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PRDM1/Blimp-1 Directs Germ Cell versus Neural Cell Pathway. During Early Human Embryonic Differentiation

PRDM1-teamTeam members(from left to right): PhD student I-Ying Lin, Dr. Kuo-I Lin, Dr. Hung-Chih Kuo.In search for the root cause of human diseases related to gene deregulation has not been easy. In the newest published Stem Cell Reports Journal (Cell Press), Dr. Kuo-I Lin of Genomics Research Center, Dr. Hung-Chih Kuo of Institute of Cellular and Organismic Biology and colleagues have described in detail how they coordinated stem cell technology, bioinformatics and molecular biology, to discover new tasks of a familiar plasma cell modulator at very early human embryonic development. In this report, the protein PRDM1 found inside the nucleus of a differentiating embryonic stem cell plays a crucial role in switching the direction of the differentiation pathway to the reproductive path rather than the neural cell path. It is more than likely that when the regulating effort goes biased at the early stage, the grown human body would be affected accordingly.

PRDM1 is not new to the Lin’s lab at all. PRDM1 is also known as Blimp-1, which has been a focal study subject in Lin’s lab for quite a period of time. In Lin’s prior study, PRDM1 appears to have a regulatory role at various events within human body, including being the controller in making plasma cells, and as a guardian of the epidermal immune system.

There are researches done in mice that showed when PRDM1 gene was knocked out, the reproductive functions of mice went wrong. This gave the research team an idea to investigate if PRDM1 has the same effect toward human reproductive system, and how exactly PRDM1 participates in it. If the mechanism is understood, possible resolutions of fixing the problematic reproductive systems at root cause would then be potentially doable.

Imagine, upon day 4 or 5 of a human embryos’s inception, there are around one hundred embryonic cells formed, and some of them are pluripotent, that is, they possess the power of differentiating into any type of cells in a human body and to give rise to pluripotent embryonic stem (ES) cells in vitro. Ultimately, different types of cells are formed. So, what exactly made a pluripotent cell divide and grow into different lineages? That is a mystery which has not been fully understood yet.

First of all, the team wanted to confirm if PRDM1 could be found in the germline lineages in human embryos, if so, they could go on to study if PRDM1 in human has the same role in mice as far as germline cell development is concerned. By observing embryonic cells from abortuses in 2nd trimester, they have found clearly that PRDM1 can be spotted in the testis and ovary of embryos. Further, they observed that PRDM1 appeared together with OCT4, which is known to appear during early developmental stage of ES cells.

Since it is confirmed at this point that in human embryos, PRDM1 shows up at early stages of gonadal development, they’d like to know further how it works. Nowadays, with the maturity of related technology, it is quite feasible to study human development related questions with human ES cells, since they have the pluripotent characteristics as early preimplantation embryos do. Therefore, Lin’s group teamed up with Dr. Hung-Chih Kuo, an expert in pluripotent stem cell biology .

In stem cell research, there are already known ways to make ES cells develop into germline lineage. Together, they experimented with three different differentiating paths to culture the ES cells and identified PRDM1 as a necessary and sufficient player in the formation of human ES cells derived germline cells.

Previously, Dr. Kuo’s lab. has identified two growth factors, BMP4 and WNT3A, that can efficiently induce germline cells from human ES cells. By looking into their correlation with PRDM1, the team found that these known growth factors trigger the expression of PRDM1, and thus help the generation of germline cells down the road. By knocking PRDM1 down, the formation of germline cells would present problems. Thus, PRDM1 is the key element in the whole process. Another test with additional PRDM1 expressed into ES cells along with the addition of growth factors results in the formation of germline cells in a much abundant quantity.

By working with Dr. Chen-Hsiang Yeang from Institute of Statistical Science, using DNA microarry technology and bioinformatics, the team showed the global gene expression profiles of human ES cells expressing PRDM1 resemble to those of early stage of human germ cells.

Since OCT4, SOX2 and NANOG are three known controllers maintain ES cells, the team would like to know if PRDM1 regulates any of them. To their surprise, SOX2 is targeted by PRDM1. SOX2 is also known a controller in neural development. In their observation, PRDM1 and SOX2 turn out as rivals at the early stage of development. When the growth factors trigger the expression of PRDM1 in human ES cells, PRDM1 will inhibit SOX2 and thus in turn promotes the production of germline cells. On the other hand, by adding more SOX2, it appeared that more neural cells will form.

This study of PRDM1 in directing germline generation by inhibiting neural cells in human ES cells has opened a whole new chapter in stem cell research. The Academia Sinica research team has identified PRDM1 matters much earlier in human life by controlling the generation of germline cells vs. neural cells, which has extended the role of PRDM1 in the regulation of the functions of immune system in a grown human body.

The complete research paper can be read online at: http://www.cell.com/stem-cell-reports/abstract/S2213-6711%2813%2900177-X

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