Abstract
[Truncated] The reproductive system of small ruminants is affected by a variety of environmental factors, including socio-sexual signals, photoperiod and nutrition. Genotype controls the final outcome, but nutrition is particularly important in geographical regions where the quality and quantity of pasture are poor during the breeding season. In males, the problem of poor feed availability is exacerbated by a decrease in appetite and the end result is major losses in both body mass and testis mass, and therefore sperm production. It is not clear whether the reductions in testis mass and numbers of sperm are accompanied by changes in the quality of the sperm. Moreover, we know little of the physiological, cellular and molecular processes involved. In this thesis, these processes are explored.
Sertoli cells were the focus of attention because they provide nutritional and structural support for germ cells. We therefore expected the reduction in sperm production by under-fed sheep to be correlated with decreases in the number or function of the Sertoli cells. Another possibility is that, in underfed animals, there is an increase in apoptosis of the germ cells, thus explaining the reductions in sperm output and perhaps explaining any changes in the quality of the sperm that are eventually ejaculated.
It seems likely that the responses to changes in nutrition are mediated by small RNAs (including micro-RNAs and piwi-RNAs), mRNAs and alternative pre-mRNA splicing, within the Sertoli cells. These mRNA-based mechanisms are thought to be associated with apoptosis and spermatogenesis. In this thesis, therefore, I tested the general hypothesis that, in adult male sheep, under-nutrition will reduce sperm quality, due to germ cell apoptosis, that these responses will be explained by reductions in Sertoli cell function, and that such effects are mediated by changes in the expression of small RNAs and mRNAs, and by alternative pre-mRNA splicing.
Sertoli cells were the focus of attention because they provide nutritional and structural support for germ cells. We therefore expected the reduction in sperm production by under-fed sheep to be correlated with decreases in the number or function of the Sertoli cells. Another possibility is that, in underfed animals, there is an increase in apoptosis of the germ cells, thus explaining the reductions in sperm output and perhaps explaining any changes in the quality of the sperm that are eventually ejaculated.
It seems likely that the responses to changes in nutrition are mediated by small RNAs (including micro-RNAs and piwi-RNAs), mRNAs and alternative pre-mRNA splicing, within the Sertoli cells. These mRNA-based mechanisms are thought to be associated with apoptosis and spermatogenesis. In this thesis, therefore, I tested the general hypothesis that, in adult male sheep, under-nutrition will reduce sperm quality, due to germ cell apoptosis, that these responses will be explained by reductions in Sertoli cell function, and that such effects are mediated by changes in the expression of small RNAs and mRNAs, and by alternative pre-mRNA splicing.
| Original language | English |
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| Qualification | Doctor of Philosophy |
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| Publication status | Unpublished - Mar 2015 |