In vivo analysis of developmentally and evolutionarily dynamic protein-DNA interactions regulating transcription of the Pgk2 gene during mammalian spermatogenesis

Decreased Ubiquitination and Acetylation of Histones 3 and 4 Are Associated with Obesity-Induced Disorders of Spermatogenesis in Mice

BACKGROUND

Obesity, a chronic metabolic disorder, is related to cardiovascular diseases, diabetes, cancer, and reproductive disorders. The relationship between obesity and male infertility is now well recognized, but the mechanisms involved are unclear. We aimed to observe the effect of obesity on spermatogenesis and to investigate the role of histone ubiquitination and acetylation modifications in obesity-induced spermatogenesis disorders.

METHODS

Thirty male C57BL/6J mice were randomly divided into two groups. The control group was fed with a general maintenance diet (12% fat), while a high-fat diet (HFD) group was fed with 40% fat for 10 weeks; then, they were mated with normal females. The fertility of male mice was calculated, testicular and sperm morphology were observed, and the expression levels of key genes and the levels of histone acetylation and ubiquitination modification during spermatogenesis were detected.

RESULTS

The number of sperm was decreased, as well as the sperm motility, while the number of sperm with malformations was increased. In the testes, the mRNA and protein expression levels of gonadotropin-regulated testicular RNA helicase (GRTH/DDX25), chromosome region maintenance-1 protein (CRM1), high-mobility group B2 (HMGB2), phosphoglycerate kinase 2 (PGK2), and testicular angiotensin-converting enzyme (tACE) were decreased. Furthermore, obesity led to a decrease in ubiquitinated H2A (ubH2A) and reduced levels of histone H3 acetylation K18 (H3AcK18) and histone H4 acetylation K5, K8, K12, and K16 (H4tetraAck), which disrupted protamine 1 (Prm1) deposition in testis tissue.

CONCLUSION

These results suggest that low levels of histone ubiquitination and acetylation are linked with obesity-induced disorders during spermatogenesis, contributing to a better understanding of obesity-induced damage to male reproduction.

Proteomic biomarkers in seminal plasma as predictors of reproductive potential in azoospermic men

Introduction

Azoospermia, characterized by an absence of sperm in the ejaculate, represents the most severe form of male infertility. While surgical sperm retrieval in obstructive azoospermia (OA) is successful in the majority of cases, patients with non-obstructive azoospermia (NOA) show retrieval rates of only about 50% and thus frequently have unnecessary surgery. Surgical intervention could be avoided if patients without preserved spermatogenesis are identified preoperatively. This prospective study aimed to discover biomarkers in seminal plasma that could be employed for a non-invasive differential diagnosis of OA/NOA in order to rationalize surgery recommendations and improve success rates.

Methods

All patients signed written informed consent, underwent comprehensive andrological evaluation, received human genetics to exclude relevant pathologies, and patients with azoospermia underwent surgical sperm retrieval. Using label-free LC-MS/MS, we compared the proteomes of seminal plasma samples from fertile men (healthy controls (HC), n=8) and infertile men diagnosed with 1) OA (n=7), 2) NOA with successful sperm retrieval (mixed testicular atrophy (MTA), n=8), and 3) NOA without sperm retrieval (Sertoli cell-only phenotype (SCO), n=7). Relative abundance changes of two candidate markers of sperm retrieval, HSPA2 and LDHC, were confirmed by Western Blot.

Results

We found the protein expression levels of 42 proteins to be significantly down-regulated (p ≤ 0.05) in seminal plasma from SCO NOA patients relative to HC whereas only one protein was down-regulated in seminal plasma from MTA patients. Analysis of tissue and cell expression suggested that the testis-specific proteins LDHC, PGK2, DPEP3, and germ-cell enriched heat-shock proteins HSPA2 and HSPA4L are promising biomarkers of spermatogenic function. Western blotting revealed a significantly lower abundance of LDHC and HSPA2 in the seminal plasma of men with NOA (SCO and MTA) compared to controls.

Discussion

The results indicate that certain testis-specific proteins when measured in seminal plasma, could serve as indicators of the presence of sperm in the testis and predict the success of sperm retrieval. Used in conjunction with conventional clinical assessments, these proteomic biomarkers may assist in the non-invasive diagnosis of idiopathic male infertility.

Novel Aspects of cAMP-Response Element Modulator (CREM) Role in Spermatogenesis and Male Fertility

Spermatogenesis is a very complex process with an intricate transcriptional regulation. The transition from the diploid to the haploid state requires the involvement of specialized genes in meiosis, among other specific functions for the formation of the spermatozoon. The transcription factor cAMP-response element modulator (CREM) is a key modulator that triggers the differentiation of the germ cell into the spermatozoon through the modification of gene expression. CREM has multiple repressor and activator isoforms whose expression is tissue-cell-type specific and tightly regulated by various factors at the transcriptional, post-transcriptional and post-translational level. The activator isoform CREMτ controls the expression of several relevant genes in post-meiotic stages of spermatogenesis. In addition, exposure to xenobiotics negatively affects CREMτ expression, which is linked to male infertility. On the other hand, antioxidants could have a positive effect on CREMτ expression and improve sperm parameters in idiopathically infertile men. Therefore, CREM expression could be used as a biomarker to detect and even counteract male infertility. This review examines the importance of CREM as a transcription factor for sperm production and its relevance in male fertility, infertility and the response to environmental xenobiotics that may affect CREMτ expression and the downstream regulation that alters male fertility. Also, some health disorders in which CREM expression is altered are discussed.

Non-Invasive Diagnostics of Male Spermatogenesis from Seminal Plasma: Seminal Proteins

The compounds of seminal plasma have great potential as biomarkers of male fertility and can be used as a diagnostic tool for types of azoospermia. Azoospermia occurs in approximately 1% of the male population, and for an effective therapy of this form of male infertility, it is important to distinguish between obstructive and non-obstructive azoospermia. Proteins in seminal plasma can serve as biomarkers for diagnosing azoospermia. Considering the various types of obstructions, a combination of multiple proteins is advisable for diagnostic purposes. In this context, testicular and epididymal proteins are particularly significant, as they are specific to these tissues and typically absent in ejaculate during most obstructions. A combination of multiple biomarkers is more effective than the analysis of a single protein. This group of markers contains TEX101 and ECM1 proteins, combined detections of these two bring a diagnostic output with a high sensitivity and specificity. Similar results were observed for combined detection of TEX101 and SPAG1. The effective using of specific biomarkers from seminal plasma can significantly improve the existing approaches to diagnosis of the causes of male infertility.

Identifying the Potential Roles of PBX4 in Human Cancers Based on Integrative Analysis

PBX4 belongs to the pre-B-cell leukemia homeobox (PBX) transcription factors family and acts as a transcriptional cofactor of HOX proteins participating in several pathophysiological processes. Recent studies have revealed that the dysregulation of PBX4 is closely related to multiple diseases, especially cancers. However, the research on PBX4’s potential roles in 33 cancers from the Cancer Genome Atlas (TCGA) is still insufficient. Therefore, we performed a comprehensive pan-cancer analysis to explore the roles of PBX4with multiple public databases. Our results showed that PBX4 was differentially expressed in 17 types of human cancer and significantly correlated to the pathological stage, tumor grade, and immune and molecular subtypes. We used the Kaplan–Meier plotter and PrognoScan databases to find the significant associations between PBX4 expression and prognostic values of multiple cancers. It was also found that PBX4 expression was statistically related to mutation status, DNA methylation, immune infiltration, drug sensitivity, and immune checkpoint blockade (ICB) therapy. Additionally, we found that PBX4 was involved in different functional states of multiple cancers from the single-cell resolution perspective. Enrichment analysis results showed that PBX4-related genes were enriched in the cell cycle process, MAPK cascade, ncRNA metabolic process, positive regulation of GTPase activity, and regulation of lipase activity and mainly participated in the pathways of cholesterol metabolism, base excision repair, herpes simplex virus 1 infection, transcriptional misregulation in cancer, and Epstein–Barr virus infection. Altogether, our integrative analysis could help in better understanding the potential roles of PBX4 in different human cancers.

Combined Analysis of Gut Microbiota and Plasma Metabolites Reveals the Effect of Red-Fleshed Apple Anthocyanin Extract on Dysfunction of Mice Reproductive System Induced by Busulfan

Busulfan is currently an indispensable anti-cancer drug, but the side effects on male reproductive system are so serious. Meanwhile, red-fleshed apples are natural products with high anthocyanin content. In this research, we analyzed the effect of red-fleshed apple anthocyanin extract (RAAE) on busulfan-treated mice. Compared with the busulfan group, main plasma biochemical indicators were significantly improved after RAAE treatment. Compared with BA0 (busulfan without RAAE) group, total antioxidant capacity(T-AOC) and the activity of superoxide dismutase (SOD) and glutathione catalase (GSH-Px) in RAAE treatment groups were obviously increased, while the activity of alanine aminotransferase (ALT) and aspartate aminotransferase (AST) were significantly decreased. Malondialdehyde (MDA) was significantly decreased in the RAAE groups. In addition, we found RAAE alleviated busulfan-disrupted spermatogenesis through improving genes expression which are important for spermatogenesis, such as DDX4, PGK2, and TP1. Furthermore, we found that RAAE increased beneficial bacteria Akkermansia and Lactobacillaceae, and significantly depleted harmful bacteria Erysipelotrichia. The correlation studies indicated that RAAE ameliorated busulfan-induced rise in LysoPC levels through regulating gut microbial community and their associated metabolites. In conclusion, this study extends our understanding of the alleviated effect of RAAE on busulfan-induced male reproductive dysfunction through regulating the relationships between gut microbiota and metabolites.

Secretions released from mesenchymal stem cells improve spermatogenesis restoration of cytotoxic treatment with busulfan in azoospermia mice

This study aimed at the efficacy of sequential treatment of bone marrow-derived mesenchymal stem cell secretion for busulfan-treated azoospermia in mice. The conditioned media (CM) was obtained from bone marrow mesenchymal stem cells (MSCs) or 293 cells. Chemically induced azoospermia mice received 200 μl MSC-CM or 293-CM twice a week intravenously for three consecutive weeks. The histological assessment of spermatogenic recovery quantifying the expression of meiosis-associated genes, and Sertoli cell barrier functional factors were assessed. The characteristics of TM4 cells (Sertoli cell line) after pre-incubation of MSC-CM in vitro were also obtained. The MSC-CM group had the most spermatogenic colonies among the three groups (p < .05), but no spermatids were seen. Expressions of the meiosis-associated genes Dazl, Vasa, Miwi, Stra8, CyclinA1, Pgk2 and Scp3 in MSC-CM testis were remarkably higher compared with 293-CM and busulfan groups respectively (p < .05). The levels of Sertoli cell barrier functional factors, for example ICAM-1 and N-cadherin, were significantly increased during MSC-CM treatment (p < .05). Moreover, pre-incubation of MSC-CM particularly accelerated the CD54 (ICAM-1) and CD44 expressions of TM4 cells and promoted cell inherent adhesion. MSC-CM treatment can significantly improve the short-term restoration of spermatogonial structures of chemically induced azoospermia related to facilitating Sertoli cell adhesion integrity.

Testicular biopsies microarray analysis reveals circRNAs are involved in the pathogenesis of non-obstructive azoospermia

Circular RNAs (circRNAs) have been reported to be involved in many diseases. But there is no report on circRNAs in non-obstructive azoospermia (NOA). The purpose of this paper is to explore the circular RNA expression profile and potential functions of circRNAs in NOA patients. We first preformed circRNA expression profiling analysis using a circRNA microarray in testicular samples from NOA and obstructive azoospermia (OA) patients. CircRNAs were validated by qRT-PCR. Bioinformatics analysis were used to construct the ceRNA network. GO and KEGG enrichment analysis were performed by using DAVID. Microarray analysis identified 82 differentially expressed circRNAs in NOA specimens. The differential expression of hsa_circRNA_402130, hsa_circRNA_072697, hsa_circRNA_030050, hsa_circRNA_100812 and hsa_circRNA_406168 was confirmed by qRT-PCR. Enrichment analysis revealed the association of hsa_circRNA_402130 and hsa_circRNA_072697 with multiple signaling pathways. The data indicated that circRNAs were significantly dysregulated in NOA specimens and might involve in the pathogenesis of NOA.

Arsenic influences spermatogenesis by disorganizing the elongation of spermatids in adult male mice

Arsenic (As) has become a major problem in maintaining the environment and human health due to its wide application in the production of agriculture and industry. Many studies indicate that As can affect spermatogenesis process and lower sperm quality. However, the undergoing molecular mechanism is unclear. For this, forty-eight 8-week old adult male mice were divided into four groups of twelve each, which were administrated to 0, 0.2, 2, 20 ppm As₂O₃ in their drinking water respectively for six months. The results showed that As treatment reduced sperm counts and increased the sperm malformation ratio of mice. Interestingly, both the amounts of round and elongated spermatids, and the ratios of spermatids elongation were decreased significantly by As exposure. Furthermore, the structure of Chromatoid Body (CB) which presents a typical nebulous shape in round spermatids after spermatogenesis arrested, and the mRNA expression levels of gene TDRD1, TDRD6 and TDRD7 related to CB were changed by arsenic. Again, the mRNA and protein expression levels of the markers DDX25 and CRM1 in haploid periods of spermatogenesis and the associated proteins HMG2, PGK2, and H4 with DDX25 regulation were declined significantly with As treatment. Taken together; it reveals that As interferes with spermatogenesis by disorganizing the elongation of spermatids. H4, HMG2 and PGK2 are regulated by DDX25 which interacts with CRM1 and may play a vital role in spermatogenesis disorder induced by As exposure, which maybe provides one of the underlying mechanisms for As-induced male reproductive toxicity.

Fluoride-induced unrestored arrest during haploid period of spermatogenesis via the regulation of DDX25 in rats

The effect of fluoride as an ongoing topic has attracted much attentions due to the decline in overall human fertility worldwide. However, whether fluorine causes a temporary stimulus or permanent damage to the male reproductive system, as well as the mechanism of fluoride influencing spermatogenesis remained unclear. 48 adult male rats were randomly divided into four groups (twelve each). Control group received the distilled water, while the other three groups were treated with 25, 50, 100 mg/L NaF via drinking water for 8 weeks. Six rats from each group were selected randomly to detect the levels of various indices related to spermatogenesis. The remaining rats were given only distilled water and left for recovery of a period of 2 weeks. Results showed that the levels of serum CK, ALP, CHE, BUN, UA, and Cr, testis morphology and the ultrastructure of sperm acrosome and chromatoid body (CB) were significantly changed by fluoride. Interestingly, the elongated spermatid counts, spermatids elongation ratio, and mRNA expressions of Prm1/2 and MIWI, TDRD1, TDRD 6, TDRD7, PABP, and Hsp72 related to CB decreased markedly in fluoride treatment groups compared to the control. Furthermore, the expression levels of DDX25 and associated regulatory proteins like CRM1, HMG2, H4, TP2, and PGK2 were down-regulated by fluoride. After 2-weeks withdrawal period, out of the 19 altered spermatogenesis indicators, 15 indicators in 100 mg/L group and 3 indicators in 50 mg/L group still exhibited a significant change, while none showed change in 25 mg/L group. These results proved that the reversibility of fluoride toxicity is dose-dependent on the male reproductive system. Meanwhile, fluoride caused unrestored arrest during the haploid period of spermatogenesis, where reduced DDX25 and associated regulatory proteins play a crucial role in this process, which could provide the underlying insights to the toxic mechanism of fluoride induced male reproductive toxicity.

Protein profile of Dabry's sturgeon (Acipenser dabryanus) spermatozoa and relationship to sperm quality

Knowledge of conditions affecting sperm quality is essential for efficient culture of fish for commercial purposes and conservation of species. Two-dimensional gel electrophoresis and matrix-assisted laser desorption/ionization time of flight mass spectrometry were used to characterize the proteomic profile of Acipenser dabryanus spermatozoa relative to motility and fertilization capacity. There were differential amounts of protein in 313 spots in spermatozoa of males classified to have relatively greater or lesser spermatozoa quality. The functions of 43 of 50 selected proteins were identified. The proteins in 14 spots were involved in metabolism, and of these, proteins in 11 spots were highly abundant in spermatozoa of males categorized to have spermatozoa of greater quality, including pyruvate kinase, enolase B, phosphoglycerate kinase, lactate dehydrogenase, cytosolic malate dehydrogenase, brain creatine kinase b, Ckmb protein, and nucleoside diphosphate kinase. The proteins involved in mechanics of flagellum movement were identified, including the dynein intermediate chain, radial spoke head 1 homolog; ropporin-1-like, Bardet-Biedl syndrome 5, ADP-ribosylation factor-like protein 3, tektin-4, gamma-actin, and tubulin cytoskeleton proteins to be differentially abundant in spermatozoa that were classified relatively greater or lesser quality. Heat shock proteins, copper/zinc superoxide dismutase and peroxiredoxins, which are involved in stress response were of differential abundance in spermatozoa from males with spermatozoa in the two different classification groups. Proteins were also detected that are involved in protein folding and binding, or hydrolase activity. The results are valuable for the prediction of sperm quality and for reproduction management in A. dabryanus and other threatened species.

Species-specific expression of phosphoglycerate kinase 2 (PGK2) in the developing porcine testis

Whereas stage-specific markers for spermatogonial cells have been well investigated in mouse, the specific markers of germ cells in the testis of domestic animals have not been well defined. Phosphoglycerate kinase (PGK), an enzyme that converts 1,3-bisphosphoglycerate and adenosine diphosphate to 3-phosphoglycerate and adenosine triphosphate, has two isozymes: PGK1 and PGK2. In mouse, PGK1 exists only during the early stages of spermatogenesis, and PGK2 is then expressed during the pachytene spermatocyte stage. In this study, we investigated the localization of PGK2 in the developing porcine testis, and compared the similarities and differences in its expression with that of the PGK2 in mouse. The PGK2 protein was found to be exclusively expressed in spermatids of the adult mouse testis, whereas PGK2-positive cells were observed in the prepubertal and postpubertal testes of pigs. Based on this result, we examined the expression of PGK2 in in vitro-cultured porcine undifferentiated spermatogonia and found it to be maintained in the cultured cells. To verify this result and identify the spermatogonial stem cell-like potential in recipient testes, PKH26 dye-stained PGK2-positive cells were transplanted into the testes of busulfan-treated immunodeficient mouse that had been depleted of both testicular germ cells and somatic cells. The transplanted cells colonized the recipient testis at 8 weeks post transplantation, and fluorescence microscopy identified the cells in the basement membranes of the seminiferous tubules of the injected mouse. Taken together, our results suggest that PGK2 is expressed differently in the testes of mouse and pigs according to developmental stage. This finding should contribute to the study of spermatogenesis and the production of transgenic domestic animals through in vitro spermatogonial sperm cell culture.

Germ cell-intrinsic requirement for the homeodomain transcription factor PKnox1/Prep1 in adult spermatogenesis

PKnox1 (also known as Prep1) belongs to the TALE family of homeodomain transcription factors that are critical for regulating growth and differentiation during embryonic and postnatal development in vertebrates. We demonstrate here that PKnox1 is required for adult spermatogenesis in a germ cell-intrinsic manner. Tamoxifen-mediated PKnox1 loss in the adult testes, as well as its germ cell-specific ablation, causes testis hypotrophy with germ cell apoptosis and, as a consequence, compromised spermatogenesis. In PKnox1-deficient testes, spermatogenesis was arrested at the c-Kit⁺ spermatogonia stage, with a complete loss of the meiotic spermatocytes, and was accompanied by compromised differentiation of the c-Kit⁺ spermatogonia. Taken together, these results indicate that PKnox1 is a critical regulator of maintenance and subsequent differentiation of the c-Kit⁺ stage of spermatogonia in the adult testes.

Transcriptome analysis of highly purified mouse spermatogenic cell populations: gene expression signatures switch from meiotic-to postmeiotic-related processes at pachytene stage

Background

Spermatogenesis is a complex differentiation process that involves the successive and simultaneous execution of three different gene expression programs: mitotic proliferation of spermatogonia, meiosis, and spermiogenesis. Testicular cell heterogeneity has hindered its molecular analyses. Moreover, the characterization of short, poorly represented cell stages such as initial meiotic prophase ones (leptotene and zygotene) has remained elusive, despite their crucial importance for understanding the fundamentals of meiosis.

Results

We have developed a flow cytometry-based approach for obtaining highly pure stage-specific spermatogenic cell populations, including early meiotic prophase. Here we combined this methodology with next generation sequencing, which enabled the analysis of meiotic and postmeiotic gene expression signatures in mouse with unprecedented reliability. Interestingly, we found that a considerable number of genes involved in early as well as late meiotic processes are already on at early meiotic prophase, with a high proportion of them being expressed only for the short time lapse of lepto-zygotene stages. Besides, we observed a massive change in gene expression patterns during medium meiotic prophase (pachytene) when mostly genes related to spermiogenesis and sperm function are already turned on. This indicates that the transcriptional switch from meiosis to post-meiosis takes place very early, during meiotic prophase, thus disclosing a higher incidence of post-transcriptional regulation in spermatogenesis than previously reported. Moreover, we found that a good proportion of the differential gene expression in spermiogenesis corresponds to up-regulation of genes whose expression starts earlier, at pachytene stage; this includes transition protein-and protamine-coding genes, which have long been claimed to switch on during spermiogenesis. In addition, our results afford new insights concerning X chromosome meiotic inactivation and reactivation.

Conclusions

This work provides for the first time an overview of the time course for the massive onset and turning off of the meiotic and spermiogenic genetic programs. Importantly, our data represent a highly reliable information set about gene expression in pure testicular cell populations including early meiotic prophase, for further data mining towards the elucidation of the molecular bases of male reproduction in mammals.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-016-2618-1) contains supplementary material, which is available to authorized users.

Dephosphorylation of Tak1 at Ser412 greatly contributes to the spermatocyte-specific testis toxicity induced by (5R)-5-hydroxytriptolide in C57BL/6 mice

(5R)-5-Hydroxytriptolide (LLDT-8), a novel triptolide derivative, will proceed to phase II clinical trials for the treatment of rheumatoid arthritis and cancer. However, the selection of disease and patients is largely limited by the testis toxicity, yet toxicity mechanisms are still poorly understood. In this study, LLDT-8 dose and time-dependently decreased the testes weight, germinal cell layers and induced abnormal spermatid development. Analysis of the germ cell-specific marker showed that spermatocytes were more sensitive to LLDT-8, which was confirmed by the in vitro sensitivity assay with spermatocyte-like GC-2spd and sertoli-like TM4 cells. In GC-2spd, LLDT-8 induced G1/S arrest and apoptosis. MAPK activity screening identified that TGF-β activated kinase 1 (Tak1) is critical in LLDT-8 induced apoptosis. LLDT-8 reduced the Tak1 protein and dephosphorylated Tak1 at Ser412 in GC-2spd and the testes, but not in TM4. RNAi mediated depletion or pharmacologic inhibition of Tak1 induced apoptosis in GC-2spd. Meanwhile, activating Tak1 rescued up to 50% of the GC-2spd cells from the apoptosis induced by LLDT-8. Altogether, our study firstly revealed the important role of Tak1 in the survival of spermatocytes, and dephosphorylation of Tak1 at Ser412 may contribute to the spermatocyte-specific testis toxicity induced by LLDT-8.

Gestational form of Selenium in Free-Choice Mineral Mixes Affects Transcriptome Profiles of the Neonatal Calf Testis, Including those of Steroidogenic and Spermatogenic Pathways

In areas where soils are deficient in Selenium (Se), dietary supplementation of this trace mineral directly to cattle is recommended. Because Se status affects testosterone synthesis and frequency of sperm abnormalities, and the form of Se supplemented to cows affects tissue-specific gene expression, the objective of this study was to determine whether the form of Se consumed by cows during gestation would affect the expression of mRNAs that regulate steroidogenesis and/or spermatogenesis in the neonatal calf testis. Twenty-four predominantly Angus cows were assigned randomly to have individual, ad libitum, access of a mineral mix containing 35 ppm of Se in free-choice vitamin-mineral mixes as either inorganic (ISe), organic (OSe), or a 50/50 mix of ISe and OSe (MIX), starting 4 months prior to breeding and continuing throughout gestation. Thirteen male calves were born over a 3-month period (ISe, n = 5; OSe, n = 4; MIX, n = 4), castrated within 2 days of birth, and extracted testis RNA subjected to transcriptomal analysis by microarray (Affymetrix Bovine 1.0 ST arrays) and targeted gene expression analysis by real-time reverse-transcription PCR (RT-PCR) of mRNAs encoding proteins known to affect steroidogenesis and/or spermatogenesis. The form of dam Se affected (P < 0.05) the expression of 853 annotated genes, including 17 mRNAs putatively regulating steroidogenesis and/or spermatogenesis. Targeted RT-PCR analysis indicated that the expression of mRNA encoding proteins CYP2S1 (cytochrome P450, family 2, subfamily S, polypeptide 1), HSD17B7 (hydroxysteroid (17β) dehydrogenase 7), SULT1E1 (sulfotransferase family 1E, estrogen preferring, member 1), LDHA (lactate dehydrogenase A), CDK5R1 (cyclin-dependent kinase 5, regulatory subunit 1), and LEP (leptin) was affected (P < 0.05) by form of Se consumed by dams of developing bull calves, while AKR1C4 (aldo-keto reductase family 1, member C4) and CCND2 (cyclin D2) tended (P < 0.09) to be affected. Our results indicate that form of Se fed to dams during gestation affected the transcriptome of the neonatal calf testis. If these profiles are maintained throughout maturation, then the form of Se fed to dams may impact bull fertility and the development of Se form-dependent mineral mixes that target gestational development of the testis are warranted.

Characteristics of testis-specific phosphoglycerate kinase 2 and its association with human sperm quality

STUDY QUESTION

Is there an association between the expression of phosphoglycerate kinase (PGK) 2 in spermatozoa and sperm quality in both elderly men and young asthenozoospermia patients?

SUMMARY ANSWER

Spermatozoa from elderly men and young asthenozoospermia patients show decreased expression of PGK2, which has a close positive relationship with sperm quality.

WHAT IS KNOWN ALREADY

PGK1 and PGK2 are involved in spermatogenesis and thought to be related to sperm motility. However, limited information is known about their temporal-spatial expression in human spermatogenesis and their relationship with sperm quality.

STUDY DESIGN, SIZE, DURATION

This was a case-control study including 30 healthy young males (aged 28-31 years), 30 elderly men (aged 68-70 years), and 30 asthenozoospermic patients (aged 25-40 years, progressive motility <32%) who donated semen samples. Furthermore, young testes samples were obtained from five fathers (27-33 years old) who had died in car accidents, while aged testes samples were obtained from five elderly fathers (78-82 years old) who were prostate cancer patients.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Semen samples from young adults, elderly men and asthenozoospermic patients were prepared, and their parameters were assessed by Computer-Aided Sperm Analysis (CASA). Sperm proteins were extracted for western blot analysis. Immunohistochemistry was used to characterize the cellular localization of PGK1 and PGK2 in testes samples. Sperm immunofluorescence quantification experiments identified the differential expression of PGK1 and PGK2 in sperm from young adults, elderly men and asthenozoospermic patients. Antibodies against PGK1 and PGK2 were used to test their influence on sperm motility and penetration into viscous media. A modified Kremer test using methyl cellulose was adopted to assess sperm function via penetration into viscous media.

MAIN RESULTS AND THE ROLE OF CHANCE

Cellular localization analysis showed that PGK1 was mainly expressed in spermatogonia whereas PGK2 was mainly expressed in round spermatids. Expression levels of both PGKs were significantly decreased in the testis with ageing (P < 0.05). Western blot and immunofluorescence quantification showed markedly lower expression of PGK2 (P < 0.05) in sperm from elderly men or asthenozoospermic patients compared sperm from with healthy young men. Sperm functional analysis validated the close relationship between expression of PGK2 and sperm motility (staining percentage, r = 0.60, P < 0.05; intensity, r = 0.59, P < 0.05). Use of an anti-PGK2 antibody on sperm significantly decreased their ability to penetrate into a cervical mucus substitute (P < 0.05).

LIMITATIONS, REASONS FOR CAUTION

Before any clinical applications using PGK2 to assess sperm quality can be developed, more cases should be used to evaluate this approach.

WIDER IMPLICATIONS OF THE FINDINGS

The study provides new insights into the role of PGKs in male reproduction. The results also indicate that PGK2 is a promising molecular candidate for the assessment of sperm quality and the screening of male contraceptive targets.

STUDY FUNDING/COMPETING INTERESTS

This work was supported by grants from the National Natural Science Foundation of China (no. 81300533, 81370013 and 81000277) and Shandong Provincial Natural Science Foundation, China (ZR2013HQ002). The authors declare no competing financial interests.

The role of breast cancer resistance protein (Bcrp/Abcg2) in triptolide-induced testis toxicity

Triptolide possesses unique immunosuppressive and anti-tumor activities. However, its clinical use is limited by the cumulative toxicity in the testis and the mechanisms are poorly understood.

Co-regulation of pluripotency and genetic integrity at the genomic level

The Disposable Soma Theory holds that genetic integrity will be maintained at more pristine levels in germ cells than in somatic cells because of the unique role germ cells play in perpetuating the species. We tested the hypothesis that the same concept applies to pluripotent cells compared to differentiated cells. Analyses of transcriptome and cistrome databases, along with canonical pathway analysis and chromatin immunoprecipitation confirmed differential expression of DNA repair and cell death genes in embryonic stem cells and induced pluripotent stem cells relative to fibroblasts, and predicted extensive direct and indirect interactions between the pluripotency and genetic integrity gene networks in pluripotent cells. These data suggest that enhanced maintenance of genetic integrity is fundamentally linked to the epigenetic state of pluripotency at the genomic level. In addition, these findings demonstrate how a small number of key pluripotency factors can regulate large numbers of downstream genes in a pathway-specific manner.

Sequence-specific promoter elements regulate temporal-specific changes in chromatin required for testis-specific activation of the Pgk2 gene

The phosphoglycerate kinase-2 (Pgk2) gene is regulated in a tissue-, cell type-, and developmental stage-specific manner during spermatogenesis and is required for normal sperm motility and fertility in mammals. Activation of Pgk2 transcription is regulated by testis-specific demethylation of DNA and binding of testis-specific transcription factors to enhancer and core promoter elements. Here, we show that chromatin remodeling including reconfiguration of nucleosomes and changes in histone modifications is also associated with transcriptional activation of the Pgk2 gene during spermatogenesis. Developmental studies indicate that the order of events involved in transcriptional activation of the Pgk2 gene includes demethylation of DNA in T₁- and T₂-prospermatogonia, binding of a factor to the CAAT box in type A and B spermatogonia, followed by recruitment of chromatin remodeling factors, displacement of a nucleosome from the Pgk2 promoter region, binding of factors to the Pgk2 core promoter and enhancer regions, and, finally, initiation of transcription in primary spermatocytes. Transgene studies show that Pgk2 core promoter elements are required to direct demethylation of DNA and reconfiguration of nucleosomes, whereas both enhancer and core promoter elements are required to direct changes in histone modifications and initiation of transcription. These results provide novel insight into the developmental order of molecular events required to activate tissue-specific transcription of the Pgk2 gene, the distinct elements in the 5'-regulatory region of the Pgk2 gene that regulate each of these events, and the relationship among these events in that each step in this process appears to be a necessary prerequisite for the subsequent step.

Connecting cis-elements and trans-factors with mechanisms of developmental regulation of mRNA translation in meiotic and haploid mammalian spermatogenic cells

mRNA-specific regulation of translational activity plays major roles in directing the development of meiotic and haploid spermatogenic cells in mammals. Although many RNA-binding proteins (RBPs) have been implicated in normal translational control and sperm development, little is known about the keystone of the mechanisms: the interactions of RBPs and microRNAs withcis-elements in mRNA targets. The problems in connecting factors and elements with translational control originate in the enormous complexity of post-transcriptional regulation in mammalian cells. This creates confusion as to whether factors have direct or indirect and large or small effects on the translation of specific mRNAs. This review argues that gene knockouts, heterologous systems, and overexpression of factors cannot provide convincing answers to these questions. As a result, the mechanisms involving well-studied mRNAs (Ddx4/Mvh,Prm1,Prm2, andSycp3) and factors (DICER1, CPEB1, DAZL, DDX4/MVH, DDX25/GRTH, translin, and ELAV1/HuR) are incompletely understood. By comparison, mutations in elements can be used to define the importance of specific pathways in regulating individual mRNAs. However, few elements have been studied, because the only reliable system to analyze mutations in elements, transgenic mice, is considered impractical. This review describes advances that may facilitate identification of the direct targets of RBPs and analysis of mutations incis-elements. The importance of upstream reading frames in the developmental regulation of mRNA translation in spermatogenic cells is also documented.

Pyruvate dehydrogenase complex: mRNA and protein expression patterns of E1α subunit genes in human spermatogenesis

During spermatogenesis, germ cells undergo a complex process of cell differentiation and morphological restructuring, which depends on the coordinated expression of different genes. Some vital examples are those involved in cell energy metabolism, namely the genes encoding the E1α subunit of pyruvate dehydrogenase complex: the somatic PDHA1 (X-linked) and the testis-specific PDHA2 (autosomal). There are no data related to the study at the RNA and protein levels of PDHA genes during human spermatogenesis. The present study aimed to describe the mRNA and protein expression patterns of the human PDHA genes during spermatogenesis. Expression profiles of the PDHA1 and PDHA2 genes were characterized using different human tissues and cells. Diploid and haploid germ cells fractions were obtained from testis tissues. The mRNA profiles were analyzed by quantitative RT-PCR, whereas the protein profiles were evaluated by immunohistochemistry, western blotting and two-dimensional electrophoresis. Expression of the PDHA1 gene was found in all somatic cells, whereas expression of PDHA2 gene was restricted to germ cells. The switch from X-linked to autosomic gene expression occurred in spermatocytes. Data suggest the activation of PDHA2 gene expression is most probably a mechanism to ensure the continued expression of the protein, thus allowing germ cell viability and functionality.

Dynamic expression pattern and subcellular localization of the Rhox10 homeobox transcription factor during early germ cell development

Homeobox genes encode transcription factors that regulate diverse developmental events. The largest known homeobox gene cluster - the X-linked mouse reproductive homeobox (Rhox) cluster - harbors genes whose expression patterns and functions are largely unknown. Here, we report that a member of this cluster, Rhox10, is expressed in male germ cells. Rhox10 is highly transcribed in spermatogonia in vivo and is upregulated in response to the differentiation-inducing agent retinoic acid in vitro. Using a specific RHOX10 antiserum that we generated, we found that RHOX10 protein is selectively expressed in fetal gonocytes, germline stem cells, spermatogonia, and early spermatocytes. RHOX10 protein undergoes a dramatic shift in subcellular localization as germ cells progress from mitotically arrested gonocytes to mitotic spermatogonia and from mitotic spermatogonia to early meiotic spermatocytes, consistent with RHOX10 performing different functions in these stages.

A-MYB (MYBL1) stimulates murine testis-specific Ldhc expression via the cAMP-responsive element (CRE) site

Generally, knowledge of the mechanism regulating gene expression in primary spermatocytes is incomplete. We have used the lactate dehydrogenase gene (Ldhc) as a model to explore these mechanisms during spermatogenesis. Its 100-bp core promoter contained two essential elements common to many genes, a GC box and a CRE site. Here we report results that support a model in which transcription factor MYBL1 acts as a coactivator directing tissue-specific expression via the CRE cis element. We hypothesize that this is a common mechanism involving activation of multiple genes in the primary spermatocyte. MYBL1 is expressed predominantly as a tissue-specific transcription factor in spermatocytes and breast epithelial cells. Our finding that LDHC expression is lost in 21-day testes of MYBL1 mutant mice supports our hypothesis. In the GC1-spg germ cell line exogenous MYBL1 induces activity 4- to 8-fold, although extracts from these cells do not show MYBL1 binding activity for the Myb consensus sequences in the Ldhc promoter by EMSA. Rather, MYBL1 stimulates expression from a synthetic promoter containing only CRE elements, suggesting MYBL1 activates the promoter by interacting with protein that binds to a CRE element. Mutation of three Myb sites does not affect Ldhc promoter activity significantly (P > 0.05). CREB-binding protein (CBP) is a coactivator that interacts with CRE-binding protein CREB. We show that the transactivation domain (TAD) in MYBL1 interacts with the KIX domain in CBP, and the TAD domain and DNA binding domain in MYBL1 each interact with the CREB N-terminal domain. MYBL1 also stimulated expression from testis-specific genes Pgk2 (phosphoglycerate kinase 2) and Pdha2 (pyruvate dehydrogenase alpha 2) promoters, each of which contains CRE promoter elements and is expressed in primary spermatocytes. We propose that MYBL1 directs germ cell-specific activation via the CRE site of certain genes that are activated specifically in the primary spermatocyte, although other, more indirect effects of MYBL1 remain a possible explanation for our results.

Crystal structure of Plasmodium falciparum phosphoglycerate kinase: evidence for anion binding in the basic patch

3-Phosphoglycerate kinase (EC 2.7.2.3) is a key enzyme in the glycolytic pathway and catalyzes an important phosphorylation step leading to the production of ATP. The crystal structure of Plasmodium falciparum phosphoglycerate kinase (PfPGK) in the open conformation is presented in two different groups, namely I222 and P6(1)22. The structure in I222 space group is solved using MAD and refined at 3Å whereas that in P6(1)22A is solved using MR and refined at 2.7Å. I222 form has three monomers in asymmetric unit whereas P6(1)22 form has two monomers in the asymmetric unit. In both crystal forms a sulphate ion is located at the active site where ATP binds, but no Mg(2+) ion is observed. For the first time another sulphate ion is found at the basic patch where the 3-phosphate of 1,3-biphosphoglycerate normally binds. This was found in both chains of P6(1)22 form but only in chain A of I222 form.

MYBBP1A: a new Ipr1's binding protein in mice

Infection with mycobacterium tuberculosis (MTB) can cause different outcomes in hosts with variant genetic backgrounds. Previously, we identified an intracellular pathogen resistance 1 (Ipr1) gene with the role of resistance of MTB infection in mice model. However, until now, its binding proteins have been little known even for its human homology, SP110. In this study, the homology for mouse Ipr1 in canines was found to have an extra domain structure, h.1.5.1. And 30 potential candidate proteins were predicted to bind canine Ipr1, which were characterized of the interacting structure with the h.1.5.1. Among them, MYBBP1A was verified to bind with both Ipr1 and eGFP-Ipr1 in mouse macrophage J774A.1 clone 21 cells using co-immunoprecipitation method. And with the constructed high-confidence Ipr1-involved network, we suggested that Ipr1 might be involved in apoptosis pathway via MYBBP1A.

Microarray-based analysis of cell-cycle gene expression during spermatogenesis in the mouse

Mammalian spermatogenesis is a continuum of cellular differentiation in a lineage that features three principal stages: 1) a mitotically active stage in spermatogonia, 2) a meiotic stage in spermatocytes, and 3) a postreplicative stage in spermatids. We used a microarray-based approach to identify changes in expression of cell-cycle genes that distinguish 1) mitotic type A spermatogonia from meiotic pachytene spermatocytes and 2) pachytene spermatocytes from postreplicative round spermatids. We detected expression of 550 genes related to cell-cycle function in one or more of these cell types. Although a majority of these genes were expressed during all three stages of spermatogenesis, we observed dramatic changes in levels of individual transcripts between mitotic spermatogonia and meiotic spermatocytes and between meiotic spermatocytes and postreplicative spermatids. Our results suggest that distinct cell-cycle gene regulatory networks or subnetworks are associated with each phase of the cell cycle in each spermatogenic cell type. In addition, we observed expression of different members of certain cell-cycle gene families in each of the three spermatogenic cell types investigated. Finally, we report expression of 221 cell-cycle genes that have not previously been annotated as part of the cell cycle network expressed during spermatogenesis, including eight novel genes that appear to be testis-specific.

Phosphoglycerate kinase 2 (PGK2) is essential for sperm function and male fertility in mice

Phosphoglycerate kinase 2 (PGK2), an isozyme that catalyzes the first ATP-generating step in the glycolytic pathway, is encoded by an autosomal retrogene that is expressed only during spermatogenesis. It replaces the ubiquitously expressed phosphoglycerate kinase 1 (PGK1) isozyme following repression of Pgk1 transcription by meiotic sex chromosome inactivation during meiotic prophase and by postmeiotic sex chromatin during spermiogenesis. The targeted disruption of Pgk2 by homologous recombination eliminates PGK activity in sperm and severely impairs male fertility, but does not block spermatogenesis. Mating behavior, reproductive organ weights (testis, excurrent ducts, and seminal vesicles), testis histology, sperm counts, and sperm ultrastructure were indistinguishable between Pgk2(-/-) and wild-type mice. However, sperm motility and ATP levels were markedly reduced in males lacking PGK2. These defects in sperm function were slightly less severe than observed in males lacking glyceraldehyde-3-phosphate dehydrogenase, spermatogenic (GAPDHS), the isozyme that catalyzes the step preceding PGK2 in the sperm glycolytic pathway. Unlike Gapdhs(-/-) males, the Pgk2(-/-) males also sired occasional pups. Alternative pathways that bypass the PGK step of glycolysis exist. We determined that one of these bypass enzymes, acylphosphatase, is active in mouse sperm, perhaps contributing to phenotypic differences between mice lacking GAPDHS or PGK2. This study determined that PGK2 is not required for the completion of spermatogenesis, but is essential for sperm motility and male fertility. In addition to confirming the importance of the glycolytic pathway for sperm function, distinctive phenotypic characteristics of Pgk2(-/-) mice may provide further insights into the regulation of sperm metabolism.

Activation and repression domains within the promoter of the rat cathepsin L gene orchestrate sertoli cell-specific and stage-specific gene transcription in transgenic mice

In murine testes, only Sertoli cells express the cathepsin L (Ctsl) gene, and this expression is restricted to stages V-VIII of the cycle. Our previous transgenic analysis of Tg (-2065/+977) demonstrated that this expression is regulated by a approximately 2-kb promoter. To begin to elucidate this regulation, we analyzed the in vivo expression of two new transgenes, Tg (-935/+977) and Tg (-451/+977). Tg (-935/+977) was expressed by Sertoli cells but, in contrast to Tg (-2065/+977), was expressed at all stages of the cycle, by spermatocytes, by the vascular endothelium, and by seven other organs. Tg (-451/+977) was not expressed by Sertoli cells but by spermatogenic cells and by the brain. Lack of expression of Tg (-451/+977) by Sertoli cells was not due to a lack of essential cis-acting elements. Transient transfection analysis of primary cultures of mature rat Sertoli cells demonstrated that in mature Sertoli cells, most of the activity of the Ctsl promoter is accounted for by one of two redundant upstream GC motifs and an Initiator that are within 100 bp of the transcription start site. We conclude that transcriptional repressors upstream from nucleotide -935 of the rat Ctsl gene restrict testicular expression of this gene to Sertoli cells at stages V-VIII. At these stages, transcriptional activators located between nucleotides -935 and -452 promote access of the transcriptional machinery to the two GC boxes and to the Initiator. Thus, upstream repressors and activators as well as cis-acting elements near the transcription start site control stage-specific Ctsl transcription by Sertoli cells.

Identification and characterization of a novel testis-specific gene CKT2, which encodes a substrate for protein kinase CK2

Protein kinase CK2 is a serine/threonine kinase known to phosphorylate numerous substrates. CK2 is implicated in several physiologic and pathologic processes, particularly in cancer biology. CK2 is comprised of several subunits, including CK2α, CK2α′ and CK2β. Inactivation of CK2α′ leads to chromatin degeneration of germ cells, resulting in male sterility. To identify additional targets of CK2α′ in testes and to determine the role of CK2α′ in germ cell nuclear integrity, GST pull-down and protein–protein interaction assays were conducted. A novel testis-specific gene, CKT2 (CK2 Target protein 2), was found whose product interacts with and is phosphorylated by CK2 in vitro and in vivo. CKT2 is a 30.2 kDa protein with one coiled-coil domain and six putative phosphorylation sites. High expression of CKT2 correlated with chromatin condensation of spermatids in murine testes. Findings reported herein demonstrate that CKT2 is a target protein of native CK2α′ in testes and suggest that CKT2 plays a role in chromatin regulation of male germ cells.

RNA-based gene duplication: mechanistic and evolutionary insights

Gene copies that stem from the mRNAs of parental source genes have long been viewed as evolutionary dead-ends with little biological relevance. Here we review a range of recent studies that have unveiled a significant number of functional retroposed gene copies in both mammalian and some non-mammalian genomes. These studies have not only revealed previously unknown mechanisms for the emergence of new genes and their functions but have also provided fascinating general insights into molecular and evolutionary processes that have shaped genomes. For example, analyses of chromosomal gene movement patterns via RNA-based gene duplication have shed fresh light on the evolutionary origin and biology of our sex chromosomes.

Glycolytic enzyme inhibitors in cancer treatment

BACKGROUND

The radio- and chemotherapeutics currently used for the treatment of cancer are widely known to be characterized by a low therapeutic index. An interesting approach to overcoming some of the limits of these techniques is the exploitation of the so-called Warburg effect, which typically characterizes neoplastic cells. Interestingly, this feature has already been utilized with good results, but only for diagnostic purposes (PET and SPECT). From a pharmacological point of view, drugs able to perturb cancer cell metabolism, specifically at the level of glycolysis, may display interesting therapeutic activities in cancer.

OBJECTIVE

The pharmacological actions of these glycolytic enzyme inhibitors, based primarily on ATP depletion, could include: i) amelioration of drug selectivity by exploiting the particular glycolysis addiction of cancer cell; ii) inhibition of energetic and anabolic processes; iii) reduction of hypoxia-linked cancer-cell resistance; iv) reduction of ATP-dependent multi-drug resistance; and v) cytotoxic synergism with conventional cancer treatments.

CONCLUSION

Several glycolytic inhibitors are currently in preclinical and clinical development. Their clinical value as anticancer agents, above all in terms of therapeutic index, strictly depends on a careful reevaluation of the pathophyiological role of the unique metabolism of cancer cells in general and of Warburg effect in particular.

Molecular and functional characterization of the murine ldh2 promoter region: Sp-binding GC-box domains are the key cis-elements regulating ldh2 gene expression during spermatogenesis

The goal of the present study was to elucidate the specific transcriptional mechanisms that regulate ldh2 gene expression during the early stages of spermatogenesis. DNA sequence analysis of the 1.0-kb ldh2 promoter region directly upstream of the transcriptional start site indicated the presence of three SP-protein binding GC-box elements and the absence of TATA and CAAT boxes. Functional characterization studies of the mouse ldh2 promoter were performed in the SV40 transformed mouse spermatogonial cell line, GC-1 spg. Transfection/transient expression studies using full-length and truncated ldh2 promoter/luciferase reporter constructs revealed that all three of the SP-binding cis-regulatory GC-box elements are required for optimal ldh2 promoter activity. Additional site-directed mutagenesis studies indicated that the two most proximal GC-box sites play essential regulatory roles in mediating basal ldh2 promoter activity. These studies suggest that the expression of the ldh2 gene in spermatogonia and early spermatocytes are regulated by SP-mediated transcriptional mechanisms.

A cytoplasmic variant of the KH-type splicing regulatory protein serves as a decay-promoting factor for phosphoglycerate kinase 2 mRNA in murine male germ cells

Phosphoglycerate kinase 2 (PGK2) is a germ cell-specific protein whose mRNA is translationally regulated in the mammalian testis. Using RNA affinity chromatography with the 3'-untranslated region (UTR) of Pgk2 mRNA and adult testis extracts, several associated proteins including a novel isoform of the AU-rich element RNA-binding protein and KH-type splicing regulatory protein (KSRP) were identified. KSRP, a protein of approximately 75 kDa, is widely expressed in somatic and germ cells where it is primarily nuclear. In addition to the approximately 75-kDa KSRP, a approximately 52-kD KSRP, t-KSRP, is present in the cytoplasm of a subpopulation of germ cells. t-KSRP binds directly to a 93-nt sequence (designated the F1 region) of the 3'-UTR of the Pgk2 mRNA and destabilizes Pgk2 mRNA constructs in testis extracts and in transfected cells. We conclude that this testicular variant of the multifunctional nucleic acid-binding protein, KSRP, serves as a decay-promoting factor for Pgk2 mRNA in male germ cells.

Expression patterns of SP1 and SP3 during mouse spermatogenesis: SP1 down-regulation correlates with two successive promoter changes and translationally compromised transcripts

Because of their prominent roles in regulation of gene expression, it is important to understand how levels of Krüpple-like transcription factors SP1 and SP3 change in germ cells during spermatogenesis. Using immunological techniques, we found that both factors decreased sharply during meiosis. SP3 declined during the leptotene-to-pachytene transition, whereas SP1 fell somewhat later, as spermatocytes progressed beyond the early pachytene stage. SP3 reappeared for a period in round spermatids. For Sp1, the transition to the pachytene stage is accompanied by loss of the normal, 8.2-kb mRNA and appearance of a prevalent, 8.8-kb variant, which has not been well characterized. We have now shown that this pachytene-specific transcript contains a long, unspliced sequence from the first intron and that this sequence inhibits expression of a reporter, probably because of its many short open-reading frames. A second testis-specific Sp1 transcript in spermatids of 2.4 kb also has been reported previously. Like the 8.8-kb variant, it is compromised translationally. We have confirmed by Northern blotting that the 8.8-, 8.2-, and 2.4-kb variants account for the major testis Sp1 transcripts. Thus, the unexpected decline of SP1 protein in the face of continuing Sp1 transcription is explained, in large part, by poor translation of both novel testis transcripts. As part of this work, we also identified five additional, minor Sp1 cap sites by 5' rapid amplification of cDNA ends, including a trans-spliced RNA originating from the Glcci1 gene.

MSY2 and polypyrimidine tract binding protein 2 stabilize mRNAs in the mammalian testis

MSY2 is a highly conserved and abundant DNA/RNA-binding protein that functions as a global stabilizer/translational suppressor of mRNAs in male germ cells. The polypyrimidine tract binding protein, PTBP2, is an RNA-binding protein that splices nuclear transcripts and stabilizes specific mRNAs in the cytoplasm. The mechanisms whereby MSY2 selects and stabilizes a large group of male germ cell mRNAs and PTBP2 stabilizes specific mRNAs such as the phosphoglycerate kinase 2 mRNA in the testis and in transfected cells will be discussed.