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Low retinoic acid levels mediate regionalization of the Sertoli valve in the terminal segment of mouse seminiferous tubules.

ABSTRACT: In mammalian testes, undifferentiated spermatogonia (A_undiff) undergo differentiation in response to retinoic acid (RA), while their progenitor states are partially maintained by fibroblast growth factors (FGFs). Sertoli valve (SV) is a region located at the terminal end of seminiferous tubule (ST) adjacent to the rete testis (RT), where the high density of A_undiff is constitutively maintained with the absence of active spermatogenesis. However, the molecular and cellular characteristics of SV epithelia still remain unclear. In this study, we first identified the region-specific AKT phosphorylation in the SV Sertoli cells and demonstrated non-cell autonomous specialization of Sertoli cells in the SV region by performing a Sertoli cell ablation/replacement experiment. The expression of Fgf9 was detected in the RT epithelia, while the exogenous administration of FGF9 caused ectopic AKT phosphorylation in the Sertoli cells of convoluted ST. Furthermore, we revealed the SV region-specific expression of Cyp26a1, which encodes an RA-degrading enzyme, and demonstrated that the increased RA levels in the SV region disrupt its pool of A_undiff by inducing their differentiation. Taken together, RT-derived FGFs and low levels of RA signaling contribute to the non-cell-autonomous regionalization of the SV epithelia and its local maintenance of A_undiff in the SV region.

SUBMITTER: Imura-Kishi K

PROVIDER: S-EPMC7806815 | biostudies-literature | 2021 Jan

REPOSITORIES: biostudies-literature

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Low retinoic acid levels mediate regionalization of the Sertoli valve in the terminal segment of mouse seminiferous tubules.

Imura-Kishi Kasane K Uchida Aya A Tsunekawa Naoki N Suzuki Hitomi H Takase Hinako M HM Hirate Yoshikazu Y Kanai-Azuma Masami M Hiramatsu Ryuji R Kurohmaru Masamichi M Kanai Yoshiakira Y

Scientific reports 20210113 1

In mammalian testes, undifferentiated spermatogonia (A<sub>undiff</sub>) undergo differentiation in response to retinoic acid (RA), while their progenitor states are partially maintained by fibroblast growth factors (FGFs). Sertoli valve (SV) is a region located at the terminal end of seminiferous tubule (ST) adjacent to the rete testis (RT), where the high density of A<sub>undiff</sub> is constitutively maintained with the absence of active spermatogenesis. However, the molecular and cellular c ...[more]

PMID: 33441739

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Project description:BackgroundInfertile men with non-obstructive azoospermia (NOA) have impaired spermatogenesis. Dilated and un-dilated atrophic seminiferous tubules are often present in the testes of these patients, with the highest likelihood of active spermatogenesis in the dilated tubules. Little is known about the un-dilated tubules, which in NOA patients constitute the majority. To advance therapeutic strategies for men with NOA who fail surgical sperm retrieval we aimed to characterize the spermatogonial stem cell microenvironment in atrophic un-dilated tubules.MethodsTestis biopsies approximately 3x3x3 mm3 were obtained from un-dilated areas from 34 patients. They were classified as hypospermatogenesis (HS) (n=5), maturation arrest (MA) (n=14), and Sertoli cell only (SCO) (n= 15). Testis samples from five fertile men were included as controls. Biopsies were used for histological analysis, RT-PCR analysis and immunofluorescence of germ and Sertoli cell markers.ResultsAnti-Müllerian hormone mRNA and protein expression was increased in un-dilated tubules in all three NOA subtypes, compared to the control, showing an immature state of Sertoli cells (p<0.05). The GDNF mRNA expression was significantly increased in MA (P=0.0003). The BMP4 mRNA expression showed a significant increase in HS, MA, and SCO (P=0.02, P=0.0005, P=0.02, respectively). The thickness of the tubule wall was increased 2.2-fold in the SCO-NOA compared to the control (p<0.05). In germ cells, we found the DEAD-box helicase 4 (DDX4) and melanoma-associated antigen A4 (MAGE-A4) mRNA and protein expression reduced in NOA (MAGE-A: 46% decrease in HS, 53% decrease in MA, absent in SCO). In HS-NOA, the number of androgen receptor positive Sertoli cells was reduced 30% with a similar pattern in mRNA expression. The γH2AX expression was increased in SCO as compared to HS and MA. However, none of these differences reached statistical significance probably due to low number of samples.ConclusionsSertoli cells were shown to be immature in un-dilated tubules of three NOA subtypes. The increased DNA damage in Sertoli cells and thicker tubule wall in SCO suggested a different mechanism for the absence of spermatogenesis from SCO to HS and MA. These results expand insight into the differences in un-dilated tubules from the different types of NOA patients.

Project description:Mammalian spermatogenesis is a complex biological process that occurs within a highly organized tissue, the seminiferous epithelium. The coordinated maturation of spermatogonia, spermatocytes and spermatids suggests the existence of precise programs of gene expression in these cells as well as in their neighboring somatic Sertoli cells. The objective of this study was to elucidate genes encoding the proteins that execute these programs. Rat seminiferous tubules at stages I, II-III, IV-V, VI, VIIa,b, VIIc,d, VIII, IX-XI, XII, XIII-XIV of the cycle were isolated by microdissection and Sertoli cells, spermatogonia plus early spermatocytes, pachytene spermatocytes and spermatids were purified from enzymatically-dispersed testes. Microarray analysis using Rat Genome 230 2.0 arrays identified a total of 16,971 probe sets that recognized transcripts. A comparison with the transcriptome of other tissues identified 398 testis-specific probe sets, which therefore are potential targets for the development of new contraceptives. Sequential waves of cell and stage-specific gene expression are associated with progression of germ cells through the stages of the cycle of the seminiferous epithelium and 1612 probe sets recognized transcripts whose expressions varied at least 4-fold across the stages of the cycle. Pathway analyses reveal that entire biological processes are regulated cyclically in testicular cells. Important among these are cell cycle and DNA repair. Thus, stage-specific gene expression is a widespread and fundamental characteristic of spermatogenic cells and Sertoli cells. Experiment Overall Design: Seminiferous tubules at the following stages or groups of stages were isolated by transillumination-assisted microdissection: I, II-III, IV-V, VI, VIIa,b, VIIc,d, VIII, IX-XI, XII, XIII-XIV. Twenty-five segments of tubules, 2 m in length, were collected at each stage or group of stages from each rat. Tubules from two separate animals were pooled to form one sample from each stage or groups of stages. A total of 5 independent samples per stage or groups of stages were analyzed. Mature Sertoli cells were isolated to about 85% purity (n=4). Three groups of germ cells were isolated by centrifugal elutriation from enzyme-dispersed testes: round spermatids (n=4), pachytene spermatocytes (n=4) and spermatogonia plus early spermatocytes (n=3) . Purity of these cells has been shown to vary between 85% to 95%

Dataset Information

Low retinoic acid levels mediate regionalization of the Sertoli valve in the terminal segment of mouse seminiferous tubules.

Publications

Low retinoic acid levels mediate regionalization of the Sertoli valve in the terminal segment of mouse seminiferous tubules.

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