Mice, ASOs, siRNAs and Antibodies
C57BL/6 mice were obtained from the Model Animal Research Center of Nanjing University. All mice were housed with 12/12 h light/dark cycles, at 22 °C and allowed free access to water and food.
ASOs and siRNAs were synthesized by Ribobio (Guangzhou, China). Specific sequences are provided in supplementary information Table S1. ASOs used in Figure 1C were diluted with nuclease-free water to different concentrations within 20-500 μM, and injected into the testis with the maximum injection volume (4 μL). siRNAs we used in this article were chemically modified with 2’-OM (2-methoxyethyl) and cholesterol to improve the stability and biodistribution[53].
Primary antibodies used in this article are listed as follow: rabbit anti-Vimentin (ab92547, Abcam, USA), rabbit anti-SOX9 (AB5535, Merck Millipore, German), rabbit anti-DDX4 (ab13840, Abcam, USA) and rabbit anti-SYCP3 (ab15093, Abcam, USA), rabbit anti-SYCP1 (ab15090, Abcam, USA), rabbit anti-MLH1 (550838, BD, USA).
In vivo knockdown through microinjection
Microinjection of ASOs and siRNAs were operated as previously described[60]. Mice of 3-week-old were anesthetized by tri-bromoethanol and one testis was exteriorized through incisions on abdomen. A mixture of 3 μL of ASO dilutions or siRNA dilutions and 1 μL tracer Trypan blue was injected into seminiferous tubule through the microinjection apparatus (FemtoJet 4i, Eppendorf) under a stereoscopic microscope. The testis was placed back to the abdominal cavity after injection. After both sides of testes were finished with injection, the incisions were closed with sutures. Each injected mouse was kept warm by putting hot water bag in cage until they wake up.
RNA extraction and RT-PCR
Testes were collected 48 hours or 10 days after injection to measure knockdown efficiency. Total RNA was extracted using TRIzol reagent (Thermo Fisher Scientific, USA) following the manufacturer’s instructions. 1μg RNA was reversed transcribed into cDNA with PrimeScript RT Master Mix (RR036A, TaKaRa, Tokyo, Japan) according to the manufacturer’s instructions. Real time PCR was performed using TB Green Premix Ex Taq II(RR820A, TaKaRa, Tokyo, Japan) on Applied Biosystems StepOnePlus Real-Time PCR System. Relative expression of target RNA was determined after normalization to 36B4 gene. The sequences of all primers used in this experiment are provided in additional file 2 Table S1.
Rapid amplification of cDNA ends (RACE) analysis
Total RNA was extracted from C57BL/6 mouse testis. 5’RACE and 3’RACE were performed using the SMARTer® RACE 5’/3’ Kit (Clontech, Mountain View, CA) according to the manufacturer’s instructions. The following gene-specific primers (GSP) are used for PCR:
5’-TGGCAAGCAACAAACACCCTAGTTGGC-3’ (5’RACE GSP);
5’-CTTGGGTATCAGCTCCACCAACAAGGT-3’ (3’RACE GSP).
Fluorescence in situ hybridization (FISH) and immunofluorescence
Testes were fixed in 4% PFA overnight at 4 °C, dehydrated by graded ethanol (70%, 95%, 100%) and embedded in paraffin. Embedded testes were sectioned into 5 μm. FISH was performed with RNAscope@ multiplex fluorescent reagent kit (Advanced Cell Diagnostics, USA) as manufacturer’s instructions[61]. Target probes were obtained from RNAscope@. After the last procedure of FISH, sections were treated in 1×PBS for 5 min and then blocked in blocker (10% FBS, 1% BSA, 1% Triton X-100, 0.05% Tween-20) for 1 hr at room temperature (RT). Testis sections were incubated with the following antibodies at 4 °C overnight: rabbit anti-Vimentin (1:250), rabbit anti-SOX9 (1:400), rabbit anti-DDX4 (1:200) and rabbit anti-SYCP3 (1:100). Texas red or FITC-conjugated secondary antibodies (Vector Laboratories, USA) were incubated at 37 °C for 1 hr and sections were washed 3 times in PBST (1×PBS containing 0.2% Tween-20). Samples were mounted in microslide shield with DAPI. Fluorescent signals were detected on a confocal microscope (LSM800, Carl Zeiss, German).
Isolation of nuclear and cytoplasmic fractions
Subcellular extracts were prepared as described[60]. 30-40 mg testis tissue was homogenized in 400 μL Cytoplasmic Extraction Buffer (CT Buffer, 250 mM sucrose, 10 mM Tris-HCl (pH 8.0), 10 mM MgCl2, 1 mM EGTA, 1×protease inhibitor cocktail III, 0.4 μL RNasin (N251B, Promega, USA)) with 100 strokes. The lysis was centrifuged at 300×g for 5 min, and the supernatant was collected as cytoplasmic fraction. Add 1 mL TRIzol reagent per 200 μL supernatant and stored at -80℃. The pellet seen as nuclei fraction was washed three times in 500 μL CT Buffer and centrifuged at 300×g for 5 min. Add 1 mL TRIzol and homogenize the pellet by 1 mL syringe with 0.4 mm needle. RNA was extracted as above.
TUNEL assays, chromosome spread and immunofluorescence
TUNEL was performed on the testis sections with TUNEL BrightGreen Apoptosis Detection Kit (A112-01, Vazyme, China) according to the manufacturer’s instructions. Chromosome spread of prophase I spermatocytes were performed as previous described[62]. The following primary antibodies were used in morphology analysis of chromosome: rabbit anti-SYCP1 (1:100), rabbit anti-SYCP3 (1:100), rabbit anti-MLH1 (1:100). Slides were washed in 1×PBS for 5 min, and then blocked with 10% goat serum in PBST ( 1×PBS containing 0.1% Tween 20 ) for 1 hr at RT. After incubated with primary antibodies overnight at 4 °C, slides were treated with PBST for 3 times. Secondary antibodies were incubated at 37 °C for 1 hr. Wash slides in PBST for 3 times. All the slides were mounted in microslide shield with DAPI. Immunofluorescence for all samples was examined under laser scanning confocal microscope (LSM800, Carl Zeiss, German).
Statistical analysis
All values were presented as mean ± S.D. Statistical analysis was performed with Student’s t test (*p<0.05; **p<0.01; ***p<0.001) using Prism 7.0 (GraphPad Software, La Jolla, CA, USA). NS means not significant.