The nuclear fibrous layer is commonly found in higher eukaryotic cells. It is a fibrin sheet under the inner nuclear envelope. The fiber diameter is about 10 nanometers, and the fibers are arranged neatly in a fibrous network. The nuclear fibrous layer is connected with the nuclear matrix in the nucleus, and connected with the intermediate fibers outside the nucleus, forming a unified grid structure system that runs through the nucleus and cytoplasm. It is located between the inner nuclear membrane and chromatin, and is closely related to the nuclear membrane, chromatin, and nuclear pore complex. The nuclear fibrin binds outward to the proteins on the inner nuclear membrane, and inwardly stains. Qualitative combination of specific segments. Its thickness varies from cell to cell and ranges from 30 to 100 nm.
In some eukaryotic cells, the nuclear fibrous layer structure between the inner nuclear membrane and chromatin can be directly observed by ultra-thin section electron microscopy. The thickness of the nuclear fibrous layer is 30-100 nm. It is a very thin structure. Observable only after removal of nuclear membrane and chromatin. Immunocytochemical studies have shown that the nuclear fibrous layer is ubiquitous in at least the nuclei of higher eukaryotic cells. The core fiber layer has a diameter of about 10 nm, is arranged vertically and horizontally, and is woven into a network in an orthogonal shape, distributed between the inner nuclear membrane and chromatin. It is generally considered that the core fiber layer structure has a spherical or cage network as a whole, and a sheet structure as a cross section. In dividing cells, the nuclear fibrous layer disintegrates and exists as a monomer in the cytoplasm.
Biological functions of laminin
Maintain the shape of the nucleus
Many studies have shown that the nuclear fibrous layer is essential for maintaining the shape of the nucleus. In mouse spermatocytes, deletion of laminin B3, which is specifically expressed by spermatocytes, leads to a change in the nucleus shape from spherical to hooked. In fact, the expression of exogenous laminin B3 in COP5 fibroblasts can also lead to changes in nuclear morphology. Changes in nuclear morphology were also observed in mice encoding the laminin A / C gene knockout and N. elegans. In addition, the human HIV virus VPR protein can induce local disintegration of the nuclear fibrous layer, eventually leading to visible bubbles in the nuclear pores. 
Maintain cell size
In Xenopus egg cell nuclear extract, nuclear laminin controls the size of the nucleus. After the nuclear fibrous layer was immune-deleted in the nuclear extract, although the assembly of the nuclear membrane was still in progress, the nucleus became smaller.
Tissues involved in nuclear membranes
The ultrastructure study found that the core fiber layer filaments are arranged perpendicular to each other in a two-dimensional space, intertwined into a grid structure, and interact with certain subunits of the nuclear pore complex (NPC), thereby anchoring the NPC at the corresponding position of the nuclear membrane. In Drosophila, after the laminin Dm0 is deleted, it can be observed that NPCs float on the nuclear membrane and eventually gather together. Similarly, similar results were observed in lmn-1 deleted nematodes.
Change in life activity
The most significant structural reorganization of the nuclear fiber layer occurs during the division phase. During the cell division process, the nuclear fiber layer disaggregates and reassembles. In the early stage of division, the nuclear membrane disintegrated, the nuclear fibrous layer was disaggregated, and nuclear fibrin proteins were diffused into the cytoplasm. At the end of division, when the nuclear membrane reappears, it reassembles around the chromosome and forms in the nuclear fibrous layer of the cell. During cell division, the level of phosphorylation of nuclear fibronectin changes significantly, and it is highly phosphorylated in the early stage of division, while dephosphorylation occurs in the final stage. Laminin phosphorylation may be an important part of the amplification reaction of the phosphorylation cascade in the pre-dividing cells. This phosphorylation cascade can coordinate the reorganization of many cell structures in the division in time.