Comparative transcriptomics in adipose tissue of wild African elephants (Loxodonta africana)

Adipose tissue (AT) was reported to influence reproductive functions through regulation of the
hypothalamus-pituitary-gonadal axis, and infertility in captive African elephants has been correlated to
obesity. Next generation sequencing was utilised to generate transcriptomes of peri-renal AT from culled
wild adults. RNA was extracted using Qiagen RNeasy Mini Kit, followed by quality evaluation with
Agilent 2100 Bioanalyzer. RNA transcription was quantified using RNA-Seq (Illumina HiSeq). A total of
63,041,074 (F1), 83,963,786 (F2), and 56,783,624 (M1) paired reads were obtained. Differential gene
expressions (DGE) were analysed using edgeR (www.bioconductor.org/packages/release/bioc/html/edgeR.html).
Statistically significant DGE related to adipogenesis, lipogenesis and energy homeostasis were validated
using qRT-PCR (ELOVL5, FASN, LEP, NR2F2, PPARγ, RXRα, SCD). DGE were also evaluated between
sexes and ages (adult-juveniles) through qRT-PCR. Hierarchical clustering of gene expressions in adults
revealed that genes expressed by the non-pregnant female (F2) was closer to those of the young growing
bull, compared to the lactating female (F1). Furthermore, pregnant or lactating females showed a higher
energy expenditure and lower lipogenesis level compared to young growing males. This may be due to
high energy requirement for maintenance of pregnancy and lactation. However, energy homeostasis of the
juveniles appeared to be more comparable between sexes, as mRNA expression failed to show a clear
pattern of differential expression. This is indicative of similar growth rate in these juveniles. Results from
this study provides baseline data on the dynamics of AT in wild African elephants. Ultimately, knowledge
generated will be used to improve management and fertility of captive African elephants.