The discovery and characteriazation of MPF

We three:Liu yuan; A zuo;

Xiao xue

MPF represents “maturation promoting factor”( 促成熟因子 ). They are a dozen of proteins produced by germ cell in meiosis ， which induce the germ cell to mature.

The discovery of MPF is a springing. How was it discovered?

Longlong ago,before the discovery of MPF, the experiment about the cell cycle had been undergoing and the technique was developing.

One prominent early approach to studying control of the cell cycle was to introduce a nucleus from one phase of the cell cycle into a cytoplasm from another. Techniques for making such nucleo-cytoplasmic hybrid cells, including nuclear transplantation and cell fusion, became available in the 1950s, but it was not until the late 1960s that they were used to study cell cycle activities such as the initiation of DNA synthesis and the condensation of chromosomes. This type of experiment included nuclear transplantation by injection in frog oocytes and eggs (Gurdon and Woodland, 1968), excision and transplantation of cytoplasmic fragments in protozoa (De Terra, 1969), and virus-mediated fusion between tissue culture cells (Johnson and Rao, 1971).

Conclution

In all cases the nucleus conformed to the cell cycle stage of the cytoplasm, indicating that cytoplasmic factors control nuclear activities during the cell cycle.

Despite what these experiments revealed about the organization of the cell cycle, none of them provided any clue to the identity of the factors responsible for cytoplasmic control over the nucleus. Nor could any of the experiments be readily adapted to provide an assay with which to identify those factors and study their biochemical mechanisms. That would require an experimental system in which cytoplasm from particular stages of the cell cycle could be isolated and used to cause a transition from one phase of the cell cycle to another.

So the MPF discoverer choosed the “frog oocyte( 卵母细胞 )” to try to identify the molecular machinery that drives the cell cycle. And it worked.

What is “M-maturation”?And how does oocyte become mature in vivo?

Maturation is the term used to describe the egg’s progression from the end of G2 phase through the rest of meiosis.

Another saying is that maturation is the progression from the broken down of egg’s nucleus to the end of the first meiotic division.

The process is initiated in response to stimulation of the ovary( 卵巢 ) by gonadotropin( 促性腺激素 ), a small peptide hormone secreted by the pituitary( 垂体 ). The hormone causes the greatly enlarged oocyte nucleus (called the "germinal vesicle") to break down and its chromosomes to condense, and the oocyte then enters and completes the first meiotic division, passes through prophase of the second, and finally arrests as an unfertilized egg at metaphase of the second division. Fertilization relieves this arrest and the egg begins dividing mitotically.

Maturation in vivo pituitary( 垂体 ).

secrete

gonadotropin( 促性腺激素 ),

ovary( 卵巢 )

The oocyte in ovary is induced to mature.Its enlarged nucleus break down and its chromosomes condense.

arrests at the metaphase of the second division.

The arrest will be relieved by fertilization.

More attempt

They found that it was not pituitary gonadotropin （垂体释放的促性腺激素） , but progesterone （黄体酮） secreted from follicle cells stimulated by gonadotropin, that acts on the oocyte to induce its maturation.

How progesterone acted upon the oocyte ?

First, in order to find the target for progesterone action, the hormone was injected directly into oocytes up to an internal concentration of 0.5 μg/ml. However, none of the progesterone-injected oocytes matured, while oocytes exposed to the same doses of the hormone in their culture medium did.

Inject progesterone into oocyte

Inject progesterone to the external medium surround

ing the oocyte

NO response Maturate

Therefore, it was assumed that progesterone could act only on the surface of the oocyte, and that the hormone must create a signal in the cytoplasm that acts on the nucleus to initiate maturation (Masui and Markert, 1971).

Donor oocyte Recipient oocyte

Treat with progesterone

Several hours Maturate?

Who can?

The hours is illustrated as the abscrissa( 横坐标 ) in Figure 1 on

page 617

The ratio of frequency of induced maturation is illustrated as the ordinate( 纵

坐标 ) in Figure 1.

Fully grown,immature oocyte

Cytoplasm in different stage

The different circle shows the different amount of the donor cytoplasm per oocyto.,the unit of

which is nanoliers(nl)

The figure indicated that the cytoplasm taken from oocytes during the first 12 hours following progesterone treatment had little or no effect on recipient oocytes.

After this period,the cytoplasm can induce maturation in the recipient oocyto.

And the effectiveness of cytoplasm reaches the top about 20 hours after progesterone treatment,

at last declined by 40 hours.

Recipient oocyte maturation ratio

Donor oocyte meiosis stage

12

Donor oocyte Recipient oocyte

So what factors the donor oocyte produced in the cytoplasm induced the maturation of recipient oo

cyte?

The discoverer named it “maturation promoting factor” which is represented MP

F!

Cytoplasm in different stage

Now the MPF has been discovered. And many initial work has been done. However, the curiosity which push the exploration forward hasn’t been satisfied.

What contribution does MPF to meiosis of oocyte? How does it control the meiosis?

What’s the construction of MPF? Does it have any relation to cyclin?