Cell Proliferation and Cortical Cell Production in Relation to Wool Growth

Abstract

Aust. J. Bioi. Sci., 1979, 32, 317-27 The relationship of wool growth to cell proliferation in the follicle bulb and to the subsequent migration and growth of the fibre cortical cells was investigated in 10 Peppin Merino sheep. These sheep had been maintained on a low, medium or high level of nutrient intake to ensure a wide range in wool growth. The number and mitotic activity of the germinal cells in the follicle bulb were determined after administration of colchicine. Cortical cell size was measured following isolation of the fibre cells by acid-treatment of wool.The average fibre production of the follicle varied from 4·1 x 10 4 to 13·2 X 10 4 IIm3/day in these sheep. There were also substantial differences between sheep in the mitotic activity of the germinal cells in the bulb, the rate of cell proliferation being highly correlated with the average daily fibre production of the follicle (r = + O' 88, n = 10). However, the size of the germinal cell population differed from sheep to sheep and was not closely related to the level of fibre production (r = + 0'48, n = 10). The average turnover time of these cells was inversely related to fibre production and varied from 41·6 to 19·4 h (r = -0'82, n = 10).Multiple regression analysis of the data showed that the average daily fibre production of the follicle was largely determined by the number of germinal cells present in the bulb and their rate of proliferation (R = + O· 95, n = 10). Variations in cell turnover time and in cortical cell size were not significant in influencing the rate of fibre production. In these sheep, the average cortical cell varied in size from 658 to 1279 11m3 and the positive correlation (r = + 0·83, n = 10) found between cell size and fibre production is considered to merely reflect an allometric relationship. . The proportion of germinal cells contributing to the fibre cortex was found to be small and variable, ranging from 9·4 to 17· 8 %. Furthermore, this proportion was not related to the nutritional level of these sheep, and it· is thought that the variability in the distribution of cells to the fibre may be attributed to genetic differences between sheep.

Mitotic Activity in Cells of the Wool Follicle Bulb

“…cell division) phase and not the keratinization (i.e. protein synthesis) phase of fibre formation and this has since been corroborated by the work of Wilson and Short (1979). They found that while cortical cell size (presumed to be an indicator of the rate of protein synthesis) was correlated with the rate of fibre production, variations in cell size did not significantly influence the rate of fibre output.…”

“…5), as would be anticipated on a priori grounds and indeed as was demonstrated in the pioneering work of Schinckel (1962) and later by Wilson and Short (1979). Schinckel (1961Schinckel ( , 1962 concluded that the rate-limiting step in wool production per follicleis the proliferative (i.e.…”

“…Regardless of the cause of the rhythm it is clear that it must be taken into account when absolute estimates of the mean daily mitotic rate are required and, when comparing treatments, care should be taken to restrict comparisons to the same time of the day. Failure to account for the rhythm may have led Wilson and Short (1979) to underestimate the mean rate of cell division and hence overestimate the proportion of dividing cells entering the fibre cortex (these authors took their biopsy samples at 0945 h when mitotic rate in the present experiment was lowest).…”

“…Of 10 sheep treated by Wilson and Short (1979), seven died, while several sheep in the study of Schinckel (1961) suffered diarrhoea and subsequently died following colchicine treatment. The dose required for full metaphase arrest at the follicle level is clearly close to the toxic dose.…”

Migration and Keratinization of Cells in Wool Follicles

“…Various studies have been made of the effects of plane of nutrition on cell proliferation in wool follicles (Schinckel 1962;Fraser 1965;Short et al 1965;Wilson and Short 1979), but there is relatively little information on the effects of plane of nutrition on cell migration (Chapman 1971) or keratinization in wool fibres (Marston 1946).…”