African clawed frog (Xenopus laevis) oocytes

Date:7 August 2012 Tags:, ,

Vincent Pasque, University of Cambridge

This confocal micrograph shows stage V–VI oocytes (800–1 000 micron diameter) of an African clawed frog (Xenopus laevis), a model organism used in cell and developmental biology research. Each oocyte is surrounded by thousands of follicle cells, shown in the image by staining DNA blue. Blood vessels, which provide oxygen to the oocyte and follicle cells, are shown in red. The ovary of each adult female Xenopus laevis contains up to 20 000 oocytes. Mature Xenopus laevis oocytes are approximately 1,2 mm in diameter, much larger than the eggs of many other species.

Why was this image created?
Vincent and his colleagues are researching ways to perform cell replacement therapies in humans to replace damaged tissue. Replacement cells need to be derived from the patient to avoid problems of rejection and the need for immunosuppression. For example, skin cells from patients can be reprogrammed into an embryonic state, allowing them to form any cell of the human body. However, only a few cells can be induced to go back in development, and the efficiency of deriving new heart, pancreas or liver cells from these cells is very limited.

Xenopus oocytes are being used to understand nuclear reprogramming to increase its efficiency, with the long-term aim of providing patient-specific replacement cells. By transplanting the nuclei of adult cells into frog oocytes, scientists can identify the mechanisms by which somatic cells (cells of the body) can be reprogrammed. To allow scientists to inject inside the oocytes for experiments, the follicle cells need to be removed. To ensure that the removal procedure has worked, follicle cells can be easily visualised, as depicted in this picture of an untreated oocyte.

Why is Xenopus laevis used as a model organism?
Xenopus is one of the main model organisms used in cell and developmental biology. Xenopus research has helped to uncover key fundamental mechanisms of embryonic development, including morphogenesis, cell differentiation, organogenesis, cell cycle regulation, regeneration and nuclear reprogramming. The main advantage of using Xenopus is that it provides numerous and large oocytes and eggs. Importantly for Vincent’s research, Xenopus have the remarkable ability to reprogram the nucleus of an adult cell, for example skin or muscle, to form an oocyte or embryonic-type cell. These cells possess the ability to form all other cell types in the body.

The 12th Wellcome Image Awards were announced on 20 June 2012, recognising the creators of the most informative, striking and technically excellent images among recent acquisitions to Wellcome Images, as chosen by a panel of judges.