Untersuchungen zum keimbahnspezifischen Lamin B3 Protein in Vertebraten

Lamins are type V intermediate filamentproteins. The germline specific lamin B3 is a spliceproduct of the LMNB2 gene. So far this protein is only detected in mouse, where its expression is restricted to spermatogenetic cells. One aim of this work was to search for lamin B3 sequences of other vertebrates in gene- and EST-databases. Rat and human B3 EST clones were found and thereby the existance of lamin B3 in these species could be proven. A corresponding situation could be excluded for Takifugu rubripes and Tetraodon nigroviridis. These species probably do not contain lamin B3. Further genebank analysis and biochemical and histological experiments showed that no lamin B3 protein is expressed during spermatogenesis of Xenopus laevis. These results indicate that the lamin B3 protein is an invention of the mammalian lineage. Additionally it was shown that the composition of the lamina during spermatogenesis of Xenopus is different from that in rodents. The behaviour of a human lamin B3 was characterized in Xenopus oocytes, Xenopus embryos and different somatic culture cells. In oocytes the human lamin B3 protein behaves like a typical B-type lamin. In contrast lamin B3 expression in Xenopus embryos has a dominant-negative-effect and it induces apoptosis at gastrulation. The ectopic expression of lamin B3 in somatic culture cells induces dramatic alterations of the nuclei.