Molecular orientations in an extruded collagenous composite, the marginal rib of the egg capsule of the dogfish Scyliorhinus canicula ; a novel lyotropic liquid crystalline arrangement and its origin in the spinnerets

Abstract

The egg case of the dogfish, Scyliorhinus canicula is a composite material largely constructed from collagen fibrils. It is formed as a drawn extrusion from transverse rows of spinnerets within the lining of the nidamental gland. In the L 2 layer, which forms over 90% of the thickness of the marginal rib, each spinneret extrudes a flattened ribbon which runs the length of the rib and measures approximately 150 x 8.5 μm in cross section. The structure of these ribbons and the orientation of collagen molecules and fibrils within them has been investigated in a correlative study using: low angle x-ray diffraction; bright field microscopy of peeled preparations; transmission (TEM) and scanning (SEM) electron microscopy; confocal and quantitative polarizing microscopy. The way in which the molecular orientations are defined within the spinneret has been followed by SEM of fixed material from actively secreting nidamental glands. The extruded ribbon showed a predominantly biaxial fibril orientation in low angle x-ray diffraction patterns recorded with the beam passing horizontally through the marginal rib. This x-ray pattern is derived from a remarkably regular parabolic arrangement of fibrils superficially resembling that seen in biological twisted nematic liquid crystals. However, evidence is presented here that the arrangement in the marginal rib is novel, apparently arising from authentically curved fibres showing a splayed- or bent- rather than twisted-nematic construction. Evidence is also presented that the spinnerets are able to control molecular orientations in a nematic liquid crystal to produce this and the other arrangements seen in the egg case.

In vitro formation by reverse dialysis of collagen gels containing highly oriented arrays of fibrils

“…It is not known whether the patterns of molecular orientations observed in the gels result from authentically curved fibers 16 or from a twisted nematic organization 46 though the very low pitch makes the latter suggestion unlikely. It is possible that the slow rotation of the molecular axis may represent an Sdeformation of a nematic phase 47 resulting from a slight difference in the bulk of N and C terminal nonhelical peptides.…”

“…Once molecular orientations are defined by liquid crystallization in acidic solutions, increasing the pH under warm conditions results in the formation of fibrils without a change in molecular orientations. 40,[15][16][17] This is thought to depend on the prolonged relaxation time for the highly elongated molecules. 28,17 From the above consideration it seems likely that liquid crystallization is responsible for the formation of the highly ordered arrays of fibrils when water is removed by reverse dialysis, as described above.…”

“…12 Five g of the cleaned, blotted tendons were swollen in 25 mL of 0.1M acetic acid for [16][17][18][19][20] h. The tendons then were centrifuged at 4000 g for 30 min at 4°C, and the supernatant concentrated solution containing collagen and other matrix components was stored at the same temperature for up to 3 weeks. The collagen concentration in the final solution was approximately 0.3% w/v (Sircol assay kit, Quibis Ltd.).…”

Quantitative image analysis of birefringent biological material

“…1. The results of this investigation, reported in detail elsewhere (Knight et al, 1996), suggest that rheological interaction with nematic liquid crystallization is responsible for producing the bent nematic arrangement seen in this material. This interpretation is consistent with observations from low-angle X-ray diffraction, bright-field microscopy, electron microscopy and confocal microscopy performed on the same material (Knight et al, 1996).…”

“…The results of this investigation, reported in detail elsewhere (Knight et al, 1996), suggest that rheological interaction with nematic liquid crystallization is responsible for producing the bent nematic arrangement seen in this material. This interpretation is consistent with observations from low-angle X-ray diffraction, bright-field microscopy, electron microscopy and confocal microscopy performed on the same material (Knight et al, 1996). The quantitative imaging technique described in this paper is unique in that it gives detailed anatomical information as well as physical information concerning birefringence, orientation and degree of coherent phase ordering of the molecules making up the tissues.…”