THE INHIBITORY EFFECTS OF LECTINS ON THE EXPOSURE OF NEW MEMBRANE DURING THE FIRST CLEAVAGE OF RANA AMURENSIS EGGS

The new membrane of cleavinganurian eggs,normally situated in thefirst cleavage furrow,exposed extensively after the fertilization membranehad been removed (Plate Ⅰ,Fig.1).The exposure of new membrane couldbe strongly inhibited if the denudedeggs of Rana and Xenopus had ??been immersed in high concentrationof lectins (WGA or SBA) before clea-vage (Plate Ⅰ,Fig.2).The higher theconcentration,the longer the egg im-mersed,the stronger was the inhibition.Lectins bound to egg surface specifi-cally and extensively as shown by fluorescence microscopy and electron mic-rographes respectively.Eggs immersedin lectin solution had a thickest surfacecoat (Plate Ⅰ,Fig.8) and least exprosureof new membrane (Plate Ⅰ,Fig.2).Eggs first treated with alkaline solution(0.024 N 20 mins.) then in lectin solu-tions had a thinner surface coat (PlateⅠ,Fig.9) and less exposure of new membrane (Plate Ⅰ,Fig.3).Eggs withoutany treatment had scarcely any surfacecoat (Plate Ⅰ,Fig.10) and more exposure (Plate Ⅰ,Fig.1).This inverserelationship between the thickness ofsurface coat and the extent of exposureof new membrane suggested that theinhibitory effects of lectins might resultfrom an "exoskeleton" formed by themultivalent lectins bound on egg sur-face.This suggestion was supported bythe fact that the new membrane exposed extensively on eggs first immersed inlectins and then in monovalent compe-titive inhibitors of lectins. In scanning electron micrographs(Plate Ⅰ,Fig.4 and 5),flower-like orfeather-like appearances persisted fora long time in eggs strongly inhibitedby lectins.This might be explained asGeuskens et al.postulated that "thebinding of microfilaments to the membrane could be increased by the bindingof WGA to its rcceptors…".In elec-tron micrographs (Plate Ⅰ,Fig.9 and12) narrow deep identations of plasmamembrane along with the surface coatwere frequantly found in cortex ofalkaline treated or untreated eggs inlectin solutions,these figures impliedthat microfilaments were interfered bythe lectins through their binding toreceptors.If it to be the case,lectinscould also disturb the microfilaments inthe region of the cleavage furrow andblock the exposure of new membrane. As had been described previous-ly,in some eggs immersed in lectinsolution,new membrane appeared atthe beginning of cleavage but fadedaway later,and in most of them newmembrane still remained to be seen.It indicated that new membrane mightbe formed but hindered in the cleavagefurrow.In fact,the hinderence of theformed new membrane really existed,since the area of new membrane in-creased rapidly within 5 mins.incase the blocked eggs were transferredfrom lectin solution to Barth medium.So that the inhibitory effects of lectinswere not due to the cause of shortageof new membrane.