Presence of protein complex is prerequisite for aragonite crystallization in the nacreous layer.

We have isolated a protein complex from the nacreous layer of pearl beads and oyster shells. This complex was mainly composed of pearlin and pearl keratin. Addition of a minute amount of the complex to a calcium-carbonate-saturated solution containing Mg2+ induced aragonite crystallization.

Emergence of the Extrachromosomal Circular DNA Complexes as One of the Earliest Signals of Cellular Differentiation in the Early Development of Mouse Embryo: (mouse embryo/teratocarcinoma/mica-press-adsorption/circular DNA complex/DNA rearrangement).

A small number of mouse embryos and embryonal carcinoma cells were pressed by mica sheet; then the extruded DNA complexes were adsorbed to mica and processed for electron microscopy. Extrachromosomal circular DNA complexes longer than 1 μm emerged during the compaction process of mouse embryos and during the differentiation of embryonal carcinoma cells induced with retinoic acid. These DNA molecules are discussed as possible products of developmental gene rearrangements occurring in the chromosomal DNA.