The lamin code.

Unicellular eukaryotes and metazoa present a nuclear envelope (NE) and metazoa express in it one or more lamins that give rise to the nuclear lamina. The expression of different types of lamins is related to the complexity of the organism and the expression of type-A lamins is related to the initial steps of tissue-specific cell differentiation. Several posttranslational modifications characterize the expression of lamin A in the course of cell differentiation, and the alteration of this expression pattern leads to impressive phenotypic diseases that are collectively referred to as laminopathies. This indicates a link between differential lamin A expression and tissue-specific cell commitment, and makes it conceivable that the lamin posttranslational modifications constitute a lamin code, utilized by metazoan cells to induce tissue-specific cell differentiation. Although the rules of this code are not yet deciphered, at the moment, the presence of adaptors, represented by NE transmembrane proteins (NETs), and of effectors, constituted by epigenetic repressors that modulate chromatin arrangement and gene expression, strongly supports the possibility that the rules of lamin modification represent one of the organic codes that characterize cell evolution.