BIOL-500Fibre
The wool-producing ‘factory’ is the 50 million or so follicles embedded in the skin of sheep. This unit covers in detail, how these follicles form, what cellular and molecular processes produce the fibre, how genetics and nutrition affect these processes, and how genetic engineering might be used to produce a better fibre. With an understanding of the biology of the skin and the fleece, the characteristics of the wool follicle and fibre can be related to production, technology and the processing of wool.
The wool fibre is a complex composite comprising some 70 or so proteins in about 10 different cell types. This theme examines the detailed composition, formation and structure of the wool fibre.

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BIOL-500-050Understanding Molecular Biology
A basic understanding of the principles of molecular biology is necessary to fully appreciate the mechanisms of follicle function.
BIOL-500-050-100From genes to proteins
To understand many aspects of wool biology and how wool biology may impact on wool production, a basic understanding of molecular biology is required. This module describes the structure of DNA, transcription and translation, important steps between the gene and protein.
BIOL-500-050-200Cloning vectors
This module describes how DNA can be moved from one cell to another by using vectors. Apart from being able to manipulate DNA using restriction enzymes and ligase, we need some mechanism of transporting the DNA from one cell to another or to somewhere for further treatment. In some ways vectors are a bit like forceps because they allow us to hold a particular gene in a way that we can manipulate it. The use of vectors and the three common types of vectors, plasmids, phage and cosmids, are described in this module.
BIOL-500-050-300DNA modification enzymes
The most important tools to molecular biologists are DNA modification enzymes because these enable scientists to cut and paste, mutate and engineer DNA. A restriction endonuclease and DNA ligase are discussed in this module but there are many that are beyond the scope of this resource. The restriction endonucleases allow DNA to be cut at specific sites and DNA ligase allows pieces of DNA to be stuck together.
BIOL-500-100Protein Composition of Fibres
These modules cover the composition of wool fibres and factors influencing composition.
BIOL-500-100-050Basic fibre composition
This module outlines the basic components of the fibre and provides the amino acid composition of wool fibres.
BIOL-500-100-100Fibre keratins
Keratins are the major constituent of fibres. Keratins are built in an arrangement of intermediate filaments embedded in a nonfilamentous matrix. The filaments form the bulk of the cortical cells. This module explains what keratins are, explains the jargon used to describe keratins and outlines the major protein groups found in keratins.
BIOL-500-100-150Sulfur distributions in fibre shafts
Numerous microscopic studies, mainly using TEM (transmission electron microscope), on sections of mammalian hair follicles have provided an abundance of morphological data to explain the cellular composition and ultrastructural details of the processes involved in hair formation. This module shows the distribution of sulfur along the shaft that aids in the interpretation of fibre formation.
BIOL-500-100-200The effect of sulfur status in the diet on the protein composition of wool
Various physiological, genetic, nutritional and pathogenic states affect wool production and quality. By examining the protein composition of the fibres, it is possible to determine how the abnormal state is affecting the wool. This module demonstrates how diet affects protein composition of wool.
BIOL-500-100-250Disease and protein composition of mammalian fibres
This module demonstrates how diseases affect protein composition of human hair, and this situation is compared and contrasted with the effect on fibre composition and wool growth of sulfur deficiency in the diet of sheep.
BIOL-500-100-300Effect of EGF on the protein composition of wool
This module demonstrates how a hormone (epidermal growth factor; EGF) affects protein composition of wool.
BIOL-500-100-350The inheritance of protein composition in hair
This module illustrates how genetics can affect the proteins of hair.
BIOL-500-200Fibre Formation
The production of wool fibres depends on the coordinated expression of the keratin gene families. The expression of these genes and the stages of fibre formation are outlined.
BIOL-500-200-050Stages in the formation of the cortex
Numerous microscopic studies, mainly using TEM, on sections of mammalian hair follicles have provided an abundance of morphological data to explain the cellular composition and ultrastructural details of the processes involved in hair formation. These microscopic studies are illustrated to describe the formation of the cortex in this module.
BIOL-500-200-100Stages in the formation of the cuticle
Formation of the mature fibre cuticle from germinal epithelial cells is a complex process which involves highly specified changes in cell shape, protein synthesis and formation of specialised intermolecular cross links to form the various resistant barriers of the exocuticle. This module describes the formation of the cuticle using transmission electron microscope images to illustrate the changes from the bulb to the separation of the fibre from the follicle in the pilary canal. These notes are drawn from a study of fibre surface characterisation, which is aimed at resolving particular aspects concerning the structural nature of the emerging fibre surface and the various intercellular matrices together with the origin of these separate entities.
BIOL-500-200-150Cysteine rich KAP proteins
Keratin genes encode the structural proteins of wool. These include both the keratin intermediate filaments and the keratin associated proteins. The structure, expression and chromosomal location of the keratin genes are known, as is the regulation of the genes. Some mutations of these genes lead to interesting hair phenotypes. This module describes the cysteine rich family of the keratin associated proteins.
BIOL-500-200-200Expression of keratin genes
This module describes where and when the keratin genes are active and the mechanisms that control keratin gene expression.
BIOL-500-200-250High Glycine/Tyrosine Keratin Associated Proteins
This module describes the glycine/tyrosine rich KAPs which form part of the matrix proteins.
BIOL-500-200-300Keratin associated protein genes
This module describes the keratin associated protein genes.
BIOL-500-200-350Keratin IF genes
Keratin genes encode the structural proteins of wool. These include both the keratin intermediate filaments and the keratin associated proteins. This module describes the keratin IF genes.
BIOL-500-200-400The Reaction Diffusion system and fibre formation
This module describes the role of the reaction diffusion (RD) system in the follicle bulb and its effect on cell differentiation. The role of a substance produced in the dermal papilla which then diffuses rapidly away from the papilla through the bulb is discussed.
BIOL-500-200-450Mutations of keratin genes
This module describes some genetic mutations of the keratin genes in the skin and follicle.
BIOL-500-300Fibre Structure
The unique properties of the wool fibre are a consequence of the chemical properties of keratin and the physical nature of the fibre. These modules describe the detailed chemical and physical characteristics of wool fibres.
BIOL-500-300-025General fibre stucture
This module contains a schematic diagram and a photomicrograph of the general structure of the fibre. The outermost layer of the fibre is called the cuticle, which surrounds the major component of the fibre, the cortex. In broad fibres (>30 µm) a medulla is present in the centre of the fibre.
BIOL-500-300-050Detailed fibre diagram
Epithelial-mesenchymal interactions are essential for follicle initiation and a number of molecules have been implicated in follicle initiation and development. This module examines the role of the epithelium and mesenchyme in skin appendage formation.
BIOL-500-300-075Cortex structure
This module describes the structure of the cortex of fibres. There are photomicrographs and descriptions of individual cortical cells and the different types of cortical cells that form the cortex. For more detailed descriptions see the modules “Detailed Cortex structure” and “Cortex formation”.
BIOL-500-300-100Detailed structure of the cortex
Cortical cells normally account for the bulk of the fibre and are responsible for most of its mechanical properties. Cortex ultrastructure differs markedly in appearance from the cuticle. Numerous microscopic studies, mainly using TEM, on sections of mammalian hair follicles have provided an abundance of morphological data to explain the cellular composition and ultrastructural details of the processes involved in hair formation. This module contains a transmission electron micrograph of the structure of the cortex.
BIOL-500-300-125Cuticle structure
This module describes the structure of the fibre cuticle and includes photographs of cuticle scale patterns and a diagram of cuticle cell structure. For more detailed descriptions of the cuticle see the modules “Detailed Cuticle Structure” and “Cuticle Formation”.
BIOL-500-300-150Detailed fibre cuticle structure
Fibre cuticle cells are composed of a series of layers (laminations) varying in thickness and staining characteristics. This module describes the structure of the cuticle using transmission electron microscope images to illustrate the cuticle structure and diagrams showing the location of each of the intercellular components of the fibre cuticle cell.
BIOL-500-300-200Keratin stucture
The interior of the cortical cells of fibrous keratin tissue such as wool consists predominantly of more or less longitudinally aligned protein intermediate filaments embedded in a protein matrix phase. This module briefly summarises the protein structure within these cortical cells.
BIOL-500-300-250Medulla Structure
This module describes the structure of the medulla of fibres. There are photomicrographs and descriptions of the different types of medullation that occur in fibres.
BIOL-500-300-300IF superfamily
Keratin genes encode the structural proteins of wool. These include both the keratin intermediate filaments and the keratin associated proteins. The structure, expression and chromosomal location of the keratin genes are known, as is the regulation of the genes. Some mutations of these genes lead to interesting hair phenotypes. This module describes the Intermediate Filament (IF) superfamily.
BIOL-500-300-350Dimers of intermediate filaments
Each intermediate filament consists of large numbers of so-called low-sulfur protein molecules, which are single protein chains, arranged in a specific manner. In the intermediate filament, individual low-sulfur protein molecules interact with each other to form pairs of protein chains or dimers. This module describes the formation and structure of the dimers.
BIOL-500-300-400Tetramers of intermediate filaments
Each intermediate filament consists of large numbers of so-called low-sulfur protein molecules, which are single protein chains, arranged in a specific manner. The individual low-sulfur protein molecules interact with each other to form pairs of protein chains or dimers. In turn, the dimers interact with each other to form tetramers. This module describes the tetramers of the intermediate filaments and includes an exercise addressing the understanding of bond formation between the dimers to form tetramers.
BIOL-500-300-450The molecules of the wool intermediate filaments (low sulfur proteins)
Each intermediate filament consists of large numbers of so-called low-sulfur protein molecules, which are single protein chains, arranged in a specific manner. This module describes in detail the structure of the low-sulfur proteins.
BIOL-500-300-500Subfilaments of the intermediate filaments
Each intermediate filament consists of large numbers of so-called low-sulfur protein molecules, which are single protein chains, arranged in a specific manner. The individual low-sulfur protein molecules interact with each other to form pairs of protein chains or dimers. In turn, the dimers interact with each other to form tetramers. Within the intermediate filament large numbers of tetramers are arranged end to end thereby constituting a long subfilament. This module briefly describes the structure of the subfilament.
BIOL-500-300-550Chemical bonding in the fibre
Each intermediate filament consists of large numbers of so-called low-sulfur protein molecules, which are single protein chains, arranged in a specific manner. The individual low-sulfur protein molecules interact with each other to form pairs of protein chains or dimers. In turn, the dimers interact with each other to form tetramers. Within the intermediate filament large numbers of tetramers are arranged end to end thereby constituting a long subfilament; the tetramer, with its four constituent protein chains, is regarded as the repeating unit in the longitudinal direction. A small number of subfilaments, probably eight, are bundled together side by side in a cylindrical arrangement, with a certain stagger between them in the longitudinal direction, to form the intermediate filament.

This module contains a number of questions and answers to test the understanding of the structure of the mammalian hard a-keratins which is covered by information contained in the modules “Keratin Structure”, “The molecules of the wool intermediate filaments”, “Dimers of Intermediate Filaments”, “Tetramers of Intermediate Filaments” and “Subfilaments of Intermediate Filaments”.

BIOL-500-400Fibre Nutrition
Some features of the functioning of follicles are similar to those of all mammalian cells while others are unique. In this section biochemical processes involved in follicle function are examined.
BIOL-500-400-050General amino acid transport systems
Protein metabolism in the follicle is essential for wool growth. Without protein metabolism, fibre formation would be impossible (see the module “”Basic fibre composition””). Protein metabolism is much more than simple fibre formation. It is also includes transport of amino acids from the plasma into the cells, amino acid metabolism and polyamine synthesis. This module describes the mechanisms involved in transporting amino acids across membranes.
BIOL-500-400-075Tricarboxylic Acid (TCA) Cycle 
Wool and hair follicles have high requirements for energy and amino acids to maintain their very high rate of cell division and protein synthesis and yet skin (and therefore the follicles) receives a highly variable supply of blood and oxygen. The skin and follicles have therefore developed some interesting features of energy metabolism to cope with this variation. The major energy substrates are glucose and glutamine.Glucose is metabolised by aerobic and anaerobic pathways, whereas glutamine is metabolised by glutaminolysis. There is also a store of glycogen in the outer root sheath.

Glucose is metabolised in follicles by 3 pathways:

  • anaerobic or aerobic glycolysis (90%)
  • the TCA cycle (7%)
  • the pentose phosphate pathway (3%)

The metabolic requirements of the cells in the skin mirror those in the remainder of the body. It is therefore reasonable to expect that the skin and hair follicle will exhibit similar biochemical pathways to other tissues. The enzymes and metabolites of glucose metabolism have been extensively studied and, qualitatively, the intermediary metabolism of skin and follicle do not differ significantly from other tissues in the body. There are several pathways by which glucose may be metabolised. A brief outline is presented here but further detail can be obtained from standard biochemistry text books.

The glucose that is not metabolised to lactate is oxidised via the pentose phosphate pathway or the tricarboxylic acid cycle. This module describes the TCA cycle.

BIOL-500-400-100Glutaminolysis
This module describes the use of glutamine as an energy source through glutaminolysis.
BIOL-500-400-150Glycolysis
The enzymes and metabolites of glucose metabolism have been extensively studied and, qualitatively, the intermediary metabolism of skin and follicle do not differ significantly from other tissues in the body. There are several pathways by which glucose may be metabolised. A brief outline is presented here but further detail can be obtained from standard biochemistry text books. This module describes the metabolism of glucose by glycolysis.
BIOL-500-400-200Glycolysis & glutaminolysis
This module summarises the current knowledge about energy metabolism in follicles. Glutamine is a significant energy substrate for both the skin and hair follicles. These tissues demonstrate high rates of aerobic glycolysis and glutaminolysis and they share characteristics of other tissues having this metabolic pattern.
BIOL-500-400-225Oxidative phosphorylation 
There are several pathways by which glucose may be metabolised. A brief outline is presented here but further detail can be obtained from standard biochemistry text books. This module describes oxidative phosphorylation.
BIOL-500-400-250Pentose phosphate pathway
Glucose that is not metabolised to lactate is oxidised via the pentose phosphate pathway or the tricarboxylic acid cycle. This module describes the pentose phosphate pathway.
BIOL-500-400-300Sulfur amino acid metabolism 
This module illustrates three metabolic pathways in which methionine is involved:

  • transulfuration pathway (conversion of methionine to cysteine and then cystine);
  • the use of methionine for protein synthesis; and
  • the use of methionine for polyamine synthesis.
BIOL-500-500 Pigmentation 
Pigmented fibres can cost the wool industry dearly. This section looks at factors that affect the levels of pigmented fibres in white wool. Genetic control of pigmentation and the function of melanocytes are two of the factors examined.
BIOL-500-500-050Effect of age and environment on pigmentation
Most but not all pigmentation faults in Merino sheep depend on the genotype of the sheep. However, the age of the sheep and the environment also have interactive effects on phenotype. The function of melanocytes is covered in the module “Regulation of Melanin Synthesis”. This module discusses the effects of age and the environment on levels of pigmented fibres in white wool.
BIOL-500-500-100Regulation of melanin synthesis
Pigmentation in mammals is caused by melanins which are produced by specialised pigment cells called melanocytes. Pigmentation is affected by both the distribution of melanocytes and their function or level of activity. The regulation of melanocyte function is controlled by genes which affect the activity of the alpha MSH receptor, genes which code for pigment enzymes and genes which affect cell shape. This module describes regulation of melanin synthesis i.e. pigment production in melanocytes present in the skin and wool follicle.
BIOL-500-500-150Melanocyte distribution
This module demonstrates how the distribution of melanocytes affects fibre and skin pigmentation and the genes that control the pattern and numbers of melanocytes in the skin.
BIOL-500-500-200Genetic regulation of melanin synthesis 
The regulation of melanocyte function is controlled by genes which affect the activity of the MSH (melanocyte stimulating hormone) receptor and enzymes and genes which affect cell shape. This module discusses some of the genes which control melanocyte activity in sheep.
BIOL-500-500-250Mouse pigmentation genes 
Genetic control of pigmentation is highly complex. In sheep, over 19 genes and 44 alleles (gene variants) have been identified which affect coat colour. However only 2 of the genes causing changes in pigmentation have been (partly) characterised at a molecular level. Much of our understanding is therefore based on other species. In mice about 50 genes with over 130 alleles have been identified by classical genetics. An increasing number of these genes have been characterised by the identification of their gene products and DNA sequencing, leading to a better understanding of their mechanisms of action and of the interactions between different genes. This module discusses the genes which control melanocyte activity and distribution in mice.