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P I Hynd

Publications and source records attributed to P I Hynd.

18 recordsLinked to original sources
PubMed2000

Expression of the homeobox gene, Barx2, in wool follicle development.

We have cloned ovine Barx2, a member of the Bar class of homeobox genes, and present the first description of Barx2 expression in wool follicle development. Barx2 is uniformly expressed in the embryonic ectoderm but is transiently downregulated during the initiation of follicle morphogenesis. Subsequently, Barx2 is expressed throughout the epithelial component of the developing follicle except for a small group of cells at the leading edge of the follicle placode. These Barx2-negative cells are destined to form the follicle bulb and are the progenitors of the inner root sheath and hair shaft. In adult follicles, Barx2 is expressed throughout the outer root sheath but not in the inner root sheath or hair shaft, or in dermal cells associated with the follicle. The pattern of Barx2 expression in follicle morphogenesis is similar to that of the cell adhesion molecule E-cadherin, a similarity that echoes Barx2 coexpression with the L1 cell adhesion molecule in other tissues during mouse embryogenesis. Barx2 is also expressed in tongue and esophagus, two other keratinizing tissues, and we speculate that Barx2 may have a general function in controlling adhesive processes in keratinizing epithelia.

Animals↗
PubMed1999

Dynamic expression of ornithine decarboxylase in hair growth.

Ornithine decarboxylase (ODC) is the key enzyme in the synthesis of polyamines, small cationic molecules believed to have a role in many cellular processes such as cell migration, proliferation and differentiation. We show that ODC expression is associated with cell proliferation and commitment in hair follicle development and hair growth. In embryonic epidermis, ODC is expressed in ectodermal cells at sites where follicles develop, and persists in cells at the leading edge of the follicle placode. ODC is abundantly expressed in proliferating bulb cells of anagen follicles, except for a pocket of cells at the base of the bulb. Entry of the follicle into catagen is accompanied by a down-regulation of ODC expression, which is not resumed until a new follicle is initiated. In vibrissae, ODC expression is more complex. ODC is expressed not only in the bulb but also in the hair shaft, presenting a striking biphasic pattern. Additionally, ODC is expressed in a group of outer root sheath cells in the vicinity of the follicle bulge, the putative site of hair follicle stem cells.

Animals↗
PubMed1999

Wool follicle matrix cells: culture conditions and keratin expression in vitro.

Wool follicle matrix cell cultures were initiated as explants from Tukidale (carpet wool) sheep primary follicle bulbs after removal of the outer root sheath. Successful explantation required coculture on collagen with intact dermal papillae. Cells had a typical epidermal morphology (pavements of flattened. polyhedral cells). Extracellular matrix from dermal papillae, conditioned media, separation of dermal papilla from bulb matrices by tissue culture inserts and feeder layers were unable to support matrix cell explantation. Cultures could be maintained for up to 14 passages during which time the cells became larger with an increased cytoplasmic/nuclear ratio and irregular outline. Proliferation of matrix cells was greater on laminin than with either collagen type I or type IV. Proliferation was considerably reduced under serum-free conditions. This was most apparent at low calcium (0.09 mmol/L). By Northern hybridization matrix cells were found to express keratin K18 at all stages of culture. Keratin K 1.15 expression was evident by the tenth passage. The wool-specific keratin K2.10 was not detected. The data demonstrate that successful wool matrix cell culture is achievable. Keratin gene expression occurs in these cells and varies with the stage of culture.

Animals↗
PubMed1997

Serum-free culture of wool follicles: effects of nutrients, growth factors and hormones.

A serum-free culture system allowed the continued growth of fibre from follicles for 8-10 days. Fibre growth was responsive to changes in the level of calcium, glucose and amino acids in the culture medium, and was stimulated by the inclusion of insulin (10 micrograms/mL) in the medium. Culture of follicles in the presence of conditioned media from dermal papilla cells or of mitomycin-treated dermal papilla cells had no effect on fibre growth. Neither thyroid hormones nor hydrocortisone altered fibre growth. The progressive decline in fibre growth during follicle culture was accompanied by morphological changes in the follicle bulb. Oxidative damage did not appear to be the cause of these changes as there was no increase in fibre growth rate or longevity when antioxidants were used. This model provides a useful system to study the direct effects of various hormonal, nutritional and growth factors of fibre growth and follicle metabolism.

Animals↗
PubMed1996

Inhibition of polyamine synthesis alters hair follicle function and fiber composition.

The activities of ornithine decarboxylase and S-adenosylmethionine decarboxylase, two of the enzymes involved in the synthesis of the polyamines, were found to be high in follicle-rich homogenates of sheep skin, and to be responsive to the nutrition of the animal. Systemic provision of the inhibitor of ornithine decarboxylase, alpha difluoromethylornithine, markedly altered the length, diameter, and composition of the fiber, the last being accompanied by an increase in the proportion of the fiber occupied by paracortical cells and an increase in the level of mRNA encoding a cysteine-rich family of keratin proteins. The growth of wool follicles cultured in media containing alpha-difluoromethylornithine was not inhibited, even at high concentrations. In contrast, low concentrations of methylglyoxal (bis)guanylhydrazone, the inhibitor of S-adenosylmethionine decarboxylase, completely inhibited fiber growth in culture follicles. Addition of spermidine to the media overcame this inhibition but spermine had no effect. Further evidence that spermine is not required for normal follicle function was provided by incubating follicles with the specific inhibitor of spermine synthase, n-butyl-1,3-diaminopropane. This inhibitor, even at high concentrations, had no effect on fiber growth in vitro. Spermidine partially overcame the growth depression that occurred in follicles cultured in methionine-deficient media, suggesting that part of the requirement for methionine is for spermidine synthesis in the follicle. These investigations provide strong evidence that the polyamines in general , and spermidine in particular, play a major role in hair growth.

Adenosylmethionine Decarboxylase↗
PubMed1994

The effect of zinc deficiency on wool growth and skin and wool follicle histology of male Merino lambs.

The aims of this work were to quantify the requirements of Zn for wool growth in growing male Merino lambs, and to describe the histological lesions of Zn deficiency in skin and wool follicles. Four groups of male Merino lambs (n 4) weighing 22 kg were fed ad lib. for 96 d on diets that contained 4 (basal diet), 10, 17 or 27 mg Zn/kg. Sheep in a fifth group were fed on the diet containing 27 mg Zn/kg, but were pair-fed to sheep on the 4 mg Zn/kg diet. Zn was added to the basal diet as ZnSO4 to give the respective treatment concentrations. Sheep fed on the diet containing 4 mg Zn/kg showed clinical signs of Zn deficiency and lower feed intakes and wool growth than sheep in the other groups. Their wool fibres were improperly keratinized and the wool follicles contained a higher proportion of apoptotic bodies than other groups. There was no evidence of parakeratosis and the rate of bulb-cell production was not affected. Sheep from other groups showed no clinical signs of Zn deficiency, and mean feed intakes and growth rates did not differ significantly between sheep fed on diets containing 10, 17 or 27 mg Zn/kg. However, wool growth was reduced in sheep fed on the diet containing 10 mg Zn/kg compared with those fed on diets containing 17 or 27 mg/kg. The mean concentration of Zn in the plasma at which wool growth was 90% of maximum was 0.5 mg/l. The equivalent value for the diet was 12 mg/kg, with 95% confidence intervals of 8 to 16 mg/kg. The results suggest that Zn deficiency reduces wool growth through a specific mechanism, perhaps involving impaired protein synthesis.

Animals↗
PubMed1994

Dietary cysteine regulates the levels of mRNAs encoding a family of cysteine-rich proteins of wool.

The abomasal or intravenous infusion of sulphur-containing amino acids such as cysteine or methionine into sheep on low-quality diets increases the sulphur content of the wool by increasing the synthesis of proteins containing a cysteine content of approximately 30 mol %. To investigate the molecular and cellular basis of this nutritional effect, quantitative analyses of wool keratin mRNA and protein levels, and follicle cortical cell type, were undertaken in sheep intravenously infused with cysteine. Northern blot analyses revealed that the mRNA levels of one gene family encoding cysteine-rich keratin-associated proteins (KAP4 family) expressed in the wool follicle cortex, increased approximately 5-6 times. Furthermore, the response was rapid as the mRNA levels increased approximately 3.5 times after 1 d of the cysteine infusion and, by 1 d post-infusion, they had fallen, approaching their basal level. No changes in the mRNA levels encoding the intermediate filament or the other keratin-associated protein families of lower cysteine content were observed. Concomitantly, two-dimensional polyacrylamide gel electrophoresis analysis of wool proteins showed a striking increase in the abundance of a group of cysteine-rich keratin-associated proteins in the wool by the end of the infusion period, returning to basal levels by 3 weeks later. At the cellular level, KAP4 expression was localized to the follicle paracortical cells, and the proportion of paracortical cells and the extent of KAP4 expression paralleled the changes in the cysteine infusion status of the sheep.

Amino Acid Sequence↗
PubMed1993

Adrenalectomy of sheep: a novel technique.

A rapid technique for adrenalectomy of sheep was developed. Bilateral adrenalectomy was performed in a single stage operation by inducing ischaemia with latex rings of the type used commonly for the castration of lambs and calves. The success of the technique was demonstrated by failure of exogenous ACTH to increase circulating cortisol concentrations. Adrenal steroid replacement was used to maintain the sheep during the post-operative period (cortisol 0.25 mg.kg-1, deoxycorticosterone acetate 0.05 mg.kg-1). Adrenalectomised sheep were maintained for up to 20 days without glucocorticoid, provided a lowered dose of mineralocorticoid was administered (0.04 mg.kg-1 x day-1). Adrenalectomised sheep had significantly (P < 0.007) lower packed cell volume (23.75%) than normal sheep (31.24%), across a broad range of cortisol concentrations (0 to 734 ng/mL), indicating that plasma cortisol may not reflect true blood concentrations when drawing comparisons between adrenalectomised and normal sheep.

Adrenalectomy↗
PubMed1990

The use of high-energy electrons to depilate the breech of sheep.

The use of high-energy electrons for permanently depilating areas of sheep skin was evaluated. The most effective dose of electrons for depilation was 17.5Gy. Histological changes in skin treated at this dose were examined in one sheep over 18 months and in 5 sheep over 89 d. Effects of treatment on bodyweight gains and fleece growth were examined by comparing the productivity of a further 5 sheep treated on the breech with high-energy electrons, with that of conventionally mulesed sheep (n = 5) and untreated controls (n = 5). Electron treatment resulted in immediate death of cells in the germinative region of the wool follicle bulbs. Within 10 d of treatment the treated areas were completely depilated. Wool follicle shafts in the treated areas regressed rapidly towards the epidermis and remained quiescent for the whole trial (89 d). A sheep treated 18 months previously has remained largely depilated, although a few sparse fibres are present. Epidermal acanthosis and orthokeratosis were present at 26 d after treatment. The thickened stratum corneum then sloughed off, but the epidermis remained acanthotic for the entire trial. Sweat glands and most sebaceous glands were destroyed by the treatment and were replaced by fibrotic, avascular tissue in the dermis. In all other respects the external appearance of the electron-treated breech was similar to that of mulesed sheep. There were no apparent side-effects of treatment. Neither mulesing nor electron treatment altered weight gains or fleece growth rates.

Animals↗
PubMed1988

Increases in ovulation rate in lupin-fed ewes are initiated by increases in protein digested post-ruminally.

Parous Merino ewes were maintained outdoors in feedlots during the beginning of the spontaneous breeding season and fed a maintenance ration of wheaten hay. For 14 days, ewes in each of 4 groups (N = 40/group) were given supplements of lupin grain or formaldehyde-treated casein and/or wheat starch. These were calculated to supply equivalent amounts of protein post-ruminally and/or digestible energy. Supplementation with lupin grain significantly increased ovulation rate by 37% by increasing the proportion of ewes with two ovulations. Similar increases in ovulation rate were achieved by increasing the supply of digestible protein post-ruminally in the casein and casein + starch-supplement groups. Increasing the intake of digestible energy separately in the starch-supplement group did not increase ovulation rate. It is concluded that increases in ovulation rate in ewes fed a lupin supplement are the result of significant increases in the amount of protein digested post-ruminally.

Animals↗
PubMed1988

Anatomy of the blood supply to the flank of the sheep.

The anatomy of the a circumflexa ilium profunda supplying the flank of the sheep was investigated in 25 sheep. Two constant branches were identified by dissection and angiography, and the cutaneous areas they supply identified. The arterial system was put to two separate experimental uses successfully.

Angiography↗
PubMed1986

Mitotic activity in cells of the wool follicle bulb.

Mitotic activity in the cells of the germinative region of wool follicle bulbs was quantified by using small (0.1-0.5 ml) intradermal doses of colchicine and selective staining of the metaphase-blocked nuclei using either crystal violet, iodine and eosin or haematoxylin and eosin. The number of metaphase nuclei present 3 h after colchicine administration increased with colchicine dose from 0 to 1 microgram and thereafter remained relatively constant up to 200 micrograms colchicine. The accumulation of metaphase nuclei was linear for up to 6 h after intradermal colchicine. The metaphase-blocking effect of intradermal colchicine was confined to a radius of less than 5 cm from the injection site, allowing a number of estimates of mitotic rates to be made over a small area of skin. Such estimates revealed little variation in mitotic activity over the midside region of the sheep, although there were substantial differences in follicle activity at different sites over the body. The technique is simple, allows serial or concurrent estimates of mitotic activity to be made in the same animal, and eliminates problems associated with intravenous colchicine administration. It was used to derive the relationship between follicle activity and fibre production after nutritional changes, and to define the time course of mitotic events after administration of the antimitotic defleecing agent cyclophosphamide.

Animal Nutritional Physiological Phenomena↗