A new model for stratum corneum keratin structure, function, and formation is 
presented. The structural and functional part of the model, which hereafter is 
referred to as "the cubic rod-packing model", postulates that stratum corneum 
keratin intermediate filaments are arranged according to a cubic-like 
rod-packing symmetry with or without the presence of an intracellular lipid 
membrane with cubic-like symmetry enveloping each individual filament. The new 
model could account for (i) the cryo-electron density pattern of the native 
corneocyte keratin matrix, (ii) the X-ray diffraction patterns, (iii) the 
swelling behavior, and (iv) the mechanical properties of mammalian stratum 
corneum. The morphogenetic part of the model, which hereafter is referred to as 
"the membrane templating model", postulates the presence in cellular space of a 
highly dynamic small lattice parameter (<30 nm) membrane structure with 
cubic-like symmetry, to which keratin is associated. It further proposes that 
membrane templating, rather than spontaneous self-assembly, is responsible for 
keratin intermediate filament formation and dynamics. The new model could 
account for (i) the cryo-electron density patterns of the native keratinocyte 
cytoplasmic space, (ii) the characteristic features of the keratin network 
formation process, (iii) the dynamic properties of keratin intermediate 
filaments, (iv) the close lipid association of keratin, (v) the insolubility in 
non-denaturating buffers and pronounced polymorphism of keratin assembled in 
vitro, and (vi) the measured reduction in cell volume and hydration level 
between the stratum granulosum and stratum corneum. Further, using 
cryo-transmission electron microscopy on native, fully hydrated, vitreous 
epidermis we show that the subfilametous keratin electron density pattern 
consists, both in corneocytes and in viable keratinocytes, of one axial 
subfilament surrounded by an undetermined number of peripheral subfilaments 
forming filaments with a diameter of approximately 8 nm.