Northern white rhinoceros skin cells turned into egg precursors

(ORDO NEWS) — Scientists were able to obtain from the skin cells of the female northern white rhinoceros cells similar to the primary germ cells – those from which gametes are obtained during development.

The subspecies is considered extinct, but scientists are looking for ways to restore the population.

Northern white rhinos (Ceratotherium simum cottoni) are thought to be extinct in the wild. There are only two females left on Earth – mother and daughter, Najin and Fatu, and the last male, Sudan, died in 2018.

Scientists are trying to revive the subspecies with the help of assisted reproductive technologies: they have already fertilized the eggs of females with spermatozoa left over from the last males.

But so far scientists have managed to obtain only three viable embryos, which, most likely, will bear females of a close subspecies – the southern white rhinoceros (more on attempts of scientists to help rhinos, read the blog “Test Tube Mom: How Artificial Follicles and Eggs Can Help Rhinos and Us”).

There is a limiting factor in creating embryos in this way. The ovarian reserve in rhinoceroses, like in humans, is organic: the female is born with a certain number of gametes, which are consumed during her life.

A possible solution could be the creation of germ cells from somatic cells, that is, skin or eye cells.

First, somatic cells need to be made stem cells, that is, those that can become any cells, and only then grow them under such conditions that they become the desired populations. But finding such conditions is a complex process.

A group of scientists led by Katsuhiko Hayashi (Katsuhiko Hayashi) came close to this: they made cells similar to the primary germ cells.

They decided to start work with embryonic stem cells obtained from southern white rhinos: they picked up the necessary conditions for the transition.

In order to monitor the transformation, the scientists monitored the POU5F1/OCT3/4 and PRDM1/BLIMP1 genes, since their expression is specific in primary germ cells.

Next, the authors incubated the cells under such conditions to obtain cells similar to the primary germ cells.

Northern white rhinoceros skin cells turned into egg precursors 2
Schematic of the transformation of embryonic stem cells (ESCs) into primordial germ cell-like cells (PGCLCs). They were first treated with a mixture of pre-induction factors, after which they proceeded to transform into cells similar to the primary germ cells

After that, the scientists worked with cells that, after cultivation, remained positive for the expression of both genes.

They also turned out to have increased expression of genes indicating belonging to primary germ cells: SOX17, PRDM1 and NANOS3. The authors of the study also managed to propagate these cells.

They remained at the stage of development of the early precursors of gametes and acquired the ability to move – due to the formation of filopodia – thread-like protrusions of the membrane.

Northern white rhinoceros skin cells turned into egg precursors 3
Cells similar to primordial germ cells (left) acquired the ability to move through filopodia, which are not found in the initial population of -embryonic stem cells (right)

After developing the method, the authors proceeded to the main thing – obtaining cells similar to primary germ cells from cells of the northern white rhinoceros.

To do this, they needed fibroblasts – skin cells, and the deceased female Nabira turned out to be the donor.

Stem cells were made from them, and then reporter constructs similar to those built into the cells of the southern white rhino were also embedded.

Using transcriptome analysis, the scientists concluded that the differentiation of northern white rhino cells into OGBT cells proceeds similarly to that of the southern subspecies, which means they were able to make cells similar to primary germ cells.

Research is one of the first steps. Next, you will need to figure out how to make the germ cells themselves from cells similar to the primary germ cells and what to do after that.

Poaching is one of the reasons northern white rhinos have become extinct in the wild. People exterminate rhinoceros to get their horn, which traditional medicine ascribes healing properties.

Read about what other animals suffer from pseudoscientific methods of healing in the text “Horns and legs”.

Something else

Female rhinoceroses, such as Dicerorhinus sumatrensis, are found to have uterine fibroids, a disease also found in humans.

Who knows, maybe in the near future rhinos will become a model object for studying fibroids and help scientists learn more about it and find a treatment.

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