed differentiation to the kidney, this requires
an understanding of the events involved in moving from pluripotency to mesoderm
and from here to the kidney. As the molecular nature of these events has not been
dissected in human, the field draws on our understanding of embryogenesis in the
mouse.
M.H. Little et al.