Ca(2+)/calmodulin-dependent protein kinase IV is expressed in spermatids and targeted to chromatin and the nuclear matrix

Transcriptional, biochemical, and immunohistochemical analyses of CaMKKβ/2 splice variants that co-localize with CaMKIV in spermatids

Ca2+/calmodulin-dependent protein kinase kinase (CaMKK) phosphorylates and activates downstream protein kinases, including CaMKI, CaMKIV, PKB/Akt, and AMPK; thus, regulates various Ca2+-dependent physiological and pathophysiological pathways. Further, CaMKKβ/2 in mammalian species comprises multiple alternatively spliced variants; however, their functional differences or redundancy remain unclear. In this study, we aimed to characterize mouse CaMKKβ/2 splice variants (CaMKKβ-3 and β-3x). RT-PCR analyses revealed that mouse CaMKKβ-1, consisting of 17 exons, was predominantly expressed in the brain; whereas, mouse CaMKKβ-3 and β-3x, lacking exon 16 and exons 14/16, respectively, were primarily expressed in peripheral tissues. At the protein level, the CaMKKβ-3 or β-3x variants showed high expression levels in mouse cerebrum and testes. This was consistent with the localization of CaMKKβ-3/-3x in spermatids in seminiferous tubules, but not the localization of CaMKKβ-1. We also observed the co-localization of CaMKKβ-3/-3x with a target kinase, CaMKIV, in elongating spermatids. Biochemical characterization further revealed that CaMKKβ-3 exhibited Ca2+/CaM-induced kinase activity similar to CaMKKβ-1. Conversely, we noted that CaMKKβ-3x impaired Ca2+/CaM-binding ability, but exhibited significantly weak autonomous activity (approximately 500-fold lower than CaMKKβ-1 or β-3) due to the absence of C-terminal of the catalytic domain and a putative residue (Ile478) responsible for the kinase autoinhibition. Nevertheless, CaMKKβ-3x showed the ability to phosphorylate downstream kinases, including CaMKIα, CaMKIV, and AMPKα in transfected cells comparable to CaMKKβ-1 and β-3. Collectively, CaMKKβ-3/-3x were identified as functionally active and could be bona fide CaMKIV-kinases in testes involved in the activation of the CaMKIV cascade in spermatids, resulting in the regulation of spermiogenesis.

Testicular heat stress, a historical perspective and two postulates for why male germ cells are heat sensitive

Herein, we compare the different experimental regimes used to induce testicular heat stress and summarise their impact on sperm production and male fertility. Irrespective of the protocol used, scrotal heat stress causes loss of sperm production. This is first seen 1-2 weeks post heat stress, peaking 4-5 weeks thereafter. The higher the temperature, or the longer the duration of heat, the more pronounced germ cell loss becomes, within extreme cases this leads to azoospermia. The second, and often underappreciated impact of testicular hyperthermia is the production of poor-quality spermatozoa. Typically, those cells that survive hyperthermia develop into morphologically abnormal and poorly motile spermatozoa. While both apoptotic and non-apoptotic pathways are known to contribute to hyperthermic germ cell loss, the mechanisms leading to formation of poor-quality sperm remain unclear. Mechanistically, it is unlikely that testicular hyperthermia affects messenger RNA (mRNA) abundance, as a comparison of four different mammalian studies shows no consistent single gene changes. Using available evidence, we propose two novel models to explain how testicular hyperthermia impairs sperm formation. Our first model suggests aberrant alternative splicing, while the second model proposes a loss of RNA repression. Importantly, neither model requires consistent changes in RNA species.

Ca2+/calmodulin-dependent Protein Kinases in Leukemia Development

Ca²⁺/calmodulin (CaM) signaling is important for a wide range of cellular functions. It is not surprised the role of this signaling has been recognized in tumor progressions, such as proliferation, invasion, and migration. However, its role in leukemia has not been well appreciated. The multifunctional Ca²⁺/CaM-dependent protein kinases (CaMKs) are critical intermediates of this signaling and play key roles in cancer development. The most investigated CaMKs in leukemia, especially myeloid leukemia, are CaMKI, CaMKII, and CaMKIV. The function and mechanism of these kinases in leukemia development are summarized in this study.

CaMK4 promotes abortion-related Th17 cell imbalance by activating AKT/mTOR signaling pathway

PROBLEM

The balance of the immune microenvironment along the maternal-fetal interface is closely related to pregnancy outcomes, with excessive inflammatory reactions leading to the occurrence of pathological pregnancy outcomes such as abortion. CaMK4 has been reported to play a significant role in autoimmune diseases through the regulation of Th17 cells. However, whether CaMK4 is associated with spontaneous abortion or the immune microenvironment along the maternal-fetal interface remains unclear.

METHODS OF STUDY

In this study, we constructed normal pregnancy and LPS-induced abortion models in mice, and a CaMK4 inhibitor called KN-93 was administered to investigate the changes in and mechanisms of the immune response. The expression of CaMK4 was evaluated in the uteroplacental complex and spleen. Furthermore, the infiltration and function of Th17 cells were estimated in peripheral tissues and the uteroplacental complex.

RESULTS

The expression of CaMK4 in the uteroplacental complex and spleen was significantly higher in the LPS-treated group than in the normal pregnancy group. KN-93, the CaMK4 inhibitor, reversed fetal resorption and excessive inflammation. In detail, KN-93 led to reduced infiltration of Th17 cells into peripheral tissues and the uteroplacental complex, and the functions of Th17 cells were inhibited. In addition, CaMK4 promoted the AKT/mTOR signaling pathway, which is one of the mechanisms that regulate the immune microenvironment.

CONCLUSION

CaMK4 is a critical regulator that promotes the expansion of Th17 cells and enhances their functions through the AKT/mTOR signaling pathway. The inhibition of CaMK4 can reverse the immune imbalance along the maternal-fetal interface and improve pregnancy outcomes.

In Depth Analysis of Kinase Cross Screening Data to Identify CAMKK2 Inhibitory Scaffolds

The calcium/calmodulin-dependent protein kinase kinase 2 (CAMKK2) activates CAMK1, CAMK4, AMPK, and AKT, leading to numerous physiological responses. The deregulation of CAMKK2 is linked to several diseases, suggesting the utility of CAMKK2 inhibitors for oncological, metabolic and inflammatory indications. In this work, we demonstrate that STO-609, frequently described as a selective inhibitor for CAMKK2, potently inhibits a significant number of other kinases. Through an analysis of literature and public databases, we have identified other potent CAMKK2 inhibitors and verified their activities in differential scanning fluorimetry and enzyme inhibition assays. These inhibitors are potential starting points for the development of selective CAMKK2 inhibitors and will lead to tools that delineate the roles of this kinase in disease biology.

Regulation of Multifunctional Calcium/Calmodulin Stimulated Protein Kinases by Molecular Targeting

Multifunctional calcium/calmodulin-stimulated protein kinases control a broad range of cellular functions in a multitude of cell types. This family of kinases contain several structural similarities and all are regulated by phosphorylation, which either activates, inhibits or modulates their kinase activity. As these protein kinases are widely or ubiquitously expressed, and yet regulate a broad range of different cellular functions, additional levels of regulation exist that control these cell-specific functions. Of particular importance for this specificity of function for multifunctional kinases is the expression of specific binding proteins that mediate molecular targeting. These molecular targeting mechanisms allow pools of kinase in different cells, or parts of a cell, to respond differently to activation and produce different functional outcomes.

The Multi-Functional Calcium/Calmodulin Stimulated Protein Kinase (CaMK) Family: Emerging Targets for Anti-Cancer Therapeutic Intervention

The importance of Ca²⁺ signalling in key events of cancer cell function and tumour progression, such as proliferation, migration, invasion and survival, has recently begun to be appreciated. Many cellular Ca²⁺-stimulated signalling cascades utilise the intermediate, calmodulin (CaM). The Ca²⁺/CaM complex binds and activates a variety of enzymes, including members of the multifunctional Ca²⁺/calmodulin-stimulated protein kinase (CaMK) family. These enzymes control a broad range of cancer-related functions in a multitude of tumour types. Herein, we explore the cancer-related functions of these kinases and discuss their potential as targets for therapeutic intervention.

Genetic Factors Affecting Sperm Chromatin Structure

Spermatozoa genome has unique features that make it a fascinating field of investigation: first, because, with oocyte genome, it can be transmitted generation after generation; second, because of genetic shuffling during meiosis, each spermatozoon is virtually unique in terms of genetic content, with consequences for species evolution; and finally, because its chromatin organization is very different from that of somatic cells or oocytes, as it is not based on nucleosomes but on nucleoprotamines which confer a higher order of packaging. Histone-to-protamine transition involves many actors, such as regulators of spermatid gene expression, components of the nuclear envelop, histone-modifying enzymes and readers, chaperones, histone variants, transition proteins, protamines, and certainly many more to be discovered.In this book chapter, we will present what is currently known about sperm chromatin structure and how it is established during spermiogenesis, with the aim to list the genetic factors that regulate its organization.

Binding studies and biological evaluation of β-carotene as a potential inhibitor of human calcium/calmodulin-dependent protein kinase IV

Human calcium/calmodulin-dependent protein kinase IV (CAMKIV), a member of Ser/Thr kinase family, is associated with cancer, cerebral hypoxia and neurodegenerative diseases. β-carotene is a colored organic compound, abundant in plants and fruits and is used in cancer prevention. Here, we report a strong binding affinity of β-carotene with CAMKIV using molecular docking, fluorescence binding and isothermal titration calorimetry methods. Furthermore, β-carotene also reduces the enzyme activity of CAMKIV moderately as observed during ATPase assay. To see the role of β-carotene on cell proliferation and apoptosis, cancerous cells (HeLa, HuH7and MCF-7) and normal (HEK-293-T) cell lines were used. Admirable anticancer activity of β-carotene was observed. We further performed propidium iodide and DAPI (4',6-diamidino-2-phenylindole) assays to understand the mechanism of anticancer activity of β-carotene at molecular level. Our findings provide a newer insight into the use of β-carotene in cancer prevention and protection via inhibition of CAMKIV by regulating the signaling pathways.

Design, synthesis, and biological evaluation of pyrimidine derivatives as potential inhibitors of human calcium/calmodulin-dependent protein kinase IV

Calcium/calmodulin-dependent protein kinase IV (CAMKIV) is a multifunctional Ser/Thr kinase, associated with cerebral hypoxia, cancer, and neurodegenerative diseases. Here, we report design, synthesis, and biological evaluation of seven pyrimidine-substituted novel inhibitors of CAMKIV. We successfully synthesized and extensively characterized (ESI-MS, ¹ H NMR, and ¹³ C NMR studies) seven compounds that are showing appreciable binding affinity to the CAMKIV. Molecular docking and fluorescence binding studies revealed that compound 1 is showing very high binding free energy (ΔG = -11.52 kcal/mol) and binding affinity (K = 9.2 × 10¹⁰ m^-1 ) to the CAMKIV. We further performed MTT assay to check the cytotoxicity and anticancer activity of these compounds. An appreciable IC₅₀ (39 μm) value of compound 1 was observed on human hepatoma cell line and nontoxic till the 400 μm on human embryonic kidney cells. To ensure anticancer activity of all these compounds, we further performed propidium iodide assay to evaluate cell viability and DNA content during the cell cycle. We found that compound 1 is again showing a better anticancer activity on both human hepatoma and human embryonic kidney cell lines.

Urea-induced denaturation of human calcium/calmodulin-dependent protein kinase IV: a combined spectroscopic and MD simulation studies

Calcium/calmodulin-dependent protein kinase IV (CaMKIV) is a multifunctional enzyme which belongs to the Ser/Thr kinase family. CaMKIV plays important role in varieties of biological processes such as gene expression regulation, memory consolidation, bone growth, T-cell maturation, sperm motility, regulation of microtubule dynamics, cell-cycle progression, and apoptosis. To measure stability parameters, urea-induced denaturation of CaMKIV was carried out at pH 7.4 and 25°C, using three different probes, namely far-UV CD, near-UV absorption, and tryptophan fluorescence. A coincidence of normalized denaturation curves of these optical properties suggests that urea-induced denaturation is a two-state process. Analysis of these denaturation curves gave values of 4.20 ± 0.12 kcal mol^-1, 2.95 ± 0.15 M, and 1.42 ± 0.06 kcal mol^-1 M^-1 for [Formula: see text] (Gibbs free energy change (ΔG_D) in the absence of urea), C_m (molar urea concentration ([urea]) at the midpoint of the denaturation curve), and m (=∂ΔG_D/∂[urea]), respectively. All these experimental observations have been fully supported by 30 ns molecular dynamics simulation studies.

Effect of pH on the structure, function, and stability of human calcium/calmodulin-dependent protein kinase IV: combined spectroscopic and MD simulation studies

Human calcium/calmodulin-dependent protein kinase IV (CAMKIV) is a member of Ser/Thr protein kinase family. It is regulated by the calcium-calmodulin dependent signal through a secondary messenger, Ca(2+), which leads to the activation of its autoinhibited form. The over-expression and mutation in CAMKIV as well as change in Ca(2+) concentration is often associated with numerous neurodegenerative diseases and cancers. We have successfully cloned, expressed, and purified a functionally active kinase domain of human CAMKIV. To observe the effect of different pH conditions on the structural and functional properties of CAMKIV, we have used spectroscopic techniques such as circular diachroism (CD) absorbance and fluorescence. We have observed that within the pH range 5.0-11.5, CAMKIV maintained both its secondary and tertiary structures, along with its function, whereas significant aggregation was observed at acidic pH (2.0-4.5). We have also performed ATPase activity assays under different pH conditions and found a significant correlation between the structure and enzymatic activities of CAMKIV. In-silico validations were further carried out by modeling the 3-dimensional structure of CAMKIV and then subjecting it to molecular dynamics (MD) simulations to understand its conformational behavior in explicit water conditions. A strong correlation between spectroscopic observations and the output of molecular dynamics simulation was observed for CAMKIV.

Ca(2+)/Calmodulin-Dependent Protein Kinase IV Promotes Interplay of Proteins in Chromatoid Body of Male Germ Cells

The chromatoid body is a granule-like structure of male germ cells, containing many proteins and RNAs, and is important for spermatogenesis. However, the molecular mechanisms for the formation and function of the chromatoid body are still elusive. Here, we report that Ca(2+)/calmodulin-dependent protein kinase IV (CaMKIV) accumulates in the chromatoid body by immunofluorescence staining, indicating that CaMKIV is a new component of the chromatoid body. Furthermore, we find that CaMKIV can interplay with the other components of the chromatoid body by immunoprecipitation: mouse VASA homologue (MVH), mouse homologue of PIWI, PIWIL1 (MIWI), and kinesin KIF17b. Importantly, interplay between KIF17b and MVH or MIWI can be potentially regulated by CaMKIV. These results imply that CaMKIV plays a role in maintenance the structure of chromatoid body by regulating the associations of proteins in it.

Biphasic role of calcium in mouse sperm capacitation signaling pathways

Mammalian sperm acquire fertilizing ability in the female tract in a process known as capacitation. At the molecular level, capacitation is associated with up-regulation of a cAMP-dependent pathway, changes in intracellular pH, intracellular Ca(2+), and an increase in tyrosine phosphorylation. How these signaling systems interact during capacitation is not well understood. Results presented in this study indicate that Ca(2+) ions have a biphasic role in the regulation of cAMP-dependent signaling. Media without added Ca(2+) salts (nominal zero Ca(2+)) still contain micromolar concentrations of this ion. Sperm incubated in this medium did not undergo PKA activation or the increase in tyrosine phosphorylation suggesting that these phosphorylation pathways require Ca(2+). However, chelation of the extracellular Ca(2+) traces by EGTA induced both cAMP-dependent phosphorylation and the increase in tyrosine phosphorylation. The EGTA effect in nominal zero Ca(2+) media was mimicked by two calmodulin antagonists, W7 and calmidazolium, and by the calcineurin inhibitor cyclosporine A. These results suggest that Ca(2+) ions regulate sperm cAMP and tyrosine phosphorylation pathways in a biphasic manner and that some of its effects are mediated by calmodulin. Interestingly, contrary to wild-type mouse sperm, sperm from CatSper1 KO mice underwent PKA activation and an increase in tyrosine phosphorylation upon incubation in nominal zero Ca(2+) media. Therefore, sperm lacking Catsper Ca(2+) channels behave as wild-type sperm incubated in the presence of EGTA. This latter result suggests that Catsper transports the Ca(2+) involved in the regulation of cAMP-dependent and tyrosine phosphorylation pathways required for sperm capacitation.

Inhibition of CaMKK2 reverses age-associated decline in bone mass

Decline in bone formation is a major contributing factor to the loss of bone mass associated with aging. We previously showed that the genetic ablation of the tissue-restricted and multifunctional Ca(2+)/calmodulin (CaM)-dependent protein kinase kinase 2 (CaMKK2) stimulates trabecular bone mass accrual, mainly by promoting anabolic pathways and inhibiting catabolic pathways of bone remodeling. In this study, we investigated whether inhibition of this kinase using its selective cell-permeable inhibitor STO-609 will stimulate bone formation in 32 week old male WT mice and reverse age-associated of decline in bone volume and strength. Tri-weekly intraperitoneal injections of saline or STO-609 (10 μM) were performed for six weeks followed by metabolic labeling with calcein and alizarin red. New bone formation was assessed by dynamic histomorphometry whereas micro-computed tomography was employed to measure trabecular bone volume, microarchitecture and femoral mid-shaft geometry. Cortical and trabecular bone biomechanical properties were assessed using three-point bending and punch compression methods respectively. Our results reveal that as they progress from 12 to 32 weeks of age, WT mice sustain a significant decline in trabecular bone volume, microarchitecture and strength as well as cortical bone strength. However, treatment of the 32 week old WT mice with STO-609 stimulated apposition of new bone and completely reversed the age-associated decrease in bone volume, quality, as well as trabecular and cortical bone strength. We also observed that regardless of age, male Camkk2(-/-) mice possessed significantly elevated trabecular bone volume, microarchitecture and compressive strength as well as cortical bone strength compared to age-matched WT mice, implying that the chronic loss of this kinase attenuates age-associated decline in bone mass. Further, whereas STO-609 treatment and/or the absence of CaMKK2 significantly enhanced the femoral mid-shaft geometry, the mid-shaft cortical wall thickness and material bending stress remained similar among the cohorts, implying that regardless of treatment, the material properties of the bone remain similar. Thus, our cumulative results provide evidence for the pharmacological inhibition of CaMKK2 as a bone anabolic strategy in combating age-associated osteoporosis.

A mutation study of sperm head shape and motility in the mouse: lessons for the clinic

Mouse mutants that show effects on sperm head shape, the sperm tail (flagellum), and motility were analysed in a systematic way. This was achieved by grouping mutations in the following classes: manchette, acrosome, Sertoli cell contact, chromatin remodelling, and mutations involved in complex regulations such as protein (de)phosphorylation and RNA stability, and flagellum/motility mutations. For all mutant phenotypes, flagellum function (motility) was affected. Head shape, including the nucleus, was also affected in spermatozoa of most mouse models, though with considerable variation. For the mutants that were categorized in the flagellum/motility group, generally normal head shapes were found, even when the flagellum did not develop or only poorly so. Most mutants are sterile, an occasional one semi-sterile. For completeness, the influence of the sex chromosomes on sperm phenotype is included. Functionally, the genes involved can be categorized as regulators of spermiogenesis. When extrapolating these data to human sperm samples, in vivo selection for motility would be the tool for weeding out the products of suboptimal spermiogenesis and epididymal sperm maturation. The striking dependency of motility on proper sperm head development is not easy to understand, but likely is of evolutionary benefit. Also, sperm competition after mating can never act against the long-term multi-generation interest of genetic integrity. Hence, it is plausible to suggest that short-term haplophase fitness i.e., motility, is developmentally integrated with proper nucleus maturation, including genetic integrity to protect multi-generation fitness. We hypothesize that, when the prime defect is in flagellum formation, apparently a feedback loop was not necessary as head morphogenesis in these mutants is mostly normal. Extrapolating to human-assisted reproductive techniques practice, this analysis would supply the arguments for the development of tools to select for motility as a continuous (non-discrete) parameter.

A multi-faceted approach to understanding male infertility: gene mutations, molecular defects and assisted reproductive techniques (ART)

BACKGROUND

The assisted reproductive techniques aimed to assist infertile couples have their own offspring carry significant risks of passing on molecular defects to next generations.

RESULTS

Novel breakthroughs in gene and protein interactions have been achieved in the field of male infertility using genome-wide proteomics and transcriptomics technologies.

CONCLUSION

Male Infertility is a complex and multifactorial disorder.

SIGNIFICANCE

This review provides a comprehensive, up-to-date evaluation of the multifactorial factors involved in male infertility. These factors need to be first assessed and understood before we can successfully treat male infertility.

Common variants in genes of the postsynaptic FMRP signalling pathway are risk factors for autism spectrum disorders

Autism spectrum disorders (ASD) are heterogeneous disorders with a high heritability and complex genetic architecture. Due to the central role of the fragile X mental retardation gene 1 protein (FMRP) pathway in ASD we investigated common functional variants of ASD risk genes regulating FMRP. We genotyped ten SNPs in two German patient sets (N = 192 and N = 254 families, respectively) and report association for rs7170637 (CYFIP1; set 1 and combined sets), rs6923492 (GRM1; combined sets), and rs25925 (CAMK4; combined sets). An additional risk score based on variants with an odds ratio (OR) >1.25 in set 1 and weighted by their respective log transmitted/untransmitted ratio revealed a significant effect (OR 1.30, 95 % CI 1.11-1.53; P = 0.0013) in the combined German sample. A subsequent meta-analysis including the two German samples, the "Strict/European" ASD subsample of the Autism Genome Project (1,466 families) and a French case/control (541/366) cohort showed again association of rs7170637-A (OR 0.85, 95 % CI 0.75-0.96; P = 0.007) and rs25925-G (OR 1.31, 95 % CI 1.04-1.64; P = 0.021) with ASD. Functional analyses revealed that these minor alleles predicted to alter splicing factor binding sites significantly increase levels of an alternative mRNA isoform of the respective gene while keeping the overall expression of the gene constant. These findings underpin the role of ASD candidate genes in postsynaptic FMRP regulation suggesting that an imbalance of specific isoforms of CYFIP1, an FMRP interaction partner, and CAMK4, a transcriptional regulator of the FMRP gene, modulates ASD risk. Both gene products are related to neuronal regulation of synaptic plasticity, a pathomechanism underlying ASD and may thus present future targets for pharmacological therapies in ASD.

Decreased levels of Ca²⁺-calmodulin-dependent protein kinase IV in the testis as a contributing factor to reduced fertility in male Crybb2⁻/⁻ mice

βB2-crystallin (Crybb2), a member of the βγ-crystallin superfamily, in conjunction with α-crystallin, constitute the major proteins of the mammalian eye lens. Crybb2 is also expressed outside the lens, and certain related functions in these tissues have been reported. In the present study, in order to define the physiological role of Crybb2, we generated mice with a targeted deletion of the Crybb2 gene. Surprisingly, fertility was markedly reduced in male homozygous knockout mice compared to wild-type (WT) mice. Further experiments were performed to explore the underlying mechanism of subfertility in male Crybb2⁻/⁻ mice. Our results showed that Crybb2 was mainly expressed in the spermatogonia from the testes of mice with the WT C57BL/C genetic background. The testes of 4-week-old Crybb2⁻/⁻ mice were significantly hyperplastic, and no significant difference was found within 3 weeks postpartum. Additionally, there was a marked increase in the proliferation and apoptosis of germ cells, and the biological defects of these cells correlated with the decreased Bcl-2 levels, which correlated with the reduction of Ca²⁺-calmodulin-dependent protein kinase IV (CaMKIV) in the testis. These results suggest that the reduced fertility of Crybb2⁻/⁻ male mice may result from the disordered proliferation and apoptosis of germ cells in the testis, possibly due to reduced CaMKIV from the loss of Crybb2.

Novel mutations in calcium/calmodulin-dependent protein kinase IV (CAMK4) gene in infertile men

Calcium/calmodulin-dependent protein kinase IV (CAMK4) is a multifunctional serine/threonine protein kinase, which plays an important role in the spermatogenesis by phosphorylating protamines. It has been shown to be involved in the regulation of human sperm motility. Moreover, the Camk4 knockout mice were infertile because of severely reduced sperm count and morphological abnormalities. As no study is available on the association of this gene with male infertility, we analysed all the exons of CAMK4 gene in ethnically matched 283 infertile and 268 fertile Indian men. We identified twenty nucleotide substitutions, of which twelve were novel. Of these novel variants, eight were exclusively detected in infertile men. Moreover, two infertile men-specific mutations were non-synonymous replacing amino acids at the highly conserved region. In silico analysis predicted both of these mutations as 'deleterious'. In addition to nucleotide substitutions, we identified five novel insertion-deletion mutations; of these, g.150264_66delGCG was exclusively found in two oligoasthenoteratozoospermic men. In silico analysis of infertile men exclusive mutations predicted that they can alter/diminish the potential binding sites of splicing factors, which may affect the mRNA splicing and protein translation. Our study suggests that the mutations in CAMK4 may lead to abnormal semen parameters.

Epigenetics and its role in male infertility

Male infertility is a common and complex problem affecting 1 in 20 men. Despite voluminous research in this field, in many cases, the underlying causes are unknown. Epigenetic factors play an important role in male infertility and these have been studied extensively. Epigenetic modifications control a number of processes within the body, but this review will concentrate on male fertility and the consequences of aberrant epigenetic regulation/modification. Many recent studies have identified altered epigenetic profiles in sperm from men with oligozoospermia and oligoasthenoteratozoospermia. During gametogenesis and germ cell maturation, germ cells undergo extensive epigenetic reprogramming that involves the establishment of sex-specific patterns in the sperm and oocytes. Increasing evidence suggests that genetic and environmental factors can have negative effects on epigenetic processes controlling implantation, placentation and fetal growth. This review provides an overview of the epigenetic processes (histone-to-protamine exchange and epigenetic reprogramming post-fertilization), aberrant epigenetic reprogramming and its association with fertility, possible risks for ART techniques, testicular cancer and the effect of environmental factors on the epigenetic processes.

The role of molecular regulation and targeting in regulating calcium/calmodulin stimulated protein kinases

Calcium/calmodulin-stimulated protein kinases can be classified as one of two types - restricted or multifunctional. This family of kinases contains several structural similarities: all possess a calmodulin binding motif and an autoinhibitory region. In addition, all of the calcium/calmodulin-stimulated protein kinases examined in this chapter are regulated by phosphorylation, which either activates or inhibits their kinase activity. However, as the multifunctional calcium/calmodulin-stimulated protein kinases are ubiquitously expressed, yet regulate a broad range of cellular functions, additional levels of regulation that control these cell-specific functions must exist. These additional layers of control include gene expression, signaling pathways, and expression of binding proteins and molecular targeting. All of the multifunctional calcium/calmodulin-stimulated protein kinases examined in this chapter appear to be regulated by these additional layers of control, however, this does not appear to be the case for the restricted kinases.

Surfing the wave, cycle, life history, and genes/proteins expressed by testicular germ cells. Part 3: developmental changes in spermatid flagellum and cytoplasmic droplet and interaction of sperm with the zona pellucida and egg plasma membrane

Spermiogenesis constitutes the steps involved in the metamorphosis of spermatids into spermatozoa. It involves modification of several organelles in addition to the formation of several structures including the flagellum and cytoplasmic droplet. The flagellum is composed of a neck region and middle, principal, and end pieces. The axoneme composed of nine outer microtubular doublets circularly arranged to form a cylinder around a central pair of microtubules is present throughout the flagellum. The middle and principal pieces each contain specific components such as the mitochondrial sheath and fibrous sheath, respectively, while outer dense fibers are common to both. A plethora of proteins are constituents of each of these structures, with each playing key roles in functions related to the fertility of spermatozoa. At the end of spermiogenesis, a portion of spermatid cytoplasm remains associated with the released spermatozoa, referred to as the cytoplasmic droplet. The latter has as its main feature Golgi saccules, which appear to modify the plasma membrane of spermatozoa as they move down the epididymal duct and hence may be partly involved in male gamete maturation. The end product of spermatogenesis is highly streamlined and motile spermatozoa having a condensed nucleus equipped with an acrosome. Spermatozoa move through the female reproductive tract and eventually penetrate the zona pellucida and bind to the egg plasma membrane. Many proteins have been implicated in the process of fertilization as well as a plethora of proteins involved in the development of spermatids and sperm, and these are high lighted in this review.

Epigenetic reprogramming of the male genome during gametogenesis and in the zygote

During post-meiotic maturation, male germ cells undergo a formidable reorganization and condensation of their genome. During this phase most histones are globally acetylated and then replaced by sperm-specific basic proteins, named protamines, which compact the genome into a very specific structure within the sperm nucleus. Several studies suggest that this sperm-specific genome packaging structure conveys an important epigenetic message to the embryo. This paper reviews what is known about this fundamental, yet poorly understood, process, which involves not only global changes of the structure of the haploid genome, but also localized specific modifications of particular genomic regions, including pericentric heterochromatin and sex chromosomes. After fertilization, the male genome undergoes a drastic decondensation, and rapidly incorporates new histones. However, it remains different from the maternal genome, bearing specific epigenetic marks, especially in the pericentric heterochromatin region. The functional implications of male post-meiotic and post-fertilization genome reprogramming are not well known, but there is experimental evidence to show that it affects early embryonic development.

The orphan nuclear receptor NUR77 regulates hormone-induced StAR transcription in Leydig cells through cooperation with Ca2+/calmodulin-dependent protein kinase I

Cholesterol transport in the mitochondrial membrane, an essential step of steroid biosynthesis, is mediated by a protein complex containing the steroidogenic acute regulatory (StAR) protein. The importance of this transporter is underscored by mutations in the human StAR gene that cause lipoid congenital adrenal hyperplasia, male pseudohermaphroditism, and adrenal insufficiency. StAR transcription in steroidogenic cells is hormonally regulated and involves several transcription factors. The nuclear receptor NUR77 is present in steroidogenic cells, and its expression is induced by hormones known to activate StAR expression. We have now established that StAR transcription in cAMP-stimulated Leydig cells requires de novo protein synthesis and involves NUR77. We found that cAMP-induced NUR77 expression precedes that of StAR both at the mRNA and protein levels in Leydig cells. In these cells, small interfering RNA-mediated NUR77 knockdown reduces cAMP-induced StAR expression. Chromatin immunoprecipitation assays revealed a cAMP-dependent increase in NUR77 recruitment to the proximal StAR promoter, whereas transient transfections in MA-10 Leydig cells confirmed that NUR77 can activate the StAR promoter and that this requires an element located at -95 bp. cAMP-induced StAR and NUR77 expression in Leydig cells was found to require a Ca2+/calmodulin-dependent protein kinase (CaMK)-dependent signaling pathway. Consistent with this, we show that within the testis, CaMKI is specifically expressed in Leydig cells. Finally, we report that CaMKI transcriptionally cooperates with NUR77, but not steroidogenic factor 1, to further enhance StAR promoter activity in Leydig cells. All together, our results implicate NUR77 as a mediator of cAMP action on StAR transcription in steroidogenic Leydig cells and identify a role for CaMKI in this process.

Nuclear regulator Pygo2 controls spermiogenesis and histone H3 acetylation

Mammalian spermiogenesis, a process where haploid male germ cells differentiate to become mature spermatozoa, entails dramatic morphological and biochemical changes including remodeling of the germ cell chromatin. Proteins that contain one or more plant homeodomain (PHD) fingers have been implicated in the regulation of chromatin structure and function. Pygopus 2 (Pygo2) belongs to a family of evolutionarily conserved PHD finger proteins thought to act as co-activators of Wnt signaling effector complexes composed of beta-catenin and LEF/TCF transcription factor. Here we analyze mice containing hypomorphic alleles of pygopus 2 (Pygo2 or mpygo2) and uncover a beta-catenin-independent involvement of the Pygo2 protein in spermiogenesis. Pygo2 is expressed in elongating spermatids at stages when chromatin remodeling occurs, and block of Pygo2 function leads to spermiogenesis arrest and consequent infertility. Analysis of spermiogenesis in Pygo2 mutants reveals reduced expression of select post-meiotic genes including protamines, transition protein 2, and H1fnt, all of which are required for germ cell chromatin condensation, and drastically altered pattern of histone H3 hyperacetylation. These findings suggest that Pygo2 is involved in the chromatin remodeling events that lead to nuclear compaction of male germ cells.

Prm3, the fourth gene in the mouse protamine gene cluster, encodes a conserved acidic protein that affects sperm motility

The protamine gene cluster containing the Prm1, Prm2, Prm3, and Tnp2 genes is present in humans, mice, and rats. The Prm1, Prm2, and Tnp2 genes have been extensively studied, but almost nothing is known about the function and regulation of the Prm3 gene. Here we demonstrate that an intronless Prm3 gene encoding a distinctive small acidic protein is present in 13 species from seven orders of mammals. We also demonstrate that the Prm3 gene has not generated retroposons, which supports the contention that genes that are expressed in meiotic and haploid spermatogenic cells do not generate retroposons. The Prm3 mRNA is first detected in early round spermatids, while the PRM3 protein is first detected in late spermatids. Thus, translation of the Prm3 mRNA is developmentally delayed similar to the Prm1, Prm2, and Tnp2 mRNAs. In contrast to PRM1, PRM2, and TNP2, PRM3 is an acidic protein that is localized in the cytoplasm of elongated spermatids and transfected NIH-3T3 cells. To elucidate the function of PRM3, the Prm3 gene was disrupted by homologous recombination. Sperm from Prm3(-/-) males exhibited reductions in motility, but the fertility of Prm3(-/-) and Prm3(+/+) males was similar in matings of one male and one female. We have developed a competition test in which a mutant male has to compete with a rival wild-type male to fertilize a female; the implications of these results are also discussed.

Physiological roles of the Ca2+/CaM-dependent protein kinase cascade in health and disease

Numerous hormones, growth factors and physiological processes cause a rise in cytosolic Ca2+, which is translated into meaningful cellular responses by interacting with a large number of Ca2(+)-binding proteins. The Ca2(+)-binding protein that is most pervasive in mediating these responses is calmodulin (CaM), which acts as a primary receptor for Ca2+ in all eukaryotic cells. In turn, Ca2+/CaM functions as an allosteric activator of a host of enzymatic proteins including a considerable number of protein kinases. The topic of this review is to discuss the physiological roles of a sub-set of these protein kinases which can function in cells as a Ca2+/CaM-dependent kinase signaling cascade. The cascade was originally believed to consist of a CaM kinase kinase that phosphorylates and activates one of two CaM kinases, CaMKI or CaMKIV. The unusual aspect of this cascade is that both the kinase kinase and the kinase require the binding of Ca2+/CaM for activation. More recently, one of the CaM kinase kinases has been found to activate another important enzyme, the AMP-dependent protein kinase so the concept of the CaM kinase cascade must be expanded. A CaM kinase cascade is important for many normal physiological processes that when misregulated can lead to a variety of disease states. These processes include: cell proliferation and apoptosis that may conspire in the genesis of cancer; neuronal growth and function related to brain development, synaptic plasticity as well as memory formation and maintenance; proper function of the immune system including the inflammatory response, activation of T lymphocytes and hematopoietic stem cell maintenance; and the central control of energy balance that, when altered, can lead to obesity and diabetes. Although the study of the CaM-dependent kinase cascades is still in its infancy continued analysis of the pathways regulated by these Ca2(+)-initiated signaling cascades holds considerable promise for the future of disease-related research.

Calmodulin-dependent kinase IV links Toll-like receptor 4 signaling with survival pathway of activated dendritic cells

Microbial products, including lipopolysaccharide (LPS), an agonist of Toll-like receptor 4 (TLR4), regulate the lifespan of dendritic cells (DCs) by largely undefined mechanisms. Here, we identify a role for calcium-calmodulin-dependent kinase IV (CaMKIV) in this survival program. The pharmacologic inhibition of CaMKs as well as ectopic expression of kinase-inactive CaMKIV decrease the viability of monocyte-derived DCs exposed to bacterial LPS. The defect in TLR4 signaling includes a failure to accumulate the phosphorylated form of the cAMP response element-binding protein (pCREB), Bcl-2, and Bcl-xL. CaMKIV null mice have a decreased number of DCs in lymphoid tissues and fail to accumulate mature DCs in spleen on in vivo exposure to LPS. Although isolated Camk4-/- DCs are able to acquire the phenotype typical of mature cells and release normal amounts of cytokines in response to LPS, they fail to accumulate pCREB, Bcl-2, and Bcl-xL and therefore do not survive. The transgenic expression of Bcl-2 in CaMKIV null mice results in full recovery of DC survival in response to LPS. These results reveal a novel link between TLR4 and a calcium-dependent signaling cascade comprising CaMKIV-CREB-Bcl-2 that is essential for DC survival.

Identification of ten novel genes involved in human spermatogenesis by microarray analysis of testicular tissue

OBJECTIVE

To identify novel genes that are down-regulated in the testicular tissue of infertile men.

DESIGN

Prospective study.

SETTING

University-based reproductive clinics and genetics laboratory.

PATIENTS

Nine patients with normal spermatogenesis, and 15 patients with maturation arrest (MA) or Sertoli cell-only syndrome (SCOS).

INTERVENTION

Testicular samples of patients with the same histology were pooled for complementary DNA (cDNA) microarray analysis.

MAIN OUTCOME MEASURE

Novel, down-regulated genes.

RESULTS

In total, 300 genes were significantly down-regulated in SCOS or MA samples, and 10 novel sterility-related genes were identified. Of the 10 novel genes, 6 genes (Hs.126780, Hs.553658, Hs.274135, Hs.268122, Hs.531701, and Hs.171130) encode proteins with predictable functional domains, and all these functional domains are believed to correlate with spermatogenesis and/or spermiogenesis. Conversely, the other 4 genes (Hs.351582, Hs.407480, Hs.552781, and Hs.355570) do not encompass known functional domains. Two genes (Hs.407480 and Hs.552781) lack mouse orthologues. Most novel genes showed a testis-specific expression pattern in both mice and humans. Reverse transcription-polymerase chain reaction (RT-PCR) showed three distinct types of developmental stage-dependent expressions of message ribonucleic acid (mRNA) for these novel genes in murine testes.

CONCLUSION

These 10 novel genes provide targets to elucidate novel pathways involved in human spermatogenesis.

Infertility with defective spermiogenesis in mice lacking AF5q31, the target of chromosomal translocation in human infant leukemia

AF5q31 (also called MCEF) was identified by its involvement in chromosomal translocation with the gene MLL (mixed lineage leukemia), which is associated with infant acute lymphoblastic leukemia. Several potential roles have been proposed for AF5q31 and other family genes, but the specific requirements of AF5q31 during development remain unclear. Here, we show that AF5q31 is essential for spermatogenesis. Although most AF5q31-deficient mice died in utero and neonatally with impaired embryonic development and shrunken alveoli, respectively, 13% of AF5q31-deficient mice thrived as wild-type mice did. However, the male mice were sterile with azoospermia. Histological examinations revealed the arrest of germ cell development at the stage of spermiogenesis, and virtually no spermatozoa were seen in the epididymis. AF5q31 was found to be preferentially expressed in Sertoli cells. Furthermore, mutant mice displayed severely impaired expression of protamine 1, protamine 2, and transition protein 2, which are indispensable to compact the haploid genome within the sperm head, and an increase of apoptotic cells in seminiferous tubules. Thus, AF5q31 seems to function as a transcriptional regulator in testicular somatic cells and is essential for male germ cell differentiation and survival. These results may have clinical implications in the understanding of human male infertility.

Calmodulin-dependent protein kinase IV regulates hematopoietic stem cell maintenance

The hematopoietic stem cell (HSC) gives rise to all mature, terminally differentiated cells of the blood. Here we show that calmodulin-dependent protein kinase IV (CaMKIV) is present in c-Kit+ ScaI+ Lin(-/low) hematopoietic progenitor cells (KLS cells) and that its absence results in hematopoietic failure, characterized by a diminished KLS cell population and by an inability of these cells to reconstitute blood cells upon serial transplantation. KLS cell failure in the absence of CaMKIV is correlated with increased apoptosis and proliferation of these cells in vivo and in vitro. In turn, these cell biological defects are correlated with decreases in CREB-serine 133 phosphorylation as well as in CREB-binding protein (CBP) and Bcl-2 levels. Re-expression of CaMKIV in Camk4-/- KLS cells results in the rescue of the proliferation defects in vitro as well as in the restoration of CBP and Bcl-2 to wild type levels. These studies show that CaMKIV is a regulator of HSC homeostasis and suggest that its effects may be in part mediated via regulation of CBP and Bcl-2.

Identification of a novel testis-specific gene and its potential roles in testis development/spermatogenesis

AIM

To identify and characterize a novel gene with potential roles in testis development and spermatogenesis.

METHODS

A cDNA microarray was constructed from a human testis large insert cDNA library and hybridized with probes of human or mouse adult and fetal testes. Differentially expressed genes were isolated and sequenced. RT-PCR was used to test the tissue distribution of the genes of interest and in situ hybridization was performed to localize the gene expression in the mouse testis. A range of bioinformatical programs including Gene Runner, SMART, NCBI Blast and Emboss CpGPlot were used to characterize the new gene's feature.

RESULTS

A novel testis-specific gene, NYD-SP5, was differentially expressed in fetal and adult testes. The deduced protein structure of NYD-SP5 was found to contain an IQ motif (a short calmodulin-binding motif containing conserved Ile and Gln residues), a Carbamate kinase-like domain, a Zn-dependent exopeptidase domain and a lactate dehydrogenase (LDH) C-terminal-like domain. RT-PCR analysis revealed that NYD-SP5 was predominantly expressed in the testis but not in other 15 tissues examined. In situ hybridization and RT-PCR examinations revealed that the expression of NYD-SP5 was confined in the male germ cell but not present in the somatic cell in the testes.

CONCLUSION

NYD-SP5 is a newly found testis-specific gene with potential roles in testis development and spermatogenesis through a calmodulin-activated enzyme.

KIN17 encodes an RNA-binding protein and is expressed during mouse spermatogenesis

Genotoxic agents deform DNA structure thus eliciting a complex genetic response allowing recovery and cell survival. The Kin17 gene is up-regulated during this response. This gene encodes a conserved nuclear protein that shares a DNA-binding domain with the bacterial RecA protein. The KIN17 protein binds DNA and displays enhanced expression levels in proliferating cultured cells, suggesting a role in nuclear metabolism. We investigated this by studying the expression profile of KIN17 protein during mouse spermatogenesis. As expected, the expression level of Kin17 is higher in proliferating than in differentiated cells. KIN17 is selectively extracted from this tissue by detergents and a fraction was tightly associated with the nuclear matrix. Germinal cells ubiquitously express Kin17 and the protein is located mainly in the nucleus except in elongated spermatids where cytoplasmic staining is also observed. Sertoli and germ cells that are no longer mitotically active express KIN17, suggesting a general role in all testicular cell types. In adult testis a significant proportion of KIN17 co-purifies with polyadenylated RNA. KIN17 directly binds RNA, preferentially poly(G) and poly(U) homopolymers. These results together with the identification of KIN17 as a component of the human spliceosome indicate that this protein may participate in RNA processing.

Evidence of the presence of calcium/calmodulin-dependent protein kinase IV in human sperm and its involvement in motility regulation

The mechanisms involved in the regulation of mammalian sperm motility are not well understood. Calcium ions (Ca(2+)) have been suggested to play a key role in the maintenance of motility; nevertheless, how Ca(2+) modulates this process has not yet been completely characterized. Ca(2+) can bind to calmodulin and this complex regulates the activity of multiple enzymes, including Ca(2+)/calmodulin-dependent protein kinases (CaM kinases). Results from this study confirmed that the presence of Ca(2+) in the incubation medium is essential for maintaining human sperm motility. The involvement of CaM kinases in Ca(2+) regulation of human sperm motility was evaluated using specific inhibitors (KN62 and KN93) or their inactive analogues (KN04 and KN92 respectively). Sperm incubation in the presence of KN62 or KN93 led to a progressive decrease in the percentage of motile cells; in particular, incubation with KN62 also reduced sperm motility parameters. These inhibitors did not alter sperm viability, protein tyrosine phosphorylation or the follicular fluid-induced acrosome reaction; however, KN62 decreased the total amount of ATP in human sperm. Immunological studies showed that Ca(2+)/calmodulin-dependent protein kinase IV (CaMKIV) is present and localizes to the human sperm flagellum. Moreover, CaMKIV activity increases during capacitation and is inhibited in the presence of KN62. This report is the first to demonstrate the presence of CaMKIV in mammalian sperm and suggests the involvement of this kinase in the regulation of human sperm motility.

Establishment of male-specific epigenetic information

The setting of male-specific epigenetic information is a complex process, which involves a major global re-organisation, as well as localized changes of the nucleus structure during the pre-meiotic, meiotic and post-meiotic stages of the male germ cell differentiation. Although it has long been known that DNA methylation in targeted regions of the genome is associated with male-specific genomic imprinting, or that most core histones are hyperacetylated and then replaced by sperm-specific proteins during the post-meiotic condensation of the nucleus, many questions remain unanswered. How these changes interact, how they affect the epigenetic information and how the paternal epigenetic marks contribute to the future genome are indeed major issues remaining to be explored.

Up-regulation of basal transcriptional activity of the cytochrome P450 cholesterol side-chain cleavage (CYP11A) gene by isoform-specific calcium-calmodulin-dependent protein kinase in primary cultures of ovarian granulosa cells

Intracellular calcium ions (Ca2+) regulate steroidogenesis in the placenta, adrenal gland, testis, and ovary. Earlier data indicate that Ca2+/calmodulin-dependent protein kinase (CamK) may mediate Ca(2+)-dependent up-regulation of CYP11A (cholesterol side-chain cleavage). To examine this notion further, we assessed the expression and actions of isotype-specific CamK on in vitro transcription of the swine CYP11A gene promoter in primary cultures of ovarian granulosa-luteal cells. RT-PCR and oligodeoxynucleotide sequencing identified gene transcripts encoding CamKII and IV in granulosa and theca cells and corpora lutea. DNA sequence homology with the cognate human and rat genes was 97 and 94% (CamKII) and 96 and 88% (CamKIV), respectively. SDS-PAGE and isoform-specific immunoblotting corroborated expression of CamKII (approximately 52 kDa) and CamKIV (approximately 60 kDa) proteins. To monitor transcriptional control, granulosa-luteal cells were transfected transiently with a putative 5'-upstream regulatory region of the homologous CYP11A gene -2320 to +23 bp from the transcriptional start site driving luciferase (CYP11A/luc). Coexpression of constitutively active CamKIV elevated basal transcription by 3.5 +/- 0.2-fold (P < 0.001), whereas inactive mutant CamKIV and native CamKII had no effect. Forskolin, an activator of adenylyl cyclase, stimulated expression of CYP11A/luciferase by 4.5 +/- 0.9-fold (P < 0.001) and did not enhance transcriptional drive by exogenous CamKIV. Preliminary promoter-deletional analyses showed that a proximal 5'-fragment -100 to +23 bp, but not -50/+23 bp, retained full responsiveness to CamKIV (4.5 +/- 0.4-fold; P < 0.001). Threefold cotransfection of -100/+23 bp CYP11A/luciferase, active CamKIV, and a dominant-negative mutant of the cAMP-responsive element binding protein (10, 100, and 250 ng) inhibited CamKIV-stimulated transcriptional activity by 17, 47, and 48% (pooled sem+/- 2%) [P < 0.01]. The dominant-negative mutant of the cAMP-responsive element binding protein also repressed forskolin's stimulation of -100/+23 CYP11A/luciferase by 12, 38, and 52% (P < 0.01). Based on these ensemble outcomes, we postulate that endogenous CamKIV may serve as a Ca(2+)-dependent effector mechanism to maintain basal CYP11A gene expression in ovarian granulosa-luteal cells.

Identification of Ca2+-dependent calmodulin-binding proteins in rat spermatogenic cells as complexes of the heat-shock proteins

Ca2+-calmodulin (CaM)-binding proteins in rat testes were characterized by assays for CaM-binding activity using the CaM-overlay method on transblots of electrophoresed gels and purification by gel-filtration, ion exchange, and adsorption chromatographies. A major CaM-binding protein complex (CaMBP) was identified and found to be comprised of three proteins with molecular masses 110, 100, and 70 kDa. Amino acid sequence analyses of lysylendopeptidase digests from these proteins indicated that all of the constituents of CaMBP are very similar to the members of the heat-shock protein family, i.e., the 110-kDa protein is similar to the APG-2/94 kDa rat ischemia-responsive protein, the 100-kDa protein is similar to the rat counterpart of the mouse APG-1/94 kDa osmotic stress protein, and the 70-kDa protein is similar to the rat testis-specific major heat-shock protein (HSP70). Immunohistochemistry using anti-CaMBP and anti-CaM antibodies demonstrated that CaMBP was co-localized with CaM in the cytoplasm of pachytene spermatocytes and nuclei of round spermatids. In addition, CaMBP, but not CaM, was localized at a high level in the residual bodies of elongated spermatids. The possible relevance of CaMBP to regulation of cell cycle progression and spermatogenesis is discussed in this paper.

Protamine 2 deficiency leads to sperm DNA damage and embryo death in mice

Cytokinesis is incomplete in spermatogenic cells, and the descendants of each stem cell form a clonal syncytium. As a result, a heterozygous mutation in a gene expressed postmeiotically affects all of the haploid spermatids within a syncytium. Previously, we have found that disruption of one copy of the gene for either protamine 1 (PRM1) or protamine 2 (PRM2) in the mouse results in a reduction in the amount of the respective protein, abnormal processing of PRM2, and inability of male chimeras to transmit either the mutant or wild-type allele derived from the 129-genotype embryonic stem cells to the next generation. Although it is believed that protamines are essential for compaction of the sperm nucleus and to protect the DNA from damage, this has not been proven experimentally. To test the hypothesis that failure of chimeras to transmit the 129 genotype to offspring was due to alterations in the organization and integrity of sperm DNA, we used the single-cell DNA electrophoresis (comet) assay, ultrastructural analysis, and the intracytoplasmic sperm injection (ICSI) procedure. Comet assay demonstrated a direct correlation between the fraction of sperm with haploinsufficiency of PRM2 and the frequency of sperm with damaged DNA. Ultrastructural analysis revealed reduced compaction of the chromatin. ICSI with PRM2-deficient sperm resulted in activation of most metaphase II-arrested mouse eggs, but few were able to develop to the blastocyst stage. These findings suggest that development fails because of damage to paternal DNA and that PRM2 is crucial for maintaining the integrity of sperm chromatin.

Roles of transition nuclear proteins in spermiogenesis

The transition nuclear proteins (TPs) constitute 90% of the chromatin basic proteins during the steps of spermiogenesis between histone removal and the deposition of the protamines. We first summarize the properties of the two major transition nuclear proteins, TP1 and TP2, and present concepts, based on their time of appearance in vivo and in vitro properties, regarding their roles. Distinct roles for the two TPs in histone displacement, sperm nuclear shaping, chromatin condensation, and maintenance of DNA integrity have been proposed. More definitive information on their roles in spermiogenesis has recently been obtained using mice with null mutations in the Tnp1 or Tnp2 genes for TP1 and TP2, respectively. In these mice, histone displacement and sperm nuclear shaping appear to progress quite normally. Spermatid nuclear condensation occurs, albeit in an abnormal fashion, and the mature sperm of the Tnp -null mutants are not as condensed as wild-type sperm. There is also evidence that sperm from these mutant mice contain an elevated level of DNA strand breaks. The mutant sperm showed several unexpected phenotypes, including a high incidence of configurational defects, such as heads bent back on midpieces, midpieces in hairpin configurations, coils, and clumps, other midpiece defects, reduced levels of proteolytic processing of protamine 2 during maturation, and reduced motility. The two TPs appear partly to compensate for each other as both Tnp1 - and Tnp2 -null mice were able to produce offspring, and appear to have largely overlapping functions as the two mutants had similar phenotypes.

A complex deoxyribonucleic acid response element in the rat Ca(2+)/calmodulin-dependent protein kinase IV gene 5'-flanking region mediates thyroid hormone induction and chicken ovalbumin upstream promoter transcription factor 1 repression

Ca(2+)/calmodulin-dependent protein kinase IV (CaMKIV) is regulated by T(3) in a time- and concentration-dependent manner in the developing rat brain and plays an important role in neuronal-specific gene regulation. T(3) treatment, but not retinoic acid (RA), stimulated endogenous CaMKIV mRNA 5-fold in mouse embryonic stem (ES) cells differentiated into neurons. We localized a region -750 to -700 in the CaMKIV gene 5'-flanking region that conferred T(3) responsiveness and bound thyroid hormone receptor (TR), retinoic acid receptor (RAR), and chicken ovalbumin upstream promoter-transcription factor 1 (COUP-TF1). T(3) and RA treatment stimulated the CaMKIV hormone response element. Cotransfection of a COUP-TF1 expression vector repressed the T(3) response and augmented the RA response. Mutational analysis identified three half-sites arranged in a direct repeat (AB) and overlapping inverted repeat (BC), required for functional induction and receptor binding. TR and RAR bound predominantly to the BC portion of the element and COUP-TF1 to the AB region, with a close correlation of binding and functional studies. COUP-TF1 binding did not influence TR/retinoid X receptor binding but modestly augmented RAR/retinoid X receptor binding. A single element confers T(3) and COUP-TF1 regulation of CaMKIV expression.

Male infertility, impaired spermatogenesis, and azoospermia in mice deficient for the pseudophosphatase Sbf1

Pseudophosphatases display extensive sequence similarities to phosphatases but harbor amino acid alterations in their active-site consensus motifs that render them catalytically inactive. A potential role in substrate trapping or docking has been proposed, but the specific requirements for pseudophosphatases during development and differentiation are unknown. We demonstrate here that Sbf1, a pseudophosphatase of the myotubularin family, is expressed at high levels in seminiferous tubules of the testis, specifically in Sertoli's cells, spermatogonia, and pachytene spermatocytes, but not in postmeiotic round spermatids. Mice that are nullizygous for Sbf1 exhibit male infertility characterized by azoospermia. The onset of the spermatogenic defect occurs in the first wave of spermatogenesis at 17 days after birth during the synchronized progression of pachytene spermatocytes to haploid spermatids. Vacuolation of the Sertoli's cells is the earliest observed phenotype and is followed by reduced formation of spermatids and eventual depletion of the germ cell compartment in older mice. The nullizygous phenotype in conjunction with high-level expression of Sbf1 in premeiotic germ cells and Sertoli's cells is consistent with a crucial role for Sbf1 in transition from diploid to haploid spermatocytes. These studies demonstrate an essential role for a pseudophosphatase and implicate signaling pathways regulated by myotubularin family proteins in spermatogenesis and germ cell differentiation.

CaMKIV/Gr is dispensable for spermatogenesis and CREM-regulated transcription in male germ cells

The calcium/calmodulin-dependent protein kinase type IV/Gr (CaMKIV/Gr) is expressed in male germ cells and spermatids and has been implicated in controlling the differentiation of germ cells into mature spermatozoa. The function of CaMKIV/Gr in spermatogenesis was investigated using CaMKIV/Gr-deficient mice generated by targeted gene disruption. CaMKIV/Gr-deficient males exhibited normal spermatogenesis, and their fertility was similar to that of wild-type littermates. Notwithstanding the function of CaMKIV/Gr as an activator of cAMP response element (CRE)-dependent transcription, mRNA levels of several testis-specific CRE modulator (CREM)-regulated genes were unaltered. These results indicate that CaMKIV/Gr is not essential for spermatogenesis or for CRE-regulated gene transcription in the testis.

Spermatogenesis and the regulation of Ca(2+)-calmodulin-dependent protein kinase IV localization are not dependent on calspermin

Calspermin and Ca(2+)-calmodulin-dependent protein kinase IV (CaMKIV) are two proteins encoded by the Camk4 gene. CaMKIV is found in multiple tissues, including brain, thymus, and testis, while calspermin is restricted to the testis. In the mouse testis, both proteins are expressed within elongating spermatids. We have recently shown that deletion of CaMKIV has no effect on calspermin expression but does impair spermiogenesis by disrupting the exchange of sperm basic nuclear proteins. The function of calspermin within the testis is unclear, although it has been speculated to play a role in binding and sequestering calmodulin during the development of the germ cell. To investigate the contribution of calspermin to spermatogenesis, we have used Cre/lox technology to specifically delete calspermin, while leaving kinase expression intact. We unexpectedly found that calspermin is not required for male fertility. We further demonstrate that CaMKIV expression and localization are unaffected by the absence of calspermin and that calspermin does not colocalize to the nuclear matrix with CaMKIV.

Calmodulin as a versatile calcium signal transducer in plants

The complexity of Ca²⁺ patterns observed in eukaryotic cells, including plants, has led to the hypothesis that specific patterns of Ca²⁺ propagation, termed Ca²⁺ signatures, encode information and relay it to downstream elements (effectors) for translation into appropriate cellular responses. Ca²⁺ -binding proteins (sensors) play a key role in decoding Ca²⁺ signatures and transducing signals by activating specific targets and pathways. Calmodulin is a Ca²⁺ sensor known to modulate the activity of many mammalian proteins, whose targets in plants are now being actively characterized. Plants possess an interesting and rapidly growing list of calmodulin targets with a variety of cellular roles. Nevertheless, many targets appear to be unique to plants and remain uncharacterized, calling for a concerted effort to elucidate their functions. Moreover, the extended family of calmodulin-related proteins in plants consists of evolutionarily divergent members, mostly of unknown function, although some have recently been implicated in stress responses. It is hoped that advances in functional genomics, and the research tools it generates, will help to explain themultiplicity of calmodulin genes in plants, and to identify their downstream effectors. This review summarizes current knowledge of the Ca²⁺ -calmodulin messenger system in plants and presents suggestions for future areas of research. Contents I. Introduction 36 II. CaM isoforms and CaM-like proteins 37 III. CaM-target proteins 42 IV. CaM and nuclear functions 46 V. Regulation of ion transport 49 VI. CaM and plant responses to environmental stimuli 52 VII. Conclusions and future studies 58 Acknowledgements 59 References 59.