WHY DO WE USE FROG CELLS INSTEAD OF THOSE FROM HUMANS?
We use frog cells for our experiments for the following reasons:
1.Oocytes, eggs and sperm can be obtained year 'round (in some animals, the gametes can be obtained only at certain times of the year). Large quantities of gametes can be obtained (as opposed to human or rodent species) so that mass measurement of second messengers is feasible.
2. Xenopus oocytes are about 1.2 mm in diameter (the size of a head of a pin). This is much bigger than the average human somatic cell (10-80 microns in diameter) and means that second messengers, enzyme activators and inhibitors, even mRNA can be microinjected into the cell.
3. The oocyte can be easily cultured in the lab for up to a week (no expensive equipment is needed). This is important when one wants to incorporate radioactive label into the proteins or lipids of the cell, or if one wants a protein to be expressed from injected mRNA.
4. The induction of meiotic cell division requires only 3-6 hrs versus the longer induction time of mitosis (up to 23 hrs or so).
5. Fertilization is easily performed in a petri dish. In vitro frog fertilization does not cause much social discussion (or picketing of the labs).
6. Development of the embryo is very rapid (the first mitotic divisions occur every 30 min or so) and easily performed and observed in a petri dish.
7. Like humans, the Xenopus egg is arrested in metaphase II of meiosis and fertilization causes the completion of meiosis. There may be many other similarities between frog and human fertilization (e.g., role of IP3 and the lack of calcium-induced calcium release through ryanodine receptors).