O-092 Sperm phenotype, ICSI outcome and genetic diagnosis in case of severe asthenozoospermia with multiple morphological abnormalities of the flagellum

Study question

What are the feasibility and outcome of ICSI in case of presumably genetic severe asthenozoospermia with Multiple Morphological Abnormalities of the Flagellum (MMAF phenotype)?

Summary answer

ICSI outcome for couples with MMAF phenotype does not differ from that of other couples requiring ICSI, regardless to the genetic etiology

What is known already

Severe asthenozoospermia, especially when associated with multiple morphological abnormalities of the sperm flagellum (MMAF phenotype), results in male infertility. Recent findings confirm that a genetic etiology is frequently responsible for this phenotype. In such situations, pregnancies can be obtained using ICSI. However, few studies have provided detailed analyses of the flagellar ultrastructural defects underlying this phenotype, of its genetic etiologies and of the results of ICSI in such cases of male infertility.

Study design, size, duration

We performed a retrospective study including 25 infertile men showing severe asthenozoospermia associated with a MMAF phenotype identified through standard semen analysis. These men were recruited from an academic center for Assisted Reproduction in Paris between 2009 and 2017. Transmission electron microscopy (TEM) and Whole Exome Sequencing (WES) were performed in order to precise the sperm ultra-structural phenotype and identify causal mutations, respectively. Twenty of the 25 patients benefited from assisted reproductive therapy by ICSI.

Participants/materials, setting, methods

MMAF patients were recruited based on reduced sperm progressive motility and increased frequencies of absent, short, coiled or irregular flagella, in comparison with fertile control men. A quantified analysis of the ultrastructural defects was performed for the MMAF patients and for fertile control men. ICSI results for the MMAF patients were compared to those of 528 ICSI attempts performed for non-MMAF individuals considering the sperm parameters and the distribution of ultrastructural axonemal anomalies.

Main results and the role of chance

Thorough categorization by TEM analysis of the flagellar anomalies found in these patients brought important precisions about the structural defects underlying asthenozoospermia and sperm tail abnormalities detectable through standard microscopy. In particular, absence of the central pair of axonemal microtubules was the predominant anomaly, observed significantly more frequently than in control men (p < 0.01). Exome sequencing performed for 24 of the 25 patients (96%), identified in ten of them homozygous or compound heterozygous mutations that were described to be pathogenic (CFAP43, CFAP44, CFAP69, DNAH1, DNAH8, AK7, TTC29, MAATS1). A majority of those patients (55.5%,5/9) displayed the most severe ultra-structural defects of the axoneme. Forty ICSI attempts were performed for 20 MMAF patients. A hypo-osmotic swelling (HOS) test was required in 13 cycles (5 couples). Fertilization rate in MMAF group (65.7%) was not statistically different from the rate obtained for non-MMAF patients (66.0%) and did not differ according to the flagellar phenotype, nor to the use of HOS test, nor to the genotype. Clinical pregnancy rate per embryo transfer did not significantly differ between the MMAF group (23.3%) and the ICSI control group (37.1%). To date, 11 healthy babies were born among 20 MMAF patients.

Limitations, reasons for caution

The outcome of ICSI procedure was retrospectively assessed on a small sample and may be susceptible to recall bias. Moreover, TEM analysis was not available for some of the patients due to too low sperm concentration, and WES results are not yet available for all men included.

Wider implications of the findings

Couples requiring ICSI for presumably genetic severe asthenozoospermia should benefit precociously from appropriate phenotypic and genetic investigations. So far ICSI results appear similar to those observed in other ICSI indications. Identifying a genetic etiology and its mode of inheritance allows providing to these couples a most often reassuring genetic counseling.

Trial registration number

Not applicable

Expression of a V region-less B cell receptor confers a tolerance-like phenotype on transgenic B cells

Neoplastic B cells from H chain disease patients express a truncated B cell receptor (BCR), comprising a membrane Ig that lacks part of its extracellular domain. It has been speculated that deletion of the Ag binding domain would confer a constitutive activity on the BCR, as it has been shown for oncogenic growth factor receptors. A V region-less BCR has constitutive activity, because in transgenic mice it causes inhibition of endogenous H chain gene rearrangements and relieves the requirement for surrogate L chain in pre-B cell development. However, it has been speculated that normal Ag receptors also display constitutive activity. Here we show that transgenic B cells expressing a membrane H chain disease protein on their surface are phenotypically and functionally similar to B cells developing in the presence of their cognate Ag and that cells with normal levels of mutant BCR are eliminated in spleen via a bcl-2 sensitive pathway while progressing toward the mature stage. In contrast, cells with lower levels of mutant receptors develop as mature B cells. These findings support the view that the truncated BCR has a constitutive activity that mimics ligand binding, in analogy to what has been shown for oncogenic growth factor receptors.

Soluble Fc gamma receptors: interaction with ligands and biological consequences

Soluble Fc gamma receptors are produced by cleavage of the membrane receptors or by alternative splicing. They are found in biologic fluids. After a brief description of the structure and mode of production of soluble Fc gamma R, we address the question of ligands and function of the soluble Fc gamma R by using recombinant molecules and transgenic animals. We show that soluble Fc gamma R are not only IgG-binding factors which interfere with, and block, Fc-dependent immune reactions but also molecules that interact, in vitro, with non-Ig-ligands such as CR3 and CR4 and are trigger or regulate immune functions via these receptors.

Enhanced apoptosis in the thymus of transgenic mice expressing constitutively activated forms of human Rac2GTPase

Rac proteins constitute a subgroup of the Rho family of small GTPases and include Rac1, which is expressed ubiquitously, and Rac2, a highly homologous protein only expressed in myelo-monocytic and lymphoid cell lineages. In fibroblasts, Rac1 plays a crucial role in control of actin cytoskeleton organisation, cell growth and Ras-induced transformation. In phagocytes, Rac1 and Rac2 regulate a specific enzymatic complex, NADPH oxidase. These multiple functions have been ascribed to Rac proteins only on the basis of cell culture and in vitro biochemical studies. To examine the role of Rac2 in vivo in a T cell lineage, we have expressed either wild-type or constitutively-activated forms of human Rac2 (Rac2V12 and Rac2L61) in transgenic mice under control of the thymus specific lck proximal promoter. We report here a striking atrophy of the thymus in mice expressing even low levels of either of the activated mutants of Rac2, while expression of Rac2wt has no effect. This phenotype is correlated with a marked decrease in the number of double positive (CD4+ CD8+) and single positive (CD4+ CD8- and CD8+ CD4-) thymocytes. Cellular and molecular analyses demonstrate that this defect is due to an increase in apoptosis among thymocytes. As Rac2 is normally expressed in thymocytes and activated T cells, we propose that Rac2 dependent pathways could play an important role in control of growth and death of T cells.

Characterization of an intronless CD4 minigene expressed in mature CD4 and CD8 T cells, but not expressed in immature thymocytes

The expression of the CD4 gene undergoes a complex pattern of regulation during T cell development. Results obtained in transgenic mice suggest that a combination of proximal enhancer and a silencer from the CD4 gene is sufficient to obtain a developmentally controlled expression along T cell maturation. We generated transgenic mice expressing the human CD4 cDNA under the control of the human CD4 promoter and the murine CD4 minimal proximal enhancer. No other regulatory sequences, including the silencer, were included. The pattern of expression of this transgene is restricted to mature peripheral T cells, to the only mature heat-stable Ag(HSA)low/- single positive thymocytes, and to some NK cells. Surprisingly, no expression was found in double positive or in immature HSAhigh single positive thymocytes. These results suggest that additional, yet uncharacterized genomic sequences are necessary for CD4 expression in immature thymocytes and that there is a change in transcription factors occurring at the late states of T cell development. Finally, since this is the first combination of regulatory sequences that possess such a T mature specific pattern of expression, it should provide a novel tool to address several immunologic questions or for therapeutic purposes.

Characterization of an intronless CD4 minigene expressed in mature CD4 and CD8 T cells, but not expressed in immature thymocytes

The expression of the CD4 gene undergoes a complex pattern of regulation during T cell development. Results obtained in transgenic mice suggest that a combination of proximal enhancer and a silencer from the CD4 gene is sufficient to obtain a developmentally controlled expression along T cell maturation. We generated transgenic mice expressing the human CD4 cDNA under the control of the human CD4 promoter and the murine CD4 minimal proximal enhancer. No other regulatory sequences, including the silencer, were included. The pattern of expression of this transgene is restricted to mature peripheral T cells, to the only mature heat-stable Ag(HSA)low/- single positive thymocytes, and to some NK cells. Surprisingly, no expression was found in double positive or in immature HSAhigh single positive thymocytes. These results suggest that additional, yet uncharacterized genomic sequences are necessary for CD4 expression in immature thymocytes and that there is a change in transcription factors occurring at the late states of T cell development. Finally, since this is the first combination of regulatory sequences that possess such a T mature specific pattern of expression, it should provide a novel tool to address several immunologic questions or for therapeutic purposes.

Pre-B-cell development in the absence of lambda 5 in transgenic mice expressing a heavy-chain disease protein

BACKGROUND

Heavy-chain diseases (HCDs) are human lymphoproliferative neoplasias that are characterized by the secretion of truncated immunoglobulin heavy chains devoid of light chains. We have previously proposed--by analogy to the process by which mutated growth factor receptors can be oncogenic--that because the genetic defects in HCDs result in the production of abnormal membrane-associated heavy chains lacking an antigen-binding domain, these abnormal B-cell antigen receptors might engage in ligand-independent signalling. Normal pre-B-cell development requires the presence of the pre-B-cell receptor, formed by the association of mu heavy chains with two polypeptides--so-called surrogate light chains, Vpre-B and lambda 5--that are homologous to the variable and constant portions of immunoglobulin light chains, respectively. To assess whether amino-terminal truncation of membrane-associated heavy chains results in their constitutive activation, we have examined the ability of a HCD-associated mu protein to promote pre-B-cell development in transgenic mice.

RESULTS

When the mu HCD transgene is introduced into SCID mice, CD43- pre-B cells develop normally. To determine whether this pre-B-cell development requires surrogate light chains, we backcrossed mice expressing full-length or truncated mu transgenes with lambda 5-deficient mice. Our results show that the truncated heavy chain, but not the normal chain, is able to promote pre-B-cell development in the absence of lambda 5. We also show that truncated mu chains spontaneously aggregate at the surface of bone marrow cells.

CONCLUSIONS

Expression of the truncated mu heavy chain overrides a tightly controlled step of pre-B-cell development, which strongly suggests that a constitutive signal is delivered by the truncated mu chain disease protein. The self-aggregation of mu chain disease proteins might account for this constitutive activation. We conclude that amino-terminal truncation of heavy chains could play a role in the genesis of HCD neoplasia if it occurs at an appropriate stage of B-cell differentiation, namely in a mature B cell.

Conditional ablation of dendritic cells in transgenic mice

Dendritic cells (DC) are professional Ag-presenting cells that play a major role in T cell-mediated immune responses and in thymocyte differentiation. To better analyze their physiological importance, we sought to generate transgenic mice presenting a conditional DC deficiency. We used a strategy based on the cell-specific expression of a suicide gene. The DC-targeted expression is obtained using HIV regulatory sequences; indirect evidence has suggested that these sequences control a preferential expression in DC. The suicide gene is the herpes simplex virus type 1 thymidine kinase (HSV1-TK) which allows conditional ablation of dividing HSV1-TK-expressing cells by converting nucleoside analogs such as ganciclovir (GCV) into toxic molecules. We generated transgenic mice expressing an HSV1-TK gene transcribed from HIV regulatory sequences. A low but significant HSV1-TK expression was observed in mature DC and DC precursors grown from granulocyte-macrophage colony-stimulating factor-supplemented bone marrow cultures. These HSV1-TK-expressing DC precursors are specifically killed by GCV. We next treated transgenic mice with GCV, and obtained a specific ablation of DC in spleen and thymus. Ninety percent of spleen DC could be depleted within a week, indicating a turnover rate of approximately 15% per day. Interestingly, this DC depletion always correlated with a major thymic atrophy and disappearance of CD4+CD8+ thymocytes. This animal model should help to assess the physiological role of DC in the immune response and in thymocyte differentiation. It should also help to appreciate the consequences of DC dysfunction in pathological situations, such as HIV-infection or allograft rejection.

Conditional ablation of dendritic cells in transgenic mice

Dendritic cells (DC) are professional Ag-presenting cells that play a major role in T cell-mediated immune responses and in thymocyte differentiation. To better analyze their physiological importance, we sought to generate transgenic mice presenting a conditional DC deficiency. We used a strategy based on the cell-specific expression of a suicide gene. The DC-targeted expression is obtained using HIV regulatory sequences; indirect evidence has suggested that these sequences control a preferential expression in DC. The suicide gene is the herpes simplex virus type 1 thymidine kinase (HSV1-TK) which allows conditional ablation of dividing HSV1-TK-expressing cells by converting nucleoside analogs such as ganciclovir (GCV) into toxic molecules. We generated transgenic mice expressing an HSV1-TK gene transcribed from HIV regulatory sequences. A low but significant HSV1-TK expression was observed in mature DC and DC precursors grown from granulocyte-macrophage colony-stimulating factor-supplemented bone marrow cultures. These HSV1-TK-expressing DC precursors are specifically killed by GCV. We next treated transgenic mice with GCV, and obtained a specific ablation of DC in spleen and thymus. Ninety percent of spleen DC could be depleted within a week, indicating a turnover rate of approximately 15% per day. Interestingly, this DC depletion always correlated with a major thymic atrophy and disappearance of CD4+CD8+ thymocytes. This animal model should help to assess the physiological role of DC in the immune response and in thymocyte differentiation. It should also help to appreciate the consequences of DC dysfunction in pathological situations, such as HIV-infection or allograft rejection.

Expression of human CD4 in transgenic mice does not confer sensitivity to human immunodeficiency virus infection

Transfection of the human CD4 molecule into mouse cells does not confer susceptibility to human immunodeficiency virus type 1 (HIV-1) infection. Expression of the human CD4 molecule in transgenic mice was seen to offer some new possibilities. However, transgenic mouse T cells expressing either the human CD4 receptor, or a hybrid human/mouse CD4 receptor alone or in conjunction with human major histocompatibility complex class I molecules, were refractory to in vitro HIV-1 infection. In addition, no infection was observed after in vivo HIV inoculation to mice of these various transgenic lines. Injection of recombinant gp160 viral protein to the transgenic mice did not alter their T and B cell populations. The existence of a dominant block in mouse cells that prevents HIV entry is discussed.

A mouse minialbumin gene is specifically expressed in differentiated hepatoma cells but not in transgenic mice

A mouse genomic DNA fragment including the albumin gene in which central exons 9-12 had been deleted and flanked by 2.2 kb in 5' and 4.3 kb in 3' (minialbumin gene), was introduced into rat hepatoma cells and also into mouse embryos to produce transgenic mice. The minialbumin gene was specifically transcribed in stably transfected differentiated clones and a 47-k Da minialbumin was synthesized and secreted into the culture medium. In contrast, the transgene was not expressed in any of the seven independent transgenic mouse lines examined. This suggests that expression of the albumin gene in developing animals requires cis-regulating elements additional to those located within the immediate flanking regions of the gene, which are sufficient to elicit specific expression in differentiated hepatoma cells in culture.

Pancreatic expression of human insulin gene in transgenic mice

We have investigated the possibility of obtaining integration and expression of a native human gene in transgenic mice. An 11-kilobase (kb) human chromosomal DNA fragment including the insulin gene (1430 base pairs) was microinjected into fertilized mouse eggs. This fragment was present in the genomic DNA of several developing animals. One transgenic mouse and its progeny were analyzed for expression of the foreign gene. Synthesis and release of human insulin was revealed by detection of the human C-peptide in the plasma and urine. Human insulin mRNA was found in pancreas but not in other tissues. These findings indicate that the 11-kb human DNA fragment carries the sequences necessary for tissue-specific expression of the insulin gene and the human regulatory sequences react to homologous signals in the mouse.