Principles of miRNA/miRNA* function in plant MIRNA processing.

MicroRNAs (miRNAs) are essential regulators of gene expression, defined by their unique biogenesis, which requires the precise excision of the small RNA from an imperfect fold-back precursor. Unlike their animal counterparts, plant miRNA precursors exhibit variations in sizes and shapes. Plant MIRNAs can undergo processing in a base-to-loop or loop-to-base direction, with DICER-LIKE1 (DCL1) releasing the miRNA after two cuts (two-step MIRNAs) or more (sequential MIRNAs). In this study, we demonstrate the critical role of the miRNA/miRNA* duplex region in the processing of miRNA precursors. We observed that endogenous MIRNAs frequently experience suboptimal processing in vivo due to mismatches in the miRNA/miRNA* duplex, a key region that fine-tunes miRNA levels. Enhancing the interaction energy of the miRNA/miRNA* duplex in two-step MIRNAs results in a substantial increase in miRNA levels. Conversely, sequential MIRNAs display distinct and specific requirements for the miRNA/miRNA* duplexes along their foldback structure. Our work establishes a connection between the miRNA/miRNA* structure and precursor processing mechanisms. Furthermore, we reveal a link between the biological function of miRNAs and the processing mechanism of their precursors with the evolution of plant miRNA/miRNA* duplex structures.

A maternal dorsoventral prepattern revealed by an asymmetric distribution of ventralizing molecules before fertilization in Xenopus laevis.

The establishment of the embryonic dorsoventral axis in Xenopus occurs when the radial symmetry around the egg's animal-vegetal axis is broken to give rise to the typical symmetry of Bilaterians. We have previously shown that the Notch1 protein is ventrally enriched during early embryogenesis in Xenopus laevis and zebrafish and exerts ventralizing activity through ß-Catenin destabilization and the positive regulation of ventral center genes in X. laevis. These findings led us to further investigate when these asymmetries arise. In this work, we show that the asymmetrical distribution of Notch1 protein and mRNA precedes cortical rotation and even fertilization in X. laevis. Moreover, we found that in unfertilized eggs transcripts encoded by the ventralizing gene bmp4 are also asymmetrically distributed in the animal hemisphere and notch1 transcripts accumulate consistently on the same side of the eccentric maturation point. Strikingly, a Notch1 asymmetry orthogonal to the animal-vegetal axis appears during X. laevis oogenesis. Thus, we show for the first time a maternal bias in the distribution of molecules that are later involved in ventral patterning during embryonic axialization, strongly supporting the hypothesis of a dorsoventral prepattern or intrinsic bilaterality of Xenopus eggs before fertilization.

Interleukin-17 signaling influences CD8+ T cell immunity and tumor progression according to the IL-17 receptor subunit expression pattern in cancer cells.

IL-17 immune responses in cancer are controversial, with both tumor-promoting and tumor-repressing effects observed. To clarify the role of IL-17 signaling in cancer progression, we used syngeneic tumor models from different tissue origins. We found that deficiencies in host IL-17RA or IL-17A/F expression had varying effects on the in vivo growth of different solid tumors including melanoma, sarcoma, lymphoma, and leukemia. In each tumor type, the absence of IL-17 led to changes in the expression of mediators associated with inflammation and metastasis in the tumor microenvironment. Furthermore, IL-17 signaling deficiencies in the hosts resulted in decreased anti-tumor CD8+ T cell immunity and caused tumor-specific changes in several lymphoid cell populations. Our findings were associated with distinct patterns of IL-17A/F cytokine and receptor subunit expression in the injected tumor cell lines. These patterns affected tumor cell responsiveness to IL-17 and downstream intracellular signaling, leading to divergent effects on cancer progression. Additionally, we identified IL-17RC as a critical determinant of the IL-17-mediated response in tumor cells and a potential biomarker for IL-17 signaling effects in tumor progression. Our study offers insight into the molecular mechanisms underlying IL-17 activities in cancer and lays the groundwork for developing personalized immunotherapies.

MDM2 Regulation of HIF Signaling Causes Microvascular Dysfunction in Hypertrophic Cardiomyopathy.

BACKGROUND: Microvasculature dysfunction is a common finding in pathologic remodeling of the heart and is thought to play an important role in the pathogenesis of hypertrophic cardiomyopathy (HCM), a disease caused by sarcomere gene mutations. We hypothesized that microvascular dysfunction in HCM was secondary to abnormal microvascular growth and could occur independent of ventricular hypertrophy. METHODS: We used multimodality imaging methods to track the temporality of microvascular dysfunction in HCM mouse models harboring mutations in the sarcomere genes Mybpc3 (cardiac myosin binding protein C3) or Myh6 (myosin heavy chain 6). We performed complementary molecular methods to assess protein quantity, interactions, and post-translational modifications to identify mechanisms regulating this response. We manipulated select molecular pathways in vivo using both genetic and pharmacological methods to validate these mechanisms. RESULTS: We found that microvascular dysfunction in our HCM models occurred secondary to reduced myocardial capillary growth during the early postnatal time period and could occur before the onset of myocardial hypertrophy. We discovered that the E3 ubiquitin protein ligase MDM2 (murine double minute 2) dynamically regulates the protein stability of both HIF1α (hypoxia-inducible factor 1 alpha) and HIF2α (hypoxia-inducible factor 2 alpha)/EPAS1 (endothelial PAS domain protein 1) through canonical and noncanonical mechanisms. The resulting HIF imbalance leads to reduced proangiogenic gene expression during a key period of myocardial capillary growth. Reducing MDM2 protein levels by genetic or pharmacological methods normalized HIF protein levels and prevented the development of microvascular dysfunction in both HCM models. CONCLUSIONS: Our results show that sarcomere mutations induce cardiomyocyte MDM2 signaling during the earliest stages of disease, and this leads to long-term changes in the myocardial microenvironment.

A novel Tetrahymena thermophila sterol C-22 desaturase belongs to the fatty acid hydroxylase/desaturase superfamily.

Sterols in eukaryotic cells play important roles in modulating membrane fluidity and in cell signaling and trafficking. During evolution, a combination of gene losses and acquisitions gave rise to an extraordinary diversity of sterols in different organisms. The sterol C-22 desaturase identified in plants and fungi as a cytochrome P-450 monooxygenase evolved from the first eukaryotic cytochrome P450 and was lost in many lineages. Although the ciliate Tetrahymena thermophila desaturates sterols at the C-22 position, no cytochrome P-450 orthologs are present in the genome. Here, we aim to identify the genes responsible for the desaturation as well as their probable origin. We used gene knockout and yeast heterologous expression approaches to identify two putative genes, retrieved from a previous transcriptomic analysis, as sterol C-22 desaturases. Furthermore, we demonstrate using bioinformatics and evolutionary analyses that both genes encode a novel type of sterol C-22 desaturase that belongs to the large fatty acid hydroxylase/desaturase superfamily and the genes originated by genetic duplication prior to functional diversification. These results stress the widespread existence of nonhomologous isofunctional enzymes among different lineages of the tree of life as well as the suitability for the use of T. thermophila as a valuable model to investigate the evolutionary process of large enzyme families.

Discovery of archaeal fusexins homologous to eukaryotic HAP2/GCS1 gamete fusion proteins.

Sexual reproduction consists of genome reduction by meiosis and subsequent gamete fusion. The presence of genes homologous to eukaryotic meiotic genes in archaea and bacteria suggests that DNA repair mechanisms evolved towards meiotic recombination. However, fusogenic proteins resembling those found in gamete fusion in eukaryotes have so far not been found in prokaryotes. Here, we identify archaeal proteins that are homologs of fusexins, a superfamily of fusogens that mediate eukaryotic gamete and somatic cell fusion, as well as virus entry. The crystal structure of a trimeric archaeal fusexin (Fusexin1 or Fsx1) reveals an archetypical fusexin architecture with unique features such as a six-helix bundle and an additional globular domain. Ectopically expressed Fusexin1 can fuse mammalian cells, and this process involves the additional globular domain and a conserved fusion loop. Furthermore, archaeal fusexin genes are found within integrated mobile elements, suggesting potential roles in cell-cell fusion and gene exchange in archaea, as well as different scenarios for the evolutionary history of fusexins.

Polyfunctional KLRG-1+CD57+ Senescent CD4+ T Cells Infiltrate Tumors and Are Expanded in Peripheral Blood From Breast Cancer Patients.

Senescent T cells have been described during aging, chronic infections, and cancer; however, a comprehensive study of the phenotype, function, and transcriptional program of this T cell population in breast cancer (BC) patients is missing. Compared to healthy donors (HDs), BC patients exhibit an accumulation of KLRG-1+CD57+ CD4+ and CD8+ T cells in peripheral blood. These T cells infiltrate tumors and tumor-draining lymph nodes. KLRG-1+CD57+ CD4+ and CD8+ T cells from BC patients and HDs exhibit features of senescence, and despite their inhibitory receptor expression, they produce more effector cytokines and exhibit higher expression of Perforin, Granzyme B, and CD107a than non-senescent subsets. When compared to blood counterparts, tumor-infiltrating senescent CD4+ T cells show similar surface phenotype but reduced cytokine production. Transcriptional profiling of senescent CD4+ T cells from the peripheral blood of BC patients reveals enrichment in genes associated with NK or CD8+-mediated cytotoxicity, TCR-mediated stimulation, and cell exhaustion compared to non-senescent T cells. Comparison of the transcriptional profile of senescent CD4+ T cells from peripheral blood of BC patients with those of HDs highlighted marked similarities but also relevant differences. Senescent CD4+ T cells from BC patients show enrichment in T-cell signaling, processes involved in DNA replication, p53 pathways, oncogene-induced senescence, among others compared to their counterparts in HDs. High gene expression of CD4, KLRG-1, and B3GAT1 (CD57), which correlates with increased overall survival for BC patients, underscores the usefulness of the evaluation of the frequency of senescent CD4+ T cells as a biomarker in the follow-up of patients.

Embryonic developmental arrest in the annual killifish Austrolebias charrua: A proteomic approach to diapause III.

Diapause is a reversible developmental arrest faced by many organisms in harsh environments. Annual killifish present this mechanism in three possible stages of development. Killifish are freshwater teleosts from Africa and America that live in ephemeral ponds, which dry up in the dry season. The juvenile and adult populations die, and the embryos remain buried in the bottom mud until the next rainy season. Thus, species survival is entirely embryo-dependent, and they are perhaps the most remarkable extremophile organisms among vertebrates. The aim of the present study was to gather information about embryonic diapauses with the use of a "shotgun" proteomics approach in diapause III and prehatching Austrolebias charrua embryos. Our results provide insight into the molecular mechanisms of diapause III. Data are available via ProteomeXchange with identifier PXD025196. We detected a diapause-dependent change in a large group of proteins involved in different functions, such as metabolic pathways and stress tolerance, as well as proteins related to DNA repair and epigenetic modifications. Furthermore, we observed a diapause-associated switch in cytoskeletal proteins. This first glance into global protein expression differences between prehatching and diapause III could provide clues regarding the induction/maintenance of this developmental arrest in A. charrua embryos. There appears to be no single mechanism underlying diapause and the present data expand our knowledge of the molecular basis of diapause regulation. This information will be useful for future comparative approaches among different diapauses in annual killifish and/or other organisms that experience developmental arrest.

Occupational exposure assessment in professionals who manipulate and administer antineoplastic drugs in a university hospital in Southern Brazil.

INTRODUCTION: Our goal was to demonstrate the effects of occupational exposure to antineoplastic drugs on oxidative stress parameters and DNA damage in health professionals who manipulate and administer antineoplastic drugs in a University Hospital in Southern Brazil. METHODS: The case-control study with a longitudinal design, involved 64 individuals, 29 of them pharmacists, pharmacy technicians and nurses who were occupationally exposed to antineoplastic drugs and 35 professionals who were not exposed. Gene mutations were determined by micronucleus from salivary fluid; DNA damage by comet assay and oxidative stress parameters in whole blood were also evaluated. RESULTS: All workers exposed to antineoplastic drugs used personal protective equipment (PPE). It was demonstrated that the total nonprotein thiol and thiobarbituric acid reactive substances levels showed interaction between group and time, with higher levels one week after handling/administration of antineoplastic drugs in the exposed group (GEE, p ≤ 0.0001 and p = 0,013, respectively). Additionally, there was a group effect on the activities of the catalase and glutathione peroxidase antioxidant enzymes (GEE, p = 0.027 and p ≤ 0.0001, respectively), and workers occupationally exposed to antineoplastic drugs had higher enzyme activities compared to those not exposed. No genotoxic damage was demonstrated through the evaluated parameters. CONCLUSIONS: Despite the correct use of PPE, professionals occupationally exposed to antineoplastic drugs were more susceptible to oxidative stress than those not exposed. The evaluation of the studied parameters is especially important for the definition of conducts and practices in the area, always in search of guaranteeing the establishment of a rational policy to protect workers' health.

High IRF8 expression correlates with CD8 T cell infiltration and is a predictive biomarker of therapy response in ER-negative breast cancer.

BACKGROUND: Characterization of breast cancer (BC) through the determination of conventional markers such as ER, PR, HER2, and Ki67 has been useful as a predictive and therapeutic tool. Also, assessment of tumor-infiltrating lymphocytes has been proposed as an important prognostic aspect to be considered in certain BC subtypes. However, there is still a need to identify additional biomarkers that could add precision in distinguishing therapeutic response of individual patients. To this end, we focused in the expression of interferon regulatory factor 8 (IRF8) in BC cells. IRF8 is a transcription factor which plays a well-determined role in myeloid cells and that seems to have multiple antitumoral roles: it has tumor suppressor functions; it acts downstream IFN/STAT1, required for the success of some therapeutic regimes, and its expression in neoplastic cells seems to depend on a cross talk between the immune contexture and the tumor cells. The goal of the present study was to examine the relationship between IRF8 with the therapeutic response and the immune contexture in BC, since its clinical significance in this type of cancer has not been thoroughly addressed. METHODS: We identified the relationship between IRF8 expression and the clinical outcome of BC patients and validated IRF8 as predictive biomarker by using public databases and then performed in silico analysis. To correlate the expression of IRF8 with the immune infiltrate in BC samples, we performed quantitative multiplex immunohistochemistry. RESULTS: IRF8 expression can precisely predict the complete pathological response to monoclonal antibody therapy or to select combinations of chemotherapy such as FAC (fluorouracil, adriamycin, and cytoxan) in ER-negative BC subtypes. Analysis of immune cell infiltration indicates there is a strong correlation between activated and effector CD8+ T cell infiltration and tumoral IRF8 expression. CONCLUSIONS: We propose IRF8 expression as a potent biomarker not only for prognosis, but also for predicting therapy response in ER-negative BC phenotypes. Its expression in neoplastic cells also correlates with CD8+ T cell activation and infiltration. Therefore, our results justify new efforts towards understanding mechanisms regulating IRF8 expression and how they can be therapeutically manipulated.

Identification of key sequence features required for microRNA biogenesis in plants.

MicroRNAs (miRNAs) are endogenous small RNAs of ∼21 nt that regulate multiple biological pathways in multicellular organisms. They derive from longer transcripts that harbor an imperfect stem-loop structure. In plants, the ribonuclease type III DICER-LIKE1 assisted by accessory proteins cleaves the precursor to release the mature miRNA. Numerous studies highlight the role of the precursor secondary structure during plant miRNA biogenesis; however, little is known about the relevance of the precursor sequence. Here, we analyzed the sequence composition of plant miRNA primary transcripts and found specifically located sequence biases. We show that changes in the identity of specific nucleotides can increase or abolish miRNA biogenesis. Most conspicuously, our analysis revealed that the identity of the nucleotides at unpaired positions of the precursor plays a crucial role during miRNA biogenesis in Arabidopsis.

Genome analysis of sphingolipid metabolism-related genes in Tetrahymena thermophila and identification of a fatty acid 2-hydroxylase involved in the sexual stage of conjugation.

Sphingolipids are bioactive lipids present in all eukaryotes. Tetrahymena thermophila is a ciliate that displays remarkable sphingolipid moieties, that is, the unusual phosphonate-linked headgroup ceramides, present in membranes. To date, no identification has been made in this organism of the functions or related genes implicated in sphingolipid metabolism. By gathering information from the T. thermophila genome database together with sphingolipid moieties and enzymatic activities reported in other Tetrahymena species, we were able to reconstruct the putative de novo sphingolipid metabolic pathway in T. thermophila. Orthologous genes of 11 enzymatic steps involved in the biosynthesis and degradation pathways were retrieved. No genes related to glycosphingolipid or phosphonosphingolipid headgroup transfer were found, suggesting that both conserved and innovative mechanisms are used in ciliate. The knockout of gene TTHERM_00463850 allowed to identify the gene encoding a putative fatty acid 2-hydroxylase, which is involved in the biosynthesis pathway. Knockout cells have shown several impairments in the sexual stage of conjugation since different mating types of knockout strains failed to form cell pairs and complete the conjugation process. This fatty acid 2-hydroxylase gene is the first gene of a sphingolipid metabolic pathway to be identified in ciliates and have a critical role in their sexual stage.

Bacterial Infection Disrupts Clock Gene Expression to Attenuate Immune Responses.

The circadian clock modulates immune responses in plants and animals; however, it is unclear how host-pathogen interactions affect the clock. Here we analyzed clock function in Arabidopsis thaliana mutants with defective immune responses and found that enhanced disease susceptibility 4 (eds4) displays alterations in several circadian rhythms. Mapping by sequencing revealed that EDS4 encodes the ortholog of NUCLEOPORIN 205, a core component of the inner ring of the nuclear pore complex (NPC). Consistent with the idea that the NPC specifically modulates clock function, we found a strong enrichment in core clock genes, as well as an increased nuclear to total mRNA accumulation, among genes that were differentially expressed in eds4 mutants. Interestingly, infection with Pseudomonas syringae in wild-type (WT) plants downregulated the expression of several morning core clock genes as early as 1 h post-infection, including all members of the NIGHT LIGHT-INDUCIBLE AND CLOCK-REGULATED (LNK) gene family, and this effect was attenuated in eds4. Furthermore, lnk mutants were more susceptible than the WT to P. syringae infection. These results indicate that bacterial infection, acting in part through the NPC, alters core clock gene expression and/or mRNA accumulation in a way that favors bacterial growth and disease susceptibility.

Uso de un dispositivo alternativo de cánula nasal de alto flujo de oxígeno para la falla respiratoria aguda hipoxémica en una central de emergencias de adultos en Argentina. Estudio cuasi experimental / Use of an Alternative Oxygen High-Flow Nasal Cannula Device for Hypoxemic Acute Respiratory Failure in an Adult Emergency Department in Argentina. Quasi-Experimental Study

Objetivo: Describir los cambios observados en la frecuencia respiratoria, la frecuencia cardiaca y la puntuación de disnea antes y después de la utilización de un dispositivo alternativo de cánula nasal de alto flujo en pacientes con falla respiratoria aguda hipoxémica en una central de emergencias. Materiales y método: Estudio cuasi experimental y retrospectivo con pacientes adultos que acudieron a la central de emergencias con signos clínicos de falla respiratoria aguda hipoxémica. Los datos de frecuencia respiratoria, frecuencia cardíaca y la puntuación de disnea se recolectaron de la historia clínica electrónica antes y después de dos horas de haber utilizado un dispositivo Venturi conectado a un sistema de cánula nasal de alto flujo. Resultado: Se incluyeron 43 pacientes. La media de edad fue de 64.7 (DE 16) años. La principal causa de la falla respiratoria fue la neumonía en 18 pacientes (42%). Se observó que la frecuencia respiratoria disminuyó 8 respiraciones por minuto (p < .001), la frecuencia cardiaca disminuyó 7 latidos por minuto (p < .001) y la puntuación de la disnea disminuyó 2 puntos (p < .001). Conclusiones: Se observó una disminución significativa de las tres variables estudiadas en los pacientes que acudieron a la central de emergencias con falla respiratoria aguda hipoxémica, con la utilización de un dispositivo de oxigenoterapia no convencional, el cual podría considerarse en países con recursos limitados o en los escenarios de superpoblación, tan frecuentes en las centrales de emergencia.

Use of an Alternative Oxygen High-Flow Nasal Cannula Device for Hypoxemic Acute Respiratory Failure in an Adult Emergency Department in Argentina. Quasi-Experimental Study

Objective: To describe changes observed in respiratory rate, heart rate and dyspnea score before and after using an alternative highflow nasal cannula device in patients with hypoxemic acute respiratory failure in an Emergency Department. Materials and Method: Quasi-experimental, retrospective study with adult patients who went to the Emergency Department with clinical signs of hypoxemic acute respiratory failure. Data from respiratory rate, heart rate and dyspnea score were gathered from the electronic medical records of the patients both before and after using a Venturi device connected to a high-flow nasal cannula system two hours. Result: 43 patients were included. The mean age was 64.7 years (SD 16). The main cause of respiratory failure was pneumonia in 18 patients (42%). We observed a decrease of 8 breaths per minute (p < .001) in the respiratory rate, and 7 beats per minute (p < .001) in the heart rate; and there was a 2-point decrease in the dyspnea score (p < .001). Conclusions: We observed a significant decrease in the three variables under study in patients who went to the Emergency Department with hypoxemic acute respiratory failure, using a non-conventional oxygen therapy device, which could become useful in countries with limited resources or in cases of overcrowding, so common in the Emergency Departments

Gene identification and functional characterization of a Δ12 fatty acid desaturase in Tetrahymena thermophila and its influence in homeoviscous adaptation to low temperature.

Homeoviscous adaptation in poikilotherms is based in the regulation of the level of desaturation of fatty acids, variation in phospholipids head groups and sterol content in the membrane lipids, in order to maintain the membrane fluidity in response to changes in environmental temperature. Increased proportion of unsaturated fatty acids is thought to be the main response to low-temperature acclimation, which is mostly achieved by fatty acid desaturases. Genome analysis of the ciliate Tetrahymena thermophila and a gene knockout approach has allowed us to identify one Δ12 FAD and to study its activity in the original host and in a yeast heterologous expression system. The "PUFA index" -relative content of polyunsaturated fatty acids compared to the sum of saturated and monounsaturated fatty acid content- was ~57% lower at 15 °C and 35 °C in the Δ12 FAD gene knockout strain (KOΔ12) compared to WT strain. We characterized the role of T. thermophila Δ12 FAD on homeoviscous adaptation and analyzed its involvement in cellular growth, cold stress response, and membrane fluidity, as well as its expression pattern during temperature shifts. Although these alterations allowed normal growth in the KOΔ12 strain at 30 °C or higher temperatures, growth was impaired at temperatures of 20 °C or lower, where homeoviscous adaptation is impaired. These results stress the importance of Δ12 FAD in the regulation of cold adaptation processes, as well as the suitability of T. thermophila as a valuable model to investigate the regulation of membrane lipids and evolutionary conservation and divergence of the underlying mechanisms.

IL-17RA-Signaling Modulates CD8+ T Cell Survival and Exhaustion During Trypanosoma cruzi Infection.

The IL-17 family contributes to host defense against many intracellular pathogens by mechanisms that are not fully understood. CD8+ T lymphocytes are key elements against intracellular microbes, and their survival and ability to mount cytotoxic responses are orchestrated by several cytokines. Here, we demonstrated that IL-17RA-signaling cytokines sustain pathogen-specific CD8+ T cell immunity. The absence of IL-17RA and IL-17A/F during Trypanosoma cruzi infection resulted in increased tissue parasitism and reduced frequency of parasite-specific CD8+ T cells. Impaired IL-17RA-signaling in vivo increased apoptosis of parasite-specific CD8+ T cells, while in vitro recombinant IL-17 down-regulated the pro-apoptotic protein BAD and promoted the survival of activated CD8+ T cells. Phenotypic, functional, and transcriptomic profiling showed that T. cruzi-specific CD8+ T cells derived from IL-17RA-deficient mice presented features of cell dysfunction. PD-L1 blockade partially restored the magnitude of CD8+ T cell responses and parasite control in these mice. Adoptive transfer experiments established that IL-17RA-signaling is intrinsically required for the proper maintenance of functional effector CD8+ T cells. Altogether, our results identify IL-17RA and IL-17A as critical factors for sustaining CD8+ T cell immunity to T. cruzi.

Involvement of fibroblast growth factor 2 (FGF2) and its receptors in the regulation of mouse sperm physiology.

Fibroblast growth factor 2 (FGF2) and its receptors (FGFRs) have been described in several tissues, where they regulate cellular proliferation, differentiation, motility and apoptosis. Although FGF2/FGFRs expression in the male reproductive tract has been reported, there is scarce evidence on their presence in the female reproductive tract and their involvement in the modulation of sperm function. Therefore, the objective of this study was to determine the expression of FGF2 in the female reproductive tract and to assess the role of the FGF2/FGFRs system in the regulation of sperm physiology using the murine model. FGF2 was detected in uterus and oviduct protein extracts, and it was immunolocalized in epithelial cells of the uterus, isthmus and ampulla, as well as in the cumulus oophorus-oocyte complex. The receptors FGFR1, FGFR2, FGFR3 and FGFR4 were immunodetected in the flagellum and acrosomal region of sperm recovered from the cauda epididymis. Analysis of testis sections showed the expression of FGFRs in germ cells at different stages of the spermatogenesis, suggesting the testicular origin of the sperm FGFRs. Sperm incubation with recombinant FGF2 (rFGF2) led to increased sperm motility and velocity and to enhanced intracellular Ca2+ levels and acrosomal loss compared to the control. In conclusion, this study shows that FGF2 is expressed in tissues of the female reproductive tract. Also, the fact that functional FGFRs are present in mouse sperm and that rFGF2 affects sperm motility and acrosomal exocytosis, suggests the involvement of this system in the in vivo regulation of sperm function.