Heterochromatin and nucleolar organizers during first meiotic prophase in quail oocytes

Abstract

The study of chromosomes in oocytes of the quail shows, at the pachytene stage, that microchromosomes are made of a euchromatic segment and a heterochromatic juxtacentromeric region. The heterochromatic regions of the microchromosomes amalgamate between themselves so as to constitute bulky chromocentres from which radiate the euchromatic segments which remain free. At late pachytene, nucleoli appear at the contact of these chromocentres. When the oocytes reach the diplotene stage, the nucleoli become quite large. They are stuck against chromocentres and establish a very close relationship with the euchromatic segments of the microchromosomes which surround or penetrate them. These observations lead one to think that the euchromatic segments of microchromosomes could be bearing nucleolar organizers. The close relations that the nucleolar organizers develop with the bulk of the nucleolus could explain its Feulgen-positive character in the quail.