Wool Follicles Research Articles

Effect of sex and birth status on the wool follicle population in unselected Corriedale sheep

ABSTRACTThe follicle population of 44 purebred 20-month-old Corriedale ewes and rams was examined for effects due to sex and birth status. Twin birth resulted in a lower ratio of secondary to primary follicles at 20 months of age in these medium follicle-density animals. This effect is similar to that reported for the high follicle-density Australian Merino. Similarly, the ewes had a lower ratio of secondary to primary follicles than the rams.

Fleece characteristics and the wool follicle population of the Merilin, a Uruguayan sheep breed

ABSTRACTTotal follicle density, primary follicle density, secondary follicle density, secondary/primary ratio and incidence of medullated fibres were studied in skin specimens from 78 2-year-old Merilin rams representing nine parent studs in Uruguay. The limited data available suggest that the studs sampled may fall into various groups, although separation into distinct groups is not equally well defined for all variables measured. Consequently, a firm conclusion about the Merilin awaits further information on fleece weight, staple length and body weight.

Epidermal growth factor: a critical factor in fetal maturation?

Epidermal growth factor (EGF) infused over 3-14 days into fetal sheep of 110-125 days gestation resulted in a number of morphological and endocrine changes. Striking hypertrophy of the skin, wool follicles and their accessory structures was seen, together with a reduction in the ratio of secondary to primary follicles and degenerative changes in wool fibres associated with shedding of fibres. Adrenal, thyroid, liver and kidney weights were increased while thymus weight was decreased. The increase in adrenal size resulted from cortical hypertrophy and was associated with increased cortisol secretion. Thyroid hypertrophy was accompanied by an increase in colloid stores, decreased plasma thyroxine and reverse triiodothyronine (T3) concentrations, unchanged plasma T3 and thyroid-binding globulin and raised thyrotropin (TSH) levels. Thyrotropin receptor affinity and content per gram of tissue were unchanged. Fetal and maternal plasma prolactin and growth hormone levels, and fetal plasma placental lactogen levels, were unchanged, although there was a significant rise in maternal plasma placental lactogen concentrations with high doses of EGF. Other maturational parameters such as switching from fetal to adult haemoglobin and liver glycogen content were unaffected.

Genetic studies of South Australian Merino sheep. 2. Environmental effects on wool and body traits at 15-16 months of age

The effects of years, sex, type of birth (i.e. whether or not multiple birth) and age of dam on 26 wool and body traits of South Australian Merino sheep were estimated by least-squares analysis. Years and sex had highly significant effects on all traits. Of the main production traits, type of birth had a significant effect on body weight, greasy and clean fleece weight and total wool follicle number, while age of dam only had a significant effect on body weight and greasy fleece weight. The possible consequences of failing to correct body weight and greasy and clean fleece weights for type of birth and age of dam were considered and it was concluded that, although in some years correction of these traits may not be warranted, in other years correction may be necessary to prevent selection against fecundity and an increase in the generation interval. The main components contributing to the 6.0 % difference between fleece weights of singles and twins were surface area, total follicle number and wrinkle score. The difference between fleece weights of animals from older ewes and animals from maidens was only 1.5 %; surface area was the main contributor to this deviation.

Theoretical Mechanism for Crimp

A mechanism for crimp in wool fibres is proposed in which the inner root sheath of the wool follicle and the fibre cuticle rotate around the fibre cortex in the region just above the follicle bulb. The rotational movement of the fibre cuticle is passed on to groups of microfibrils in the cortical cells of the fibre through a gearing action, which causes them to be twisted into helices or spirals with the result that the cortical cells tend to shorten. The fibre deforms while still in the follicle causing the position of the fibre cortex near the bulb to change. This changes the magnitude and direction of the rotational movement of the inner root sheath and cuticle. A mathematical model of the mechanism is developed and several crimp forms, produced by using the model, are compared to those commonly observed.

The Isolation of Wool Keratin Messenger RNA from Sheep

A method for the isolation of polysomal RNA from plucked wool follicle tissue is described. When translated in a reticulocyte lysate cell-free system, the products encoded by the RNA are electrophoretically identical to the low-sulfur and high-sulfur wool keratins. Since non-keratin translation products were not detected, the keratin mRNA species appear to be the predominant messenger component of the polysomal RNA. Sucrose gradient fractionation of the polysomal RNA gave rise to 2 discrete peaks of keratin mRNA, with mean sizes of 21S and 11S. The 21S fraction coded for the low-sulfur and larger high-sulfur wool keratins, while the 11S fraction coded for proteins smaller than about 20000 daltons, possibly the high-tyrosine keratins and smaller high-sulfur keratins. The keratin mRNA can be separated from the bulk ribosomal RNA by oligo(dT) cellulose chromatography, and hence is presumed to contain a terminal poly(rA) tract.

Migration and keratinization of cells in wool follicles.

Migration of cells in wool follicles of an adult Merino sheep was studied autoradiographically in skin samples taken at intervals after an intravenous injection of [3H]thymidine. Fibre and inner root sheath cells incorporated [3H]thymidine in a cone-shape region of the follicle bulb. Labelled inner sheath cells migrated out of the bulb ahead of contemporaneous cells in the fibre and remained in advance, although to a progressively lesser extent, until the inner sheath cells sloughed into the follicle lumen. Outer root sheath cells incorporated [3H]thymidine along the length of the follicle. Cells in the proximal half of the outer sheath migrated inwards and distally and sloughed into the follicle lumen before contemporaneous inner sheath cells. Other cells in the distal half of the outer sheath migrated past the level where cells from the proximal population were shed and also sloughed into the lumen. In the most distal part of the outer sheath, which formed the epidermis-like lining of the follicle canal, little migration of cells was observed during 8 days of observation. The specific activity of tritium in fibres plucked from the same sheep at intervals after the intravenous injection of [3H]thymidine was determined by scintillation counting and assessed in terms of cell migration and hardening of the fibres. The time which the specific activity of solvent-degreased fibres reached a maximum was found to give an estimate of the time for cells in the fibre to migrate to the upper limit of the keratogenous zone. When the plucked fibres were extracted with 8 M urea the times of the maximum specific activities of the urea-dispersible and urea-insoluble material provided respectively estimates of the times at which hardening of the fibres began and ended. The effects of different planes of nutrition were examined in two other Merino sheep by radioassay of fibres plucked after intravenous injections of [3H]thymidine given after equilibration period of at least 2 months on each level of feeding. A high plane of nutrition the rate of cell migration and hastened the onset of hardening of the fibres, but prolonged the hardening process. The prolongation of the hardening process was confirmed by the specific activities of fibres plucked after intravenous injections of [35S]cystine.

Effects of internally administered N-[5-(4-aminophenoxy)pentyl]phthalimide on wool follicles and skin of sheep.

When N-[5-(4-aminophenoxy)pentyl]phthalimide was administered to sheep in sufficient quantities to permit manual removal of the fleece (400 mg/kg body weight orally, or 75 mg/kg body weight intravenously during a period of 48 h), cell division ceased in the wool follicle bulbs within 1 day. Dark-staining bodies (autophagic vacuoles) developed concomitantly in the cytoplasm of the bulb cells. The nuclei of cells in the keratogenous zones of the fibres became pycnotic 2 days after dosing and subsequent keratinization of these portions of the fibres was impaired. All the follicles retrogressed prior to day 7 after dosing, and the root ends which formed on the fibres moved towards the skin surface, reaching the level of the sebaceous glands by day 7. At this time mitotic activity recommenced around the dermal papillae in about 50% of the follicles. A small number of tips of new fibres emerged from the skin surface of some of the depilated sheep by day 14. The root ends on the fibres in the fleeces harvested at days 7-15 were fragmented with various degrees of taper. By 21 days, most follicles were growing emergent fibres. Thickening of the epidermis, increase in sebaceous gland size and decrease in skin thickness occurred in some of the depilated sheep. Smaller doses of the compound (200 mg/kg body weight orally or 40 mg/kg body weight intravenously during 24 h) produced weakness in the wool. Fewer autophagic vacuoles were present in follicle bulbs 1 day after dosing and not all follicles regressed. The weakened region of the fleece contained a mixture of shed fibre ends and continuously growing fibres with thin regions proximal to poorly keratinized lengths of fibre. No change was observed in other components of the skin of the sheep with weakened wool. The follicular changes produced by this compound are similar in some respects to those produced by other depilatory compounds or that occur during natural cyclic hair growth.

Changes in the matrix proteins of wool and mouse hair following the administration of depilatory compounds.

After sheep were defleeced with mimosine, cyclophosphamide or N-[5-(4-aminophenoxy)pentyl]-phthalimide, the first samples of the new growth of wool differed markedly in composition from the pretreatment samples, there being substantial reductions in the high-tyrosine proteins and increases in the high-sulfur proteins. Similar results were obtained with mice dehaired with mimosine and with sheep treated with low levels of mimosine which resulted in weakened wool rather than depilation. The composition of later samples of the regrowth wool showed progressive changes with time. The high-tyrosine proteins tended to approach the pretreatment levels, although this may take up to 12 weeks to occur, whereas the levels of high-sulfur proteins, after the initial increase, often fell below normal. In experiments involving defleecing with cyclophosphamide, the level of the latter proteins was still below normal after 3 months. The possibility that this altered protein composition of keratin fibres is characteristic of that portion of fibre first produced by a new or regenerating follicle was investigated in sheep and mice. It was found that wool follicles regenerating after plucking, and newly operating follicles in young sheep and mice, also produced wool and hair with a reduced content of high-tyrosine proteins. It is suggested, therefore, that the apparent long-term inhibition of the high-tyrosine proteins may not be the direct consequence of the administration of the chemical but rather be characteristic of normal wool and hair regrowth. Infusion of an amino acid mixture lacking methionine into the abomasum of sheep caused the growth of weak wool but did not suppress the synthesis of the high-tyrosine proteins. This is in contrast with previous findings that treatments which weaken wool also suppress high-tyrosine proteins.

The effects of heat stress on the development of the foetal lamb

Environmental heat stress in tropical sheep suppressed lamb birth weight, but the animals which did not experience hyperthermia under natural environmental conditions gave birth to significantly heavicr (P<0.01) lambs than their less adapted counterparts. Climate chamber studies designed to simulate the rectal temperature patterns of tropical sheep demonstrated that, without nutritional intervention, heat stress during the last month of pregnancy significantly retarded foetal growth (birth weight 2.3 kg v. 3.4 kg; P< 0.01) and maturation of wool follicles (P< 0.01). By comparison, severe nutritional restrictions during the last 3 months of pregnancy also caused a significant reduction in lamb birth weight (3.2 kg v. 3.9 kg; P<O.01), but this difference was not so marked.

Efficiency of wool production and the mechanics of wool follicle production

Abstract The net efficiencies of conversion of feed to wool of Corriedale ewes and rams were determined during a 6-month feeding trial. Skin biopsy samples were taken at the end of the trial and sectioned transversely. The ratio of area of cross-section of fibre to area of cross-section of fibre plus inner root sheath is termed the production ratio. This ratio was determined from follicle cross-sections of a restricted segment of the follicle length and identified by the specific staining used. The relationship between net efficiency and production ratio was highly significant; the correlation coefficient was + 0.68 (P < 0.01).

Study of the wool follicle population in the ¾ Barki and ¾ Ossimi crosses with Merino

Study of the wool follicle population in the ¾ Barki and ¾ Ossimi crosses with Merino

Thyroxine and wool follicle activity

ABSTRACTSerum thyroxine levels were observed in 15 Soay ewes and seven rams for 1 year. From June to November the ewes had thyroxine concentrations 40% higher than the rams, and the level in both sexes increased from December to May, demonstrating a seasonal cycle in thyroxine level that could be associated with the annual wool growth cycle. To hasten the onset of wool follicle activity, nine Wiltshire sheep were given thyroxine implants in autumn when the follicles normally become inactive, but only a slight increase in follicle activity occurred. Eighteen Soay sheep were given thiouracil orally for 1 month in spring in an attempt to block a possible seasonal increase in thyroxine secretion that might be associated with the normal regrowth of wool, but no retardation of the spring regrowth was obtained.

The Cytology and Cytochemistry of the Wool Follicle

Publisher Summary The hair or wool follicle is surrounded by a basement membrane around which lies the connective-tissue sheath. In hair follicles, the basement membrane is slightly periodic acid/schiff-positive; it contains highly sulfated glycosaminoglycans. This chapter discusses the events occurring during the formation of the wool or hair fiber. The complexity of the follicle is now well established, particularly with respect to the interrelationships between dermal and epithelial components and the different cell lines during differentiation. Cytological and cytochemical studies, although still in their infancy, have already indicated that many more levels of complexity exist. Moreover, several processes for which more mechanistic explanations have been used are being shown to have a cytological basis. This trend may be expected to continue. It is becoming increasingly evident that the full significance of many studies will not be revealed unless they can be related to known and specified cell components. Cytological techniques will play an important part in this area.

Studies on the in vitro metabolism of [3H]cortisol and [3H]oestradiol by sheep skin and wool roots.

The in vitro metabolism of [3H]cortisol, [3H]cortisone and [3H]estradiol-17 beta by adult sheep skin and wool follicle tissue (wool roots) was examined. The main metabolic product of the incubation of [3H]cortisol with sheep skin was [3H]cortisone, and the conversion was reversible. Wool roots were unable to carry out detectable interconversion, nor did this tissue give rise to other significant metabolites. Sheep skin and wool roots both rapidly converted [3H]oestradiol-17 beta to [3H]oestrone and the conversion could be carried out by follicle and non-follicle skin structures. It is suggested that sheep skin contains both 11 beta- and 17 beta-hydroxysteroid dehydrogenases, but that wool follicles contain only the latter enzyme.

Effects of iodine supplementation of pregnant and lactating ewes on the growth and maturation of their offspring

Iodine supplementation (20 mg KI twice weekly) to ewes during the last month of pregnancy and the first 3 months of lactation increased productivity. Production traits enhanced by this treatment included the birth weight (3.9 vs 3.5 kg; P &lt; 0.01), survival (84% vs 64 %), growth rate (P &lt; 0.05), and mature SIP wool follicle ratio of lambs (1 4.9 � 1.2 vs 10.3 � 1.6). These differences were most apparent in animals receiving a low plane of nutrition (i.e. intake restricted to maintain ewe liveweight at approximately 32 kg). There were no marked changes in the body composition of lambs in the treated groups. The control animals in these studies exhibited only marginally depressed plasma thyroxine levels (4.7 � 0.4 �g %). Iodine supplementation can be used to partly circumvent the low productivity of tropical Merinos receiving a low plane of nutrition. More marked benefits could probably arise from treating animals which normally demonstrate low plasma thyroxine levels.

6—THE RELATIONSHIP BETWEEN THE RESISTANCE TO COMPRESSION OF WOOL BULKS AND FOLLICLE CURVATURE

It is shown that there are strong relationships between the resistance to compression, the felt-ball diameter, and the curvature of the parent wool follicles. The relationship of these properties with follicle curvature is stronger than that with staple-crimp frequency.

Effects of abomasal supplements of methionine on the wool follicles and skin of wheat-fed sheep.

In wheat-fed sheep, supplemented abomasally with 1.5-6.0 g methionine per day, poor formation and improper keratinization of the wool fibres were evident 4 days after the start of the methionine supplementation. This led to kinking of the fibres. Subsequently severe distortion of the fibres, accompanied by gross thickening of the outer root sheaths, occurred in the distal (upper) halves of most follicles. Within this thickened region partial degradation of the distorted fibres occurred before emergence from the skin surface, causing a marked reduction in the tensile strength of the wool. It is postulated that kinking of the fibres stimulated the accumulation of outer root sheath cells, which led to hyperactivity of the process that normally degrades the inner root sheath, so that the poorly keratinized fibres were also partly degraded. Thickening of the epidermis and cellular infiltration of the upper dermis sometimes occurred during the infusions of methionine, whereas there were negligible effects on the sebaceous and sweat glands. Disappearance of the excess accumulation of outer root sheath cells after cessation of the methionine supplementation occurred gradually following improvement in keratinization and elimination of kinking of the fibres.

Regeneration of wool follicles in autografts of sheep skin

Three experiments involving six sheep were carried out at three different times in the annual wool growth cycle. Forty-eight full-thickness fitted autografts were sampled 2 h, 6 h, 24 h, 48 h, 3, 4, 5, 7, 9, 11, 14, 21 and 28 days after grafting. The histopathology of the grafts is described. Individual variation in 'take' was probably related to the speed with which vascular integrity was reestablished between graft and bed. Delayed acceptance caused the death of pilosebaceous units. In a successful graft, wool follicle regeneration appears to occur in three main ways: (1) an inactive follicle regenerates from the dormant bulb at about seven days, (2) follicles that were active at the time of grafting have first to form a papilla stalk, and such follicles did not become active until 11 days, (3) sometimes one or more outgrowths appeared at higher levels suggesting follicle regeneration by branching. In addition there were a few instances of de novo downgrowth of follicle plugs from the epidermis. Wool growth on the graft therefore arises almost entirely from the reorganisation of preexisting follicles.

Morphological and Protein Synthesis Changes in Skin during Wool Follicle Regeneration after Plucking and Mimosine Administration

The regeneration of wool follicles after plucking of the wool fibres is compared with the regeneration which occurs after treatment of sheep with the DNA synthesis inhibitor mimosine. The process has been examined by labelling skin proteins in vitro with [3Hlleucine, separating them electrophoretically and measuring the radioactivity of the various proteins. The results show that keratin biosynthesis is not detectable during the early stages of follicle regeneration, and that the pattern of protein synthesis changes is similar whether regeneration follows plucking or mimosine treatment.