[Experimental analysis of mechanism concerning the environmental temperature effect on acquisition of capability in toad oocyte to resume meiotic division].

Full-grown oocytes derived from Bufo bufo gargarizans rearing in high temperature environment (28-30 degrees C), called high temperature oocytes, never underwent germinal vesicle breakdown (GVBD) after progesterone stimulation, no MPF was detected in their ooplasm, but some events which manifested normally at the beginning of progesterone induced maturation process were revealed in these oocytes. It is worth notice an another kind of maturation promoting substance(s) appeared in the ooplasm of high temperature oocyte after the hormone treatment, which was capable of triggering the resumption of meiotic division of the full-grown oocytes derived from hibernating toad (called low temperature oocytes). It is a hibernation factor-dependent maturation promoting substance (HF-MPS), which appeared after decrease of the oocyte endogenous cAMP level. Its appearance depended upon the oocyte protein synthesis, and its activity to inducing GVBD of low temperature oocytes did not inhibited by puromycin. HF-MPS differs from MPF in maturation promoting activity, as low temperature (10 degrees C) delayed obviously HF-MPS' activity but did not influence the rate of GVBD induced by MPF. Further more, probably due to the lack of "hibernation factor(s)", no expression of p34cdc2 gene was detected in high temperature oocytes (unpublished data), neither HF-MPS nor MPF could amplify autocatalytically in the oocytes. So the low temperature (below 15 degrees C) was found to be indispensable for the toad oocyte maturation. If one day we can prove HF-MPS appeared also in the course of oocyte maturation induced by progesterone, the relationship between HF-MPS and MPF may be: [formula: see text] All these discoveries indicated above make a reasonable explanation of the geographical distribution of the toad which was restricted in the region north to the 23 degrees north latitude and east to the 100 degrees east longitude in China.