[Polypeptide growth factors from the loach embryo at the blastula stage]

Substances which (depending on their dose) stimulate [3H]thymidine incorporation into the trichloracetic acid insoluble fraction of the in vitro cultured mouse NIH-3T3 cells were isolated from the blastoderm and from the yolk of the teleost fish loach embryos (8-9 hours after the eggs' fertilization) by the acid-ethanol extraction method. In the medium which contained the 0.5% fetal calf serum with addition of 100 micrograms/ml of the above mentioned substances the stimulation of labeled thymidine incorporation into cellular DNA achieved 44-56% of the level which was detected in the presence of 10% serum. The pepsin and trypsin treatment led to a significant decrease in the mitogenic activity of the both investigated factors, that confirmed their polypeptide structure. The factors are sufficiently thermostable as they retain almost completely the activity after 30 min heating at 56 degrees C and lose less than 70% of their activity after boiling for 5 min. Gel-filtration of the growth factors from the loach embryos' yolk on the Biogel P-60 column has shown that the growth stimulating activity is mainly concentrated in the fraction which contains the polypeptides with molecular weight about 5 kDa. The significance of mitogenic factors in the loach embryos at the earliest stages of the embryonic development is discussed.