The three-dimensional arrangement of intermediate filament in Romney wool cortical cells Jonathan P. Caldwell a, * , David N. Mastronarde b , Joy L. Woods a , Warren G. Bryson a a Canesis Network Ltd (formerly Wool Research Organisation of New Zealand Inc.), Private Bag 4749, Christchurch, New Zealand b University of Colorado, Boulder, CO, USA Received 23 March 2005; received in revised form 5 July 2005; accepted 7 July 2005 Available online 9 August 2005 Abstract The three-dimensional orientation and arrangement of intermediate filaments in Romney wool ortho-, meso-, and para cells has been revealed using single axis high voltage electron tomography. Modelled tomograms confirm that intermed in orthocortical cells are arranged helically, with the helical angle progressively increasing from the centre to the periphe rofibrils.Intermediate filaments in meso- and paracortical cells display parallel arrangements differing mainly in packing density, with the mesocortex packed more tightly than the paracortex. The intermediate filament arrangements observed confirm tions based on earlier two-dimensional transmission electron microscopy observations by the authors and other research It is expected that these findings will contribute to a better understanding of the biological and structural basis of wool fibre 2005 Elsevier Inc. All rights reserved. Keywords: Cortical cell; Staple crimp;Fibre curvature;High voltage electron microscopy; Intermediate filaments; Mesocortex;Orthocortex; Paracortex; Romney; Three-dimensional; Tomography; Wool 1. Introduction Wool has both singlefibre curvatureand staple crimp,the latter being the curvature of the naturally occurring lock or bundle of fibres from a fleece, and these are strongly positively related (Fish et al., 1999). The biological basis of single fibre curvature in uncon- strained fibres, free from irregularities in shape and diameter variation along their length, could originate from the relationship between several causative factors, including:differing longitudinal growth ratesof cells; differing ratios and distributions of ortho-, meso-,and paracortical cells;differing intermediate filament (IF) spatialarrangements and orientations; macrofibril size, orientation and shape; and matrix protein content in the three cortical cell types. Determining how fibre cur- vature is contributed to by IF orientation within the three cortical cell types and the proportional distribu- tion of these cortical cell types should provide knowl- edge that could lead to new fibre types for improving textile properties. Typically, in fine high crimp fibres, there is a bilateral arrangement of ortho- and paracortical cells,with the orthocortex typically found on the outside of the curve and the paracortex on the inside (Fraser and Rogers, 1955; Horio and Kondo, 1953). A third cell type, meso- cortex is often found in low abundance along the junc- tion between the ortho- and paracortical cell regions in high crimp Merino fibres (Kaplin and Whiteley, 1978; Whiteley and Kaplin, 1977). Wool of low crimp frequen- cy has been found to have an increased abundance of mesocortical cells atthe expense of the paracortex. A similar substitution of mesocortex for paracortex was observed in coarser fibres, however, the orthocortex also www.elsevier.com/locate/yjsbi Journal of Structural Biology 151 (2005) 298–305 Journal of Structural Biology 1047-8477/$ - see front matter 2005 Elsevier Inc. All rights reserved. doi:10.1016/j.jsb.2005.07.002 * Corresponding author. Fax: +64 3 3252 717. E-mail address: jonathan.caldwell@canesis.com (J.P. Caldwell).