Dynamical changes of serum lipid metabolism indicators on fat-tailed sheep
To explore the dynamic changes and lipid metabolic differences between GLT and STH, five serum biochemical parameters involved in lipid metabolism were examined between two fat-tailed breeds at different development stages of 4, 6, 8, 10, 12 months. The results showed that the average of serum TC, and NEFA at five time points are obvious different, while other parameters have no significant difference between breeds. Interestingly, only serum NEFA in ewe is significantly higher than that in rams’ values (Table S1).
The changes of these indicators with the age of month are relatively complicated (Fig. 2). In STH, serum TG concentration was the highest at 4 months of age, significantly higher than other months of age, and decreased with the increase of age; TC, NEFA, HDLC, and LDLC concentrations in serum did not change significantly with age between 4 and 10 months, but there was a tendency to decrease or increase (LDLC) at the age of 12 months. Comparatively, in GLT, TG did not change significantly between 4 and 12 months with a tendency to decrease at 12 months. TC, HDLC, and LDLC show the similar changes which firstly increase significantly and then decreases from 4 to 12 months of age. The concentration of NEFA was the highest at 4 months which was significantly higher than that at 6 and 8 months, and there was a tendency to increase at 10 months and decreased again at 12 months. Those dynamical changes indicate that the lipid metabolism pattern of STH and GLT maybe different with developmental ages.
The mRNA expression profile of SREBF1 in liver and fat tissues
To determinate the role of SREBF1 in fat metabolism regulation of fat-tailed sheep, the relative mRNA expression profile of SREEP1 in liver and adipose tissues in two breeds with different ages were detected by real-time RT-PCR (qPCR). The result showed that the global mRNA expression was significantly different between GLT and STH (P < 0.05, Fig. 3A), but no significant gender difference was found (Fig. 3B, Table S2). Merely, in female, the mRNA expresses in STH higher than those in GLT (P < 0.05, Fig. 3C). During development age, SREBF1 expresses relatively stable in either male or female or combination in GLT (Fig. 3D and 3E). However, the total mRNA level was the highest at 10 months of age, and significantly higher than that at 8 months of age (P < 0.05, Table S2). In male STH, the expression at 10-month is significantly higher than that both at 6- and 8-month (P < 0.01, Fig. 3E).
We also examined SREBF1 expression levels in liver and adipose tissues, which are involved in adipogenesis and lipid metabolism. The expression in liver was extremely higher than adipose tissues including tail (TA), great omental (GO), subcutaneous (SC), small omentum (SO), perirenal (PR), retroperitoneal (RP), and mesenteric (MT) fats in both GLT and STH (Fig. 3F, G). Similar results also were observed in males of GLT and STH. The difference is that the female of GLT have not presented a tissue-specific expression, except in MT. In STH females, the expression in MT was lower than that in liver significantly (P < 0.05).
Correlation analysis showed that the mRNA expressions between liver and Go were extremely significantly positively correlated in GLT (Table 1, r = 0.854, P < 0.01). In STH, TA and SC, PR and GO, PR and SO presented the positive correlation (r = 0.852, 0.915, or 0.979, P < 0.05). All results reveal that SREBF1 maybe plays a crucial role in fat metabolism regulation during growth and development of two breeds of fat-tailed sheep.
Table 1
Correlation coefficients of SREBF1 mRNA expression in adipose tissues between two fat-tailed sheep
Tissues | Tail fat (TA) | Great omental fat (GO) | Subcutaneous fat (SC) | Small omental fat (SO) | Perirenal fat (PR) | Retroperitoneal fat (RP) | Mesenteric fat (MT) | Liver (LV) |
TA | 1 | -0.331 | 0.852* | -0.068 | -0.346 | 0.348 | 0.516 | 0.340 |
GO | -0.160 | 1 | -0.279 | 0.516 | 0.915* | -0.521 | -0.363 | 0.665 |
SC | 0.000 | 0.074 | 1 | 0.300 | -0.039 | 0.416 | 0.322 | 0.075 |
SO | 0.138 | 0.422 | 0.132 | 1 | 0.799* | -0.046 | -0.149 | 0.653 |
PR | 0.376 | -0.256 | 0.117 | 0.297 | 1 | -0.259 | 0.070 | 0.435 |
RP | 0.165 | 0.315 | 0.306 | 0.021 | 0.301 | 1 | 0.314 | -0.423 |
MT | -0.051 | 0.511 | 0.080 | 0.666 | 0.224 | 0.425 | 1 | -0.382 |
LV | 0.223 | 0.854** | 0.121 | 0.718 | -0.208 | 0.456 | 0.617 | 1 |
The mRNA expression of SREBF2 in liver and fat tissues
Transcriptional levels of SREBF2, another member of SREBFs family, in adipose tissues and liver were further examined and shown in Fig. 4. Different from SREBF1, SREBF2 expressed significantly higher in GLT than in STH (P < 0.001, Fig. 4A) and significantly higher in female than in male (P < 0.001, Fig. 4B), especially in female of GLT (P < 0.001, Fig. 4C). The age had no significant effects on the expression in GLT (Fig. 4D). However, it expressed significantly higher at 10-month-old females than in males at the same age in GLT (P < 0.05). In STH, it reduced to the lowest point at 8-month-old in comparison to 4-month-old (P < 0.05) and then went up a little. The same changing tendency was observed in female STH (P < 0.01, Fig. 4E).
Similar to SREBF1, the expression of SREBF2 was enriched in liver than other adipose tissues. In GLT, SREBF2 mRNA expressions in liver were significantly higher than TA (P < 0.05), PR (P < 0.05) and MT (P < 0.01, Fig. 4F). In STH, SREBF2 mRNA expressions in liver were markedly higher than all the adipose tissues except GO (P < 0.001 or P < 0.0001, Fig. 4G). According to the analysis of gender, SREBF2 mRNA expressions in liver of male GLT were significantly higher than all adipose tissues. MT of GLT is the only tissue that SREBF2 mRNA expression differed significantly between male and female (P < 0.001). In female GLT, the SREBF2 mRNA levels was significantly higher in RP than in TA (P < 0.01), while there were no significant differences between any other tissues (Fig. 4H, Table S3). The correlation coefficients between SC and LV, MT and LV, PR and LV, PR and SC, PR and MT, SO and MT are significant(Table 2, P < 0.05 or P < 0.01).
Table 2
Correlation coefficients of SREBF2 mRNA expression in adipose tissues between two fat-tailed sheep
Tissues | Tail fat (TA) | Great omental fat (GO) | Subcutaneous fat (SC) | Small omental fat (SO) | Perirenal fat (PR) | Retroperitoneal fat (RP) | Mesenteric fat (MT) | Liver (LV) |
TA | 1 | -0.163 | 0.058 | -0.462 | 0.089 | -0.054 | 0.301 | -0.236 |
GO | 0.187 | 1 | 0.424 | 0.680* | 0.779* | -0.147 | -0.163 | -0.328 |
SC | 0.149 | 0.218 | 1 | 0.397 | 0.709* | -0.327 | 0.064 | 0.066 |
SO | -0.093 | 0.148 | -0.003 | 1 | 0.762* | -0.089 | -0.112 | 0.065 |
PR | 0.026 | -0.153 | 0.860** | 0.052 | 1 | -0.107 | -0.102 | -0.703 |
RP | 0.475 | 0.043 | -0.060 | -0.182 | -0.087 | 1 | 0.464 | -0.344 |
MT | 0.209 | 0.145 | 0.568 | 0.697* | 0.666* | 0.100 | 1 | -0.276 |
LV | 0.107 | 0.158 | 0.672* | 0.222 | 0.829** | 0.112 | 0.699* | 1 |
In STH, expression of SREBF2 was numerically but not significantly increased in liver of male STH, but the significantly expressions variant observed between adipose tissues, such as MT and TA, GO and RP, SC and PR (Fig. 4I). In female STH, liver showed higher expression levels than any other adipose tissues, and SREBF2 expression in MT was the lowest compared to liver and GO (P < 0.05). Further analysis results showed that the significantly positive correlation of SREBF2 expressions occurred in between GO and SO, PR and GO, PR and SC, PR and SO (Table 2, P < 0.05). These results indicated that SREBF2 also played a crucial role in the regulation of lipid metabolism during growth and development of the two breeds of fat-tailed sheep.
Associations between SREBP1/2 expressions and slaughter and tail traits
Associations between SREBF1/2 mRNA expression in eight tissues and slaughter and tail traits in sheep were analyzed. The results demonstrated that SREBF1 mRNA expressions in TA were significantly related to tail-type traits in GLT, such as absolute tail fat weight (ATW) and relative tail fat weight (RTW). The significant correlation also were found between LV and tail length (TL), LV and RTW, GO and TL, respectively. While in STH, significant correlation only occurred between SREBF1 expressions in PR and body weight (BW), as well as carcass weight (CW), which was not related to tail-type traits (Table 3).
Table 3
Correlation coefficients between SREBF1 mRNA expression in different tissues and slaughter and tail traits in sheep
Traits | Relative mRNA abundance |
Tail fat (TA) | Great omental fat (GO) | Subcutaneous fat (SC) | Small omental fat (SO) | Perirenal fat (PR) | Retroperitoneal fat (RP) | Mesenteric fat (MT) | Liver (LV) |
Guangling Large Tailed sheep(GLT) |
TL | -0.031 | 0.668* | 0.048 | 0.451 | -0.123 | 0.064 | 0.467 | 0.673* |
TW | 0.408 | 0.255 | 0.427 | 0.007 | -0.017 | 0.335 | 0.285 | 0.432 |
ATW | 0.651* | 0.213 | 0.550 | 0.237 | 0.293 | 0.311 | 0.265 | 0.433 |
RTW | 0.652* | 0.454 | 0.351 | 0.451 | 0.250 | 0.515 | 0.598 | 0.680* |
BW | 0.096 | -0.298 | 0.276 | -0.079 | 0.111 | -0.089 | -0.157 | -0.123 |
CW | 0.260 | -0.217 | 0.431 | -0.160 | 0.114 | -0.193 | -0.266 | -0.100 |
DP | 0.387 | -0.021 | 0.506 | -0.192 | 0.139 | -0.275 | -0.425 | -0.008 |
Small Tailed Han sheep(STH) |
TL | 0.704 | -0.335 | 0.445 | -0.348 | -0.218 | 0.302 | 0.305 | -0.212 |
TW | 0.379 | 0.100 | 0.230 | 0.021 | 0.207 | 0.026 | -0.196 | 0.232 |
BW | 0.047 | 0.418 | 0.040 | 0.119 | 0.711* | -0.169 | 0.135 | 0.637 |
CW | -0.005 | 0.376 | -0.010 | 0.022 | 0.728* | -0.283 | 0.145 | 0.571 |
DP | -0.358 | -0.446 | -0.410 | -0.602 | -0.147 | -0.629 | 0.018 | -0.423 |
Note: TL: tail length; TW: tail width; ATW: absolute tail fat weight; RTW: relative tail fat weight; BW: body weight; CW: carcass weight; DP: dressing percentage. *P < 0.05, ** P < 0.01. |
Relative SREBF2 mRNA abundances in liver were significantly related negatively to tail-type traits including TL, TW, and ATW in GLT. There were also significant negatively relationships between SC and TW, as well as between GO and ATW or CW. While the only significant positively correlation to CW was SREBF2 mRNA abundances in SC of STH (Table 4).
Table 4
Correlation coefficients between SREBF2 mRNA expression in different tissues and slaughter and tail traits in sheep
Traits | Relative mRNA abundance |
Tail fat (TA) | Great omental fat (GO) | Subcutaneous fat (SC) | Small omental fat (SO) | Perirenal fat (PR) | Retroperitoneal fat (RP) | Mesenteric fat (MT) | Liver (LV) |
Guangling Large Tailed sheep |
TL | -0.100 | 0.029 | -0.517 | -0.006 | -0.452 | -0.359 | -0.288 | -0.694* |
TW | -0.160 | -0.498 | -0.607* | -0.111 | -0.534 | -0.187 | -0.266 | -0.768* |
ATW | -0.339 | -0.611* | -0.441 | -0.307 | -0.253 | -0.213 | -0.388 | -0.720* |
RTW | -0.491 | -0.362 | -0.171 | -0.239 | -0.072 | -0.021 | -0.206 | -0.549 |
BW | 0.081 | -0.459 | -0.557 | -0.309 | -0.245 | -0.215 | -0.334 | -0.302 |
CW | 0.067 | -0.593* | -0.507 | -0.236 | -0.218 | -0.297 | -0.429 | -0.495 |
DP | -0.026 | -0.571 | -0.302 | -0.391 | -0.178 | -0.427 | -0.412 | -0.588 |
Small Tailed Han sheep |
TL | 0.484 | 0.486 | 0.295 | -0.074 | 0.627 | -0.094 | 0.040 | -0.204 |
TW | 0.185 | 0.278 | 0.366 | 0.042 | 0.549 | 0.082 | 0.366 | 0.101 |
BW | -0.439 | 0.268 | 0.575 | 0.530 | 0.158 | -0.425 | -0.053 | 0.473 |
CW | -0.385 | 0.234 | 0.663* | 0.528 | 0.237 | -0.424 | -0.042 | 0.475 |
DP | 0.361 | -0.266 | 0.302 | -0.136 | 0.080 | 0.214 | 0.070 | -0.123 |
Note: TL: tail length; TW: tail width; ATW: absolute tail fat weight; RTW: relative tail fat weight; BW: body weight; CW: carcass weight; DP: dressing percentage. *P < 0.05, ** P < 0.01 |
Location and function prediction of SREBP1/2
According to SREBP1/2 expression levels in different tissues, age, and breeds, the location and function of SREBP1/2 in cell were analyzed by bioinformatics approaches. The subcellular locations results showed that SREBP1 and SREBP2 working mainly in different parts inside cells (Fig. 5A). About 78.30% of SREBP1 distributed in nucleus, and the rest in cytoplasm, vesicles of secretory system, plasma membrane, and endoplasmic reticulum. Unlike in SREBP1, only 30.40% of SREBP2 can be predicted in nucleus and 39.1% in the endoplasmic reticulum. In addition, it also distributed in vacuole, cytoplasm, and vesicles of secretory system, Golgi and mitochondria.
Functional prediction shows that both SREBP1 and SREBP2 play roles in many biological processes (Fig. 5B). SREBP1 mainly functioned in purines and pyrimidines, replication and transcription, and regulatory function, while SREBP2 mainly functioned in the process of transport and binding, purines and pyrimidines, translation and central intermediary metabolism.