TCTP is expressed in rumen epithelium cell throughout postnatal period
To probe the potential roles of TCTP in rumen development, we first examined whether TCTP is presented in rumen epithelia. We detected mRNA transcripts for TCTP in rumen epithelium from birth to day 60. Among all the time points, we found the expression level of TCTP mRNA transcripts was the highest in the rumen epithelium of day 0, while it decreased to a relatively low level on day 15. Then the TCTP mRNA expression in rumen epithelium gradually increased along with the age of sheep to day 45 and it decreased to a relatively low level at the age of day 60 (Fig. 1b).
We then detected the protein expression of TCTP in rumen epithelia. Different from its mRNA expression, we found TCTP protein expression remained in a relatively low level from day 0 to day 15 of postnatal life. TCTP protein expression then significantly increased at day 30 of age (p<0.05) and gradually decreased until day 60 (Fig. 1c and d).
To better evaluate the expression of TCTP in rumen epithelia, we also determined the localization of TCTP on rumen epithelium before weaning. We found TCTP expressed in stratum basale cells at the age of day 0. On day 15 of life, TCTP was only expressed in stratum basale cell and stratum spinosum cell, while we found TCTP expressed in stratum basale, stratum spinosum and stratum granulosum after day 30 of postnatal life (Fig. 1a).
At last we evaluated the intensity of TCTP staining in rumen epithelium. We found the a few staining of TCTP in stratum basale on day 0 of postnatal life. The staining then changed from faint to strong from day 15 to day 45 of age and decreased to moderate on day 60. On day 30 and day 45 of age, we found relative stronger staining of TCTP on the top of the papillae comparing with the staining in the middle or the bottom of papillae. The staining of TCTP followed the similar pattern in stratum spinosum and stratum granulosum. We found no staining of TCTP in stratum corneum (Table 2).
Table 2 Intensity of immunohistochemical staining of TCTP in rumen epithelia
|
D0
|
D15
|
D30
|
D45
|
D60
|
stratum basale
|
+/-
|
+/-
|
++
|
++
|
+
|
stratum spinosum
|
-
|
+
|
++
|
++
|
+
|
stratum granulosum
|
-
|
+/-
|
+++
|
+++
|
+
|
stratum corneum
|
-
|
-
|
-
|
-
|
-
|
Note that: +/- means a few staining; + means faint staining; ++ means moderate staining; +++ means strong staining;
The histological and morphological changes of ruminal papillae during postnatal stage
To determine the function of TCTP during sheep rumen papillae development, we then evaluated its histological and morphological changes from birth to 60 days old. The body weight and rumen weight increased following the age of sheep. However, the papillae length decreased from 621.8±9.2μm to 538.1±17.3μm at first 15 days of postnatal life. Thereafter, the papilla undergo a period of growth from 538.1±17.3μm to 2211.1±56.6μm until 60 days of age (Table 3). The proportion of rumen weight to the whole stomach decreased in the first 15 days of life and gradually increased to 64.40±1.33% afterward (Table 4). The growth rate of rumen papillae was -5.58μm per day from day 0 to day 15 of age. Then it became 50.50μm per day at the stage of day 15 to day 30, afterward it decreased to 31.20μm per day (Table 5).
On the first day of Hu Sheep postnatal life, the papillae were formed by a single layer of stratum basale cells that covered papillary core. The papillary core was covered by several layers of stratified squamous cells. Outside the stratified squamous cells were covered by serosa. At the age of day 15, the rumen epithelia formed tongue-shaped papilla, which were constituted by stratum basale, stratum spinosum and stratum granulosum. On this stage, the papillary cores were larger than that of day 0 and all the papillae were closely connected. At 30 days of age, we found the space between papillae larger than that of day 15, and one or two layers of stratum corneum could be clearly observed in most papillae. The papillae were also covered by serosa. At 45 days of age, the stratum corneum covered all the papillae except the top of papillae, which were still covered by serosa. In spite of more layers of stratified squamous cells, we didn’t found significant histological changes of ruminal papillae at 60 days of age, when comparing with day 45 (Fig. 2).
Table 3 The papillae length, bodyweight and rumen weight of Hu sheep at different ages
|
age
|
Day 0
|
Day 15
|
Day 30
|
Day 45
|
Day 60
|
Papillae length(μm)
|
621.8±9.2b
|
538.1±17.3a
|
1295.6±27.1c
|
1739.8±73.0d
|
2211.1±56.6e
|
Body weight(kg)
|
3.49±0.11
|
6.91±0.13
|
9.90±0.25
|
13.89±0.37
|
18.08±0.68
|
Rumen weight(g)
|
6.7±0.4
|
16.2±1.3
|
52.1±7.4
|
164.5±13.9
|
288.3±30.0
|
Note: data are presented as mean±sem, n=5, p<0.05 is considered significance.
Table 4. The proportion of rumen, reticulum, omasum and abomasum weight to the whole stomach %
age
|
Rumen
|
Reticulum
|
omasum
|
abomasum
|
0
|
30.99±0.92d
|
11.57±1.13a
|
9.10±1.23a
|
48.34±1.10b
|
15
|
24.48±0.81e
|
8.74±1.07b
|
6.88±0.48ab
|
59.91±1.54a
|
30
|
43.27±2.73c
|
7.31±0.24b
|
6.13±0.32b
|
42.28±2.80b
|
45
|
58.92±0.75b
|
9.88±0.85a
|
4.47±0.36c
|
26.73±1.15c
|
60
|
64.40±1.33a
|
10.93±1.14a
|
5.85±0.17b
|
18.82±0.47d
|
Note: data are presented as mean±sem, n=5, p<0.05 is considered significance.
Table. 5 The average growing rate of papillae length at different stage μm/day
|
stage
|
Day 0-day 15
|
Day 15-day 30
|
Day 30-day 45
|
Day 45-day 60
|
growth rate
|
-5.58
|
50.50
|
29.61
|
31.20
|
TCTP is involved in stratum basale cell proliferation
We then used Ki67 as indicator of cell proliferation to determine the role of TCTP in rumen papillae growth. We found faint staining of Ki67 in the cytoplasm of stratum basale cell and stratum spinosum cell, while the strong staining that indicated cell division were only detected in stratum basale cells (Fig. 3 a). Hence, we have counted the number of Ki67 positive cells in stratum basale. The ratio of Ki67 positive cells in stratum basale remained in a very low level from day 0 to day 15 of sheep postnatal life. It then significantly increased at day 30 of age and remained until day 45 of age (p<0.05). Finally, the ratio significantly decreased on day 60 (p<0.05) (Fig. 3 b).
AKT expression and phosphorylation during Hu Sheep postnatal life
To explore the relationship between AKT signaling pathway and TCTP, we first determined the localization of AKT in rumen epithelia tissue. We found strong staining of AKT in the stratum basale cells of day 0 sheep. The staining then turned to faint in day 15 stratum basale cell. In day 30, day 45 and day 60 sheep rumen epithelia, we found moderate staining of AKT in stratum basale cell, stratum spinosum cell and stratum granulosum cell (Fig. 4 a). Then we evaluated the AKT phosphorylation by western blot. The phosphorylation of AKT was relative low on day 0, while it significantly increased on day 15 (p<0.05). Then the AKT t phosphorylation level gradually decreased until day 45. On day 60 of age, the AKT phosphorylation level was a little bit higher than that of day 45 (Fig. 4 b and c).
The changes of SCFAs concentration in rumen fluid during Hu Sheep postnatal life
Since the SCFAs are associated rumen papillae growth, we also measured the SCFAs in the rumen fluid of Hu Sheep before weaning. We found no rumen fluid on day 0 of age, and among all the five Hu Sheep we chose to sacrifice, only one rumen contained a few rumen fluid, which was not enough for SCFAs measurement (data not shown). The concentration of acetic acid in rumen fluid was relative lower on day 30 and day 45 of age, while it significantly increased to 85.34±3.37 μmol/ml on day 60 (p<0.05). The concentration of propionic acid on day 30 was 10.48±4.28 μmol/ml, then it significantly increased to 73.55±8.39 μmol/ml on day 60 of age (p<0.05). The valeric acid concentration on day 60 also significantly rose on day 60 comparing with that of day 30. We didn’t find significant change on the concentration of butyric acid, isobutyric acid and isocaleric acid. Since the ratio of acetic acid/propionic acid was considered important in rumen development, we found its ratio was 6.19±2.46 on day 30, then it significantly decreased from day 45 to day 60 (p<0.05) (Table 6).
Table 6 SCFAs concentration in rumen fluid
|
age
|
Day 0
|
Day 15
|
Day 30
|
Day 45
|
Day 60
|
acetic acid, μmol/ml
|
-
|
-
|
48.83±15.24b
|
47.60±6.97b
|
85.34±3.37a
|
propionic acid, μmol/ml
|
-
|
-
|
10.48±4.28c
|
31.84±13.94b
|
73.55±8.39a
|
butyric acid, μmol/ml
|
-
|
-
|
8.93±3.61
|
10.20±1.86
|
10.03±2.11
|
isobutyric acid, μmol/ml
|
-
|
-
|
0.82±0.05
|
0.81±0.20
|
0.83±0.15
|
valeric acid, μmol/ml
|
-
|
-
|
1.17±0.33b
|
2.13±0.51ab
|
2.86±0.25a
|
isovaleric acid, μmol/ml
|
-
|
-
|
1.53±0.20
|
1.24±0.32
|
1.27±0.20
|
acetic acid/propionic acid
|
|
|
6.19±2.46a
|
2.30±0.47b
|
1.27±0.20c
|
Note: data are presented as mean±sem, n=5, p<0.05 is considered significance.