Herlitz's junctional epidermolysis bullosa is linked to mutations in the gene (LAMC2) for the gamma 2 subunit of nicein/kalinin (LAMININ-5)

Basal lamina assembly

From studies of the 'classical' components, models for the assembly and structure of an idealized basal lamina have been developed. In particular, the evidence supports the concept of enmeshed collagen and laminin polymers, in which nidogen/entactin acts as a bridge between these molecules and provides anchorage for diverse matrix components. Different basement membranes, however, possess different members of the basic basal lamina families, such as the newly described alpha 6 (IV) collagen, alpha 2 (merosin) laminin, and beta 3 laminin (in kalinin/nicein) chains. Even though these members share homologous domains and sequences, and are likely to share certain functions, they also possess unique characteristics that are expected to provide for basal lamina heterogeneity. A combination of genetic, recombinant and biochemical approaches are now being applied to elucidate the special roles of both old and new components.

Developmental expression of nicein adhesion protein (laminin-5) subunits suggests multiple morphogenic roles

Nicein/kalinin (laminin-5) is a heterotrimeric laminin-like adhesion protein, which is secreted at the basement membrane of subsets of epithelia and is involved in the etiology of junctional epidermolysis bullosa, a severe human blistering disease characterized by disadhesion of epidermis from dermis. cDNA clones encoding the three chains of mouse nicein and antibodies specific to each polypeptide were used to examine the expression of the protein in the developing mouse embryo from 10.5 day post coitum to 7 days after birth. At various stages of development, co-expression of the three chains of nicein was observed in amnion, skin, and in epithelia of respiratory, urinary and digestive systems. High level expression of nicein was seen in enamel-secreting ameloblasts in developing teeth. Cell-specific distribution of nicein was also detected in other specialized tissues representative of the three primary embryonic germ layers with prominent secretory or protective functions. Differential and focal expression of nicein subunits was observed in the choroid plexus and the floor plate of the neural tube. Messenger for the heavy chain of nicein was detected in the floor plate, where mouse s-laminin messengers were also found. This suggests that nicein genes may play a role in the migration and polarization of motor neurons in the developing spinal cord.