TRANSLATION OF MATERNAL MESSENGER-RNA DURING EARLY OOGENESIS IN A TELOTROPHIC-MEROISTIC INSECT (DYSDERCUS-INTERMEDIUS)

The previtellogenic oocyte of Dysdercus intermedius is provided with m aternal mRNAs synthesized by trophocytes and transported via the troph ic cord towards the ooplasm in this trophocyte-oocyte syncytium. Mater nal mRNA accumulation occurs in the absence of transcriptional activit y in the oocyte nucleus suggesting that ooplasmic protein synthesis is regulated at the translational level, Trophocytes and oocytes were is olated from each other and separated from the surrounding somatic tiss ues (''skinning''), The distribution of cytosolic proteins in the trop hocyte-oocyte syncytium at 72 h of adult age was analysed in extracts of ''skinned'' trophocytes and oocytes by 2-D gel electrophoresis foll owed by silver staining: 78 acidic proteins are accumulated in the tro phocyte compartment and 59 of these proteins also appear after silver staining the oocyte extracts. When protein synthesis was analysed in 2 -D gels by fluorography, oocytes were found to synthesize a less compl ex set of proteins than trophocytes: no proteins characterized by a pi between 6.2 and 6.9 (''pI window'') were synthesized in ''skinned'' o ocytes incubated separately in the S-35-methionine-containing in vitro medium, The 59 silver stained ooplasmic proteins have two sources: th e trophocytes deliver 46% of ooplasmic proteins via the trophic cord a nd 32% can be attributed to ooplasmic protein synthesis based on mater nal mRNAs, 87% of the latter proteins are more acidic than 6.2. Since the cytosolic pH (determined with proton-selective microelectrodes) av eraged 7.4, all proteins separated in 2-D gels are negatively charged in vivo. The synthesis of basic proteins was determined by IEF slab ge ls in the native state. Fluorography revealed the synthesis of three b asic proteins in trophocytes as well as in oocytes, Two of them are cl ose to their isoelectric points (pI 7.3, 7.4) whereas the third (pI 8. 3) is positively charged in vivo.