Molecular mechanisms of livestock adaptation

Abstract

Food producing animals in the developing world are exposed to a myriad of inevitable abiotic stressors that are fundamentally different from those animals in intensive production systems of the developed countries. The gamut of stressors that impairs the productivity includes, but not limited to, vagaries of the monsoon, scarce grazing resources, exposure to industrial contaminants. Understanding the cellular and molecular mechanisms behind the short and long-term adaptation required by tropical food animals is necessary to evaluate mitigatory measures aimed at improving productivity. Cellular proteins are affected by stressors resulting in increased population of proteins with non-native conformations due to improper folding. Heat shock proteins (HSPs) are a family of approximately a dozen proteins that are evolutionarily conserved. Many HSPs function as molecular chaperones with critical roles as regulator of protein folding and structural function. Studies done on the unicellular yeast depict the temporal variation in the gene expression profile when various stressors are used as treatment and thereby many common environment-specific response genes (CER) were identified constituting the 18-38% of the genome. CER genes constitute induced expression of classical heat shock genes, osmotic stress protectants such as polyols and trehalose, protein degradation enzyme, genes involved in increased membrane permeability and ion transport, as well as compensatory expression of isozymes or allozymes, and free radical scavengers such as superoxide dismutase, glutathione system, and cytochrome P450. Many of these genes are hypothesized to have common stress response elements (STRE) consensus sequences in their promoter region and are activated by common transcription factors such as Msn2 and Msn4 bringing coordinate regulation and global expression of genes under stress conditions. CER also constitute genes which are repressor genes associated with translation and protein synthesis to shunt energy in favor of large-scale ATP requirement for the chaperone function. Cells in response to stress also bring about changes in ratio of saturated lipids to unsaturated lipids in their membrane to alter flexibility as well as transport across membrane, which correspond to homoviscous adaptation. Knowledge on the molecular mechanism of environmental stress is still in its infancy and may eventually explain the biodiversity of the animal genetic resources.