Developmental regulation of elongase enzyme expression in broiler chick adipose tissue
Piacquadio, K., R. Mihelic, and B. H. Voy.  2019.  Poultry Science, vol. 98, E-suppl.1.

Abstract:
Objective. Enriching adipose tissue of broiler chicks with docosahexaenoic acid (DHA; 22:6 n-3) could have a dual benefit for the broiler industry by both attenuating accretion of excess fat (Beckford et al., 2017) and by increasing nutritional value of the market product for consumers. The objective of this study was to characterize the patterns of very long chain fatty acid elongase (ELOVL) gene expression during adipose development and to assess the relative roles of ELOVL2 and ELOVL7 in endogenous DHA synthesis in broilers. Experimental design. Adipose tissue was collected from broiler chicks (n=5-7/age) at embryonic days 13, 15 and 17 (subcutaneous (SQ)) and at 7 and 14 d post-hatch (SQ, abdominal (AB) and neck) and snap-frozen. Materials and methods. Total RNA was isolated from each depot, quantified, quality-checked, and used to synthesize cDNA. A targeted RNAseq approach was used to profile expression of a panel of adipose- and lipid-related genes, including six elongase genes (ELOVLS 2, 3, 4, 5, 6, 7). Primers for the panel were designed using Primer3Plus (primer3plus.com) to span exon boundaries, using the RefSeq for each gene as template. Raw sequencing reads were aligned to the chicken genome (Galgal 5.0) and reads were counted using CLC Genomics Workbench (Qiagenbioinformatics.com). Statistical analysis. RNAseq data were analyzed for effects of age and depot in SAS (V 9.4) using ANOVA and least squares means for contrasts (alpha=0.05). Results. Expression levels of five of the six ELOVL genes (ELOVL2, 3, 4, 5 & 7) varied significantly with age in SQ adipose (p<0.05). Expression of ELOVL2 was relatively low in embryonic adipose, increased sharply at day 7, and returned to lower levels by 14d, with 7d levels significantly higher than at all other ages (p<0.05). In contrast, ELOVL7 was expressed at relatively high levels in the embryo, with significantly lower levels at 7d (~ 2.5-fold vs, E17; p<0.05). Unlike each of the other ELOVL genes, expression of ELOVL7 significantly increased from day 7 to 14 (~5-fold, p<0.05), and it was the most abundantly expressed elongase in SQ, AB and neck fat after hatch. In contrast, expression of ELOVL2 significantly decreased from 7 to 14 d in SQ and AB fat (p<0.05). Conclusions. Based on gene expression, these results suggest that the novel elongase ELOVL7, which has not been characterized in chickens, may play the predominant role in synthesizing DHA in chick adipose tissue, both during embryonic development and after hatch. Further investigation of this enzyme and its regulation may reveal ways to enhance endogenous synthesis of DHA in broilers.