Paola Grimaldi

Developmental expression of BMP4/ALK3/SMAD5 signaling pathway in the mouse testis: a potential role of BMP4 in spermatogonia differentiation.

It is well established that the c-kit gene plays an essential role in the proliferation of differentiating spermatogonia in prepuberal mice. However, the mechanisms that regulate the onset of spermatogenesis, i.e. differentiation of spermatogonial stem cells and c-kit expression, are poorly understood. Here we identify a novel signal transduction system in mouse prepuberal testis regulating this developmental event, involving bone morphogenetic protein 4 (BMP4) and its transduction machinery. BMP4 is produced by Sertoli cells very early in the postnatal life and is successively down regulated in peri-puberal Sertoli cells. Its receptor Alk3 and the R-Smad Smad5 are specifically expressed both in proliferating primordial germ cells and in postnatal spermatogonia. BMP4 stimulation of cultured spermatogonia induces Smad4/5 nuclear translocation and the formation of a DNA-binding complex with the transcriptional coactivator p300/CBP. In vitro exposure of undifferentiated spermatogonia to BMP4 exerts both mitogenic and differentiative effects, inducing [3H]thymidine incorporation and Kit expression. As a result of the latter event, Kit-negative spermatogonia acquire sensitivity to Stem Cell Factor.

The endocannabinoid system and pivotal role of the CB2 receptor in mouse spermatogenesis

The exact role of the endocannabinoid system (ECS) during spermatogenesis has not been clarified. We used purified germ cell fractions representative of all phases of spermatogenesis and primary cultures of spermatogonia. This approach allowed the precise quantification of the cannabinoid receptor ligands, anandamide and 2-arachidonoylglycerol, and of the expression at transcriptional and transductional levels of their metabolic enzymes and receptors. Our data indicate that male mouse germ cells possess an active and complete ECS, which is modulated during meiosis, and suggest the presence of an autocrine endocannabinoid signal during spermatogenesis. Mitotic cells possess higher levels of 2-arachidonoylglycerol, which decrease in spermatocytes and spermatids. Accordingly, spermatogonia express higher and lower levels of 2-arachidonoylglycerol biosynthetic and degrading enzymes, respectively, as compared to meiotic and postmeiotic cells. This endocannabinoid likely plays a pivotal role in promoting the meiotic progression of germ cells by activating CB2 receptors. In fact, we found that the selective CB2 receptor agonist, JWH133, induced the Erk 1/2 MAPK phosphorylation cascade in spermatogonia and their progression toward meiosis, because it increased the number of cells positive for SCP3, a marker of meiotic prophase, and the expression of early meiotic prophase genes.

An SRY‐negative XX male with Huriez syndrome

This report studies a 42‐year‐old 46,XX patient affected by palmoplantar keratoderma, clinically classified as Huriez syndrome. The patient showed a male phenotype with apparently normal male features including testicular development. Cytogenetic and chromosomal painting analysis excluded the presence of translocation of the Y chromosome. PCR analysis of genomic DNA failed to detect the presence of the testis‐determining gene, SRY. The presence of other Y‐chromosome genes, known to be involved in testicular maturation and spermatogenesis, has also been analyzed. The data suggest that the sex reversal in this 46,XX male patient is due to a defect on a yet unidentified autosomal or X‐linked sex‐determining gene. The relationship between the sex reversion and the presence of sclerotylosis is discussed.

Type-1 (CB1) Cannabinoid Receptor Promotes Neuronal Differentiation and Maturation of Neural Stem Cells

Neural stem cells (NSCs) are self-renewing cells that can differentiate into multiple neural lineages and repopulate regions of the brain after injury. We have investigated the role of endocannabinoids (eCBs), endogenous cues that modulate neuronal functions including neurogenesis, and their receptors CB1 and CB2 in mouse NSCs. Real-time PCR and Western blot analyses indicated that CB1 is present at higher levels than CB2 in NSCs. The eCB anandamide (AEA) or the CB1-specific agonist ACEA enhanced NSC differentiation into neurons, but not astrocytes and oligodendrocytes, whereas the CB2-specific agonist JWH133 was ineffective. Conversely, the effect of AEA was inhibited by CB1, but not CB2, antagonist, corroborating the specificity of the response. CB1 activation also enhanced maturation of neurons, as indicated by morphometric analysis of neurites. CB1 stimulation caused long-term inhibition of the ERK1/2 pathway. Consistently, pharmacological inhibition of the ERK1/2 pathway recapitulated the effects exerted by CB1 activation on neuronal differentiation and maturation. Lastly, gene array profiling showed that CB1 activation augmented the expression of genes involved in neuronal differentiation while decreasing that of stemness genes. These results highlight the role of CB1 in the regulation of NSC fate and suggest that its activation may represent a pro-neuronal differentiation signal.

The faah gene is the first direct target of estrogen in the testis: role of histone demethylase LSD1

Estrogen (E2) regulates spermatogenesis, yet its direct target genes have not been identified in the testis. Here, we cloned the proximal 5′ flanking region of the mouse fatty acid amide hydrolase (faah) gene upstream of the luciferase reporter gene, and demonstrated its promoter activity and E2 inducibility in primary mouse Sertoli cells. Specific mutations in the E2 response elements (ERE) of the faah gene showed that two proximal ERE sequences (ERE2/3) are essential for E2-induced transcription, and chromatin immunoprecipitation experiments showed that E2 induced estrogen receptor β binding at ERE2/3 sites in the faah promoter in vivo. Moreover, the histone demethylase LSD1 was found to be associated with ERE2/3 sites and to play a role in mediating E2 induction of FAAH expression. E2 induced epigenetic modifications at the faah proximal promoter compatible with transcriptional activation by remarkably decreasing methylation of both DNA at CpG site and histone H3 at lysine 9. Finally, FAAH silencing abolished E2 protection against apoptosis induced by the FAAH substrate anandamide. Taken together, our results identify FAAH as the first direct target of E2.

Molecular genetics of male infertility: Stem cell factor/c-kit system

PROBLEM: Infertility, affects about 5% of human males and genetic factors are recognized in approximately 30% of them. The mouse represents a good model to study autosomal genes that might play a role in spermatogenesis. In mice, mutations in the c‐kit gene and in the gene encoding stem cell factor (SCF) cause pleiotropic defects among which sterility. A possible involvement of the SCF/c‐kit system in human spermatogenesis was investigated.

The Endocannabinoid System and Spermatogenesis

Spermatogenesis is a complex process in which male germ cells undergo a mitotic phase followed by meiosis and by a morphogenetic process to form mature spermatozoa. Spermatogenesis is under the control of gonadotropins, steroid hormones and it is modulated by a complex network of autocrine and paracrine factors. These modulators ensure the correct progression of germ cell differentiation to form mature spermatozoa. Recently, it has been pointed out the relevance of endocannabinoids as critical modulators of male reproduction. Endocannabinoids are natural lipids able to bind to cannabinoid receptors and whose levels are regulated by specific biosynthetic and degradative enzymes. Together with their receptors and metabolic enzymes, they form the “endocannabinoid system” (ECS). In male reproductive tracts, they affect Sertoli cell activities, Leydig cell proliferation, germ cell differentiation, sperm motility, capacitation, and acrosome reaction. The ECS interferes with the pituitary-gonadal axis, and an intricate crosstalk between ECS and steroid hormones has been highlighted. This mini-review will focus on the involvement of the ECS in the control of spermatogenesis and on the interaction between ECS and steroid hormones.

Cyclic Adenosine Monophosphate (cAMP) Stimulation of the Kit Ligand Promoter in Sertoli Cells Requires an Sp1-Binding Region, a Canonical TATA Box, and a cAMP-Induced Factor Binding to an Immediately Downstream GC-Rich Element

Abstract Expression of Kit ligand (KL) mRNA is induced in primary prepuberal Sertoli cells by FSH and by other agents that increase cAMP levels. The cAMP effect is exerted at the transcriptional level and appears to be cell type specific, since it is not observed in other KL-expressing primary cells or cell lines. Deletion analysis of the 5′-flanking region of the mouse KL gene shows that the proximal promoter sequence between −88 and +8 from the transcriptional start site is necessary and sufficient to obtain the full cAMP responsiveness of the promoter in primary mouse Sertoli cells. In the −88/+8 promoter region, several cis-acting elements play a role in cAMP response. The −88/−56 sequence is necessary for full induction of the gene, since its removal causes a drastic decrease in cAMP responsiveness; however, cAMP-stimulated expression is still observed with the minimal promoter region between −55 and +8. A more detailed mutational analysis of the minimal promoter region shows that mutations in the canonical TATA box sequence and in an immediately downstream GC-rich element completely abolish cAMP responsiveness. DNA-binding experiments show that transcription factor Sp1 binds to the −88/−56 fragment of the KL proximal promoter in both control and cAMP-stimulated cells, whereas a new cAMP-induced complex is observed when the −55/+8 minimal promoter region is used as probe. The canonical TATA box sequence is essential for formation of the latter complex. We also show that the binding of an unknown nuclear factor (different from Sp1, Egr-1, Rnf6, and AP-2) to a GC-rich element between −19 and +8 increases after cAMP treatment, and this effect seems to be specific of primary Sertoli cells. Thus, cAMP-induced transcription from the KL gene promoter in primary mouse Sertoli cells is mediated by a complex interaction among a Sp1-binding region, factors recognizing the canonical TATA box sequence, and a not yet identified cAMP-induced factor binding a GC-rich sequence just downstream from it.

Microgravity Promotes Differentiation and Meiotic Entry of Postnatal Mouse Male Germ Cells

A critical step of spermatogenesis is the entry of mitotic spermatogonia into meiosis. Progresses on these topics are hampered by the lack of an in vitro culture system allowing mouse spermatogonia differentiation and entry into meiosis. Previous studies have shown that mouse pachytene spermatocytes cultured in simulated microgravity (SM) undergo a spontaneous meiotic progression. Here we report that mouse mitotic spermatogonia cultured under SM with a rotary cell culture system (RCCS) enter into meiosis in the absence of any added exogenous factor or contact with somatic cells. We found that isolated Kit-positive spermatogonia under the RCCS condition enter into the prophase of the first meiotic division (leptotene stage), as monitored by chromosomal organization of the synaptonemal complex 3 protein (Scp3) and up-regulation of several pro-meiotic genes. SM was found to activate the phosphatidyl inositol 3 kinase (PI3K) pathway and to induce in Kit-positive spermatogonia the last round of DNA replication, typical of the preleptotene stage. A PI3K inhibitor abolished Scp3 induction and meiotic entry stimulated by RCCS conditions. A positive effect of SM on germ cell differentiation was also observed in undifferentiated (Kit-negative) spermatogonia, in which RCCS conditions stimulate the expression of Kit and Stra8. In conclusion, SM is an artificial environmental condition which promotes postnatal male germ cell differentiation and might provide a tool to study the molecular mechanisms underlying the switch from mitosis to meiosis in mammals.

Modulation of the endocannabinoid-degrading enzyme fatty acid amide hydrolase by follicle-stimulating hormone

Follicle-stimulating hormone (FSH) is a glycoprotein that transmits its signals via a G protein-coupled receptor. As yet, not many targets of FSH have been identified, able to justify the critical role of this hormone on reproductive events. On the other hand, among the biological activities of the endocannabinoid anandamide (AEA), growing interest has been attracted by the regulation of mammalian fertility. Recently, we have shown that treatment of mouse primary Sertoli cells with FSH enhances the activity of the AEA hydrolase (fatty acid amide hydrolase, FAAH), whereas it does not affect the enzymes that synthesize AEA, nor the level of the AEA-binding type-2 cannabinoid and type-1 vanilloid receptors. In addition, diacylglycerol lipase and monoacylglycerol lipase, which, respectively, synthesize and degrade the other major endocannabinoid 2-arachidonoylglycerol, were not regulated by FSH. Interestingly, FAAH stimulation by FSH occurred through protein kinase A and aromatase-dependent pathways that were able to modulate FAAH activity (via phosphorylation of accessory proteins) and faah gene expression (via an estrogen response element on the promoter region). Taken together, these data identify FAAH as the only target of FSH among the elements of the endocannabinoid system, with a critical impact on Sertoli cell proliferation, and thus spermatogenesis and male reproduction.