Abstract
In avians, yolk synthesis is regulated by incorporation of portomicrons from the diet, transport of lipoproteins from the liver, and release of lipids from adipose tissue; however, the extent to which lipolysis in adipose tissue contributes to yolk synthesis and egg production has yet to be elucidated. G0/G1 switch gene 2 (G0S2) is known to bind and inhibit adipose triglyceride lipase (ATGL), the rate-limiting enzyme in lipolysis. The objective of this study was to determine whether overexpression of the G0S2 gene in adipose tissue could successfully inhibit endogenous ATGL activity associated with egg laying. Two independent lines of transgenic quail overexpressing G0S2 had delayed onset of egg production and reduced number of eggs over a six-week period compared to non-transgenic quail. Although no differences in measured parameters were observed at the pre-laying stage (5 weeks of age), G0S2 transgenic quail had significantly larger interclavicular fat pad weights and adipocyte sizes and lower NEFA concentrations in the serum at early (1 week after laying first egg) and active laying (5 weeks after laying first egg) stages. Overexpression of G0S2 inhibited lipolysis during early and active laying, which drastically shifted the balance towards a net accumulation of triacylglycerols and increased adipose tissue mass. Thereby, egg production was negatively affected as less triacylglycerols were catabolized to produce lipids for the yolk.
Highlights
Adipose tissue is the main storage organ for triacylglycerols (TAG) and can undergo lipolysis to mobilize nonesterified fatty acids (NEFA) in response to stimuli, such as low food intake, heavy exercise, or yolk development in avians [1,2]
Overexpression of G0S2 inhibits TAG catabolism in adipose tissue, which is necessary for egg production efficiency
Comparison of adipose weights at active laying stages revealed that FG1 and FG3 transgenic quail had about 2.0-fold (p < 0.05) and about 1.6-fold (p < 0.05) more subcutaneous adipose tissue around the interclavicular region, respectively, than non-transgenic quail. These results demonstrate that G0S2 transgenic quail continually gain adipose mass as they age, while increases in adipose mass was attenuated by uninhibited lipolysis in non-transgenic quail
Summary
Adipose tissue is the main storage organ for triacylglycerols (TAG) and can undergo lipolysis to mobilize nonesterified fatty acids (NEFA) in response to stimuli, such as low food intake, heavy exercise, or yolk development in avians [1,2]. Lipolysis is catalyzed by adipose triglyceride lipase (ATGL), which cleaves the fatty acid at the sn-1 position from the glycerol backbone of TAG molecules and is the rate-limiting enzyme in this process [1]. G0S2 expression has been positively correlated with adipocyte differentiation and accumulation of lipids in several species, including mice, pigs, chickens, and humans [4,5,7,8,9,10]
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