AN OBSERVATION ON THE NUCLEAR ULTRASTRUCTURAL CHANGES DURING THE EMBRYOGENESIS OF CYNOPS ORIENTALIS
Soo Shi-huang (Shanghai Institute of Cell Biology,Academia Sinica)
Tseng(1982) reported that the nuclei of early gastrula ectoderm of Cynops orien-talis changed markedly in their ultrastructure after treatment with Ca~(++)-free Holtfreter so-lution or with the extract of guinea pig bone marrow.We examined the nuclear ultrastruc-tural changes during normal embryogenesis of Cynops orientalis.The results have been sum-marised as follows: 1.From the beginning(St.10) to the end(St.16) of gastrulation,the nuclei of ec-toderma] cells contain numerous condensed heterochromatin clumps with different sizes and irregular shapes and they are distributed randomly in the nuclei (Plate I.Fig.1).About 4.5 hours after the end of gastrulation heterochromatin clumps in the nuclei of neuro-epithelial cells have transformed into diffused euchromatin.This period seems to be a turning point of morphogenesis.Up to neu-rula chromatin exists in dispersed form in the nuclei. 2.Chromatin dispersion occurs not only in the nuclei of neuro-epithelial cells but also in the nuclei of epithelial (Plate III Fig.6) and mesodermal cells. 3.Determination of the presumptive neu-ro-epithelium to neural tissue is a progres-sive process taking place during the period from late gastrula to early neurula.Chroma-tin dispersion seems to take place at the early stage of neural determination. 4.The significance of ultrastructural changes of chromatin and the relationship of cbromatin dispersion and cell differentiation have been discussed.