Molecular recognition of the Tes LIM2-3 domains by the actin-related protein Arp7A

Development of functional spermatozoa in mammalian spermiogenesis

Infertility is a global health problem affecting one in six couples, with 50% of cases attributed to male infertility. Spermatozoa are male gametes, specialized cells that can be divided into two parts: the head and the flagellum. The head contains a vesicle called the acrosome that undergoes exocytosis and the flagellum is a motility apparatus that propels the spermatozoa forward and can be divided into two components, axonemes and accessory structures. For spermatozoa to fertilize oocytes, the acrosome and flagellum must be formed correctly. In this Review, we describe comprehensively how functional spermatozoa develop in mammals during spermiogenesis, including the formation of acrosomes, axonemes and accessory structures by focusing on analyses of mouse models.

Deletion of ACTRT1 is associated with male infertility as sperm acrosomal ultrastructural defects and fertilization failure in human

STUDY QUESTION

Could actin-related protein T1 (ACTRT1) deficiency be a potential pathogenic factor of human male infertility?

SUMMARY ANSWER

A 110-kb microdeletion of the X chromosome, only including the ACTRT1 gene, was identified as responsible for infertility in two Chinese males with sperm showing acrosomal ultrastructural defects and fertilization failure.

WHAT IS KNOWN ALREADY

The actin-related proteins (e.g. ACTRT1, ACTRT2, ACTL7A, and ACTL9) interact with each other to form a multimeric complex in the subacrosomal region of spermatids, which is crucial for the acrosome-nucleus junction. Actrt1-knockout (KO) mice are severely subfertile owing to malformed sperm heads with detached acrosomes and partial fertilization failure. There are currently no reports on the association between ACTRT1 deletion and male infertility in humans.

STUDY DESIGN, SIZE, DURATION

We recruited a cohort of 120 infertile males with sperm head deformations at a large tertiary hospital from August 2019 to August 2023. Genomic DNA extracted from the affected individuals underwent whole exome sequencing (WES), and in silico analyses were performed to identify genetic variants. Morphological analysis, functional assays, and ART were performed in 2022 and 2023.

PARTICIPANTS/MATERIALS, SETTING, METHODS

The ACTRT1 deficiency was identified by WES and confirmed by whole genome sequencing, PCR, and quantitative PCR. Genomic DNA of all family members was collected to define the hereditary mode. Papanicolaou staining and electronic microscopy were performed to reveal sperm morphological changes. Western blotting and immunostaining were performed to explore the pathological mechanism of ACTRT1 deficiency. ICSI combined with artificial oocyte activation (AOA) was applied for one proband.

MAIN RESULTS AND THE ROLE OF CHANCE

We identified a whole-gene deletion variant of ACTRT1 in two infertile males, which was inherited from their mothers, respectively. The probands exhibited sperm head deformations owing to acrosomal detachment, which is consistent with our previous observations on Actrt1-KO mice. Decreased expression and ectopic distribution of ACTL7A and phospholipase C zeta were observed in sperm samples from the probands. ICSI combined with AOA effectively solved the fertilization problem in Actrt1-KO mice and in one of the two probands.

LIMITATIONS, REASONS FOR CAUTION

Additional cases are needed to further confirm the genetic contribution of ACTRT1 variants to male infertility.

WIDER IMPLICATIONS OF THE FINDINGS

Our results reveal a gene-disease relation between the ACTRT1 deletion described here and human male infertility owing to acrosomal detachment and fertilization failure. This report also describes a good reproductive outcome of ART with ICSI-AOA for a proband.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by the Chongqing medical scientific research project (Joint project of Chongqing Health Commission and Science and Technology Bureau, 2023MSXM008 and 2023MSXM054). There are no competing interests to declare.

TRIAL REGISTRATION NUMBER

N/A.

Genetic mechanisms of fertilization failure and early embryonic arrest: a comprehensive review

BACKGROUND

Infertility and pregnancy loss are longstanding problems. Successful fertilization and high-quality embryos are prerequisites for an ongoing pregnancy. Studies have proven that every stage in the human reproductive process is regulated by multiple genes and any problem, at any step, may lead to fertilization failure (FF) or early embryonic arrest (EEA). Doctors can diagnose the pathogenic factors involved in FF and EEA by using genetic methods. With the progress in the development of new genetic technologies, such as single-cell RNA analysis and whole-exome sequencing, a new approach has opened up for us to directly study human germ cells and reproductive development. These findings will help us to identify the unique mechanism(s) that leads to FF and EEA in order to find potential treatments.

OBJECTIVE AND RATIONALE

The goal of this review is to compile current genetic knowledge related to FF and EEA, clarifying the mechanisms involved and providing clues for clinical diagnosis and treatment.

SEARCH METHODS

PubMed was used to search for relevant research articles and reviews, primarily focusing on English-language publications from January 1978 to June 2023. The search terms included fertilization failure, early embryonic arrest, genetic, epigenetic, whole-exome sequencing, DNA methylation, chromosome, non-coding RNA, and other related keywords. Additional studies were identified by searching reference lists. This review primarily focuses on research conducted in humans. However, it also incorporates relevant data from animal models when applicable. The results were presented descriptively, and individual study quality was not assessed.

OUTCOMES

A total of 233 relevant articles were included in the final review, from 3925 records identified initially. The review provides an overview of genetic factors and mechanisms involved in the human reproductive process. The genetic mutations and other genetic mechanisms of FF and EEA were systematically reviewed, for example, globozoospermia, oocyte activation failure, maternal effect gene mutations, zygotic genome activation abnormalities, chromosome abnormalities, and epigenetic abnormalities. Additionally, the review summarizes progress in treatments for different gene defects, offering new insights for clinical diagnosis and treatment.

WIDER IMPLICATIONS

The information provided in this review will facilitate the development of more accurate molecular screening tools for diagnosing infertility using genetic markers and networks in human reproductive development. The findings will also help guide clinical practice by identifying appropriate interventions based on specific gene mutations. For example, when an individual has obvious gene mutations related to FF, ICSI is recommended instead of IVF. However, in the case of genetic defects such as phospholipase C zeta1 (PLCZ1), actin-like7A (ACTL7A), actin-like 9 (ACTL9), and IQ motif-containing N (IQCN), ICSI may also fail to fertilize. We can consider artificial oocyte activation technology with ICSI to improve fertilization rate and reduce monetary and time costs. In the future, fertility is expected to be improved or restored by interfering with or supplementing the relevant genes.

A novel homozygous mutation in ACTL7A leads to male infertility

Male infertility, a global public health problem, exhibits complex pathogenic causes and genetic factors deserve further discovery and study. We identified a novel homozygous missense mutation c.224A > C (p.D75A) in ACTL7A gene in two infertile brothers with teratozoospermia by whole-exome sequencing (WES). In vitro fertilization (IVF) and intracytoplasmic sperm injection (ICSI) showed fertilization failure of the two affected couples. The three-dimensional (3D) models showed that a small section of α-helix transformed into random coil in the mutant ACTL7A protein and mutant amino acid lacked a hydrogen bond with Ser170 amino acid. Immunofluorescence revealed that ACTL7A protein was degraded in sperms of patients. Transmission electron microscopy (TEM) analysis of sperms from the infertile patients showed that the irregular perinuclear theca (PT) and acrosomal ultrastructural defects. Furthermore, ACTL7A mutation caused abnormal localization and reduced the expression of PLCZ1 in sperms of the patients, which may be the key reasons for the fertilization failure after ICSI. Our findings expand the spectrum of ACTL7A mutations and provide novel theoretical basis for genetic counseling.

Pathogenic variant in ACTL7A causes severe teratozoospermia characterized by bubble-shaped acrosomes and male infertility

Teratozoospermia is a common factor associated with male infertility. However, teratozoospermia characterized by bubble-shaped acrosomes (BSAs) has not yet been identified in men and the causative genes are unknown. The present study is of a patient with severe teratozoospermia characterized by BSA and carrying a variant (c.1204G>A, p. Gly402Ser) of actin-like 7A (ACTL7A). For further verification, we generated an Actl7a-mutated mouse model (p.Gly407Ser) carrying an equivalent variant to that in the patient. We found that homozygous Actl7a-mutated (Actl7aMut/Mut) male mice were sterile, and all their sperm showed acrosomal abnormalities. We detected, by transmission electron microscopy, that during acrosomal biogenesis the acrosome detaches from the nuclear membrane in Actl7aMut/Mut mice. Furthermore, mutant ACTL7A failed to attach to the acroplaxome and was discharged by cytoplasmic droplets, which led to the absence of ACTL7A in epididymal spermatozoa in mice. The mutant sperm failed to activate the oocyte, and sperm-borne oocyte activation factor PLCζ discharge accompanied by ACTL7A was observed, leading to total fertilization failure (TFF). Immunoprecipitation followed by liquid chromatography-mass spectrometry showed that several differentially expressed proteins participate in acrosome assembly and actin filament organization. Furthermore, assisted oocyte activation by calcium ionophore exposure successfully overcame TFF in the couple with an ACTL7A pathogenic variant. Our study defined a novel phenotype of an acrosomal abnormality characterized by BSA, revealed the underlying mechanism of a pathogenic variant in ACTL7A, and provided a genetic marker and potential therapeutic option for male infertility.

Loss of perinuclear theca ACTRT1 causes acrosome detachment and severe male subfertility in mice

The perinuclear theca (PT) is a cytoskeletal element encapsulating the sperm nucleus; however, the physiological roles of the PT in sperm are largely uncertain. Here, we reveal that ACTRT1, ACTRT2, ACTL7A and ACTL9 proteins interact to form a multimeric complex and localize to the subacrosomal region of spermatids. Furthermore, we engineered Actrt1-knockout (KO) mice to define the functions of ACTRT1. Despite normal sperm count and motility, Actrt1-KO males were severely subfertile owing to a deficiency in fertilization. Loss of ACTRT1 caused a high incidence of malformed heads and detachment of acrosomes from sperm nuclei, caused by loosened acroplaxome structure during spermiogenesis. Furthermore, Actrt1-KO sperm showed reduced ACTL7A and PLCζ protein content as a potential cause of fertilization defects. Moreover, we reveal that ACTRT1 anchors developing acrosomes to the nucleus, likely by interacting with the inner acrosomal membrane protein SPACA1 and the nuclear envelope proteins PARP11 and SPATA46. Loss of ACTRT1 weakened the interaction between ACTL7A and SPACA1. Our study and recent findings of ACTL7A/ACTL9-deficient sperm together reveal that the sperm PT-specific ARP complex mediates the acrosome-nucleus connection.

An actin-related protein that is most highly expressed in Drosophila testes is critical for embryonic development

Most actin-related proteins (Arps) are highly conserved and carry out well-defined cellular functions in eukaryotes. However, many lineages like Drosophila and mammals encode divergent non-canonical Arps whose roles remain unknown. To elucidate the function of non-canonical Arps, we focus on Arp53D, which is highly expressed in testes and retained throughout Drosophila evolution. We show that Arp53D localizes to fusomes and actin cones, two germline-specific actin structures critical for sperm maturation, via a unique N-terminal tail. Surprisingly, we find that male fertility is not impaired upon Arp53D loss, yet population cage experiments reveal that Arp53D is required for optimal fitness in Drosophila melanogaster. To reconcile these findings, we focus on Arp53D function in ovaries and embryos where it is only weakly expressed. We find that under heat stress Arp53D-knockout (KO) females lay embryos with reduced nuclear integrity and lower viability; these defects are further exacerbated in Arp53D-KO embryos. Thus, despite its relatively recent evolution and primarily testis-specific expression, non-canonical Arp53D is required for optimal embryonic development in Drosophila.

Loss of SPACA1 function causes autosomal recessive globozoospermia by damaging the acrosome-acroplaxome complex

STUDY QUESTION

Is the sperm acrosome membrane-associated protein 1 (SPACA1) gene critical to human globozoospermia?

SUMMARY ANSWER

The biallelic loss-of-function (variant of SPACA1) causes globozoospermia as a result of acrosome-acroplaxome complex damage.

WHAT IS KNOWN ALREADY

SPACA1 expression decreases in patients with globozoospermia. Spaca1 gene-disrupted mice have abnormally shaped sperm heads that resemble those of human globozoospermia.

STUDY DESIGN, SIZE, DURATION

We recruited a consanguineous family with two brothers affected by infertility as a consequence of globozoospermia. The semen analysis data and ART outcomes were collected. Exome sequencing (ES) was used to identify potential pathogenic variants. Protein-protein interaction (PPI) technologies and proteomic analysis were utilized to explore the pathogenic mechanism.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Two globozoospermic brothers and their consanguineous parents were recruited to identify the potential pathogenic variant through ES. A homozygous nonsense variant in the SPACA1 gene in both brothers inherited from the heterozygous parents was identified. Twenty normal fertile males were recruited as controls. Sperm ultrastructure was observed with transmission electron microscopy. Western blotting was performed to measure SPACA1 expression level in the sperm from the patients. Mass spectrometry (MS) analyses were used to identify differentially expressed proteins and to investigate proteins that interact with SPACA1. Co-immunoprecipitation (co-IP), yeast two-hybrid (Y2H) and immunofluorescence colocalization assays were used to confirm the PPI.

MAIN RESULTS AND THE ROLE OF CHANCE

A nonsense variant (NM_030960.2: c.53G>A; p. Trp18*) in the SPACA1 gene was identified as the pathogenic variant in a family with globozoospermia. Patient IV:1 and Patient IV:2 had a phenotype very similar to that of Spaca1 gene-disrupted mice. The nonsense variant in SPACA1 led to premature transcriptional termination in the signal peptide, which was confirmed by western blotting. MS-based proteomics analysis showed that eight interactors of SPACA1 were differentially expressed in the patients' sperm, including actin-like Protein 7A (ACTL7A), an important component of the acrosome-acroplaxome complex. The PPI of SPACA1 and ACTL7A was confirmed via co-IP and Y2H assays. Immunofluorescence showed that SPACA1 and ACTL7A colocalized in mature sperm, revealing that these proteins were coexpressed spatially.

LIMITATIONS, REASONS FOR CAUTION

Given the rarity of globozoospermia, only two patients from one family harbouring the SPACA1 variant were found. Future studies should evaluate SPACA1 variants in larger cohorts to corroborate this finding.

WIDER IMPLICATIONS OF THE FINDINGS

This study revealed that the SPACA1 gene was critical for globozoospermia, which expanded the spectrum of causative genes for globozoospermia. This study also provided evidence for ICSI clinical outcomes for patients with SPACA1-deficient globozoospermia, which may guide clinical treatment strategies. Furthermore, this study explored the pathogenesis of globozoospermia caused by SPACA1 deficiency.

STUDY FUNDING/COMPETING INTEREST(S)

This work was funded by the Precision Medical Research of National Key Research and Development Program (2018YFC1002400), National Natural Science Foundation of China (81873724), and Natural Science Foundation of Shanghai (20ZR1472700). The authors have no conflicts of interest to disclose.

TRIAL REGISTRATION NUMBER

N/A.

Stress fiber strain recognition by the LIM protein testin is cryptic and mediated by RhoA

The actin cytoskeleton is a key regulator of mechanical processes in cells. The family of LIM domain proteins have recently emerged as important mechanoresponsive cytoskeletal elements capable of sensing strain in the actin cytoskeleton. The mechanisms regulating this mechanosensitive behavior, however, remain poorly understood. Here we show that the LIM domain protein testin is peculiar in that despite the full-length protein primarily appearing diffuse in the cytoplasm, the C-terminal LIM domains alone recognize focal adhesions and strained actin, while the N-terminal domains alone recognize stress fibers. Phosphorylation mutations in the dimerization regions of testin, however, reveal its mechanosensitivity and cause it to relocate to focal adhesions and sites of strain in the actin cytoskeleton. Finally, we demonstrate that activated RhoA causes testin to adorn stress fibers and become mechanosensitive. Together, our data show that testin’s mechanoresponse is regulated in cells and provide new insights into LIM domain protein recognition of the actin cytoskeleton’s mechanical state.

Homozygous pathogenic variants in ACTL9 cause fertilization failure and male infertility in humans and mice

Total fertilization failure (TFF) can occur during in vitro fertilization (IVF) treatments, even following intracytoplasmic sperm injection (ICSI). Various male or female factors could contribute to TFF. Increasing evidence suggested that genetic variations in PLCZ1, which encodes 1-phosphatidylinositol 4,5-bisphosphate phosphodiesterase zeta-1 (PLCζ), is involved in oocyte activation and is a key male factor in TFF. In the present study, we explored the genetic variants in male individuals that led to TFF. A total of 54 couples with TFF or poor fertilization (fertilization rate < 20%) were screened, and 21 couples were determined to have a male infertility factor by the mouse oocyte activation test. Whole-exome sequencing of these 21 male individuals identified three homozygous pathogenic variants in ACTL9 (actin like 9) in three individuals. ACTL9 variations led to abnormal ultrastructure of the perinuclear theca (PT), and PLCζ was absent in the head and present in the neck of the mutant sperm, which contributed to failed normal calcium oscillations in oocytes and subsequent TFF. The key roles of ACTL9 in the PT structure and TFF after ICSI were further confirmed in an Actl9-mutated mouse model. Furthermore, assisted oocyte activation by calcium ionophore exposure successfully overcame TFF and achieved live births in a couple with an ACTL9 variant. These findings identified the role of ACTL9 in the PT structure and the correct localization of PLCζ. The results also provide a genetic marker and a therapeutic option for individuals who have undergone ICSI without successful fertilization.

A Burst of Genetic Innovation in Drosophila Actin-Related Proteins for Testis-Specific Function

Many cytoskeletal proteins perform fundamental biological processes and are evolutionarily ancient. For example, the superfamily of actin-related proteins (Arps) specialized early in eukaryotic evolution for diverse cellular roles in the cytoplasm and the nucleus. Despite its strict conservation across eukaryotes, we find that the Arp superfamily has undergone dramatic lineage-specific diversification in Drosophila. Our phylogenomic analyses reveal four independent Arp gene duplications that occurred in the common ancestor of the obscura group of Drosophila and have been mostly preserved in this lineage. All four obscura-specific Arp paralogs are predominantly expressed in the male germline and have evolved under positive selection. We focus our analyses on the divergent Arp2D paralog, which arose via a retroduplication event from Arp2, a component of the Arp2/3 complex that polymerizes branched actin networks. Computational modeling analyses suggest that Arp2D can replace Arp2 in the Arp2/3 complex and bind actin monomers. Together with the signature of positive selection, our findings suggest that Arp2D may augment Arp2's functions in the male germline. Indeed, we find that Arp2D is expressed during and following male meiosis, where it localizes to distinct locations such as actin cones-specialized cytoskeletal structures that separate bundled spermatids into individual mature sperm. We hypothesize that this unprecedented burst of genetic innovation in cytoskeletal proteins may have been driven by the evolution of sperm heteromorphism in the obscura group of Drosophila.

Disruption in ACTL7A causes acrosomal ultrastructural defects in human and mouse sperm as a novel male factor inducing early embryonic arrest

Early embryonic arrest is a challenge for in vitro fertilization (IVF). No genetic factors were previously revealed in the sperm-derived arrest of embryonic development. Here, we reported two infertile brothers presenting normal in conventional semen analysis, but both couples had no embryos for transfer after several IVF and intracytoplasmic sperm injection (ICSI). Whole-exome sequencing identified a homozygous missense mutation of ACTL7A in both brothers. This mutation is deleterious and causes sperm acrosomal ultrastructural defects. The Actl7a knock-in mouse model was generated, and male mutated mice showed sperm acrosomal defects, which were completely consistent with the observations in patients. Furthermore, the sperm from ACTL7A/Actl7a-mutated men and mice showed reduced expression and abnormal localization of PLCζ as a potential cause of embryonic arrest and failure of fertilization. Artificial oocyte activation could successfully overcome the Actl7a-mutated sperm-derived infertility, which is meaningful in the future practice of IVF/ICSI for the ACTL7A-associated male infertility.

Mutation in a flexible linker modulates binding affinity for modular complexes

Tandem beta zippers are modular complexes formed between repeated linear motifs and tandemly arrayed domains of partner proteins in which β-strands form upon binding. Studies of such complexes, formed by LIM domain proteins and linear motifs in their intrinsically disordered partners, revealed spacer regions between the linear motifs that are relatively flexible but may affect the overall orientation of the binding modules. We demonstrate that mutation of a solvent exposed side chain in the spacer region of an LHX4-ISL2 complex has no significant effect on the structure of the complex, but decreases binding affinity, apparently by increasing flexibility of the linker.

TES functions as a Mena-dependent tumor suppressor in gastric cancer carcinogenesis and metastasis

Background

In our previous study, we identified a candidate tumor suppressor gene, testin LIM domain protein (TES), in primary gastric cancer (GC). TES contains three LIM domains, which are specific interacting regions for the cell adhesion and cytoskeleton regulatory proteins. Mena is a known cytoskeleton regulator that regulates the assembly of actin filaments and modulates cell adhesion and motility by interacting with Lamellipodin (Lpd). Therefore, we hypothesized that TES plays a role as tumor suppressor in GC through interacting with Mena. This study aimed to investigate the tumor suppressive functions of TES in GC.

Methods

We explored the tumor suppressive effect of TES in GC by in vitro cell proliferation assay, colony formation assay, cell cycle analysis, Transwell assays, and in vivo tumorigenicity and metastasis assays. The interaction of TES and Mena was investigated through immunoprecipitation-based mass spectrometry. We also analyzed the expression of TES and Mena in 172 GC specimens using immunohistochemistry and investigated the clinicopathological and prognostic significance of TES and Mena in GC.

Results

TES suppressed GC cell proliferation and colony formation, induced cell cycle arrest, and inhibited tumorigenicity in vitro. Additionally, it inhibited GC cell migration and invasion in vitro and suppressed metastasis in vivo. TES interacted with Mena, and inhibited the interaction of Mena with Lpd. Transwell assays suggested that TES suppressed migration and invasion of GC cells in a Mena-dependent fashion. In GC patients with high Mena expression, the expression of TES was associated with tumor infiltration (P = 0.005), lymph node metastasis (P = 0.003), TNM stage (P = 0.003), and prognosis (P = 0.010). However, no significant association was observed in GC patients with low Mena expression.

Conclusions

We believe that TES functions as a Mena-dependent tumor suppressor. TES represents a valuable prognostic marker and potential target for GC treatment.

Electronic supplementary material

The online version of this article (10.1186/s40880-019-0347-y) contains supplementary material, which is available to authorized users.

TES inhibits colorectal cancer progression through activation of p38

The human TESTIN (TES) gene has been identified as a candidate tumor suppressor based on its location at a common fragile site – a region where loss of heterozygosity has been detected in numerous types of tumors. To investigate its role in colorectal cancer (CRC), we examined TES protein levels in CRC tissue samples and cell lines. We observed that TES was markedly reduced in both CRC tissue and cell lines. Additionally, overexpression of TES significantly inhibited cell proliferation, migration, and invasion, while increasing cell apoptosis in colon cancer cells. By contrast, shRNA-mediated TES knockdown elicited the opposite effects. TES inhibited the progression of CRC by up-regulating pro-apoptotic proteins, down-regulating anti-apoptotic proteins, and simultaneously activating p38 mitogen-activated protein kinase (MAPK) signaling pathways. Collectively, these data indicate that TES functions as a necessary suppressor of CRC progression by activating p38-MAPK signaling pathways. This suggests that TES may have a potential application in CRC diagnosis and targeted gene therapy.

Interactions between LHX3- and ISL1-family LIM-homeodomain transcription factors are conserved in Caenorhabditis elegans

LIM-Homeodomain (LIM-HD) transcription factors are highly conserved in animals where they are thought to act in a transcriptional ‘LIM code’ that specifies cell types, particularly in the central nervous system. In chick and mammals the interaction between two LIM-HD proteins, LHX3 and Islet1 (ISL1), is essential for the development of motor neurons. Using yeast two-hybrid analysis we showed that the Caenorhabditis elegans orthologs of LHX3 and ISL1, CEH-14 and LIM-7 can physically interact. Structural characterisation of a complex comprising the LIM domains from CEH-14 and a LIM-interaction domain from LIM-7 showed that these nematode proteins assemble to form a structure that closely resembles that of their vertebrate counterparts. However, mutagenic analysis across the interface indicates some differences in the mechanisms of binding. We also demonstrate, using fluorescent reporter constructs, that the two C. elegans proteins are co-expressed in a small subset of neurons. These data show that the propensity for LHX3 and Islet proteins to interact is conserved from C. elegans to mammals, raising the possibility that orthologous cell specific LIM-HD-containing transcription factor complexes play similar roles in the development of neuronal cells across diverse species.

The PET and LIM1-2 domains of testin contribute to intramolecular and homodimeric interactions

The focal adhesion protein testin is a modular scaffold and tumour suppressor that consists of an N-terminal cysteine rich (CR) domain, a PET domain of unknown function and three C-terminal LIM domains. Testin has been proposed to have an open and a closed conformation based on the observation that its N-terminal half and C-terminal half directly interact. Here we extend the testin conformational model by demonstrating that testin can also form an antiparallel homodimer. In support of this extended model we determined that the testin region (amino acids 52–233) harbouring the PET domain interacts with the C-terminal LIM1-2 domains in vitro and in cells, and assign a critical role to tyrosine 288 in this interaction.

The E3 Ubiquitin Ligase TRIM9 Is a Filopodia Off Switch Required for Netrin-Dependent Axon Guidance

Neuronal growth cone filopodia contain guidance receptors and contribute to axon guidance; however, the mechanism by which the guidance cue netrin increases filopodia density is unknown. Here, we demonstrate that TRIM9, an E3 ubiquitin ligase that localizes to filopodia tips and binds the netrin receptor DCC, interacts with and ubiquitinates the barbed-end polymerase VASP to modulate filopodial stability during netrin-dependent axon guidance. Studies with murine Trim9(+/+) and Trim9(-/-) cortical neurons, along with a non-ubiquitinatable VASP mutant, demonstrate that TRIM9-mediated ubiquitination of VASP reduces VASP filopodial tip localization, VASP dynamics at tips, and filopodial stability. Upon netrin treatment, VASP is deubiquitinated, which promotes VASP tip localization and filopodial stability. Trim9 deletion induces axon guidance defects in vitro and in vivo, whereas a gradient of deubiquitinase inhibition promotes axon turning in vitro. We conclude that a gradient of TRIM9-mediated ubiquitination of VASP creates a filopodial stability gradient during axon turning.

TESTIN Induces Rapid Death and Suppresses Proliferation in Childhood B Acute Lymphoblastic Leukaemia Cells

Background

Childhood acute lymphoblastic leukaemia (ALL) is the most common malignancy in children. Despite high cure rates, side effects and late consequences of the intensive treatments are common. Unquestionably, the identification of new therapeutic targets will lead to safer, more effective treatments. We identified TES promoter methylation and transcriptional silencing as a very common molecular abnormality in childhood ALL, irrespective of molecular subtype. The aims of the present study were to demonstrate that TES promoter methylation is aberrant, to determine the effects of TES re-expression in ALL, and to determine if those effects are mediated via TP53 activity.

Methods

Normal fetal and adult tissue DNA was isolated and TES promoter methylation determined by Sequenom MassARRAY. Quantitative RT-PCR and immunoblot were used to confirm re-expression of TES in ALL cell lines after 5’-aza-2’-deoxycytidine (decitabine) exposure or transfection with TES expression plasmids. The effects of TES re-expression on ALL cells were investigated using standard cell proliferation, cell death and cell cycle assays.

Results

In this study, we confirm that the TES promoter is unmethylated in normal adult and fetal tissues. We report that decitabine treatment of ALL cell lines results in demethylation of the TES promoter and attendant expression of TES mRNA. Re-expression of TESTIN protein in ALL cells using expression plasmid transfection results in rapid cell death or cell cycle arrest independent of TP53 activity.

Conclusions

These results suggest that TES is aberrantly methylated in ALL and that re-expression of TESTIN has anti-leukaemia effects which point to novel therapeutic opportunities for childhood ALL.

Immune Infertility Should Be Positively Diagnosed Using an Accurate Method by Monitoring the Level of Anti-ACTL7a Antibody

Infertility is currently a major public health problem. Anti-sperm antibodies (ASAs) markedly reduce sperm quality, which can subsequently lead to male and/or female infertility. The accurate detection of ASAs derived from specific spermatozoa is, therefore, clinically useful. We have focused on the spermatozoa-specific expression protein ACTL7a for many years and have developed an enzyme-linked immunosorbent assay (ELISA) to detect the concentration of anti-ACTL7a antibodies in fertile sera (n = 267) and infertile sera (n = 193). Infertile sera were collected from the positive sera of tray agglutination tests (TAT), which is a routine ASA screening methodology. We found that the concentration of anti-ACTL7a antibodies was significantly higher in the infertile sera (than in the fertile sera, P < 0.0001) and much higher in the TAT ≥ 16 infertile sera. The ELISA was much better for male sera detection (AUC = 0.9899). If we set the standard at a strongly positive value (calculated by ROC curve), the positive predictive value of the antibody detection reached 100 percent, with a false positive rate of zero. The developed ELISA method for anti-ACTL7a antibody detection is therefore sensitive, accurate, and easy to perform, making it an excellent potential tool for future clinical use.

Testin on Atherosclerosis in Rabbits

Background:

The expression of TES, a novel tumor suppressor gene, is found to be down-regulated in the left anterior descending aorta of patients with coronary artery disease (CAD) compared with non-CAD subjects. This study aimed to investigate the expression of TES during the development of atherosclerosis in rabbits.

Methods:

Thirty-two New Zealand rabbits were randomly divided into a normal diet (ND) and high-fat diet (HFD) groups. Body weight and serum lipid levels were measured at 0, 4, and 12 weeks after diet treatment. The degree of atherosclerosis in thoracic aortas was analyzed by histological examinations. The expression of Testin in the tissue samples was inspected via immunohistochemical and immunofluorescence confocal microscopy. Real time-polymerase chain reaction and Western blot analysis were performed to evaluate the expression of TES/Testin at mRNA and protein levels in the aortic tissues.

Results:

After 12 weeks postenrollment, rabbits in HFD group had a higher level of serum lipids and atherosclerotic plaque compared to ND group (P < 0.05). Testin expression was detected at high levels in the endothelium and a weak expression on the subendothelium area. The expression of TES mRNA was markedly reduced by 10-fold in the aortic tissues in the HFD group compared with the ND group (P = 0.015), and the protein level was also significantly decreased in the HFD group (P < 0.05).

Conclusions:

Reduced TES/Testin expression is associated with the development of atherosclerosis, implicating a potentially important role in the pathogenesis of atherosclerosis.

Susceptibility to Klebsiella pneumonaie infection in collaborative cross mice is a complex trait controlled by at least three loci acting at different time points

BACKGROUND

Klebsiella pneumoniae (Kp) is a bacterium causing severe pneumonia in immunocompromised hosts and is often associated with sepsis. With the rise of antibiotic resistant bacteria, there is a need for new effective and affordable control methods; understanding the genetic architecture of susceptibility to Kp will help in their development. We performed the first quantitative trait locus (QTL) mapping study of host susceptibility to Kp infection in immunocompetent Collaborative Cross mice (CC). We challenged 328 mice from 73 CC lines intraperitoneally with 104 colony forming units of Kp strain K2. Survival and body weight were monitored for 15 days post challenge. 48 of the CC lines were genotyped with 170,000 SNPs, with which we mapped QTLs.

RESULTS

CC lines differed significantly (P < 0.05) in mean survival time, between 1 to 15 days post infection, and broad sense heritability was 0.45. Distinct QTL were mapped at specific time points during the challenge. A QTL on chromosome 4 was found only on day 2 post infection, and QTL on chromosomes 8 and 18, only on day 8. By using the sequence variations of the eight inbred strain founders of the CC to refine QTL localization we identify several candidate genes.

CONCLUSION

Host susceptibility to Kp is a complex trait, controlled by multiple genetic factors that act sequentially during the course of infection.

Ena/VASP proteins cooperate with the WAVE complex to regulate the actin cytoskeleton

Ena/VASP proteins and the WAVE regulatory complex (WRC) regulate cell motility by virtue of their ability to independently promote actin polymerization. We demonstrate that Ena/VASP and the WRC control actin polymerization in a cooperative manner through the interaction of the Ena/VASP EVH1 domain with an extended proline rich motif in Abi. This interaction increases cell migration and enables VASP to cooperatively enhance WRC stimulation of Arp2/3 complex-mediated actin assembly in vitro in the presence of Rac. Loss of this interaction in Drosophila macrophages results in defects in lamellipodia formation, cell spreading, and redistribution of Ena to the tips of filopodia-like extensions. Rescue experiments of abi mutants also reveals a physiological requirement for the Abi:Ena interaction in photoreceptor axon targeting and oogenesis. Our data demonstrate that the activities of Ena/VASP and the WRC are intimately linked to ensure optimal control of actin polymerization during cell migration and development.

Biophysical properties of intrinsically disordered p130Cas substrate domain--implication in mechanosensing

Mechanical stretch-induced tyrosine phosphorylation in the proline-rich 306-residue substrate domain (CasSD) of p130Cas (or BCAR1) has eluded an experimentally validated structural understanding. Cellular p130Cas tyrosine phosphorylation is shown to function in areas without internal actomyosin contractility, sensing force at the leading edge of cell migration. Circular dichroism shows CasSD is intrinsically disordered with dominant polyproline type II conformations. Strongly conserved in placental mammals, the proline-rich sequence exhibits a pseudo-repeat unit with variation hotspots 2–9 residues before substrate tyrosine residues. Atomic-force microscopy pulling experiments show CasSD requires minimal extension force and exhibits infrequent, random regions of weak stability. Proteolysis, light scattering and ultracentrifugation results show that a monomeric intrinsically disordered form persists for CasSD in solution with an expanded hydrodynamic radius. All-atom 3D conformer sampling with the TraDES package yields ensembles in agreement with experiment when coil-biased sampling is used, matching the experimental radius of gyration. Increasing β-sampling propensities increases the number of prolate conformers. Combining the results, we conclude that CasSD has no stable compact structure and is unlikely to efficiently autoinhibit phosphorylation. Taking into consideration the structural propensity of CasSD and the fact that it is known to bind to LIM domains, we propose a model of how CasSD and LIM domain family of transcription factor proteins may function together to regulate phosphorylation of CasSD and effect machanosensing.

Mechanical stretching of cells causes the substrate domain of p130Cas (CasSD) to be phosphorylated on 15 tyrosine residues embedded along its length. CasSD is rich in proline and surprisingly well conserved in placental mammals. Stretching of CasSD by atomic force microscopy has identified that it requires far less force than normal folded proteins. Classical biophysical analyses have determined that CasSD is a typical intrinsically disordered protein, a difficult-to-study group of molecules covering about 30% of human proteins. The average size of CasSD is larger and elongated than folded globular proteins but smaller than chemically denatured proteins. We have simulated a large number of all-atom protein structures using a fast all-atom sampling method. The result is in good agreement with the experimental observation. As it is already known that stretching somehow exposes the tyrosine residues to phosphorylation, a mechanism is proposed where straightening of the p130Cas substrate domain backbone conformation through mechanical stretching can lead to dissociation of p130Cas-binding LIM domain proteins and exposure of CasSD tyrosine residues for phosphorylation. This study has led to a new model of a protein-based mechanism of force sensing at the leading edge of cells that allows the cells to feel their way as they move.

Structural basis of the interaction of the breast cancer oncogene LMO4 with the tumour suppressor CtIP/RBBP8

LIM-only protein 4 (LMO4) is strongly linked to the progression of breast cancer. Although the mechanisms underlying this phenomenon are not well understood, a role is emerging for LMO4 in regulation of the cell cycle. We determined the solution structure of LMO4 in complex with CtIP (C-terminal binding protein interacting protein)/RBBP8, a tumour suppressor protein that is involved in cell cycle progression, DNA repair and transcriptional regulation. Our data reveal that CtIP and the essential LMO cofactor LDB1 (LIM-domain binding protein 1) bind to the same face on LMO4 and cannot simultaneously bind to LMO4. We hypothesise that overexpression of LMO4 may disrupt some of the normal tumour suppressor activities of CtIP, thereby contributing to breast cancer progression.

Dynamic alterations in the expression and localization of ACTL7a during capacitation in mouse spermatozoa

OBJECTIVE

To demonstrate that capacitation in mouse spermatozoa involves alterations in the expression and localization of ACTL7a.

DESIGN

Determine the alteration in the expression level and localization of ACTL7a in the induction of capacitation in mouse spermatozoa.

SETTING

The Institute of Basic Medical Sciences, Chinese Academy of Medical Sciences, Peking Union Medical College, People's Republic of China.

ANIMAL(S)

ICR (Institute of Cancer Research) mice.

INTERVENTION(S)

None.

MAIN OUTCOME MEASURE(S)

Western blot, indirect immunostaining.

RESULT(S)

The expression of ACTL7a is upregulated via the PKA pathway and undergoes remodeling during the early period of capacitation in mouse spermatozoa.

CONCLUSION(S)

ACTL7a is an essential component of capacitation in mouse spermatozoa. The alteration in the expression and localization of ACTL7a may be the primary biochemical event in the induction of capacitation in mouse spermatozoa.

TGF-β1-induced LPP expression dependant on Rho kinase during differentiation and migration of bone marrow-derived smooth muscle progenitor cells

Lipoma preferred partner (LPP) has been identified as a protein which is highly selective for smooth muscle progenitor cells (SMPCs) and regulates differentiation and migration of SMPCs, but mechanisms of LPP expression are not elucidated clearly. The aim of the present study was to discuss the mechanisms by which LPP expression is regulated in the differentiation and migration of SMPCs induced by TGF-β1. It was found that TGF-β1 could significantly increase the expression of LPP, smooth muscle α-actin, smooth muscle myosin heavy chain (SM-MHC), and smoothelin in SMPCs. Moreover, inactivation of Rho kinase (ROK) with ROK inhibitors significantly inhibited LPP mRNA expression in TGF-β1-treated SMPCs and mouse aortic smooth muscle cells (MAoSMCs). At the same time, LPP silencing with short interfering RNA significantly decreased SMPCs migration. In conclusion, LPP appears to be a ROK-dependant SMPCs differentiation marker that plays a role in regulating SMPCs migration.

Flotillin-2 is an acrosome-related protein involved in mouse spermiogenesis

Spermatogenesis is a complex process of terminal differentiation by which mature sperms are generated, and it can be divided into three phases: mitosis, meiosis and spermiogenesis. In a previous study, we established a series of proteomic profiles for spermatogenesis to understand the regulation of male fertility and infertility. Here, we further investigated the localization and the role of flotillin-2 in spermiogenesis. Flotillin-2 expression was investigated in the testis of male CD1 mice at various developmental stages of spermatogenesis by using Western blotting, immunohistochemistry and immunofluorescence. Flotillin-2 was knocked down in vivo in three-week-old male mice using intratesticular injection of small inhibitory RNA (siRNA), and sperm abnormalities were assessed three weeks later. Flotillin-2 was expressed at high levels in male germ cells during spermatogenesis. Flotillin-2 immunoreactivity was observed in pachytene spermatocytes as a strong dot-shaped signal and in round spermatids as a sickle-shaped distribution ahead of the acrosome. Immunofluorescence confirmed flotillin-2 was localized in front of the acrosome in round spermatids, indicating that flotillin-2 was localized to the Golgi apparatus. Knockdown of flotillin-2in vivo led to a significant increase in head sperm abnormalities isolated from the cauda epididymis, compared with control siRNA-injected testes. This study indicates that flotillin-2 is a novel Golgi-related protein involved in sperm acrosome biogenesis.