Wilhelm bernhard workshop on the cell nucleus

EVIDENCES SUGGESTING THAT TRANS-CRIPTION IS INVOLVED IN HOMOLOGUE CHROMOSOME RECOGNITION AND ALIGNMENT PREVIOUS TO PAIRING IN EARLY MEIOTIC PROPHASE

Vázquez-Nin G.¹, Echeverría O.¹, Ortiz R.¹, Scassellati C.², Ubaldo E.¹, Fakan S.<sup>2

1</sup>Laboratory of Electron Microscopy, Department of Biology, Faculty of Sciences, National Autonomous University of Mexico (UNAM), Mexico; ²Center of Electron Microscopy, University of Lausanne, Switzerland
The nuclei of guinea pig spermatogonia and spermatocytes were studied by means of electron microscopic methods such as high resolution cytochemistry, immunocytochemistry, in situ hybridization, and quantitative autoradiography at light microscope level. Immunolocalization of DNA, RNA polymerase II, and hnRNPs suggest that filaments of extended chromatin resembling very small lampbrush structures and pairing elements transcribe hnRNA intensively. The immunocytochemical localization of

hnRNPs, snRNPs, and the trimethyl-guanosin cap of snRNAs demonstrates that splicing is scarce in the nucleus of spermatocytes in early meiotic prophase, in which recognition, alignment and pairing is taking place. The results of quantitative autoradiography after ³H-uridine labeling, show an intense transcription accompanied by a very slow export of RNA to the cytoplasm. These results lead us to propose that newly transcribed mRNA stays long time in the nucleus, or never leaves it, to fulfill a function related to homologous searching, recognition and alignment at molecular level, previous to pairing.