To investigate the decrease of transcription and to determine the localization of RNA molecules during spermiogenesis in the fern Scolopendrium, we have used the enzyme-gold electron microscope method. During cell differentiation, the labeling decreases over the cytoplasm and increases over the nucleus. In the latter, the nucleolus disappears at the beginning of differentiation and the gold particles that were at first situated over the dispersed chromatin are then located over the condensed chromatin. In mature gametes, gold particles linked to RNA are abundant over the dense and homogeneous nucleus and sparse over the cytoplasm. By using in situ hybridization of RNA-poly(A) tails with radioactive poly(U) probes, we have shown that these RNA molecules are mRNA; they are located in the condensed chromatin of the mature sperm nucleus.

Résumé.-La gamétogenèse mâle du Phyflitis sco/opendrium est marquée par la condensation progressive et totale de la chromatine, la disparition du nucléole et l'enroulement hélico1dal du noyau. La technique de cytochimie, utilisant la ribonucléase complexée à l'or collo1dal, montre que des AAN persistent sous lorme dispersée dans le noyau durant toute la spermiogenèse et sont étroitement associés à la chromatine du noyau condensé du gamète mOr. L'emploi de méthodes de biologie moléculaire révèle qu'il est possible d'hybrider in situ, sur coupes, une sonde radioactive 'H-poly U au niveau des noyaux hélicoYdaux des gamètes mOrs ; la seule séquence susceptible de participer à cette hybridation est la "queue• polyA des AANm. Ceuxci sont donc présents dans le gamète mOr ; ce sont des AANm longue vie ; ils permettent le transfert de l'information patemelle au zygote avant que la condensation de la chromatine mâle autorise les transcriptions.Summary.-The male gametogenesis of Phyllitis scolopendrium is characterized by the progressive and complete condensation of the chromatin, the disappearance of the nucleolus and the coiling of the nucleus. The ANasa-gold cytochamistry mathod shows thal disparsad ANAs parsis! in the nucleus, ail along spermiogenesis, and are strictly associatad with the chromatin in the condensed sperm nucleus. The in situ hybridization, on section, wlth 'H-poly U probe shows a labelling over the coilad sperm nucleus. The only sequences which are able to interact specifically with poly (U) probe ara the poly (A) !ails of the mANAs. The presence of mANAs in a condensed sperm nucleus is unusual : they are mANAs long lifa. They could allow expression of the mala genome ln the firsl stages of embryo development, whareas the male DNA, remaining in the condensed lerm, ls not yet transcribed.