Triacylglyceride physiology in the short-finned eel,Anguilla australis—changes throughout early oogenesis

Abstract

During certain stages in an animal's life cycle, energy requirements may exceed energy intake from the diet. The spawning migration of temperate eels is a textbook example of negative energy balance, forcing these fish to rely on stored fats (triacylglycerides) to provide their muscles with energy for swimming and their growing oocytes with the nutrients needed to develop and support healthy offspring. We predicted broad implications of this great need for endogenous triacylglycerides in terms of their packaging, transport, and ovarian uptake. To test this, serum lipid concentrations and transcript abundances of intestinal and hepatic triacylglyceride packagers and ovarian triacylglyceride modifiers and receivers were investigated throughout previtellogenesis (feeding phase) and into early vitellogenesis (fasting phase) in short-finned eels. A switch from exogenous to endogenous triacylglyceride packaging was seen as the liver upregulated transcript levels of apolipoprotein B and microsomal triacylglyceride transport protein and downregulated those of apolipoprotein E and lipoprotein lipase. In the intestine, the reverse response was observed. Furthermore, ovarian transcript abundances of triacylglyceride modifiers and receivers increased (apolipoprotein E, lipoprotein lipase, and vitellogenin receptor), indicative of increased triacylglyceride uptake during previtellogenesis. We propose that increased hepatic apolipoprotein B production is a conserved vertebrate response to prolonged periods of negative energy balance.

Maternal investment in fish oocytes and eggs: The molecular cargo and its contributions to fertility and early development

“…Recent findings indicate that numbers of ldlr transcripts increase in the 'previtellogenic' ovary (containing Stage I and II follicles) as the oocytes progress from primary growth into ESG (early "lipid droplet stage") and decrease with onset of vitellogenesis, whereas vtgr/vldlr transcript numbers also increase at onset of ESG, remaining elevated in early vitellogenesis (Damsteegt et al, 2015b). However, no information is available on the cellular distribution of these transcripts or their product receptor proteins.…”

Storage by lyophilization – Resulting RNA quality is tissue dependent

“…Two target genes were chosen, one known to be highly expressed in the three tissues of interest (mitochondrial ribosomal protein L36: l36) and one with a lower level of expression (low density lipoprotein receptor: ldlr). Primer sequences have been published previously (l36 [9]; ldlr [10]). A total of 40 cycles of amplification (95 C for 5 s, 62 C for 10 s, 72 C for 5 s) were run before a melting curve analysis was performed to evaluate sudden changes in fluorescence and ensure primer specificity.…”

Triacylglyceride physiology in the short-finned eel, Anguilla australis—the effects of androgen

“…Total serum cholesterol and triacylglycerol concentrations were measured by enzymatic assay using CHOD-PAP and GPO-PAP reagents (Roche), as described by Damsteegt et al (6).…”

“…Primer sequences are listed in either Damsteegt et al (6) or Setiawan et al (39). All quantitative PCRs were carried out exactly as explained in Damsteegt et al (8) and in keeping with the guidelines for the minimum information for publication of quantitative real-time PCR experiments [MIQE (2)].…”

“…An involvement in other aspects of lipid physiology might be anticipated on the basis of these findings. Indeed, increases in mRNA levels of hepatic lipidpackaging genes, as well as genes involved in ovarian lipid uptake, correlate closely with the natural increase in 11-KT in wild-caught A. australis (6). However, with the exception of ovarian lipoprotein lipase (lpl) expression, which increases both with androgen treatment and as oogenesis progresses (9), the underlying genetic mechanisms through which these androgens exert their effects are yet to be determined.…”