Removal of surface glycoproteins and transfer among Brachionus species

Abstract

Glycoproteins on the body surface of females of the rotifer Brachionus plicatilis are a key signal in their mate recognition system. When B. plicatilis Russian strain females were exposed to 50 mM EDTA or EGTA, several surface glycoproteins were removed. Females exposed to EDTA died, but remained intact and were used in mating bioassays with conspecifics males. Live control females elicited a male mating response in 21% of encounters, freeze-killed control females elicited responses in 23%, but EDTA extracted females elicited a mating response in only 5% of encounters. At least some of the EDTA-extractable proteins on the surface of females appear to be critical to male mate recognition. EDTA treated females could be exposed to proteins extracted from other females and some proteins reattached to their body surface, restoring their attractiveness to males. SDS-PAGE of these proteins revealed 15–17 prominent bands, most ranging in molecular mass from 66 to 12 kD. The EDTA-extractable proteins were separated using ion exchange chromatography and each fraction was tested for its ability to restore female attractiveness. When proteins in fraction 22 were bound to females, they restored 80% of the females’ ability to elicit male mating responses. Exposing EDTA treated females to bovine serum albumin or casein had no effect on their attractiveness to males. EDTA treated females from different Brachionus clades and species were exposed to proteins from fraction 22. Female attractiveness could be restored in most clades of B. plicatilis, but no transfer of mating attractiveness was observed to B. rotundiformis or B. ibericus females. Conspecific males treated with EDTA and exposed to proteins in fraction 22 could not be feminized and made attractive to other males. A sexual dimorphism in surface proteins therefore exists between B. plicatilis females and males. Successful transfer of glycoproteins critical in mate recognition is dependent on signal glycoprotein structure and the structure of the other proteins present on the surface of females.