Mating worms and the cystic kidney: Caenorhabditis elegans as a model for renal disease

Behavioral analysis of the huntingtin-associated protein 1 ortholog trak-1 in Caenorhabditis elegans

The precise role of huntingtin-associated protein 1 (HAP1) is not known, but studies have shown that it is important for early development and survival. A Caenorhabditis elegans ortholog of HAP1, T27A3.1 (also called trak-1), has been found and is expressed in a subset of neurons. Potential behavioral functions of three knockout lines of T27A3.1 were examined. From its suspected role in mice we hypothesize that T27A3.1 might be involved in egg hatching and early growth, mechanosensation, chemosensation, sensitivity to osmolarity, and synaptic transmission. Our studies show that the knockout worms are significantly different from the wild-type (WT) worms only in the synaptic transmission test, which was measured by adding aldicarb, an acetylcholinesterase inhibitor. The change in function was determined by measuring the number of worms paralyzed. However, when the T27A3.1 worms were tested for egg hatching and early growth, mechanosensation, chemosensation, and sensitivity to osmolarity, there were no significant differences between the knockout and WT worms. © 2016 Wiley Periodicals, Inc.

Caenorhabditis elegans, a model organism for kidney research: from cilia to mechanosensation and longevity

PURPOSE OF REVIEW

The introduction of Caenorhabditis elegans by Sydney Brenner to study 'how genes might specify the complex structures found in higher organisms' revolutionized molecular and developmental biology and pioneered a new research area to study organ development and cellular differentiation with this model organism. Here, we review the role of the nematode in renal research and discuss future perspectives for its use in molecular nephrology.

RECENT FINDINGS

Although C. elegans does not possess an excretory system comparable with the mammalian kidney, various studies have demonstrated the conserved functional role of kidney disease genes in C. elegans. The finding that cystic kidney diseases can be considered ciliopathies is based to a great extent on research studying their homologues in the nematode's ciliated neurons. Moreover, proteins of the kidney filtration barrier play important roles in both correct synapse formation, mechanosensation and signal transduction in the nematode. Intriguingly, the renal cell carcinoma disease gene product von-Hippel-Lindau protein was shown to regulate lifespan in the nematode. Last but not least, the worm's excretory system itself expresses genes involved in electrolyte and osmotic homeostasis and may serve as a valuable tool to study these processes on a molecular level.

SUMMARY

C. elegans has proven to be an incredibly powerful tool in studying various aspects of renal function, development and disease and will certainly continue to do so in the future.

Molecular anatomy of the kidney: what have we learned from gene expression and functional genomics?

The discipline of paediatric nephrology encompasses the congenital nephritic syndromes, renal dysplasias, neonatal renal tumours, early onset cystic disease, tubulopathies and vesicoureteric reflux, all of which arise due to defects in normal kidney development. Indeed, congenital anomalies of the kidney and urinary tract (CAKUT) represent 20-30% of prenatal anomalies, occurring in 1 in 500 births. Developmental biologists have studied the anatomical and morphogenetic processes involved in kidney development for the last five decades. However, with the advent of transgenic mice, the sequencing of the genome, improvements in mutation detection and the advent of functional genomics, our understanding of the molecular basis of kidney development has grown significantly. Here we discuss how the advent of new genetic and genomics approaches has added to our understanding of kidney development and paediatric renal disease, as well as identifying areas in which we are still lacking knowledge.

The cdx genes and retinoic acid control the positioning and segmentation of the zebrafish pronephros

Kidney function depends on the nephron, which comprises a blood filter, a tubule that is subdivided into functionally distinct segments, and a collecting duct. How these regions arise during development is poorly understood. The zebrafish pronephros consists of two linear nephrons that develop from the intermediate mesoderm along the length of the trunk. Here we show that, contrary to current dogma, these nephrons possess multiple proximal and distal tubule domains that resemble the organization of the mammalian nephron. We examined whether pronephric segmentation is mediated by retinoic acid (RA) and the caudal (cdx) transcription factors, which are known regulators of segmental identity during development. Inhibition of RA signaling resulted in a loss of the proximal segments and an expansion of the distal segments, while exogenous RA treatment induced proximal segment fates at the expense of distal fates. Loss of cdx function caused abrogation of distal segments, a posterior shift in the position of the pronephros, and alterations in the expression boundaries of raldh2 and cyp26a1, which encode enzymes that synthesize and degrade RA, respectively. These results suggest that the cdx genes act to localize the activity of RA along the axis, thereby determining where the pronephros forms. Consistent with this, the pronephric-positioning defect and the loss of distal tubule fate were rescued in embryos doubly-deficient for cdx and RA. These findings reveal a novel link between the RA and cdx pathways and provide a model for how pronephric nephrons are segmented and positioned along the embryonic axis.

Finding function in novel targets: C. elegans as a model organism

Despite its apparent simplicity, the nematode worm Caenorhabditis elegans has developed into an important model for biomedical research, particularly in the functional characterization of novel drug targets that have been identified using genomics technologies. The cellular complexity and the conservation of disease pathways between C. elegans and higher organisms, together with the simplicity and cost-effectiveness of cultivation, make for an effective in vivo model that is amenable to whole-organism high-throughput compound screens and large-scale target validation. This review describes how C. elegans models can be used to advance our understanding of the molecular mechanisms of drug action and disease pathogenesis.