DIETARY CYSTEINE REGULATES THE LEVELS OF MESSENGER-RNAS 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 increa ses the sulphur content of the wool by increasing the synthesis of pro teins containing a cysteine content of similar to 30 mol %. To investi gate the molecular and cellular basis of this nutritional effect, quan titative analyses of wool keratin mRNA and protein levels, and follicl e cortical cell type, were undertaken in sheep intravenously infused w ith cysteine. Northern blot analyses revealed that the mRNA levels of one gene family encoding cysteine-rich keratin-associated proteins (KA P4 family) expressed in the wool follicle cortex, increased similar to 5-6 times. Furthermore, the response was rapid as the mRNA levels inc reased similar to 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 we re observed. Concomitantly, two-dimensional polyacrylamide gel electro phoresis analysis of wool proteins showed a striking increase in the a bundance of a group of cysteine-rich keratin-associated proteins in th e wool by the end of the infusion period, returning to basal levels by 3 weeks later. At the cellular level, KAP4 expression was localized t o 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.