Kidney and urinary tract development: an apoptotic balancing act

A preliminary study of the miRNA restitution effect on CNV-induced miRNA downregulation in CAKUT

BACKGROUND

The majority of CAKUT-associated CNVs overlap at least one miRNA gene, thus affecting the cellular levels of the corresponding miRNA. We aimed to investigate the potency of restitution of CNV-affected miRNA levels to remediate the dysregulated expression of target genes involved in kidney physiology and development in vitro.

METHODS

Heterozygous MIR484 knockout HEK293 and homozygous MIR185 knockout HEK293 cell lines were used as models depicting the deletion of the frequently affected miRNA genes by CAKUT-associated CNVs. After treatment with the corresponding miRNA mimics, the levels of the target genes have been compared to the non-targeting control treatment. For both investigated miRNAs, MDM2 and PKD1 were evaluated as common targets, while additional 3 genes were investigated as targets of each individual miRNA (NOTCH3, FIS1 and APAF1 as hsa-miR-484 targets and RHOA, ATF6 and CDC42 as hsa-miR-185-5p targets).

RESULTS

Restitution of the corresponding miRNA levels in both knockout cell lines has induced a change in the mRNA levels of certain candidate target genes, thus confirming the potential to alleviate the CNV effect on miRNA expression. Intriguingly, HEK293 WT treatment with investigated miRNA mimics has triggered a more pronounced effect, thus suggesting the importance of miRNA interplay in different genomic contexts.

CONCLUSIONS

Dysregulation of multiple mRNA targets mediated by CNV-affected miRNAs could represent the underlying mechanism behind the unresolved CAKUT occurrence and phenotypic variability observed in CAKUT patients. Characterizing miRNAs located in CNVs and their potential to become molecular targets could eventually help in understanding and improving the management of CAKUT.

Retinoic acid signaling pathway perturbation impacts mesodermal-tissue development in the zebrafish embryo: Biomarker candidate identification using transcriptomics

The zebrafish embryo (ZE) model provides a developmental model well conserved throughout vertebrate embryogenesis, with relevance for early human embryo development. It was employed to search for gene expression biomarkers of compound-induced disruption of mesodermal development. We were particularly interested in the expression of genes related to the retinoic acid signaling pathway (RA-SP), as a major morphogenetic regulating mechanism. We exposed ZE to teratogenic concentrations of valproic acid (VPA) and all-trans retinoic acid (ATRA), using folic acid (FA) as a non-teratogenic control compound shortly after fertilization for 4 h, and performed gene expression analysis by RNA sequencing. We identified 248 genes specifically regulated by both teratogens but not by FA. Further analysis of this gene set revealed 54 GO-terms related to the development of mesodermal tissues, distributed along the paraxial, intermediate, and lateral plate sections of the mesoderm. Gene expression regulation was specific to tissues and was observed for somites, striated muscle, bone, kidney, circulatory system, and blood. Stitch analysis revealed 47 regulated genes related to the RA-SP, which were differentially expressed in the various mesodermal tissues. These genes provide potential molecular biomarkers of mesodermal tissue and organ (mal)formation in the early vertebrate embryo.

Multifaceted Hoxa13 function in urogenital development underlies the Hand-Foot-Genital Syndrome

Hand-Foot-Genital syndrome is a rare condition caused by mutations in the HOXA13 gene and characterized by limb malformations and urogenital defects. While the role of Hoxa13 in limb development has been extensively studied, its function during the development of the urogenital system remains elusive mostly due to the embryonic lethality of Hoxa13 homozygous mutant mice. Using a conditional inactivation strategy, we show that mouse fetuses lacking Hoxa13 function develop megaureters, hydronephrosis and malformations of the uterus, reminiscent of the defects characterizing patients with Hand-Foot-Genital syndrome. Our analysis reveals that Hoxa13 plays a critical role in Müllerian ducts fusion and in ureter remodeling by regulating the elimination of the caudal common nephric duct, eventually preventing the separation from the nephric duct. Our data also reveal a specific role for Hoxa13 in the urogenital sinus, which is in part mediated by Gata3, as well as Hoxa13 requirement for the proper organization of the ureter. Finally, we provide evidence that Hoxa13 provides positional and temporal cues during the development of the lower urogenital system, a sine qua non condition for the proper function of the urinary system.

The Origins and Functions of Tissue-Resident Macrophages in Kidney Development

The adult kidney hosts tissue-resident macrophages that can cause, prevent, and/or repair renal damage. Most of these macrophages derive from embryonic progenitors that colonize the kidney during its development and proliferate in situ throughout adulthood. Although the precise origins of kidney macrophages remain controversial, recent studies have revealed that embryonic macrophage progenitors initially migrate from the yolk sac, and later from the fetal liver, into the developing kidney. Once in the kidney, tissue-specific transcriptional regulators specify macrophage progenitors into dedicated kidney macrophages. Studies suggest that kidney macrophages facilitate many processes during renal organogenesis, such as branching morphogenesis and the clearance of cellular debris; however, little is known about how the origins and specification of kidney macrophages dictate their function. Here, we review significant new findings about the origins, specification, and developmental functions of kidney macrophages.

Coordinated cell behaviours in early urogenital system morphogenesis

The elaboration of functional kidneys during embryonic development proceeds in a stepwise manner, starting with the formation of the embryonic pro- and mesonephros, followed by the induction and growth of the final metanephric kidney. These early stages of urinary tract development are critical for the embryo as a failure in pro/mesonephros morphogenesis leads to major developmental defects, often incompatible with life. The formation of the pro/mesonephros and its central component the nephric duct, is also interesting as it offers a relatively simple system to study cell biological behaviours underlying tissue morphogenesis. This system is especially well adapted to study the questions of cell lineage specification, epithelial integrity and plasticity, tissue interactions, collective cell migration/guidance and programmed cell death. In this review, we establish the link between these cell behaviours, their molecular regulators and early genitourinary tract development.

To bud or not to bud: the RET perspective in CAKUT

Congenital anomalies of the kidneys or lower urinary tract (CAKUT) encompass a spectrum of anomalies that result from aberrations in spatio-temporal regulation of genetic, epigenetic, environmental, and molecular signals at key stages of urinary tract development. The Rearranged in Transfection (RET) tyrosine kinase signaling system is a major pathway required for normal development of the kidneys, ureters, peripheral and enteric nervous systems. In the kidneys, RET is activated by interaction with the ligand glial cell line-derived neurotrophic factor (GDNF) and coreceptor GFRα1. This activated complex regulates a number of downstream signaling cascades (PLCγ, MAPK, and PI3K) that control proliferation, migration, renewal, and apoptosis. Disruption of these events is thought to underlie diseases arising from aberrant RET signaling. RET mutations are found in 5-30 % of CAKUT patients and a number of Ret mouse mutants show a spectrum of kidney and lower urinary tract defects reminiscent of CAKUT in humans. The remarkable similarities between mouse and human kidney development and in defects due to RET mutations has led to using RET signaling as a paradigm for determining the fundamental principles in patterning of the upper and lower urinary tract and for understanding CAKUT pathogenesis. In this review, we provide an overview of studies in vivo that delineate expression and the functional importance of RET signaling complex during different stages of development of the upper and lower urinary tracts. We discuss how RET signaling balances activating and inhibitory signals emanating from its docking tyrosines and its interaction with upstream and downstream regulators to precisely modulate different aspects of Wolffian duct patterning and branching morphogenesis. We outline the diversity of cellular mechanisms regulated by RET, disruption of which causes malformations ranging from renal agenesis to multicystic dysplastic kidneys in the upper tract and vesicoureteral reflux or ureteropelvic junction obstruction in the lower tract.