Cloning of animals by nuclear transplantation has demonstrated that a somatic cell nucleus can be reprogrammed when placed in oocyte cytoplasm. The clones rarely survive, however, which suggests that the reprogramming is usually not complete. Speculating that architectural remodelling of transplanted nuclei might be an important aspect of this, Philippe Collas and co-workers have examined the structural changes that occur following nuclear transplantation (see ). They observe that transplanted mouse embryos misexpress A-type lamin intermediate filaments - DNA-binding components of the nuclear lamina that are normally present only in differentiated cells - as well as the nuclear matrix protein NuMA. The authors also find that, in common with normal embryos, the transplanted embryos retain maternal AKAP95, a scaffold protein thought to bridge chromatin and the nuclear envelope; however, AKAP95 and DNA in the transplanted nuclei are more resistant to in situ extraction, which indicates that they have higher levels of silent DNA. Collas and co-workers suggest that such inappropriate lamin and/or AKAP95 architecture could have a significant effect on chromatin modification or transcription and prevent the complete reprogramming necessary for an embryo to develop correctly.
