Differential gene expression in three regions of the hypothalamus of steers with different protein and energy intake

Abstract

<p>The hypothalamus controls feed intake in response to various physical, nutrient and hormone signals that are integrated in the arcuate nucleus (ARC). The ARC contains both orexigenic and anorexigenic neurons which communicate with the theoretical hunger (lateral hypothalamic area; LHA) and satiety (ventromedial hypothalamus; VMH) centres to control feed intake. Cattle in northern Australia have a 35 to 60% reduction in voluntary feed intake during the annual dry season (April to November) due to a very low crude protein [CP; 25 to 40g/kg dry matter (DM)] content of available pasture. This reduction in intake is likely regulated by metabolic mechanisms. It was hypothesised that gene pathways within the ARC, LHA and VMH of steers would be differentially expressed in response to the CP content of the diet and metabolisable energy (ME) intake. </p> <p>Bos indicus steers (n=15; 194 ± 10kg liveweight, mean ± S.D.) were fed a high CP-high dry matter digestibility (DMD) diet ad libitum to provide unrestricted ME intake (HCP-HDMD-U), a low CP-low DMD diet ad libitum to provide unrestricted ME intake (LCP-LDMD-U) or a HCP-HDMD diet restricted to an equivalent ME intake of the LCP-LDMD diet (HCP-HDMD-R) for 98 days. Intake of steers was significantly different between all treatments (P<0.001; 28.5, 17.0 and 9.7 gDM/kg LW.day for HCP-HDMD-U, LCP-LDMD-U and HCP-HDMD-R respectively). ME intake was significantly higher (P<0.001) for steers fed the HCP-HDMD-U (0.24 MJ/kg LW.day) but was similar for steers fed the LCP-HDMD-U and HCP-HDMD-R (0.07 MJ/kg LW.day) diets.</p> <p>Steers were euthanised and RNA was extracted from the ARC, VMH and LHA of these steers followed by preparation of cDNA libraries and subsequent sequencing on Illumina NovaSeq 6000 (producing 100 bp single end reads). FASTQ files were trimmed using ‘trimmomatic’ and mapped against Bos taurus reference genome release 9 using HISAT2 (average 56% reads mapped within genes). Within the ARC, 179 and 142 genes were differentially expressed between the HCP-HDMD-U and the LCP-LDMD-U and HCP-HDMD-R treatments, respectively. The VMH and LAT had minimal differentially expressed genes in response to dietary treatments. These data indicate the importance of the ARC in integrating signals in steers with different levels of ME intake.</p> <p>Sequencing performed by Australian Genome Research Facility, Australia. Bioinformatics performed by QFAB@QCIF, Institute of Molecular Biology, The University of Queensland. We gratefully acknowledge Meat and Livestock Australia for funding this work. D Innes was in receipt of scholarships from The University of Queensland and Meat and Livestock Australia. </p>