WHAT ROLE MIGHT LAMPBRUSH CHROMOSOMES PLAY IN MATERNAL GENE-EXPRESSION

The biological significance of lampbrush chromosomes from urodelan amp hibians is far from being elucidated. Their particularly well develope d lateral loops are the site of intense transcriptional activity, whic h can be visualized in electron microscopy using the Miller spreading procedure. All transcription units functioning in lampbrush loops synt hesize RNA at a maximum rate. In situ hybridization has provided evide nce for transcription of both unique coding sequences and highly repet itive sequences. The role of lampbrush transcripts in the production o f maternal information remains unclear. RNAs transcribed from unique c oding sequences are exported to the cytoplasm; there, they contribute either to maintaining the required level of maternal messenger RNA in a basal state during late oogenesis, or to increasing the store of the se maternal RNAs throughout oocyte growth, i.e., until stage VI. For r epetitive sequences, their intense transcription appears to be non-pro ductive, in that RNAs are not translatable and might be useless produc ts of readthrough transcription. The non-productive transcription of r epetitive sequences, the expression of which is directly related to hy perdevelopment of lateral loops, raises the issue of the role of lampb rush chromosome transcription.