Inadequate function of sterile tw5/tw32 spermatozoa overcome by intracytoplasmic sperm injection

RAC1 controls progressive movement and competitiveness of mammalian spermatozoa

Mammalian spermatozoa employ calcium (Ca2+) and cyclic adenosine monophosphate (cAMP) signaling in generating flagellar beat. However, how sperm direct their movement towards the egg cells has remained elusive. Here we show that the Rho small G protein RAC1 plays an important role in controlling progressive motility, in particular average path velocity and linearity. Upon RAC1 inhibition of wild type sperm with the drug NSC23766, progressive movement is impaired. Moreover, sperm from mice homozygous for the genetically variant t-haplotype region (tw5/tw32), which are sterile, show strongly enhanced RAC1 activity in comparison to wild type (+/+) controls, and quickly become immotile in vitro. Sperm from heterozygous (t/+) males, on the other hand, display intermediate RAC1 activity, impaired progressive motility and transmission ratio distortion (TRD) in favor of t-sperm. We show that t/+-derived sperm consist of two subpopulations, highly progressive and less progressive. The majority of highly progressive sperm carry the t-haplotype, while most less progressive sperm contain the wild type (+) chromosome. Dosage-controlled RAC1 inhibition in t/+ sperm by NSC23766 rescues progressive movement of (+)-sperm in vitro, directly demonstrating that impairment of progressive motility in the latter is caused by enhanced RAC1 activity. The combined data show that RAC1 plays a pivotal role in controlling progressive motility in sperm, and that inappropriate, enhanced or reduced RAC1 activity interferes with sperm progressive movement. Differential RAC1 activity within a sperm population impairs the competitiveness of sperm cells expressing suboptimal RAC1 activity and thus their fertilization success, as demonstrated by t/+-derived sperm. In conjunction with t-haplotype triggered TRD, we propose that Rho GTPase signaling is essential for directing sperm towards the egg cells.

Transient Sperm Starvation Improves the Outcome of Assisted Reproductive Technologies

To become fertile, mammalian sperm must undergo a series of biochemical and physiological changes known as capacitation. These changes involve crosstalk between metabolic and signaling pathways and can be recapitulated in vitro. In this work, sperm were incubated in the absence of exogenous nutrients (starved) until they were no longer able to move. Once immotile, energy substrates were added back to the media and sperm motility was rescued. Following rescue, a significantly higher percentage of starved sperm attained hyperactivated motility and displayed increased ability to fertilize in vitro when compared with sperm persistently incubated in standard capacitation media. Remarkably, the effects of this treatment continue beyond fertilization as starved and rescued sperm promoted higher rates of embryo development, and once transferred to pseudo-pregnant females, blastocysts derived from treated sperm produced significantly more pups. In addition, the starvation and rescue protocol increased fertilization and embryo development rates in sperm from a severely sub-fertile mouse model, and when combined with temporal increase in Ca²⁺ ion levels, this methodology significantly improved fertilization and embryo development rates in sperm of sterile CatSper1 KO mice model. Intracytoplasmic sperm injection (ICSI) does not work in the agriculturally relevant bovine system. Here, we show that transient nutrient starvation of bovine sperm significantly enhanced ICSI success in this species. These data reveal that the conditions under which sperm are treated impact post-fertilization development and suggest that this “starvation and rescue method” can be used to improve assisted reproductive technologies (ARTs) in other mammalian species, including humans.

Preservation of ejaculated mouse spermatozoa from fertile C57BL/6 and infertile Hook1/Hook1 mice collected from the uteri of mated females

Methods routinely used to preserve mouse spermatozoa require that the male be killed to recover spermatozoa from the epididymides. Here we obtained multiple samples of ejaculated spermatozoa from normal fertile C57BL/6 and infertile Hook1/Hook1 (formerly known as azh/azh) mutant males from uteri after mating, thus avoiding termination of the males. Ejaculated sperm were preserved by conventional cryopreservation or by rapid freezing without cryoprotection, and were injected into the oocytes by intracytoplasmic sperm injection (ICSI). The proportions of oocytes that survived, became activated, and developed into two-cell embryos were similar when comparing the two preservation methods in wild-type versus Hook1/Hook1 mice and tested mice versus controls (fresh and rapid-frozen epididymal and fresh ejaculated sperm). Two-cell embryos were transferred into the oviducts of pseudopregnant females, and fetal development was examined at Day 15 of gestation. A total of 39%-54% of transferred embryos produced with preserved ejaculated sperm implanted. Live, normal fetuses (11%-17%) were obtained in all examined groups and from all males included in the study. More implants (71%-82%) and fetuses (28%-31%) were noted in controls. Lower developmental potentials of embryos produced with preserved ejaculated sperm might be due to their capacitation status; the majority of sperm retrieved from the uterus were capacitated. This study bears significance for the maintenance and distribution of novel mouse strains. The method is applicable for all types of mice, including those with male infertility syndromes. The sole requirement is that the male of interest is able to copulate and its ejaculate contains spermatozoa.

Intracytoplasmic sperm injection effects in infertile azh mutant mice

Several reports in the literature describe men with infertility resulting from abnormal sperm head shape or decapitation defects of their spermatozoa. These defects are similar to those shown for the spermatozoa from azh (abnormal spermatozoon head shape) mice. The present study examines the efficiency and effects of intracytoplasmic sperm injection (ICSI) in successive generations of azh mice generated with this method. Three successive generations of azh mice were produced with ICSI. In all three ICSI series, more than 80% of 2-cell embryos were obtained, and more than 35% of embryos transferred gave rise to normal live offspring. In addition, ICSI was used to cross homozygous azh/azh males with homozygous azh/azh females, and live offspring were obtained. The ICSI-derived males were tested for their fecundity and abnormalities of sperm morphology. Spermatozoa from ICSI-derived azh/+ males did not show any impairment of fecundity in in vitro fertilization. These spermatozoa successfully fertilized oocytes from both C57BL/6 and B6D2F1 females, with fertilization rates ranging from 70%- 92%. The proportion of morphologically normal spermatozoa was similar in azh/+ males from three successive generations of ICSI (57.8%, 54.8%, and 49.0%, respectively), and no differences were noted when comparing ICSI-derived males with males derived by mating (57.6%) and with wild-type controls (61.6%). Detailed analysis differentiating between specific types of anomalies of sperm morphology did not reveal significant differences among the examined groups. The results of the present study demonstrate that ICSI does not enhance the azh mutation phenotype in the offspring and brings no risks when applied continuously. Moreover, serial (successive generations) ICSI is highly efficient in maintaining valuable mice with fertility problems.

Intracytoplasmic injection of spermatozoa and spermatogenic cells: its biology and applications in humans and animals

Intracytoplasmic sperm injection (ICSI) has become the method of choice to overcome male infertility when all other forms of assisted fertilization have failed. Animals in which ICSI has produced normal offspring include many species. Success rate with normal spermatozoa is well above 50% in the mouse but ICSI success rates in other animals have been low, ranging from 0.3 to 16.5%. Mouse ICSI revealed that spermatozoa that cannot participate in normal fertilization can produce normal offspring by ICSI, provided their nuclei are genomically intact. Human ICSI using infertile spermatozoa has been highly successful perhaps because of the intrinsic instability of human sperm plasma membrane. The health of children born after ICSI and other assisted fertilization techniques is of major concern. Careful analyses suggest that higher incidences of congenital malformations and/or low birth weights after assisted fertilization are largely attributable to parental genetic background and increased incidence of multiple births, rather than to the techniques of assisted fertilization. Since the physiological and nutritional environments of developing embryos may cause persisting alteration in DNA methylation, extreme caution must be exercised in handling gametes and embryos in vitro. In the mouse, round spermatid injection (ROSI) has been routinely successful but its use in humans is controversial. Whether human ROSI and assisted fertilization involving younger spermatogenic cells are medically safe must be the subject of further investigations.

Microinsemination and Nuclear Transfer Using Male Germ Cells

Microinsemination has been widely used in basic reproductive research and in human-assisted reproductive technology for treating infertility. Historically, microinsemination in mammals started with research on the golden hamster; since then, it has provided invaluable information on the mechanisms of mammalian fertilization. Thanks to advances in animal genetic engineering and germ-cell technologies, microinsemination techniques are now used extensively to identify the biological significance of genes of interest or to confirm the genetic normality of gametes produced by experimental manipulations in vitro. Fortunately, in mice, high rates of embryo development to offspring can be obtained so long as postmeiotic spermatogenic cells are used as male gametes-that is, round spermatids, elongated spermatids, and spermatozoa. For some other mammalian species, using immature spermatogenic cells significantly decreases the efficiency of microinsemination. Physically unstable chromatin and low oocyte-activating capacity are the major causes of fertilization failure. The youngest male germ cells, including primordial germ cells and gonocytes, can be used in the construction of diploid embryos by nuclear-transfer cloning. The cloned embryos obtained in this way provide invaluable information on the erasure and reestablishment of genomic imprinting in germ cells.

Production of fertile offspring from genetically infertile male mice

A number of recessive autosomal genes cause male infertility. Male mice homozygous for the blind-sterile (bs/bs) and quaking-sterile (qk/qk) gene mutations are sterile, because they either do not produce any spermatozoa or produce only a few abnormal spermatozoa. Mice lacking the cyclic AMP responsive-element modulator gene are sterile due to failure of spermiogenesis. All these mice, however, are able to produce fertile offspring when their spermatozoa or round spermatids are injected into oocytes of normal females. This implies that genetic and epigenetic elements necessary for syngamy and embryonic development are established in round spermatids and spermatozoa of these animals, even though their spermatogenic cells are destined to die (bs/bs and qk/qk) or are programmed to undergo apoptosis (cyclic AMP responsive-element modulator-null) without becoming functional spermatozoa.

Long-term preservation of mouse spermatozoa after freeze-drying and freezing without cryoprotection

The widespread production of mice with transgenes, disrupted genes and mutant genes, has strained the resources available for maintaining these mouse lines as live populations, and dependable methods for gamete and embryo preservation in these lines are needed. Here we report the results of intracytoplasmic sperm injection (ICSI) with spermatozoa freeze-dried or frozen without a cryoprotectant after storage for periods up to 1.5 years. Freeze-dried samples were stored at 4 degrees C. Samples frozen without cryoprotection were maintained at -196 degrees C. After storage, spermatozoa were injected into the oocytes by ICSI. Zygotic chromosomes and fetal development at Day 15 of gestation were examined after 0, 1, 3, 6, 9, and 12 mo of sperm storage. When fresh spermatozoa were used for ICSI, 96% of resultant zygotes contained normal chromosomes, and 58% of two-cell embryos transferred developed to normal viable fetuses. Similar results were obtained when spermatozoa were frozen without cryoprotection and then used for ICSI (87% and 45%, respectively; P > 0.05) and after 12 mo of sperm storage (mean of six endpoints examined: 87% and 52%, respectively; P > 0.05). Freeze-drying decreased the proportion of zygotes with normal karyoplates (75% vs. 96%; P < 0.001) and the proportion of embryos that developed into fetuses (35% vs. 58%; P < 0.001), but similar to freezing, there was no further deterioration during 12 mo of storage (mean of six endpoints examined: 68% and 34%, respectively; P > 0.05). Live offspring were obtained from both freeze-dried and frozen spermatozoa after storage for 1.5 yr. The results indicate that 1) the freeze-drying procedure itself causes some abnormalities in spermatozoa but freezing without cryoprotection does not and 2) long-term storage of both frozen and freeze-dried spermatozoa is not deleterious to their genetic integrity. Freezing without cryoprotection is highly successful, simple, and efficient but, like all routine sperm storage methods, requires liquid nitrogen. Liquid nitrogen is also required for freeze-drying, but sperm can then be stored at 4 degrees C and shipped at ambient temperatures. Both preservation methods are successful, but rapid freezing without cryoprotection is the preferred method for preservation of spermatozoa from mouse strains carrying unique genes and mutations.

Fertilization of oocytes and birth of normal pups following intracytoplasmic injection with spermatids in mastomys (Praomys coucha)

The mastomys is a small laboratory rodent that is native to Africa. Although it has been used for research concerning reproductive biology, in vitro fertilization (IVF) and intracytoplasmic sperm injection are very difficult in mastomys because of technical problems, such as inadequate sperm capacitation and large sperm heads. The present study was undertaken to examine whether mastomys spermatids could be used to fertilize oocytes in vitro using a microinsemination technique, because spermatids are more easily injected than mature spermatozoa into oocytes. Most mastomys oocytes (80%-90%) survived intracytoplasmic injection with either round or elongated spermatids. Round spermatids had little oocyte-activating capacity, similar to those of mice and rats, and exogenous stimuli were needed for normal fertilization. Treatment with an electric pulse in the presence of 50 microM Ca2+ followed by culture in 10 mM SrCl2 led to successful oocyte activation. After injection of round spermatids into preactivated oocytes, 93% of oocytes were normally fertilized (male and female pronuclei formed), and 100% of cultured oocytes developed to the 2-cell stage. However, none reached term after transfer into recipient females. Elongated spermatids, which correspond to steps 9-11 in rats, activated oocytes on injection without additional activation treatment. After embryo transfer, five offspring (6% per transfer) developed to term. These results indicate that microinsemination with spermatids is a feasible alternative in animal species that are refractory to IVF and sperm injection and that using later-stage spermatids may lead to increased production of viable embryos that can develop into normal offspring.

Rescue of infertile transgenic rat lines by intracytoplasmic injection of cryopreserved round spermatids

Transgenic male rats carrying human alpha-lactalbumin with thymidine kinase gene (line name; LAC3) were found to be infertile due to expression of the transgene in the testes. Furthermore, it was not possible to maintain the line even by the use of intracytoplasmic sperm injection (ICSI). Therefore, round spermatids prepared from the LAC3 rats were microinjected into strontium-activated oocytes using a Piezo-driven micromanipulator. Of 263 oocytes microinjected with LAC3 spermatids, 244 (92.8%) survived the injection and 96 (39.3%) developed to the 2-cell stage. Three viable offspring were born after transfer (1.4%, 3/219), and two offspring carried the LAC3 transgene. In the control experiment using spermatids of Wistar rats, similar proportions of post-injection survival (91.3%, 241/264), cleavage (40.2%, 97/241), and development into offspring (0.5%, 1/206) were obtained. Thus, this paper reports not only the first rat offspring derived from round spermatid injection but also the practical application of the microinsemination technique to the rescue of transgenes of infertile transgenic male rats.

Offspring derived from intracytoplasmic injection of transgenic rat sperm

The objective of the present study was to produce rat offspring by intracytoplasmic sperm injection (ICSI) using a Piezo-driven micromanipulator. Transgenic male rats carrying a green fluorescent protein gene (GFP: homozygous) were used as sperm donors. The epididymal spermatozoa were suspended and sonicated in m-KRB medium and were frozen in the same medium at -20 degrees C until use. When the sperm heads were aspirated into injection pipettes 7-10 microm in diameter and introduced into oocytes from the Wistar strain, no offspring resulted from the transfer of 59 eggs. In contrast, the sperm heads were hung on the tip of injection pipettes 2-4 microm in diameter and introduced into the oocytes, use of Piezo resulting in the production of 18 transgenic offspring carrying the GFP gene from 181 eggs transferred. The oocytes from the Sprague-Dawley strain also supported full-term development following ICSI with three offspring resulting from 163 transferred eggs. In an additional ICSI trial, spermatozoa from infertile transgenic rats carrying human lactalbumin with the thymidine kinase gene (LAC3: heterozygous) were used. The spermatozoa of the LAC3 transgenic rats appeared to be defective and immotile because of the expression of thymidine kinase in the testes, and no ICSI offspring resulted from 218 transferred eggs. These results suggest that ICSI is applicable in rats when Piezo-driven smaller pipettes are used to inject sperm heads together with a limited amount of the surrounding medium and that the ability of isolated sperm heads to participate in normal embryo development is maintained under the cryopreservation conditions employed.

Comparison of intracytoplasmic sperm injection for inbred and hybrid mice

We compared the results of intracytoplasmic sperm injection (ICSI) that leads to full term development of hybrid (B6C3F1 and B6D2F1) and inbred (C57BL/6) mouse embryos. Although fertilization and pre-implantation development of C57BL/6 eggs were similar to those of F1 hybrid eggs, post-implantation development of the embryos from C57BL/6 females was significantly poorer than those of the eggs from hybrid females. Reciprocal crosses of C57BL/6 and B6C3F1 gametes revealed that the low rate of post-implantation development of C57BL/6 embryos was due to oocyte factor(s), rather than the sperm factor.

Genes in the first and fourth inversions of the mouse t complex synergistically mediate sperm capacitation and interactions with the oocyte

The t haplotypes (t) are recent evolutionary derivatives of an alternate form of the mouse t complex region located at the proximal end of chromosome 17. This variant form of approximately 1% of the mouse genome is a source of mutations altering numerous sperm functions crucial for fertilization. Males that carry two t haplotypes (t/t) are invariably sterile. t haplotypes contain four inversions relative to the wild-type t complex (+), so that in matings involving a +/t heterozygote, t is usually transmitted as a single unit. However, rare recombinants have been recovered, which carry only part of the t genotype and express only some of the t-dependent phenotypes. Use of these partial t haplotypes in genetic crosses has resulted in the general location of the two major t male sterility factors, S1 and S2, within inversions 1 and 4, respectively. Since sterility can result from a plethora of sperm defects, we have made a detailed study of various functional parameters of sperm from mice carrying S1 or S2 heterozygously or homozygously or in combination. Both S1 and S2 contain mutations altering sperm functions, including motility, capacitation, binding to the zona pellucida, binding to the oocyte membrane, and penetration of the zona pellucida-free oocyte. Therefore it seems clear that each of these factors contains multiple genes contributing to sterility. Furthermore, our results indicate that genes within S1 interact with genes in S2 for all sperm functions examined. However, S1 and S2 genes affecting motility interact in a purely additive fashion, while S1 and S2 genes affecting most other sperm characteristics interact in a synergistic manner. Additionally, the patterns of synergism between S1 and S2 for abnormalities in capacitation, sperm-oolemma binding, and zona-free oocyte penetration are nearly identical. This suggests that these three defects are caused by mutation of the same gene within each sterility factor. These findings will not only be instrumental in matching the various t haplotype sperm defects to candidate genes for S1 and S2, but will facilitate a more comprehensive understanding of the cellular and genetic mechanisms underlying t haplotype male sterility.

Physical mapping of male fertility and meiotic drive quantitative trait loci in the mouse t complex using chromosome deficiencies

The t complex spans 20 cM of the proximal region of mouse chromosome 17. A variant form, the t haplotype (t), exists at significant frequencies in wild mouse populations and is characterized by the presence of inversions that suppress recombination with wild-type (+) chromosomes. Transmission ratio distortion and sterility are associated with t and affect males only. It is hypothesized that these phenomena are caused by trans-acting distorter/sterility factors that interact with a responder locus (Tcr(t)) and that the distorter and sterility factors are the same because homozygosity of the distorters causes male sterility. One factor, Tcd1, was previously shown to be amorphic using a chromosome deletion. To overcome limitations imposed by recombination suppression, we used a series of deletions within the t complex in trans to t chromosomes to characterize the Tcd1 region. We find that the distorter activity of Tcd1 is distinct from a linked sterility factor, originally called tcs1. YACs mapped with respect to deletion breakpoints localize tcs1 to a 1.1-Mb interval flanked by D17Aus9 and Tctex1. We present evidence for the existence of multiple proximal t complex regions that exhibit distorter activity. These studies demonstrate the utility of chromosome deletions for complex trait analysis.

Bypassing spermiogenesis for several generations does not have detrimental consequences on the fertility and neurobehavior of offspring: a study using the mouse

PURPOSE

This study was conducted to determine whether the omission of spermiogenesis and all prefertilization events for five generations in mice affects the fertility or behavior of offspring.

METHODS

Fifth-generation hybrid (C57BL/6 x DBA/2) mice were produced using round spermatid injection (ROSI). Control groups consisted of mice born after natural mating with and without sham operation. The growth, fertility, and behavior of offspring were compared. Behavior tests conducted assessed elementary reasoning (Krushinsky test), emotionality (Mouse Defense Test Battery), and spatial learning and memory (Morris water maze).

RESULTS

There were no significant differences in the growth and fertility of fifth-generation ROSI mice compared to natural fertilization mice. We also found no evidence of significant learning or behavioral deficits of the fifth-generation ROSI mice.

CONCLUSIONS

In this study, we found no evidence that bypassing the natural biological processes involved in spermiogenesis produces adverse effects on the growth, fertility, or behavior of mouse offspring.

New insights into the t-complex and control of sperm function

The mouse t-complex, located on chromosome 17, contains genes known to influence male, but not female, fertility. Although some t-complex genes are recessive lethals, t-chromosomes are maintained in the population by transmission ratio distortion. When male mice heterozygous for the t-chromosome mate with wild-type females, most offspring will possess the t-chromosome, indicating a link between t-complex genes and sperm function. Several proteins coded for by t-complex genes have been localised in the sperm flagellum, suggesting roles relating to motility. Another t-complex protein appears able to regulate the adenylyl cyclase/cAMP signal transduction pathway, known to play an important role in capacitation. Defective motility and/or failure to capacitate ("switch on") would result in poorly fertile or infertile spermatozoa. Given the existence of human homologues for many genes in the t-complex and the prevalence of "male factor" infertility, information obtained about the t-complex not only will provide insight into basic biological mechanisms but may be of future clinical relevance as well.