Nils O. Lindström

Integrated β-catenin, BMP, PTEN, and Notch signalling patterns the nephron

The different segments of the nephron and glomerulus in the kidney balance the processes of water homeostasis, solute recovery, blood filtration, and metabolite excretion. When segment function is disrupted, a range of pathological features are presented. Little is known about nephron patterning during embryogenesis. In this study, we demonstrate that the early nephron is patterned by a gradient in β-catenin activity along the axis of the nephron tubule. By modifying β-catenin activity, we force cells within nephrons to differentiate according to the imposed β-catenin activity level, thereby causing spatial shifts in nephron segments. The β-catenin signalling gradient interacts with the BMP pathway which, through PTEN/PI3K/AKT signalling, antagonises β-catenin activity and promotes segment identities associated with low β-catenin activity. β-catenin activity and PI3K signalling also integrate with Notch signalling to control segmentation: modulating β-catenin activity or PI3K rescues segment identities normally lost by inhibition of Notch. Our data therefore identifies a molecular network for nephron patterning. DOI: http://dx.doi.org/10.7554/eLife.04000.001

Fucci2a: A bicistronic cell cycle reporter that allows Cre mediated tissue specific expression in mice

Markers of cell cycle stage allow estimation of cell cycle dynamics in cell culture and during embryonic development. The Fucci system incorporates genetically encoded probes that highlight G1 and S/G2/M phases of the cell cycle allowing live imaging. However the available mouse models that incorporate Fucci are beset by problems with transgene inactivation, varying expression level, lack of conditional potential and/or the need to maintain separate transgenes—there is no transgenic mouse model that solves all these problems. To address these shortfalls we re-engineered the Fucci system to create 2 bicistronic Fucci variants incorporating both probes fused using the Thosea asigna virus 2A (T2A) self cleaving peptide. We characterize these variants in stable 3T3 cell lines. One of the variants (termed Fucci2a) faithfully recapitulated the nuclear localization and cell cycle stage specific florescence of the original Fucci system. We go on to develop a conditional mouse allele (R26Fucci2aR) carefully designed for high, inducible, ubiquitous expression allowing investigation of cell cycle status in single cell lineages within the developing embryo. We demonstrate the utility of R26Fucci2aR for live imaging by using high resolution confocal microscopy of ex vivo lung, kidney and neural crest development. Using our 3T3 system we describe and validate a method to estimate cell cycle times from relatively short time-lapse sequences that we then apply to our neural crest data. The Fucci2a system and the R26Fucci2aR mouse model are compelling new tools for the investigation of cell cycle dynamics in cell culture and during mouse embryonic development.

The PI3K Pathway Balances Self-Renewal and Differentiation of Nephron Progenitor Cells through β-Catenin Signaling

Summary Nephron progenitor cells differentiate to form nephrons during embryonic kidney development. In contrast, self-renewal maintains progenitor numbers and premature depletion leads to impaired kidney function. Here we analyze the PI3K pathway as a point of convergence for the multiple pathways that are known to control self-renewal in the kidney. We demonstrate that a reduction in PI3K signaling triggers premature differentiation of the progenitors and activates a differentiation program that precedes the mesenchymal-to-epithelial transition through ectopic activation of the β-catenin pathway. Therefore, the combined output of PI3K and other pathways fine-tunes the balance between self-renewal and differentiation in nephron progenitors.

Nephrons require Rho-kinase for proximal-distal polarity development

Epithelial tubules must have the right length and pattern for proper function. In the nephron, planar cell polarity controls elongation along the proximal-distal axis. As the tubule lengthens, specialized segments (proximal, distal etc.) begin to differentiate along it. Other epithelia need Rho-kinase for planar cell polarity but it is not known whether Rho-kinase is involved in this way in the nephron. We show that Rho-kinase is essential for the morphogenesis of nephrons, specifically for correct cell orientation and volume. We use fluorescent reporter-models and progenitor-specific markers to demonstrate that inhibition of Rho-kinase prevents proper proximal-distal axis formation, causes segments to develop abnormally, and progenitor-cell segregation to fail. Our data demonstrate the importance of Rho-kinase in normal nephron tubulogenesis and patterning.

Node retraction during patterning of the urinary collecting duct system

This report presents a novel mechanism for remodelling a branched epithelial tree. The mouse renal collecting duct develops by growth and repeated branching of an initially unbranched ureteric bud: this mechanism initially produces an almost fractal form with young branches connected to the centre of the kidney via a sequence of nodes (branch points) distributed widely throughout the developing organ. The collecting ducts of a mature kidney have a different form: from the nephrons in the renal cortex, long, straight lengths of collecting duct run almost parallel to one another through the renal medulla, and open together to the renal pelvis. Here we present time‐lapse studies of E11.5 kidneys growing in culture: after about 5 days, the collecting duct trees show evidence of ‘node retraction’, in which the node of a ‘Y’‐shaped branch moves downwards, shortening the stalk of the ‘Y’, lengthening its arms and narrowing their divergence angle so that the ‘Y’ becomes a ‘V’. Computer simulation suggests that node retraction can transform a spread tree, like that of an early kidney, into one with long, almost‐parallel medullary rays similar to those seen in a mature real kidney.

The developmental and genetic basis of ‘clubfoot’ in the peroneal muscular atrophy mutant mouse

ABSTRACT Genetic factors underlying the human limb abnormality congenital talipes equinovarus (‘clubfoot’) remain incompletely understood. The spontaneous autosomal recessive mouse ‘peroneal muscular atrophy’ mutant (PMA) is a faithful morphological model of human clubfoot. In PMA mice, the dorsal (peroneal) branches of the sciatic nerves are absent. In this study, the primary developmental defect was identified as a reduced growth of sciatic nerve lateral motor column (LMC) neurons leading to failure to project to dorsal (peroneal) lower limb muscle blocks. The pma mutation was mapped and a candidate gene encoding LIM-domain kinase 1 (Limk1) identified, which is upregulated in mutant lateral LMC motor neurons. Genetic and molecular analyses showed that the mutation acts in the EphA4–Limk1–Cfl1/cofilin–actin pathway to modulate growth cone extension/collapse. In the chicken, both experimental upregulation of Limk1 by electroporation and pharmacological inhibition of actin turnover led to defects in hindlimb spinal motor neuron growth and pathfinding, and mimicked the clubfoot phenotype. The data support a neuromuscular aetiology for clubfoot and provide a mechanistic framework to understand clubfoot in humans. Highlighted Article: The mutation in the PMA mouse model of human clubfoot was mapped and a candidate gene, Limk1, identified that was shown to cause sciatic nerve and limb abnormalities when overexpressed.

R26Fucci2aR: A global Cre-inducible cell cycle reporter mouse allowing live imaging of cell cycle progression during mouse embryonic development

Program and Abstracts of the 12th Transgenic Technology Meeting (TT2014) The Assembly Rooms, Edinburgh, Scotland, United Kingdom, 6–8 October 2014 The TT2014 Meeting is hosted by: The Roslin Institute, The University of Edinburgh, Easter Bush, Midlothian, EH25 9RG, Scotland, United Kingdom. The Cancer Research UK Beatson Institute, Garscube Estate, Switchback Road, Bearsden, Glasgow, G61 1BD, Scotland United Kingdom. The Institute of Genetics and Molecular Medicine, Western General Hospital, Crewe Road, Edinburgh, EH4 2XU United Kingdom. 123 Transgenic Res (2014) 23:827–909 DOI 10.1007/s11248-014-9820-1 Springer International Publishing Switzerland 2014

06-P019 The developmental basis of clubfoot

Idiopathic clubfoot (Talipes Equinovarus) affects 1 in 500 UK births, but its aetiology is very poorly understood, with both genetic and environmental components. We investigated the developmental and genetic basis of clubfoot in a mouse model, and provide evidence that clubfoot is a neuromuscular defect. Although the tibial branch of the sciatic nerve projected to the ventral domain of the hindlimb buds, as normal during embryogenesis, the dorsal peroneal branch of the sciatic was shown by whole-mount immunostaining to display significant defects, including a failure to fasciculate, targeting errors and, in most adults, total loss of the mature peroneal nerve. This lead to wastage of dorsal calf muscles which appeared to underlie retarded rotation of the foot during development. In contrast, the developing hindlimb vasculature was unaffected. Dorso-ventral patterning of the neural tube was found to be normal in the clubfoot mouse, and patterning of the lateral motor columns was investigated by immunohistochemistry. In summary, the ankle and tarsal deformities seen in the mouse model of clubfoot are secondary to muscle atrophy following misspecification of the peroneal branch of the sciatic nerve. This aetiology, and the underlying genetic mutation, offers a new understanding of the abnormalities and causes of human clubfoot.