Lamins

Nuclear lamins, also known as Class V intermediate filaments, are fibrous proteins providing structural function and transcriptional regulation in the cell nucleus. Nuclear lamins interact with membrane-associated proteins to form the nuclear lamina on the interior of the nuclear envelope. Lamins are present in all members of the kingdom Animalia (Metazoa), but are not found in unicellular organisms, plants, or fungi. Lamin proteins are involved in the disassembling and reforming of the nuclear envelope during mitosis, the positioning of nuclear pores, and programmed cell death. Mutations in lamin genes can result in laminopathies, some of which are potentially lethal disorders.

Nuclear lamins were first identified using electron-microscopy. However, they were not recognized as vital components of nuclear structural support until 1975. During this time period, investigations of rat liver nuclei revealed that lamins have an architectural relationship with chromatin and nuclear pores. Later in 1978, immunolabeling techniques revealed that lamins are localized at the nuclear envelope under the inner nuclear membrane. It wasn't until 1986 that an analysis of lamin cDNA clones across a variety of species supported that lamins belong to the intermediate filament (IF) protein family. Further investigations found evidence that supports that all IF proteins arose from a common lamin-like ancestor. This theory is based on the observation that organisms that contain IF proteins necessarily contain lamins as well; however, the presence of lamins is not a requirement for simultaneously containing IF proteins. Furthermore, sequence comparisons between lamins and IF proteins support that an amino-acid sequence that is characteristic of lamins is found in early forms of IF proteins. This sequence is lost in later forms of IF proteins, suggesting that the structure of later intermediate filaments diverged. After this research, investigations of lamins slowed. Studies of lamins became more popular in the 1990s when it was discovered that mutations in the genes that code for lamins can be related to muscular dystrophies, cardiomyopathies, and neuropathies. Current research is being performed to develop treatment methods for the aforementioned laminopathies and to investigate the role lamins play in the aging process.

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