Identification of Differentially Expressed Genes in Human Cryptorchid Testes Using Suppression Subtractive Hybridization

Contradictory mRNA and protein misexpression of EEF1A1 in ductal breast carcinoma due to cell cycle regulation and cellular stress

Encoded by EEF1A1, the eukaryotic translation elongation factor eEF1α1 strongly promotes the heat shock response, which protects cancer cells from proteotoxic stress, following for instance oxidative stress, hypoxia or aneuploidy. Unexpectedly, therefore, we find that EEF1A1 mRNA levels are reduced in virtually all breast cancers, in particular in ductal carcinomas. Univariate and multivariate analyses indicate that EEF1A1 mRNA underexpression independently predicts poor patient prognosis for estrogen receptor-positive (ER+) cancers. EEF1A1 mRNA levels are lowest in the most invasive, lymph node-positive, advanced stage and postmenopausal tumors. In sharp contrast, immunohistochemistry on 100 ductal breast carcinomas revealed that at the protein level eEF1α1 is ubiquitously overexpressed, especially in ER+ , progesterone receptor-positive and lymph node-negative tumors. Explaining this paradox, we find that EEF1A1 mRNA levels in breast carcinomas are low due to EEF1A1 allelic copy number loss, found in 27% of tumors, and cell cycle-specific expression, because mRNA levels are high in G1 and low in proliferating cells. This also links estrogen-induced cell proliferation to clinical observations. In contrast, high eEF1α1 protein levels protect tumor cells from stress-induced cell death. These observations suggest that, by obviating EEF1A1 transcription, cancer cells can rapidly induce the heat shock response following proteotoxic stress, and survive.

Single-cell gene expression analysis reveals diversity among human spermatogonia

STUDY QUESTION

Is the molecular profile of human spermatogonia homogeneous or heterogeneous when analysed at the single-cell level?

SUMMARY ANSWER

Heterogeneous expression profiles may be a key characteristic of human spermatogonia, supporting the existence of a heterogeneous stem cell population.

WHAT IS KNOWN ALREADY

Despite the fact that many studies have sought to identify specific markers for human spermatogonia, the molecular fingerprint of these cells remains hitherto unknown.

STUDY DESIGN, SIZE, DURATION

Testicular tissues from patients with spermatogonial arrest (arrest, n = 1) and with qualitatively normal spermatogenesis (normal, n = 7) were selected from a pool of 179 consecutively obtained biopsies. Gene expression analyses of cell populations and single-cells (n = 105) were performed. Two OCT4-positive individual cells were selected for global transcriptional capture using shallow RNA-seq. Finally, expression of four candidate markers was assessed by immunohistochemistry.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Histological analysis and blood hormone measurements for LH, FSH and testosterone were performed prior to testicular sample selection. Following enzymatic digestion of testicular tissues, differential plating and subsequent micromanipulation of individual cells was employed to enrich and isolate human spermatogonia, respectively. Endpoint analyses were qPCR analysis of cell populations and individual cells, shallow RNA-seq and immunohistochemical analyses.

MAIN RESULTS AND THE ROLE OF CHANCE

Unexpectedly, single-cell expression data from the arrest patient (20 cells) showed heterogeneous expression profiles. Also, from patients with normal spermatogenesis, heterogeneous expression patterns of undifferentiated (OCT4, UTF1 and MAGE A4) and differentiated marker genes (BOLL and PRM2) were obtained within each spermatogonia cluster (13 clusters with 85 cells). Shallow RNA-seq analysis of individual human spermatogonia was validated, and a spermatogonia-specific heterogeneous protein expression of selected candidate markers (DDX5, TSPY1, EEF1A1 and NGN3) was demonstrated.

LIMITATIONS, REASONS FOR CAUTION

The heterogeneity of human spermatogonia at the RNA and protein levels is a snapshot. To further assess the functional meaning of this heterogeneity and the dynamics of stem cell populations, approaches need to be developed to facilitate the repeated analysis of individual cells.

WIDER IMPLICATIONS OF THE FINDINGS

Our data suggest that heterogeneous expression profiles may be a key characteristic of human spermatogonia, supporting the model of a heterogeneous stem cell population. Future studies will assess the dynamics of spermatogonial populations in fertile and infertile patients.

LARGE SCALE DATA

RNA-seq data is published in the GEO database: GSE91063.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by the Max Planck Society and the Deutsche Forschungsgemeinschaft DFG-Research Unit FOR 1041 Germ Cell Potential (grant numbers SCHO 340/7-1, SCHL394/11-2). The authors declare that there is no conflict of interest.

Distinctive changes in histone H3K4 modification mediated via Kdm5a expression in spermatogonial stem cells of cryptorchid testes

PURPOSE

Gonocytes differentiate into spermatogonial stem cells, which make it possible to maintain spermatogenesis continuously throughout life. We previously reported attenuated spermatogonial stem cell activity in cryptorchid testes, which resulted in altered spermatogenesis and affected fertility. However, few groups have examined the differentiation process from gonocytes to spermatogonial stem cells. To clarify the underlying mechanisms comprehensively we performed microarray analysis to assess differential expression of transcripts between normal and undescended testes in juvenile rats.

MATERIALS AND METHODS

Using microarray analysis we compared whole mRNA expression of normal and cryptorchid testes in a rat model. We subsequently validated differential expression of candidate genes by real-time reverse transcriptase-polymerase chain reaction and performed immunohistochemistry. We also investigated the methylation status of histone H3K4 in cryptorchid testes and the GC-1 spermatogonial cell line.

RESULTS

We detected 24 up-regulated and 39 down-regulated genes. Of these genes Kdm5a expression was significantly higher in undescended testes. Immunohistochemistry showed that Kdm5a was localized in the nuclei of gonocytes, spermatogonia and spermatocytes. H3K4me2/me3 expression levels were decreased in undescended testes at 9 days postpartum. Furthermore, Kdm5a over expression in GC-1 cells led to increased expression of Esr2, Neurog3, Pou5f1, Ret and Thy1.

CONCLUSIONS

Recent investigations revealed that not only genetic but also epigenetic regulation has a role in spermatogenesis. Kdm5a is likely involved in the transformation of gonocytes into spermatogonial stem cells by transcriptional regulation of specific genes via H3K4 histone modification. To our knowledge this is the first report of epigenetic analysis of germ cell differentiation during early spermatogenesis.

Attenuation of spermatogonial stem cell activity in cryptorchid testes

PURPOSE

To elucidate the mechanism of infertility caused by cryptorchidism we focused on early stage spermatogenesis and spermatogonial stem cell activity in undifferentiated spermatogonia in cryptorchid testes.

MATERIALS AND METHODS

Histological findings and expression patterns of the stem cell marker undifferentiated embryonic cell transcription factor 1 were examined in a unilateral cryptorchid rat model. We removed unilateral descended testis and contralateral descended testis from cryptorchid and normal rats (control), respectively, 18 days postcoitum to 144 days postpartum.

RESULTS

In descended testes gonocyte differentiation into early A spermatogonia occurred at 9 days postpartum. However, this transformation was altered in undescended testes. Furthermore, the undifferentiated embryonic cell transcription factor 1 negative early A spermatogonia-to-positive early A spermatogonia ratio was significantly higher in the undescended testis group (mean ± SD 0.69 ± 0.04) than in the control (0.46 ± 0.10, p = 0.037) and descended testis (0.44 ± 0.05, p = 0.022) groups, indicating decreased early A spermatogonia with spermatogonial stem cell activity in cryptorchid testes.

CONCLUSIONS

In cryptorchid testes the differentiation from gonocytes into early A spermatogonia and the stem cell activity of early A spermatogonia were altered during the early stage of spermatogenesis, suggesting that the loss of spermatogonial stem cell activity in cryptorchid rats resulted in altered spermatogenesis, thus interfering with fertility.

Spermatogenesis in cryptorchidism

Cryptorchidism or undescended testis is the most frequent congenital abnormality in newborn boys. The process of testicular descent to the scrotum is controlled by hormones produced in Leydig cells, insulin-like3, and androgens. Variation in genetic and environmental factors might affect testicular descent. A failure of spermatogenesis and germ cell apoptosis resulting in infertility as well as an increased risk of neoplastic transformation of germ cell are the direct consequences of cryptorchidism in adulthood.

Visualization of Reinke's crystals in normal and cryptorchid testis

Within the human testis, Reinke's crystals are found in Leydig cells but their nature and function are poorly understood. The aim of our study was to investigate the properties of Reinke's crystals in man with the normal morphology of the testis (control group) and infertile patients diagnosed with cryptorchidism. 20 biopsies from infertile patients and six biopsies from men with regular spermatogenesis (20-30 years.) were used. Sections of the testis tissue were stained with haematoxylin and eosin and a modified Masson's method. Specimens were observed by bright field, confocal and transmission electron microscopy (TEM). The number of Reinke's crystals in investigated groups was determined applying stereological methods. In both groups, Reinke's crystals were noted within the cytoplasm and nuclei of Leydig cells. Some "free" crystals were found within the interstitial space, outside Leydig cells. Confocal microscopy proved to be very useful in the assessment of the shape and 3D reconstruction of the crystal. TEM analysis confirmed a hexagonal form of the crystal, while crystallographic data on sections of 70-300 nm thickness provided a better insight into the organization of the crystal lattice. Stereological analysis revealed a significant increase in the number of crystals in cryptorchid testes when compared with controls. Increased number of crystals in cryptorchid specimens leads to the assumption that the prolonged exposure to higher (abdominal) temperature might stimulate enzymes involved in the synthesis of the proteins of the crystal. However, the exact molecular nature of the crystal lattice remains in both normal and cryptorchid testis obscure.

Advances in molecular genetics of cryptorchidism

Cryptorchidism is the most common congenital disorder in boys; one major complication of this disorder is male infertility. Androgens are key hormones to complete testicular descent; therefore, impaired fetal androgen action can result in this anomaly; its molecular etiology, however, remains unknown. Recent molecular approaches might provide an opportunity to identify not only candidate genes but also several predictive markers of future fertility. The purpose of this review is to summarize the recent insight into the genetic pathway of testicular descent and the molecular etiology of isolated cryptorchidism, and discuss the prospects of treatment to achieve future fertility in such patients.