Utp14b: a unique retrogene within a gene that has acquired multiple promoters and a specific function in spermatogenesis

Whole-Exome Sequencing Reveals New Potential Mutations Genes for Primary Mucosa-Associated Lymphoid Tissue Lymphoma Arising From the Kidney

Low-grade B cell lymphomas of mucosa-associated lymphoid tissue (MALT) lymphomas involving the kidney were extremely rare, genetic alteration or molecular features was not yet explored, which may lead to limited choices for postoperative adjuvant or targeted. Whole-exome sequencing based tumor mutation profiling was performed on the tumor sample from a 77-year-old female presenting with discomfort at the waist was pathologically diagnosed as MALT lymphomas in the right kidney. We identified 101 somatic SNVs, and the majority of the identified SNVs were located in CDS and intronic regions. A total of 190 gain counts of CNVs with a total size of 488,744,073 was also investigated. After filtering with the CGC database, seven predisposing genes (ARID4A, COL2A1, FANCL, ABL2, HSP90AB1, FANCA, and DIS3) were found in renal MALT specimen. Furthermore, we compared somatic variation with known driver genes and validated three mutational driver genes including ACSL3, PHOX2B, and ADCY1. Sanger sequencing of germline DNA revealed the presence of a mutant base T of PHOX2B and a mutant base C of ADCY1 in the sequence, which were discovered for the first time in MALT lymphomas involving the kidney. Moreover, immunohistochemical analysis revealed that tumor cells were positive for CD20, CD79a, PAX5, CD21, and CD23, and expression of CD3, CD5, and CD8 were observed in reactive T lymphocytes surrounding tumor cells. These findings illustrated that concurrent aberrant PHOX2B and ADCY1 signaling may be a catastrophic event resulting in disease progression and inhibition of the putative driver mutations may be alternative adjuvant therapy for MALT lymphoma in the kidney which warrants further clinical investigation.

Analysis of DNA polymerase ν function in meiotic recombination, immunoglobulin class-switching, and DNA damage tolerance

DNA polymerase ν (pol ν), encoded by the POLN gene, is an A-family DNA polymerase in vertebrates and some other animal lineages. Here we report an in-depth analysis of pol ν–defective mice and human cells. POLN is very weakly expressed in most tissues, with the highest relative expression in testis. We constructed multiple mouse models for Poln disruption and detected no anatomic abnormalities, alterations in lifespan, or changed causes of mortality. Mice with inactive Poln are fertile and have normal testis morphology. However, pol ν–disrupted mice have a modestly reduced crossover frequency at a meiotic recombination hot spot harboring insertion/deletion polymorphisms. These polymorphisms are suggested to generate a looped-out primer and a hairpin structure during recombination, substrates on which pol ν can operate. Pol ν-defective mice had no alteration in DNA end-joining during immunoglobulin class-switching, in contrast to animals defective in the related DNA polymerase θ (pol θ). We examined the response to DNA crosslinking agents, as purified pol ν has some ability to bypass major groove peptide adducts and residues of DNA crosslink repair. Inactivation of Poln in mouse embryonic fibroblasts did not alter cellular sensitivity to mitomycin C, cisplatin, or aldehydes. Depletion of POLN from human cells with shRNA or siRNA did not change cellular sensitivity to mitomycin C or alter the frequency of mitomycin C-induced radial chromosomes. Our results suggest a function of pol ν in meiotic homologous recombination in processing specific substrates. The restricted and more recent evolutionary appearance of pol ν (in comparison to pol θ) supports such a specialized role.

The work described here fills a current gap in the study of the 16 known DNA polymerases in vertebrate genomes. Until now, experiments with genetically disrupted mice have been reported for all but pol ν, encoded by the POLN gene. To intensively analyze the role of mammalian pol ν we generated multiple Poln-deficient murine models. We discovered that Poln is uniquely upregulated during testicular development and that it is enriched in spermatocytes. This, and phylogenetic analysis indicate a testis-specific function. We observed a modest reduction in meiotic recombination at a recombination hotspot in Poln-deficient mice. Pol ν has been suggested to function in DNA crosslink repair. However, we found no increased DNA crosslink sensitivity in Poln-deficient mice or POLN-depleted human cells. This is a major difference from some previous findings, and we support our conclusion by multiple experimental approaches, and by the very low or absent expression of functional pol ν in mammalian somatic cells. The present work represents the first description and comprehensive analysis of mice deficient in pol ν, and the first thorough phenotypic analysis in human cells.

Mechanisms Regulating Spermatogonial Differentiation

Mammalian spermatogenesis is a complex and highly ordered process by which male germ cells proceed through a series of differentiation steps to produce haploid flagellated spermatozoa. Underlying this process is a pool of adult stem cells, the spermatogonial stem cells (SSCs), which commence the spermatogenic lineage by undertaking a differentiation fate decision to become progenitor spermatogonia. Subsequently, progenitors acquire a differentiating spermatogonia phenotype and undergo a series of amplifying mitoses while becoming competent to enter meiosis. After spermatocytes complete meiosis, post-meiotic spermatids must then undergo a remarkable transformation from small round spermatids to a flagellated spermatozoa with extremely compacted nuclei. This chapter reviews the current literature pertaining to spermatogonial differentiation with an emphasis on the mechanisms controlling stem cell fate decisions and early differentiation events in the life of a spermatogonium.

Increasing testicular temperature by exposure to elevated ambient temperatures restores spermatogenesis in adult Utp14b (jsd) mutant (jsd) mice

Because mutations in the human UTP14C gene are associated with male infertility, we sought to develop a method for fertility restoration in azoospermic mice with a mutation in the orthologous Utp14b(jsd) (jsd) gene that have spermatogonial arrest. The method is based on our observation that elevation of testicular temperatures restores spermatogonial differentiation in jsd mutant mice. To non-surgically raise intrascrotal temperatures we placed these mice in incubators at different elevated ambient temperatures. Exposure of jsd/jsd mice to ambient temperatures of 34.5 °C or 35.5 °C for 24 days increased the proportion of tubules with spermatocytes from 0% in untreated controls to over 80%. As those higher temperatures interfere with spermatid differentiation, the mice were then transferred to incubators at 32-32.5 °C for the next 24 days. These environments allowed differentiation to progress, resulting in up to 42% of tubules having late spermatids and about half of the mutant mice having spermatozoa in testicular suspensions. When these spermatozoa were used in intracytoplasmic sperm injection, all gave rise to viable healthy offspring with normal weight gain and fertility. The successful restoration of fertility in Utp14b mutant mice suggests that transient testicular warming might also be useful for spermatogenesis recovery in infertile men with UTP14C gene mutations.

Human diseases of the SSU processome

Ribosomes are the cellular machines responsible for protein synthesis. Ribosome biogenesis, the production of ribosomes, is a complex process involving pre-ribosomal RNA (rRNA) cleavages and modifications as well as ribosomal protein assembly around the rRNAs to create the functional ribosome. The small subunit (SSU) processome is a large ribonucleoprotein (RNP) in eukaryotes required for the assembly of the SSU of the ribosome as well as for the maturation of the 18S rRNA. Despite the fundamental nature of the SSU processome to the survival of any eukaryotic cell, mutations in SSU processome components have been implicated in human diseases. Three SSU processome components and their related human diseases will be explored in this review: hUTP4/Cirhin, implicated in North American Indian childhood cirrhosis (NAIC); UTP14, implicated in infertility, ovarian cancer, and scleroderma; and EMG1, implicated in Bowen-Conradi syndrome (BCS). Diseases with suggestive, though inconclusive, evidence for the involvement of the SSU processome in their pathogenesis are also discussed, including a novel putative ribosomopathy. This article is part of a Special Issue entitled: Role of the Nucleolus in Human Disease.

Chd5 orchestrates chromatin remodelling during sperm development

One of the most remarkable chromatin remodelling processes occurs during spermiogenesis, the post-meiotic phase of sperm development during which histones are replaced with sperm-specific protamines to repackage the genome into the highly compact chromatin structure of mature sperm. Here we identify Chromodomain helicase DNA binding protein 5 (Chd5) as a master regulator of the histone-to-protamine chromatin remodelling process. Chd5 deficiency leads to defective sperm chromatin compaction and male infertility in mice, mirroring the observation of low CHD5 expression in testes of infertile men. Chd5 orchestrates a cascade of molecular events required for histone removal and replacement, including histone 4 (H4) hyperacetylation, histone variant expression, nucleosome eviction and DNA damage repair. Chd5 deficiency also perturbs expression of transition proteins (Tnp1/Tnp2) and protamines (Prm1/2). These findings define Chd5 as a multi-faceted mediator of histone-to-protamine replacement and depict the cascade of molecular events underlying this process of extensive chromatin remodelling.

A transgenic insertion on mouse chromosome 17 inactivates a novel immunoglobulin superfamily gene potentially involved in sperm-egg fusion

Fertilization is the process that leads to the formation of a diploid zygote from two haploid gametes. This is achieved through a complex series of cell-to-cell interactions between a sperm and an egg. The final event of fertilization is the fusion of the gametes' membranes, which allows the delivery of the sperm genetic material into the egg cytoplasm. In vivo studies in the laboratory mouse have led to the discovery of membrane proteins that are essential for the fusion process in both the sperm and egg. Specifically, the sperm protein Izumo1 was shown to be necessary for normal fertility. Izumo1-deficient spermatozoa fail to fuse with the egg plasma membrane. Izumo1 is a member of the Immunoglobulin Superfamily of proteins, which are known to be involved in cell adhesion. Here, we describe BART97b, a new mouse line with a recessive mutation that displays a fertilization block associated with a failure of sperm fusion. BART97b mutants carry a deletion that inactivates Spaca6, a previously uncharacterized gene expressed in testis. Similar to Izumo1, Spaca6 encodes an immunoglobulin-like protein. We propose that the Spaca6 gene product may, together with Izumo1, mediate sperm fusion by binding an as yet unidentified egg membrane receptor.

Isolation of Sertoli, Leydig, and spermatogenic cells from the mouse testis

A thorough understanding of the events during mammalian spermatogenesis requires studying specific molecular signatures of individual testicular cell populations as well as their interaction in co-cultures. However, most purification techniques to isolate specific testicular cell populations are time-consuming, require large numbers of animals, and/or are only able to isolate a few cell types. Here we describe a cost-effective and timesaving approach that uses a single protocol to enrich multiple testicular cell populations (Sertoli, Leydig, and several spermatogenic cell populations) from as few as one mouse. Our protocol combines rigorous enzymatic digestion of seminiferous tubules with counter-current centrifugal elutriation, yielding specific testicular cell populations with >80%-95% purity.

Role of β-catenin in post-meiotic male germ cell differentiation

Though roles of β-catenin signaling during testis development have been well established, relatively little is known about its role in postnatal testicular physiology. Even less is known about its role in post-meiotic germ cell development and differentiation. Here, we report that β-catenin is highly expressed in post-meiotic germ cells and plays an important role during spermiogenesis in mice. Spermatid-specific deletion of β-catenin resulted in significantly reduced sperm count, increased germ cell apoptosis and impaired fertility. In addition, ultrastructural studies show that the loss of β-catenin in post-meiotic germ cells led to acrosomal defects, anomalous release of immature spermatids and disruption of adherens junctions between Sertoli cells and elongating spermatids (apical ectoplasmic specialization; ES). These defects are likely due to altered expression of several genes reportedly involved in Sertoli cell-germ cell adhesion and germ cell differentiation, as revealed by gene expression analysis. Taken together, our results suggest that β-catenin is an important molecular link that integrates Sertoli cell-germ cell adhesion with the signaling events essential for post-meiotic germ cell development and maturation. Since β-catenin is also highly expressed in the Sertoli cells, we propose that binding of germ cell β-catenin complex to β-catenin complex on Sertoli cell at the apical ES surface triggers a signaling cascade that regulates post-meiotic germ cell differentiation.

Androgen suppression-induced stimulation of spermatogonial differentiation in juvenile spermatogonial depletion mice acts by elevating the testicular temperature

Why both testosterone (T) suppression and cryptorchidism reverse the block in spermatogonial differentiation in adult mice homozygous for the juvenile spermatogonial depletion (jsd) mutation has been a conundrum. To resolve this conundrum, we analyzed interrelations between T suppression, testicular temperature, and spermatogonial differentiation and used in vitro techniques to separate the effects of the two treatments on the spermatogonial differentiation block in jsd mice. Temporal analysis revealed that surgical cryptorchidism rapidly stimulated spermatogonial differentiation whereas androgen ablation treatment produced a delayed and gradual differentiation. The androgen suppression caused scrotal shrinkage, significantly increasing the intrascrotal temperature. When serum T or intratesticular T (ITT) levels were modulated separately in GnRH antagonist-treated mice by exogenous delivery of T or LH, respectively, the inhibition of spermatogonial differentiation correlated with the serum T and not with ITT levels. Thus, the block must be caused by peripheral androgen action. When testicular explants from jsd mice were cultured in vitro at 32.5 C, spermatogonial differentiation was not observed, but at 37 C significant differentiation was evident. In contrast, addition of T to the culture medium did not block the stimulation of spermatogonial differentiation at 37 C, and androgen ablation with aminoglutethimide and hydroxyflutamide did not stimulate differentiation at 32.5 C, suggesting that T had no direct effect on spermatogonial differentiation in jsd mice. These data show that elevation of temperature directly overcomes the spermatogonial differentiation block in adult jsd mice and that T suppression acts indirectly in vivo by causing scrotal regression and thereby elevating the testicular temperature.

Gene expression alterations by conditional knockout of androgen receptor in adult Sertoli cells of Utp14b jsd/jsd (jsd) mice

Spermatogenesis is dependent primarily on testosterone action on the Sertoli cells, but the molecular mechanisms have not been identified. Attempts to identify testosterone-regulated target genes in Sertoli cells have used microarray analysis of gene expression in mice lacking the androgen receptor (AR) in Sertoli cells (SCARKO) and wild-type mice, but the analyses have been complicated both by alteration of germ cell composition of the testis when pubertal or adult mice were used and by differences in Sertoli-cell gene expression from the expression in adults when prepubertal mice were used. To overcome these limitations and identify AR-regulated genes in adult Sertoli cells, we compared gene expression in adult jsd (Utp14b jsd/jsd, juvenile spermatogonial depletion) mouse testes and with that in SCARKO-jsd mouse testes, since their cellular compositions are essentially identical, consisting of only type A spermatogonia and somatic cells. Microarray analysis identified 157 genes as downregulated and 197 genes as upregulated in the SCARKO-jsd mice compared to jsd mice. Some of the AR-regulated genes identified in the previous studies, including Rhox5, Drd4, and Fhod3, were also AR regulated in the jsd testes, but others, such as proteases and components of junctional complexes, were not AR regulated in our model. Surprisingly, a set of germ cell–specific genes preferentially expressed in differentiated spermatogonia and meiotic cells, including Meig1, Sycp3, and Ddx4, were all upregulated about 2-fold in SCARKO-jsd testes. AR-regulated genes in Sertoli cells must therefore be involved in the regulation of spermatogonial differentiation, although there was no significant differentiation to spermatocytes in SCARKO-jsd mice. Further gene ontogeny analysis revealed sets of genes whose changes in expression may be involved in the dislocation of Sertoli cell nuclei in SCARKO-jsd testes.

The testis-enriched histone demethylase, KDM4D, regulates methylation of histone H3 lysine 9 during spermatogenesis in the mouse but is dispensable for fertility

Epigenetic modifications, and methylation of histones in particular, dynamically change during spermatogenesis. Among various methylations of histone H3, methylation of histone H3 lysine 9 (H3K9) and its regulation are essential for spermatogenesis. Trimethytransferases as well as dimethyltransferase are required for meiotic progression. In addition, didemethylase of H3K9 is also critical for spermatogenesis through transcriptional regulation of spermatid-specific genes. However, the requirement for demethylation of trimethylated H3K9 (H3K9me3) during spermatogenesis remains to be elucidated. Here, we report the targeted disruption of KDM4D, a testis-enriched tridemethylase of H3K9. Kdm4d-null mice are viable and fertile and do not show any obvious phenotype. However, H3K9me3 accumulates significantly in Kdm4d-null round spermatids, and the distribution of methylated H3K9 in germ cells is dramatically changed. Nevertheless, the progression of spermatogenesis and the number of spermatozoa are normal, likely secondary to the earlier nuclear localization of another H3K9 tridemethylase, KDM4B, in Kdm4d-null elongating spermatids. These results suggest that demethylation of H3K9me3 in round spermatids is dispensable for spermatogenesis but that possible defects in Kdm4d-null elongating spermatids could be rescued by functional redundancy of the KDM4B demethylase.

Gene expression alterations by conditional knockout of androgen receptor in adult sertoli cells of Utp14b(jsd/jsd) (jsd) mice

Spermatogenesis is dependent primarily on testosterone action on the Sertoli cells, but the molecular mechanisms have not been identified. Attempts to identify testosterone-regulated target genes in Sertoli cells have used microarray analysis of gene expression in mice lacking the androgen receptor (AR) in Sertoli cells (SCARKO) and wild-type mice, but the analyses have been complicated both by alteration of germ cell composition of the testis when pubertal or adult mice were used and by differences in Sertoli-cell gene expression from the expression in adults when prepubertal mice were used. To overcome these limitations and identify AR-regulated genes in adult Sertoli cells, we compared gene expression in adult jsd (Utp14b(jsd/jsd), juvenile spermatogonial depletion) mouse testes and with that in SCARKO-jsd mouse testes, since their cellular compositions are essentially identical, consisting of only type A spermatogonia and somatic cells. Microarray analysis identified 157 genes as downregulated and 197 genes as upregulated in the SCARKO-jsd mice compared to jsd mice. Some of the AR-regulated genes identified in the previous studies, including Rhox5, Drd4, and Fhod3, were also AR regulated in the jsd testes, but others, such as proteases and components of junctional complexes, were not AR regulated in our model. Surprisingly, a set of germ cell-specific genes preferentially expressed in differentiated spermatogonia and meiotic cells, including Meig1, Sycp3, and Ddx4, were all upregulated about 2-fold in SCARKO-jsd testes. AR-regulated genes in Sertoli cells must therefore be involved in the regulation of spermatogonial differentiation, although there was no significant differentiation from spermatocytes in SCARKO-jsd mice. Further gene ontogeny analysis revealed sets of genes whose changes in expression may be involved in the dislocation of Sertoli cell nuclei in SCARKO-jsd testes.

Retrotransposition and genomic imprinting

Studies of large imprinted clusters, such as the Gnas locus, have revealed much about the significance of DNA methylation, transcription and other factors in the establishment and maintenance of imprinted gene expression. However, the complexity of such loci can make manipulating them and interpreting the results challenging. We review here a distinct class of imprinted genes, which have arisen by retrotransposition, and which have the potential to be used as models for the dissection of the fundamental features and mechanisms required for imprinting. They are also of interest in their own right, generating diversity in the transcriptome and providing raw material upon which selection can act.

Surfing the wave, cycle, life history, and genes/proteins expressed by testicular germ cells. Part 5: intercellular junctions and contacts between germs cells and Sertoli cells and their regulatory interactions, testicular cholesterol, and genes/proteins associated with more than one germ cell generation

In the testis, cell adhesion and junctional molecules permit specific interactions and intracellular communication between germ and Sertoli cells and apposed Sertoli cells. Among the many adhesion family of proteins, NCAM, nectin and nectin-like, catenins, and cadherens will be discussed, along with gap junctions between germ and Sertoli cells and the many members of the connexin family. The blood-testis barrier separates the haploid spermatids from blood borne elements. In the barrier, the intercellular junctions consist of many proteins such as occludin, tricellulin, and claudins. Changes in the expression of cell adhesion molecules are also an essential part of the mechanism that allows germ cells to move from the basal compartment of the seminiferous tubule to the adluminal compartment thus crossing the blood-testis barrier and well-defined proteins have been shown to assist in this process. Several structural components show interactions between germ cells to Sertoli cells such as the ectoplasmic specialization which are more closely related to Sertoli cells and tubulobulbar complexes that are processes of elongating spermatids embedded into Sertoli cells. Germ cells also modify several Sertoli functions and this also appears to be the case for residual bodies. Cholesterol plays a significant role during spermatogenesis and is essential for germ cell development. Lastly, we list genes/proteins that are expressed not only in any one specific generation of germ cells but across more than one generation.

Testicular cell adhesion molecule 1 (TCAM1) is not essential for fertility

Testicular cell adhesion molecule 1 (Tcam1) is a testis-expressed gene that is evolutionarily conserved in most mammalian species. The putative location of TCAM1 on the cell surface makes it an attractive contraceptive target to study. We found that Tcam1 transcription is enriched in the adult testis, and in situ hybridization revealed that Tcam1 is expressed in pachytene to secondary spermatocytes. Immunofluorescence for TCAM1 protein showed strong expression along cell membranes of spermatocytes and weak localization to round spermatids. In light of this evidence, we hypothesized that TCAM1 interacts with an unknown receptor on the surface of Sertoli cells and that this interaction is important for germ cell-Sertoli cell interactions. However, Tcam1 knockout mice that we generated are fertile, and testis weights and sperm counts were not significantly altered. Therefore, we conclude that TCAM1 is not essential for male fertility or germ cell function in Mus musculus.

Mouse cumulus-denuded oocytes restore developmental capacity completely when matured with optimal supplementation of cysteamine, cystine, and cumulus cells

Our objectives were to study how cysteamine, cystine, and cumulus cells (CCs), as well as oocytes interact to increase oocyte intracellular glutathione (GSH) and thereby to establish an efficient in vitro maturation system for cumulus-denuded oocytes (DOs). Using M16 that contained no thiol as maturation medium, we showed that when supplemented alone, neither cystine nor cysteamine promoted GSH synthesis of mouse DOs, but they did when used together. Although goat CCs required either cysteamine or cystine to promote GSH synthesis, mouse CCs required both. In the presence of cystine, goat CCs produced cysteine but mouse CCs did not. Cysteamine reduced cystine to cysteine in cell-free M16. When TCM-199 that contained 83 microM cystine was used as maturation medium, supplementation with cysteamine alone had no effect, but supplementation with 100 microM cysteamine and 200 microM cystine increased blastulation of DOs matured with CC coculture to a level as high as achieved in cumulus-surrounded oocytes (COCs). Similar numbers of young were produced after two-cell embryos from mouse COCs or CC-cocultured DOs matured with optimal thiol supplementation were transferred to pseudopregnant recipients. It is concluded that 1) mouse CCs can use neither cysteamine nor cystine to promote GSH synthesis, but goat CCs can use either one; 2) goat CCs promote mouse oocyte GSH synthesis by reducing cystine to cysteine, but how they use cysteamine requires further investigation; and 3) mouse DOs can use neither cystine nor cysteamine for GSH synthesis, but they restore developmental capacity completely when matured in the presence of optimum supplementation of cysteamine, cystine, and CCs.

H2A.Bbd: an X-chromosome-encoded histone involved in mammalian spermiogenesis

Despite the identification of H2A.Bbd as a new vertebrate-specific replacement histone variant several years ago, and despite the many in vitro structural characterizations using reconstituted chromatin complexes consisting of this variant, the existence of H2A.Bbd in the cell and its location has remained elusive. Here, we report that the native form of this variant is present in highly advanced spermiogenic fractions of mammalian testis at the time when histones are highly acetylated and being replaced by protamines. It is also present in the nucleosomal chromatin fraction of mature human sperm. The ectopically expressed non-tagged version of the protein is associated with micrococcal nuclease-refractory insoluble fractions of chromatin and in mouse (20T1/2) cell line, H2A.Bbd is enriched at the periphery of chromocenters. The exceedingly rapid evolution of this unique X-chromosome-linked histone variant is shared with other reproductive proteins including those associated with chromatin in the mature sperm (protamines) of many vertebrates. This common rate of evolution provides further support for the functional and structural involvement of this protein in male gametogenesis in mammals.

Retinoblastoma protein plays multiple essential roles in the terminal differentiation of Sertoli cells

Retinoblastoma protein (RB) plays crucial roles in cell cycle control and cellular differentiation. Specifically, RB impairs the G(1) to S phase transition by acting as a repressor of the E2F family of transcriptional activators while also contributing towards terminal differentiation by modulating the activity of tissue-specific transcription factors. To examine the role of RB in Sertoli cells, the androgen-dependent somatic support cell of the testis, we created a Sertoli cell-specific conditional knockout of Rb. Initially, loss of RB has no gross effect on Sertoli cell function because the mice are fertile with normal testis weights at 6 wk of age. However, by 10-14 wk of age, mutant mice demonstrate severe Sertoli cell dysfunction and infertility. We show that mutant mature Sertoli cells continue cycling with defective regulation of multiple E2F1- and androgen-regulated genes and concurrent activation of apoptotic and p53-regulated genes. The most striking defects in mature Sertoli cell function are increased permeability of the blood-testis barrier, impaired tissue remodeling, and defective germ cell-Sertoli cell interactions. Our results demonstrate that RB is essential for proper terminal differentiation of Sertoli cells.

The consequences of asynapsis for mammalian meiosis

During mammalian meiosis, synapsis of paternal and maternal chromosomes and the generation of DNA breaks are needed to allow reshuffling of parental genes. In mammals errors in synapsis are associated with a male-biased meiotic impairment, which has been attributed to a response to persisting DNA double-stranded breaks in the asynapsed chromosome segments. Recently it was discovered that the chromatin of asynapsed chromosome segments is transcriptionally silenced, providing new insights into the connection between asynapsis and meiotic impairment.

Androgen receptor in Sertoli cells is not required for testosterone-induced suppression of spermatogenesis, but contributes to Sertoli cell organization in Utp14b jsd mice

Testosterone acting through the androgen receptor (AR) maintains the arrest of spermatogonial differentiation in juvenile spermatogonial depletion (jsd mutation in the Utp14b gene) mutant adult male mice. It is not known which of the somatic cell types expressing AR mediates this inhibition. To determine whether Sertoli cells are responsible, we selectively eliminated AR in Sertoli cells in jsd mice containing a floxed-Ar gene and an anti-Müllerian hormone-Cre transgene. In these Sertoli AR-knockout (SCARKO)-jsd mice, spermatogonial differentiation did not recover. However, the normal organization of Sertoli cell nuclei was drastically disrupted in SCARKO-jsd mice compared with SCARKO or jsd mice. In addition, the extent of ectoplasmic specializations was reduced; tight junctions were not found; vinculin, an anchoring protein found in ectoplasmic specializations, became uniformly distributed in the cytoplasm; and the adult Sertoli cells showed excess heterochromatin subjacent to their nuclear envelope. Despite the abnormalities in Sertoli cells in SCARKO-jsd mice, global suppression of testosterone action and levels was still effective in restoring the differentiated germ cells, and this was accompanied by an improved arrangement of Sertoli cell nuclei. We conclude that Sertoli cells are not targets for the testosterone-mediated inhibition of spermatogonial differentiation in jsd mice, and that both AR in Sertoli cells and the presence of differentiated germ cells contribute to maintaining the organization of Sertoli cells within the seminiferous tubules.

p53-dependent apoptosis in the inhibition of spermatogonial differentiation in juvenile spermatogonial depletion (Utp14bjsd) mice

In adult male mice homozygous for the juvenile spermatogonial depletion (Utp14b jsd) mutation in the Utp14b gene, type A spermatogonia proliferate, but in the presence of testosterone and at scrotal temperatures, these spermatogonia undergo apoptosis just before differentiation. In an attempt to delineate this apoptotic pathway in jsd mice and specifically address the roles of p53- and Fas ligand (FasL) /Fas receptor-mediated apoptosis, we produced jsd mice deficient in p53, Fas, or FasL. Already at the age of 5 wk, less degeneration of spermatogenesis was observed in p53-null-jsd mice than jsd single mutants, and in 8- or 12-wk-old mice, the percentage of seminiferous tubules showing differentiated germ cells [tubule differentiation index (TDI)] was 26-29% in the p53-null-jsd mice, compared with 2-4% in jsd mutants with normal p53. The TDI in jsd mice heterozygous for p53 showed an intermediate TDI of 8-13%. The increase in the differentiated tubules in double-mutant and p53 heterozygous jsd mice was mostly attributable to intermediate and type B spermatogonia; few spermatocytes were present. Terminal deoxynucleotidyl transferase-mediated deoxyuridine triphosphate nick end labeling staining showed that most of these differentiated spermatogonia still underwent apoptosis, thereby blocking further continuation of spermatogenesis. In contrast, the percentage of tubules that were differentiated was not significantly altered in either adult Fas null-jsd mice or adult FasL defective gld-jsd double mutant mice as compared with jsd single mutants. Furthermore, caspase-9, but not caspase-8 was immunochemically localized in the adult jsd mice spermatogonia undergoing apoptosis. The results show that p53, but not FasL or Fas, is involved in the apoptosis of type A spermatogonia before/during differentiation in jsd mice that involves the intrinsic pathway of apoptosis. However, apoptosis in the later stages must be a p53-independent process.

GATA factors and androgen receptor collaborate to transcriptionally activate the Rhox5 homeobox gene in Sertoli cells

How Sertoli-specific expression is initiated is poorly understood. Here, we address this issue using the proximal promoter (Pp) from the Rhox5 homeobox gene. Its Sertoli cell-specific expression is achieved, in part, through a negative regulatory element that inhibits Pp transcription in non-Sertoli cell lines. Complementing this negative regulation is positive regulation conferred by four androgen-response elements (AREs) that interact with the androgen receptor (AR), a nuclear hormone receptor expressed at high levels in Sertoli cells. A third control mechanism is provided by a consensus GATA-binding site that is crucial for Pp transcription both in vitro and in vivo. Several lines of evidence suggested that GATA factors and AR act cooperatively to activate Pp transcription: (i) the GATA-binding site crucial for Pp transcription is in close proximity to two of the AREs, (ii) GATA and AR form a complex with the Pp in vitro, (iii) overexpression of GATA factors rescued expression from mutant Pp constructs harboring defective AREs, and (iv) incubation of a Sertoli cell line with testosterone triggered corecruitment of AR and GATA4 to the Pp. Collectively, our results suggest that the Rhox5 gene achieves Sertoli cell-specific transcription using a combinatorial strategy involving negative and cooperative positive regulation.

Large-scale, lineage-specific expansion of a bric-a-brac/tramtrack/broad complex ubiquitin-ligase gene family in rice

Selective ubiquitination of proteins is directed by diverse families of ubiquitin-protein ligases (or E3s) in plants. One important type uses Cullin-3 as a scaffold to assemble multisubunit E3 complexes containing one of a multitude of bric-a-brac/tramtrack/broad complex (BTB) proteins that function as substrate recognition factors. We previously described the 80-member BTB gene superfamily in Arabidopsis thaliana. Here, we describe the complete BTB superfamily in rice (Oryza sativa spp japonica cv Nipponbare) that contains 149 BTB domain-encoding genes and 43 putative pseudogenes. Amino acid sequence comparisons of the rice and Arabidopsis superfamilies revealed a near equal repertoire of putative substrate recognition module types. However, phylogenetic comparisons detected numerous gene duplication and/or loss events since the rice and Arabidopsis BTB lineages split, suggesting possible functional specialization within individual BTB families. In particular, a major expansion and diversification of a subset of BTB proteins containing Meprin and TRAF homology (MATH) substrate recognition sites was evident in rice and other monocots that likely occurred following the monocot/dicot split. The MATH domain of a subset appears to have evolved significantly faster than those in a smaller core subset that predates flowering plants, suggesting that the substrate recognition module in many monocot MATH-BTB E3s are diversifying to ubiquitinate a set of substrates that are themselves rapidly changing. Intriguing possibilities include pathogen proteins attempting to avoid inactivation by the monocot host.

Large-scale, lineage-specific expansion of a bric-a-brac/tramtrack/broad complex ubiquitin-ligase gene family in rice

Selective ubiquitination of proteins is directed by diverse families of ubiquitin-protein ligases (or E3s) in plants. One important type uses Cullin-3 as a scaffold to assemble multisubunit E3 complexes containing one of a multitude of bric-a-brac/tramtrack/broad complex (BTB) proteins that function as substrate recognition factors. We previously described the 80-member BTB gene superfamily in Arabidopsis thaliana. Here, we describe the complete BTB superfamily in rice (Oryza sativa spp japonica cv Nipponbare) that contains 149 BTB domain-encoding genes and 43 putative pseudogenes. Amino acid sequence comparisons of the rice and Arabidopsis superfamilies revealed a near equal repertoire of putative substrate recognition module types. However, phylogenetic comparisons detected numerous gene duplication and/or loss events since the rice and Arabidopsis BTB lineages split, suggesting possible functional specialization within individual BTB families. In particular, a major expansion and diversification of a subset of BTB proteins containing Meprin and TRAF homology (MATH) substrate recognition sites was evident in rice and other monocots that likely occurred following the monocot/dicot split. The MATH domain of a subset appears to have evolved significantly faster than those in a smaller core subset that predates flowering plants, suggesting that the substrate recognition module in many monocot MATH-BTB E3s are diversifying to ubiquitinate a set of substrates that are themselves rapidly changing. Intriguing possibilities include pathogen proteins attempting to avoid inactivation by the monocot host.