Transcriptomic analysis of different tissue layers in antler growth Center in Sika Deer (Cervus nippon)

Hengxing Ba,Tung On Yau,Chunyi Li,Datao Wang,Yudong Shang

doi:10.1186/s12864-019-5560-1

Abstract

BackgroundWith the unprecedented rapid growth rate (up to 2.75 cm/day), velvet antler is an invaluable model for the identification of potent growth factors and signaling networks for extremely fast growing tissues, mainly cartilage. Antler growth center (AGC) locates in its tip and consists of five tissue layers: reserve mesenchyme (RM), precartilage (PC), transition zone (TZ), cartilage (CA) and mineralized cartilage (MC). The aim of this study was to investigate the transcription dynamics in the AGC using RNA-seq technology.ResultsFive tissue layers in the AGC were collected from three 3-year-old male sika deer using our previously reported sampling method (morphologically distinguishable). After sequencing (15 samples; triplicates/tissue layer), we assembled a reference transcriptome de novo and used RNA-seq to measure gene expression profiles across these five layers. Nine differentially expressed genes (DEGs) were selected from our data and subsequently verified using qRT-PCR. The results showed a high consistency with the RNA-seq results (R2 = 0.80). Nine modules were constructed based on co-expression network analysis, and these modules contained 370 hub genes. These genes were found to be mainly involved in mesenchymal progenitor cell proliferation, chondrogenesis, osteogenesis and angiogenesis. Combination of our own results with the previously published reports, we found that Wnt signaling likely plays a key role not only in stimulating the antler stem cells or their immediate progeny, but also in promoting chondrogenesis and osteogenesis during antler development.ConclusionWe have successfully assembled a reference transcriptome, generated gene expression profiling across the five tissue layers in the AGC, and identified nine co-expressed modules that contain 370 hub genes and genes predorminantly expressed in and highly relevant to each tissue layer. We believe our findings have laid the foundation for the identification of novel genes for rapid proliferation and chondrogenic differentiation of antler cells.

Highlights

With the unprecedented rapid growth rate, velvet antler is an invaluable model for the identification of potent growth factors and signaling networks for extremely fast growing tissues, mainly cartilage
Further below the PC layer, pre-chondroblasts gradually maturate toward chondroblasts and chondrocytes; at the same time, the rod-like vascular streaks progressively extend from the two ends in parallel with the long axis of the antler, to form the transition zone (TZ) layer
The results showed that the higher the level the bigger the ratio (Fig. 2C), suggesting that the elevated level of up-regulated genes is positively correlated with the degree of cell differentiation in the Antler growth center (AGC)

Summary

Introduction

With the unprecedented rapid growth rate (up to 2.75 cm/day), velvet antler is an invaluable model for the identification of potent growth factors and signaling networks for extremely fast growing tissues, mainly cartilage. A growth system, where normal cells exhibit a rapid proliferation and differentiation without becoming cancerous, would be desirable in identification of potent growth factors, unique signal transduction pathways and novel regulation systems. In this regard, deer antler is an invaluable model to meet these requirements. The RM layer, the mesenchymal cells start to differentiate towards a cartilaginous lineage (PC layer), where pre-chondroblasts and newly-formed-isolated vascular streaks reside. Continuous cartilage columns (which mainly contain chondroblasts in the periphery and chondrocytes in the center) alternate with continuous vascular channels (functional vascular system) to form the CA layer, the vascularized cartilage (unique feature of antler cartilage). At the end of this proximal layer, chondroclasia, osteogenesis and osteoclasia take place simultaneously to form the MC layer, within which the smooth-surfaced the osteo-cartilage columns are converted into irregular and broken trabeculae [4]

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