Role of calmodulin in blastocyst formation in the mouse

Calcium-sensing receptor (CASR) is involved in porcine in vitro fertilisation and early embryo development

It has been demonstrated that extracellular calcium is necessary in fertilisation and embryo development but the mechanism is still not well understood. The present study mainly focussed on the extracellular calcium effector called the calcium-sensing receptor (CASR) and examined its expression in porcine gametes and embryos and its function during fertilisation and early embryo development. By using reverse transcription polymerase chain reaction, CASR was found to be expressed in porcine oocytes, spermatozoa and embryos at different developmental stages. Functionally, medium supplementation with a CASR agonist or an antagonist during in vitro fertilisation (IVF) and in vitro culture (IVC) was tested. During fertilisation, the presence of a CASR agonist increased sperm penetration rate and decreased polyspermy rate leading to an increased normal fertilisation rate. During embryo development, for the IVF embryos, agonist treatment during IVC significantly increased cleavage rate and blastocyst formation rate compared with the control group. Furthermore, parthenogenetically activated embryos showed similar results with lower cleavage and blastocyst formation rates in the antagonist group than in the other groups. It was concluded that CASR, as the effector of extracellular calcium, modulates porcine fertilisation and early embryo development.

Annotation of nerve cord transcriptome in earthworm Eisenia fetida

In annelid worms, the nerve cord serves as a crucial organ to control the sensory and behavioral physiology. The inadequate genome resource of earthworms has prioritized the comprehensive analysis of their transcriptome dataset to monitor the genes express in the nerve cord and predict their role in the neurotransmission and sensory perception of the species. The present study focuses on identifying the potential transcripts and predicting their functional features by annotating the transcriptome dataset of nerve cord tissues prepared by Gong et al., 2010 from the earthworm Eisenia fetida. Totally 9762 transcripts were successfully annotated against the NCBI nr database using the BLASTX algorithm and among them 7680 transcripts were assigned to a total of 44,354 GO terms. The conserve domain analysis indicated the over representation of P-loop NTPase domain and calcium binding EF-hand domain. The COG functional annotation classified 5860 transcript sequences into 25 functional categories. Further, 4502 contig sequences were found to map with 124 KEGG pathways. The annotated contig dataset exhibited 22 crucial neuropeptides having considerable matches to the marine annelid Platynereis dumerilii, suggesting their possible role in neurotransmission and neuromodulation. In addition, 108 human stem cell marker homologs were identified including the crucial epigenetic regulators, transcriptional repressors and cell cycle regulators, which may contribute to the neuronal and segmental regeneration. The complete functional annotation of this nerve cord transcriptome can be further utilized to interpret genetic and molecular mechanisms associated with neuronal development, nervous system regeneration and nerve cord function.

The ability to develop an activity that transfers histones onto sperm chromatin is acquired with meiotic competence during oocyte growth

Following fertilization, the oocyte remodels the sperm chromatin into the male pronucleus. As a component of this process, during meiotic maturation, oocytes develop an activity that transfers histones onto sperm DNA. To further characterize this activity, we tested whether oocytes at different stages of growth could, upon entry into metaphase of maturation, transfer histones onto sperm DNA, as judged by chromatin morphology and immunocytochemistry. Meiotically competent growing oocytes, which spontaneously enter metaphase upon culture, transferred histones onto sperm chromatin, whereas incompetent oocytes did not, even when treated with okadaic acid to induce germinal vesicle breakdown (GVBD) and chromosome condensation. When incompetent oocytes were cultured until they acquired the ability to undergo GVBD, only a small proportion also developed histone-transfer activity during maturation. However, this proportion significantly increased when the oocytes were cultured as granulosa-oocyte complexes. The failure of histone-transfer activity to develop in incompetent oocytes treated with okadaic acid was not linked to low H1 kinase activity nor rescued by injected histones. Because competent, but not incompetent, oocytes produce natural calcium oscillations, incompetent oocytes were exposed to SrCl2. One-third of treated oocytes produced at least one Ca2+ oscillation and, following insemination, the same proportion transferred histones onto sperm DNA. Histone transfer did not occur in oocytes pretreated with the Ca2+ chelator, BAPTA-AM. These results indicate that the ability to develop histone-transfer activity is acquired by growing oocytes near the time of meiotic competence, that it is separable from this event, and that it may be regulated through a Ca2+-dependent process.

Effect of intrauterine injection of chlorpromazin on implantation in the rat

In rats, injection of chlorpromazin hydrochloride (CPZ), a calmodulin antagonist, to each uterine horn had a significant (87%) anti-implantation effect and 100% antifertility effect. Both of these rates were zero in the saline control group. Polyacrylamide gel electrophoresis analysis of the uterine fluid showed a decrease in the protein content and certain changes in its chemical composition, in particular, a marked reduction in the number of bands of estradiol-induced 70 kD proteins in the experimental group. No significant difference was found in the ovarian weight and the serum estradiol (E2) and progesterone (P) levels between the two groups. These results suggest that calmodulin influences the process of implantation and this effect is not directly related to the serum concentrations of E2 and P. It is believed that CPZ probably exerted its anti-implantation effect by a direct action on the uterus.

Immunocytochemical detection and spatial distribution of myosin light-chain kinase in preimplantation mouse embryos

As a follow-up to our previous study on the role of myosin light-chain kinase (MLCK), a Ca2+/calmodulin-dependent enzyme, in the development of preimplantation mouse embryos, we examined the presence and pattern of distribution of MLCK during preimplantation development of the mouse by whole-mount, indirect immunocytochemistry and by Western blotting, using a monoclonal antibody against MLCK. At all stages of preimplantation development, the nucleus was brightly stained with an unstained region around the nucleus, and regions near the cell membrane were also brightly stained. Using the optical sectioning capability of the confocal laser scanning microscope, we found that, up to the eight-cell stage, the regions of cell contact were mostly unstained, but along with the process of compaction, cell contact regions showed a clear staining pattern along with clearing of the cytoplasm. During formation of the blastocyst, a ring of immunofluorescence was found at the margin of the blastocoel. In the blastocyst, cells of the inner cell mass were less immunofluorescent than trophectoderm cells. These staining results appear to be due to specific immunoreaction between MLCK and the antibody, because the staining patterns were abolished when the antibody was preabsorbed by MLCK purified from chicken gizzard smooth muscle. In Western blotting of blastocysts, we found a band at 130 kD. We also show by immunoblotting and immunohistochemistry of various mouse tissues that the antibody used in this study has cross-reactivity to MLCK of various muscle and non-muscle tissues of the mouse. The presence and spatial distribution of MLCK at various stages of preimplantation development of the mouse suggest that it could play a crucial role in the regulation of the contractile events involved in the initial differentiation that occurs during formation of the mouse blastocyst.

Regulation of preimplantation development of mouse embryos: effects of inhibition of myosin light-chain kinase, a Ca2+/calmodulin-dependent enzyme

We have examined the effects of ML-9 and wortmannin, which are, respectively, specific reversible and irreversible inhibitors of myosin light-chain kinase, a Ca2+/calmodulin-dependent enzyme, on preimplantation development of the mouse in an attempt to establish a regulatory role for this enzyme in preimplantation development. When late two-cell stage embryos were treated continuously with ML-9 or wortmannin at a concentration of 0, 1, 5, 10, or 15 microM, compaction and formation of the blastocyst were inhibited in a dose-dependent manner. Stage-specific treatment with ML-9 at 25 microM induced stage-specific responses of embryos after the eight-cell stage during the processes of compaction and cavitation. These morphological responses included aborted compaction, decompaction of compacted embryos, and the inability of embryos to form a cavity. These morphological effects were reversible, but, since cell proliferation was inhibited, the "recovered" embryos were small. Counting of cells on day 4 of culture, in both continuously treated and stage-specifically treated embryos, showed that the effect of ML-9 on cell proliferation was also dose-dependent. Wortmannin also had stage-specific effects at 15 microM, but these effects were irreversible and were more deleterious than those of ML-9. With neither inhibitor was there any apparent effect at the two-cell or the four-cell stage, although wortmannin inhibited cell division when applied stage-specifically at the four-cell stage. These results indicate that myosin light-chain kinase may be an important enzyme in the first steps of differentiation and in the maintenance of the differentiated state during preimplantation development of the mouse.

The preimplantation mouse embryo is a target for cannabinoid ligand-receptor signaling

Using a reverse transcription-coupled PCR, we demonstrated that both brain and spleen type cannabinoid receptor (CB1-R and CB2-R, respectively) mRNAs are expressed in the preimplantation mouse embryo. The CB1-R mRNA expression was coincident with the activation of the embryonic genome late in the two-cell stage, whereas the CB2-R mRNA was present from the one-cell through the blastocyst stages. The major psychoactive component of marijuana (-)-delta-9-tetrahydrocannabinol [(-)-THC] inhibited forskolin-stimulated cAMP generation in the blastocyst, and this inhibition was prevented by pertussis toxin. However, the inactive cannabinoid cannabidiol (CBD) failed to influence this response. These results suggest that cannabinoid receptors in the embryo are coupled to inhibitory guanine nucleotide binding proteins. Further, the oviduct and uterus exhibited the enzymatic capacity to synthesize the putative endogenous cannabinoid ligand arachidonylethanolamide (anandamide). Synthetic and natural cannabinoid agonists [WIN 55,212-2, CP 55,940, (-)-THC, and anandamide], but not CBD or arachidonic acid, arrested the development of two-cell embryos primarily between the four-cell and eight-cell stages in vitro in a dose-dependent manner. Anandamide also interfered with the development of eight-cell embryos to blastocysts in culture. The autoradiographic studies readily detected binding of [3H]anandamide in embryos at all stages of development. Positive signals were present in one-cell embryos and all blastomeres of two-cell through four-cell embryos. However, most of the binding sites in eight-cell embryos and morulae were present in the outer cells. In the blastocyst, these signals were primarily localized in the mural trophectoderm with low levels of signals in the polar trophectoderm, while little or no signals were noted in inner cell mass cells. These results establish that the preimplantation mouse embryo is a target for cannabinoid ligands. Consequently, many of the adverse effects of cannabinoids observed during pregnancy could be mediated via these cannabinoid receptors. Although the physiological significance of the cannabinoid ligand-receptor signaling in normal preimplantation embryo development is not yet clear, the regulation of embryonic cAMP and/or Ca2+ levels via this signaling pathway may be important for normal embryonic development and/or implantation.

Similar responses to pharmacological agents of 1,2-OAG-induced compaction-like adhesion of two-cell mouse embryo to physiological compaction

A comparison was made of responses to pharmacological agents between cell adhesion induced by an activator of Ca(2+)-phospholipid-dependent protein kinase (PKC) and physiological compaction in mouse embryos. An activator of PKC, 1-oleoyl-2-acetyl-sn-glycerol (1,2-OAG) induced the compaction-like adhesion of cells in two-cell embryos within 5-10 min and the adhesion lasted during the course of treatment for 1 h. W-7 and W-5 (calmodulin antagonists) and cytochalasin B and cytochalasin D (inhibitors of the polymerization of microfilaments) each completely interfered with the 1,2-OAG-induced adhesion of cells. Two-cell embryos having once shown evidence of cell adhesion in response to 1,2-OAG were decompacted when they were transferred to a medium that contained 1,2-OAG and any one of the agents described above. Colchicine and colcemid (inhibitors of the polymerization of microtubules) and tunicamycin (an inhibitor of N-linked protein glycosylation) each had no effect on the 1,2-OAG-induced adhesion of cells. In Ca(2+)-free medium, treatment with 1,2-OAG failed to induce any cell adhesion. These results are very similar to those reported for physiological compaction at the late eight-cell stage. Thus, the compaction-like adhesion of cells in mouse embryos at the two-cell stage appears to be a calmodulin-dependent process, requiring assembled microfilaments and extracellular Ca2+ ions but not microtubules or N-linked glycoproteins as is the case for the physiological compaction.

3H-uridine incorporation in early porcine embryos

The present study investigated the ontogeny of 3H-uridine incorporation into RNA as a measure for RNA synthesis in preimplantation porcine embryos from the two-cell stage up to the stage of the newly hatched blastocyst. A total of 568 embryos were cultured in vitro for 3 hr in medium (KRB plus lamb serum) containing 9 microM 3H-uridine. After disruption of cell membranes, RNA was isolated on DEAE cellulose filters, and the radioactivity was taken as a measure for the rate of RNA synthesis. No RNA synthesis was detected at the two-cell stage. From the four-cell to the morula stage, 3H-uridine incorporation per embryo increased about ninefold (P less than 0.001); in blastocyst stages, the increase between developmental stages was not statistically significant. Hatched blastocysts had the highest genomic activity. On a per cell basis, 3H-uridine incorporation was not different from the four-cell stage up to the zona pellucida-intact blastocyst and amounted to 0.29-0.37 fmol 3H-uridine incorporation/cell/3 hr. In hatched blastocysts, 3H-uridine incorporation per blastomere was increased (P less than 0.01 compared with younger stages) and amounted to 0.86 fmol 3H-uridine incorporation/cell/3 hr. It is concluded that 1) the rate of uridine incorporation depends on the cell stage in zona pellucida-intact porcine embryos and 2) uridine incorporation per blastomere is significantly increased in hatched blastocysts compared with earlier stages.

Stage-specific response of preimplantation mouse embryos to W-7, a calmodulin antagonist

Involvement of calmodulin-dependent processes in preimplantation development of mouse embryos was studied with the use of N-(6-aminohexyl)-5-chloro-1-naphthalenesulfonamide (W-7), a specific antagonist of calmodulin. At 25 microM, W-7 interfered with compaction of eight-cell embryos, caused decompaction of compacted eight-cell embryos, inhibited cavitation of late morulae, and caused collapse and degeneration of blastocysts. These effects of W-7 appear to be due to specific inhibition of calmodulin-dependent processes, because W-5, a less active analogue of W-7, was less effective in interfering with development; at 25 microM, W-5 had only a slight effect on compaction and had no effect on blastocyst formation, maintenance of blastocoels, or post-blastocyst development. In addition to the developmental effects just described, W-7 inhibited cell proliferation in four-cell embryos and reduced cell numbers of morulae after treatment at the two- to eight-cell stages. There was a marked increase in embryos' sensitivity to W-7 at the late morula stage, and the sensitivity increased further as embryos developed into blastocysts; the effects of W-7 were largely reversible after treatment at the two-cell through the compacted eight-cell stages, but not after treatment at the late morula or blastocyst stage. At the blastocyst stage, inner cell mass cells appeared to be slightly more resistant to W-7 than trophectoderm cells. This differential sensitivity became more pronounced at the late blastocyst stage: after 3.5-4-h exposure of late blastocysts to 25 microM W-7, all trophectoderm cells degenerated but most of the inner cell masses survived. From these results it appears that calmodulin-dependent processes are involved in development of mouse embryos at all of the preimplantation stages examined.

Spectrin and calmodulin in spreading mouse blastomeres

The role of spectrin and its association with calmodulin in spreading mouse blastomeres was investigated. Embryonic spectrin binds 125I-calmodulin in a calcium-dependent fashion in the blot overlay technique. Double-labeling experiments show coordinate redistribution of spectrin and calmodulin in blastomeres preparing to undergo active spreading movement. At this stage cortical spectrin staining is lost from the region of cell-substrate contact and spectrin and calmodulin become concentrated in two structures closely associated with the contacted region: a group of spherical bodies located on the cytoplasmic side of the cortical layer and a subcortical ring that marks the perimeter of the contacted region. The localization pattern of spectrin and calmodulin is also coordinated with that of actin and myosin. The results suggest that spectrin plays a role in the spreading of blastomeres and that this function may involve linkage of spectrin, calmodulin, and the cortical contractile apparatus.

Viability of blastocysts produced by aggregation of two half-embryos in the mouse

Although methods for production of chimeras from early cleavage stages have been well established, little research has been directed toward production of genetically identical chimeric offspring. This study was designed to examine survival of blastocysts produced by aggregation of two halved eight-cell stage embryos from two different mouse strains. Four blastomeres of an eight-cell embryo from a pigmented strain were aggregated with four blastomeres of an eight-cell embryo from a nonpigmented strain. Aggregates were cultured for 48 h and transferred as blastocysts to synchronized recipients of three treatment groups. Viability was determined by examining the number of offspring produced relative to the number of blastocysts transferred. Thirty-nine pups were born from 375 transferred blastocysts (10%), with 16 pups displaying coat-color chimerism. Both nonmanipulated eight-cell embryos cultured for 48 h (P < 0.05) and chimeric blastocysts (P < 0.001) displayed lower embryo survival after transfer to recipients than noncultured, nonmanipulated blastocysts used as controls. Viability of chimeric blastocysts was also lower than that of nonmanipulated embryos cultured for the same period and transferred to the same recipients (P < 0.001). Although posttransfer survival of chimeric blastocysts was low, the birth of morphologically normal offspring demonstrated that production of chimeras from half embryos was compatible with survival. Improvements in this procedure may be useful for production of tenetically identical chimeras from outbred populations, such as those commonly found in domestic livestock species.