Deciphering Mechanisms of Adipocyte Differentiation in Abdominal Fat of Broilers

The excessive deposition of abdominal fat tissue (AFT)
in broilers
has emerged as a major concern in the poultry industry. Despite some
progress in recent years, the molecular mechanisms underlying AFT
development remain ambiguous. The current study combined RNA-seq with
transposase-accessible chromatin sequencing (ATAC-seq) to map the
dynamic profiling of chromatin accessibility and transcriptional reprogramming
in AFT adipocyte differentiation in broilers at day 3 (D3) and D14.
Our results found that the levels of CDK1 and PCNA were down-regulated
at D14, D28, and D42 compared to D3, while the levels of C/EBPα
and FABP4 were up-regulated at D14 and D42 compared to D3. Meanwhile,
PPARγ was significantly up-regulated at D28 and D42. RNA-seq
of AFT identified 1705 up-regulated and 1112 down-regulated differential
expression genes (DEGs) between D3 and D14. Pathways based on up-regulated
DEGs mainly enriched some pathways related to adipocyte differentiation,
while down-regulated DEGs pointed to DNA replication, cell cycle,
and gap junction. Gene set enrichment analysis (GSEA) revealed that
DNA replication and the cell cycle were down-regulated at D14, while
the insulin signaling pathway was up-regulated. In the OA-induced
immortalized chicken preadipocyte (ICP2) model, protein dynamic changes
were consistent with AFT from D3 to D14. Same pathways were enriched
in ICP2. In addition, based on overlapped DEGs from AFT and ICP2,
enriched pathways related to adipocyte differentiation or proliferation
mentioned above were all involved. A total of 1600 gain and 16727
loss differential peaks (DPs) were identified in ICP2 by ATAC-seq.
Predicted genes from DPs at the promoter regions were enriched in
glycerophospholipid metabolism, TGF-β signaling, FoxO signaling,
and ubiquitin-mediated proteolysis. DNA motifs predicted 159 transcription
factors (TFs) based on gain and loss peaks from the promoter regions,
where 1 and 10 TFs were overlapped with up or down TFs from DEGs.
Overall, this study presents a framework for the comprehension of
the epigenetic regulatory mechanisms of adipocyte differentiation
and identifies candidate genes and potential TFs involved in AFT adipocyte
differentiation in broilers.