The membrane palmitoylated protein, MPP6, is involved in myelin formation in the mouse peripheral nervous system

A membrane skeletal molecular complex, protein 4.1G-membrane palmitoylated protein 6 (MPP6)-Lin7-cell adhesion molecule 4 (CADM4), is incorporated in Schwann cells, especially in Schmidt-Lanterman incisures (SLIs), in the mouse peripheral nervous system (PNS). MPP6, Lin7, and CADM4 are transported to SLIs by 4.1G. In this study, we created MPP6-deficient mice and evaluated myelin structure and MPP6 protein complexes. In SLIs in MPP6-deficient nerves, Lin7 was rarely detected by immunohistochemistry and western blotting, but the localization and amount of CADM4 and 4.1G were not altered. Motor activity was not significantly impaired in a tail-suspension test, but the sciatic nerves of MPP6-deficient mice had thicker myelin in internodes by electron microscopy compared to that of wild-type mice. These results indicate that the MPP6-Lin7 complex regulates myelin formation.

Riding the waves of the intercalated disc of the heart

Cardiomyocytes interact with each other at their ends through the specialised membrane complex, the intercalated disck (ID). It is a fascinating structure. It allows cardiomyocytes to interact with several neighbouring cells, thereby allowing the complex structure of the heart to develop. It acts as tension transducer, structural prop, and multi signalling domain as well as a regulator of growth. It achieves its many functions through a number of specialised domains and intercellular junctions associated with its complex folded membrane. This review outlines the results of some 20 years of fascination with the ups and downs of the ID. These include locating the spectrin-associated membrane cytoskeleton in the ID and investigating the role of Protein 4.1R in calcium signalling; structural studies of the relationship of the ID to myofibrils, sarcoplasmic reticulum and mitochondria and, finally, consideration of the role of the ID in cardiomyocyte growth and heart disease.

Spectrin and Other Membrane-Skeletal Components in Human Red Blood Cells of Different Age

BACKGROUND

Old human red blood cells (RBCs) have a reduced surface area with respect to young RBCs. If this decrease occurred through the release of vesicles similar to the spectrin-free vesicles that are shed in vitro under different experimental conditions or during storage, there would be no decrease of membrane-skeleton, but only of lipid bilayer surface area, during RBC ageing in vivo. However, we observed a decrease in spectrin and other membrane-skeletal proteins in old RBCs. Because RBCs contain components of the ubiquitin-proteasome system and other hydrolytic systems for protein degradation, we asked whether increased membrane-skeleton fragments could be detected in older RBCs.

METHODS

Four different anti-spectrin antibodies and an antibody anti-ubiquitin conjugates were used to analyse, by Western blotting, fragments of spectrin and other proteins in RBCs of different age separated in density gradients and characterized for their protein 4.1a/4.1b ratio as a cell age parameter.

RESULTS

spectrin fragments do exist in RBCs of all ages, they represent a minute fraction of all spectrin, are membrane-bound and not cytoplasmic and do not increase with cell age. Besides spectrin, other membrane-skeletal components decrease with cell age.

CONCLUSION

Observed results challenge the commonly accepted view that decrease in cell membrane throughout RBC life in vivo occurs via the release of spectrin-free vesicles.

Submembranous cytoskeletons stabilize nodes of Ranvier

Rapid action potential propagation along myelinated axons requires voltage-gated Na(+) (Nav) channel clustering at nodes of Ranvier. At paranodes flanking nodes, myelinating glial cells interact with axons to form junctions. The regions next to the paranodes called juxtaparanodes are characterized by high concentrations of voltage-gated K(+) channels. Paranodal axoglial junctions function as barriers to restrict the position of these ion channels. These specialized domains along the myelinated nerve fiber are formed by multiple molecular mechanisms including interactions between extracellular matrix, cell adhesion molecules, and cytoskeletal scaffolds. This review highlights recent findings into the roles of submembranous cytoskeletal proteins in the stabilization of molecular complexes at and near nodes. Axonal ankyrin-spectrin complexes stabilize Nav channels at nodes. Axonal protein 4.1B-spectrin complexes contribute to paranode and juxtaparanode organization. Glial ankyrins enriched at paranodes facilitate node formation. Finally, disruption of spectrins or ankyrins by genetic mutations or proteolysis is involved in the pathophysiology of various neurological or psychiatric disorders.

Expression and significance of membrane skeleton protein 4.1s in gastric carcinoma

AIM: To investigate the expression and signi-ficance of four members (4.1B, 4.1R, 4.1G and 4.1N) of membrane skeleton protein 4.1 family in human gastric carcinoma tissues.

METHODS: Expression of 4.1B, 4.1R, 4.1G and 4.1N was examined by immunohistochemistry (Envision⁺ assay) in archival paraffin-embedded gastric carcinoma tissues from 104 patients (77 males, 27 females, median age 61.7 years). Each case had detailed clinical data and surgical records. None of the patients were treated by radiotherapy or chemotherapy before surgery.

RESULTS: In gastric carcinoma, the expression of 4.1B, 4.1R, 4.1G and 4.1N was significantly different from that in normal gastric tissue (P < 0.01). The expression of 4.1B, 4.1G and 4.1N was significantly reduced when tumor differentiation became lower, which suggested these three members were significantly correlated with tumor differentiation status (P_B < 0.05, P_G < 0.01, P_N < 0.01). In gastric carcinoma with lymph node metastasis, the expression of 4.1B and 4.1N was significantly lower than that in tumors without lymph node metastasis (P_B < 0.05, P_N < 0.01).

CONCLUSION: Abnormal expression of 4.1B, 4.1G and 4.1N is related to the degree of tumor malignancy. Abnormal expression of 4.1N and 4.1B is related to lymph node metastasis of gastric cancer.

Expression of genes for human membrane skeleton protein 4.1s in colorectal carcinoma

AIM: To investigate the expression of protein 4.1 family members (4.1R, 4.1N, 4.1G, 4.1B) and to determine the pathological features of colorectal carcinoma.

METHODS: The expression of 4.1 proteins was detected with an envision immunohistochemical assay in 94 paraffin-embedded samples from patients with colorectal carcinoma. Correlations between proteins 4.1R, N, G and B and colorectal carcinoma were analyzed.

RESULTS: Expression of 4.1s in colorectal carcinoma tissues was clearly lower compared with that in normal tissue (H_c = 44.70, H_c = 31.41, H_c = 13.62; all P < 0.01), except for 4.1G. Expression of 4.1N and B in colorectal carcinoma tissues was positively correlated with cell differentiation (r_s = 0.27, r_s = 0.28; both P < 0.01). The expression of 4.1R was associated with the degree of soakage (r_s = 0.03, P < 0.01) and lymphatic metastasis (r_s = 0.24, P < 0.05); further, the expression of 4.1G was up-regulated with soakage (r_s = 0.24, P < 0.05). There was no significant relationship between expression of 4.1s in colorectal carcinoma tissue and patient age or gender.

CONCLUSION: The expression of 4.1s may participate in the occurrence and progression of colorectal carcinoma. Expression of 4.1N and 4.1B are closely related with histological grade, and proteins 4.1R and 4.1G are associated with soakage of colorectal carcinoma.