Although kidneys of equal size can vary 10-fold in nephron number at birth, discovering what regulates such variation has been hampered by a lack of quantitative parameters defining kidney development. Here we report a comprehensive, quantitative, multiscale analysis of mammalian kidney development in which we measure changes in cell number, compartment volumes, and cellular dynamics across the entirety of organogenesis, focusing on two key nephrogenic progenitor populations: the ureteric epithelium and the cap mesenchyme. In doing so, we describe a discontinuous developmental program governed by dynamic changes in interactions between these key cellular populations occurring within a previously unappreciated structurally stereotypic organ architecture. We also illustrate the application of this approach to the detection of a subtle mutant phenotype. This baseline program of kidney morphogenesis provides a framework for assessing genetic and environmental developmental perturbation and will serve as a gold standard for the analysis of other organs.

The biological significance of RBCC (N-terminal RING finger/Bbox/coiled coil) proteins is increasingly being appreciated following demonstrated roles in disease pathogenesis, tumorigenesis, and retroviral protective activity. Found in all multicellular eukaryotes, RBCC proteins are involved in a vast array of intracellular functions; but as a general rule, they appear to function as part of large protein complexes and possess ubiquitin-protein isopeptide ligase activity. Those members characterized to date have diverse C-terminal domain compositions and equally diverse subcellular localizations and functions. Using a bioinformatics approach, we have identified some new RBCC proteins that help define a subfamily that shares an identical domain arrangement (MID1, MID2, TRIM9, TNL, TRIM36, and TRIFIC). Significantly, we show that all analyzed members of this subfamily associate with the microtubule cytoskeleton, suggesting that subcellular compartmentalization is determined by the unique domain architecture, which may in turn reflect basic functional similarities. We also report a new motif called the COS box, which is found within these proteins, the MURF family, and a distantly related non-RBCC microtubule-binding protein. Notably, we demonstrate that mutations in the COS box abolish microtubule binding ability, whereas its incorporation into a nonmicrotubule-binding RBCC protein redirects it to microtubule structures. Further bioinformatics investigation permitted subclassification of the entire human RBCC complement into nine subfamilies based on their varied C-terminal domain compositions. This classification schema may aid the understanding of the molecular function of members of each subgroup and their potential involvement in both basic cellular processes and human disease.Members of the RBCC (N-terminal RING finger/B-box/coiled coil) or TRIM (tripartite motif) family of proteins perform a diverse array of cellular roles, yet are believed to share some functional properties: 1) act as a scaffold for the assembly of larger multiprotein complexes and 2) possess RING-dependent ubiquitin ligase activity (1, 2). The RBCC domain can be found in isolation or in combination with a variety of other C-terminal domains, including the NHL (NCL-1/HT2A/LIN-41 repeat), immunoglobulin, MATH (meprin and tumor necrosis factor receptor-associated factor homology), B30.2-like/RFP (Ret finger protein)/SPRY (SplA and ryanodine receptor) (the largest subgroup in humans), ARF (ADP-ribosylation factor), PHD (plant homeodomain finger), and BROMO domains (1, 2). As a family of proteins, their biological significance is perhaps best highlighted by the growing number that have a demonstrated role in disease pathogenesis, including immunological and developmental disorders, tumorigenesis, and retroviral protective activity (3-7).We have previously identified and characterized two RBCC proteins, MID1 and its closely related homolog, MID2. MID1 and MID2 contain a B30.2-like domain at their C terminus and a single fibronectin type III (FN3...

SUMMARYBranching morphogenesis is a fundamental developmental mechanism that shapes the formation of many organs. The complex three-dimensional shapes derived by this process reflect equally complex genetic interactions between branching epithelia and their surrounding mesenchyme. Despite the importance of this process to normal adult organ function, analysis of branching has been stymied by the absence of a bespoke method to quantify accurately the complex spatial datasets that describe it. As a consequence, although many developmentally important genes are proposed to influence branching morphogenesis, we have no way of objectively assessing their individual contributions to this process. We report the development of a method for accurately quantifying many aspects of branching morphogenesis and we demonstrate its application to the study of organ development. As proof of principle we have employed this approach to analyse the developing mouse lung and kidney, describing the spatial characteristics of the branching ureteric bud and pulmonary epithelia. To demonstrate further its capacity to profile unrecognised genetic contributions to organ development, we examine Tgfb2 mutant kidneys, identifying elements of both developmental delay and specific spatial dysmorphology caused by haplo-insufficiency for this gene. This technical advance provides a crucial resource that will enable rigorous characterisation of the genetic and environmental factors that regulate this essential and evolutionarily conserved developmental mechanism.

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During lymphangiogenesis in the mammalian embryo, a subset of vascular endothelial cells in the cardinal veins is reprogrammed to adopt a lymphatic endothelial fate. The prevailing model of lymphangiogenesis contends that these lymphatic precursor cells migrate away from the cardinal veins and reassemble peripherally as lymph sacs from which a lymphatic vasculature is generated. However, this model fails to account for a number of observations that, as a result, have remained anecdotal. Here, we use optical projection tomography, confocal microscopy and in vivo live imaging to uncover three key stages of lymphatic vascular morphogenesis in the mouse embryo at high resolution. First, we define territories or "pre-lymphatic clusters" of Prox1-positive lymphatic endothelial progenitor cells along the antero-posterior axis of the cardinal veins. Second, these pre-lymphatic clusters undergo progressive extrusion ("ballooning") to generate primitive lymph sacs. Third, lymphatic vessels emerge by a combination of mechanisms including sprouting from the lymph sacs and direct delamination of streams of cells from the cardinal veins. Our data support a new model for lymphatic vascular patterning and morphogenesis, as a basis for identifying the molecular cues governing these processes.