Developing mouse kidney

Bob Kao and Kieran Short, Monash University

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Three-dimensional image showing a fetal mouse kidney at embryonic day 16 (E16). The sample was dissected whole and stained for two different proteins. The protein in green is expressed in the unspecialised embryonic connective tissue that will ultimately differentiate and form the body of the kidney. The protein in red marks the developing collecting duct system, including the renal pelvis, which is clearly observed in the centre and will funnel excreted urine into the ureter.

What is OPT?

OPT stands for optical projection tomography. It is an imaging technique that allows the scientist to image whole structures in situ in three dimensions. Like normal microscopy, it uses visible light, with a detector to record the amount of light passing through the specimen. However, unlike in standard techniques the sample is not sliced before it is imaged but cleared and imaged whole. The sample is rotated 360 degrees and images are captured at different angles as the sample revolves.

Computer software combines these multiple images to create a single three-dimensional image that can be viewed from different angles and manipulated, allowing scientists to investigate how associated structures develop relative to each other.

Watch a video showing OPT in action

How does the kidney develop?

The kidney develops from an embryonic tube structure called the Wolffian duct. In the mouse, at 11.5 days post-fertilisation, a small bud is formed as an outgrowth of the Wolffian duct, which invades the surrounding tissue and begins to branch. This bud is known as the ureteric bud and signals the start of kidney development. The ureteric bud continues to grow through multiple branching (known as branching morphogenesis) into a complex structure that develops in an outwardly radial pattern.

Kidney development is under tight genetic control, with a number of genes crucial for normal development. The kidney is made up of two main regions: the medulla, which contains the collecting duct system primarily involved in the reabsorption of water, and the cortex, which contains the nephrons - the main functional unit of the kidney responsible for blood filtration.