[Intravital selection of early mouse embryos by sex and karyotypic characteristics]

The possibility of live karyotyping by a single blastomere isolated at the 2-, 4-, and 8-cell stage has been investigated. It is expedient to use to this end a single blastomere isolated from a 4-cell embryo. Three rest blastomeres formed normal morulae or blastocysts upon cultivation during 44 or 68 hrs. When the isolated blastomeres were cultivated for 14-16 hrs in a medium 0.5 micrograms/ml colcemide, 97% of blastomeres were at the metaphase stage and 72% of chromosome plates were suitable for karyotyping. The prospects of the method proposed in experimental embryology and for selection of the early embryos of farm animals by sex are discussed.

Expression of a glucose-regulated cell surface protein in early mouse embryos

A 100,000-Da glucose-regulated surface protein (100K-GRP) has previously been isolated from the cell surface and culture medium of human fibroblasts. A rabbit antiserum directed against this protein reacts with the cell surface of both human and murine cultured cells and with a broad spectrum of mammalian tissues. It is shown, via indirect immunofluorescence, that this protein is also present on cells of the developing mouse embryo and can be detected as early as the 4-cell stage. The 8-cell embryo and morula show positive surface labeling; the inner cell masses of both the pre- and postimplantation blastocysts are also positive but the trophectoderm is not. At the 6-day egg cylinder stage, the embryonic and extra-embryonic ectoderm label intensely with the antiserum and visceral endoderm shows faint labeling. No labeling can be detected on parietal endoderm or on the trophoblastic giant cells invading the uterine decidua. However, the internal cells of the ectoplacental cone exhibit bright fluorescence. The same pattern is observed on 7- to 8.5-day embryos, except that at this stage no label is associated with the visceral endoderm. In addition, mesodermal cells emerging from the primitive streak are also labeled.

Spatial distribution of blastomeres is dependent on cell division order and interactions in mouse morulae

Spatial distribution of blastomeres was examined in 16- to 30-cell morulae obtained from aggregates of 1/2----1/2 and 1/2----2/4 blastomeres. The advanced blastomeres (2/4) contributed disproportionately more inner cells while there was a corresponding decline in the contribution from the delayed blastomere (1/2) so that a balance between the total number of inner and outer cells was retained. There was, however, no marked change in the relative number of outer cells. It is suggested that once formed, the inner more adhesive cells divide relatively faster than the outer cells whose behaviour is dictated by the inner cells. The outer less adhesive cells spread over the inner cells; cell spreading is incompatible with division. The degree to which cell spreading and retardation of division of outer cells occurs may be dictated by the number of inner cells present at any one time and this partly determines the entry of further cells inside. The suggested mechanism for cell allocation is highly flexible and, indeed, essential to encompass the wide variety of patterns of cell interactions and distribution observed in morulae. It is also proposed that the retardation of division of outer cells may trigger differentiation of trophectoderm by inducing endoreduplication and the blastomeres delayed from dividing for the longest period of time may mark down the abembryonic pole and establish the embryonic-abembryonic axis.

[Rhythmic processes in early embryogenesis timed by cell division]

he data on rhythmic processes in early embryogenesis coinciding with cell divisions are considered. Possible mechanisms which determine the rhythm frequency and are its motive power are discussed, as well as the role of individual rhythmic processes in the regulation of consecutive cell cycle events. A suggestion is put forward that these rhythmic processes are transformed during subsequent development in circum-hour rhythms of some biochemical, physiological and biophysical processes discovered in the cells and organs of adult organism.

Effect of warming rate on mouse embryos frozen and thawed in glycerol

Mouse embryos (8-cell) fully equilibrated in 1.5 M-glycerol were cooled slowly (0.5 degrees C/min) to temperatures between - 7.5 and - 80 degrees C before rapid cooling and storage in liquid nitrogen (-196 degrees C). Some embryos survived rapid warming (approximately 500 degrees C/min) irrespective of the temperature at which slow cooling was terminated. However, the highest levels of survival of rapidly warmed embryos were observed when slow cooling was terminated between -25 and -80 degrees C (74-86%). In contrast, high survival (75-86%) was obtained after slow warming (approximately 2 degrees C/min) only when slow cooling was continued to -55 degrees C or below before transfer into liquid N2. Injury to embryos cooled slowly to -30 degrees C and then rapidly to -196 degrees C occurred only when slow warming (approximately 2 degrees C/min) was continued to -60 degrees C or above. Parallel cryomicroscopical observations indicated that embryos became dehydrated during slow cooling to -30 degrees C and did not freeze intracellularly during subsequent rapid cooling (approximately 250 degrees C/min) to -150 degrees C. During slow warming (2 degrees C/min), however, intracellular ice appeared at a temperature between -70 and -65 degrees C and melted when warming was continued to -30 degrees C. Intracellular freezing was not observed during rapid warming (250 degrees C/min) or during slow warming when slow cooling had been continued to -65 degrees C. These results indicate that glycerol provides superior or equal protection when compared to dimethyl sulphoxide against the deleterious effects of freezing and thawing.

The calcium-dependent cell-cell adhesion system regulates inner cell mass formation and cell surface polarization in early mouse development

The monoclonal antibody ECCD-1 inhibits Ca2+-dependent cell-cell adhesion in teratocarcinoma cells, recognizing a cell surface component of MW 124,000. When mouse embryos at various preimplantation stages were cultured in the presence of ECCD-1, the compacted morphology of the 8- to 16-cell-stage embryos was destroyed. In these embryos, cell proliferation normally occurred and development of blastocyst-like vesicles was attained. However, these embryos did not contain inner cell mass (ICM). We found that ECCD-1 affects the pattern of polarization of the cell surface in late 8- and 16-cell-stage blastomeres, as detected by staining with fluorescence-labeled concanavalin A. In normal blastomeres, the pole was always apart from the cell-cell contact plane. In those cultured in ECCD-1, formation of the pole tended to be inhibited, and if observed, the pole was close to the cell-cell contact plane. We discuss the possible mechanisms for inhibition of ICM formation caused by blocking Ca2+-dependent cell-cell adhesion between blastomeres.

Cytoplasmic and cortical factors participating in cleavage furrow formation in eggs of three amphibian genera; Ambystoma, Xenopus and Cynops

A cytoplasmic factor and a cortical factor participating in cleavage furrow formation had been previously found in Cynops eggs (Sawai, 1972). These were investigated in the present study in Ambystoma and Xenopus eggs, by the method of cytoplasmic or cortical transplantation. Results were practically similar to those previously obtained with Cynops, indicating that in all the species of eggs during cleavage, the cytoplasm localizing along the cleavage furrow possessed furrow-inducing activity, and the cortex was competent to form the furrow in response to the activity of the cytoplasmic factor. In the present work, the species specificity of the two further factors was examined among Cynops, Ambystoma and Xenopus eggs, and the factors were found to act across species.

Maturation-promoting factor induces nuclear envelope breakdown in cycloheximide-arrested embryos of Xenopus laevis

We have studied the effect of maturation-promoting factor (MPF) on embryonic nuclei during the early cleavage stage of Xenopus laevis development. When protein synthesis is inhibited by cycloheximide during this stage, the embryonic cell cycle arrests in an artificially produced G2 phase-like state, after completion of one additional round of DNA synthesis. Approximately 100 nuclei can be arrested in a common cytoplasm if cytokinesis is first inhibited by cytochalasin B. Within 5 min after injection of MPF into such embryos, the nuclear envelope surrounding each nucleus disperses, as determined histologically or by immunofluorescent staining of the nuclear lamina with antilamin antiserum. The breakdown of the nuclear envelope occurs at levels of MPF comparable to or slightly lower than those required for oocyte maturation. Amplification of MPF activity, however, does not occur in the arrested egg as it does in the oocyte. These results suggest that MPF can act to advance interphase nuclei into the first events of mitosis and show that the nuclear lamina responds rapidly to MPF.

[Experimental study on the effect of acetylspiramycin on the fertilized ova]

Growth of fertilized mouse eggs treated with acetylspiramycin (ASPM) for 24 hours in their diplophase and octaplophase was observed morphologically. Changes in function of the fertilized cells in growth process were also examined, determining cell counts, mitotic index, and sister chromatid exchange as indices. These indices were all inhibited after treatment with ASPM. However, it seems that the effect was induced by H2SO4 which was used as solvent rather than by ASPM because growth inhibition and functional changes of cells were also caused by H2SO4. Therefore, it is thought that ASPM, at the concentration of 3-10 microgram/ml, has little effect on the development of fertilized eggs.

Establishment of embryonic axes in larvae of the starfish, Asterina pectinifera

In order to clarify the relationships between the first cleavage plane and the embryonic axes, early cleavage pattern of the fertilized eggs of the starfish. Asterina pectinifera was reexamined. It was ascertained that the polar bodies were formed at the site to which the germinal vesicle had closely located before the initiation of the meiotic division, and that the first cleavage plane passed near this site of polar body formation. While some of the early embryos of this starfish were observed to show various cleavage patterns during early cleavage stage, more than 70% of the embryos developed according to, so to say, the 'typical' cleavage pattern. Next, horseradish peroxidase (HRP) was injected into one of the blastomeres of the 2-cell- or 8-cell-stage embryos. The embryos were allowed to develop up to either the early gastrula or the early bipinnaria stage and stained to detect the descendants of the blastomere injected with HRP. In early gastrulae still retaining radial symmetry, the activity of HRP injected at the 2-cell stage was found only in one side of the embryo partitioned by one of the symmetrical planes. When one of the four blastomeres lying nearer to the polar bodies at the 8-cell stage was marked with HRP, its descendants constituted one quarter of the anterior part of the gastrula, and descendants of a blastomere opposite the polar bodies were found in the posterior region of the embryo. It was concluded that the animal-vegetal (AV) axis was pre-existing in the fertilized egg and that the first cleavage plane contained this primary axis. In early bipinnariae with their dorsoventral (DV) axes already established, the region of activity of the HRP injected at the 2-cell stage was still demarcated by a plane which passed through the AV axis, but the plane of the boundary had no fixed relation to the DV axis. The results indicate that the first cleavage plane does not necessarily correspond to the median plane of the starfish larva, unlike the case in sea-urchin eggs (Hörstadius & Wolsky, 1936). In other words, the DV axis of the starfish embryo is not predetermined in the fertilized egg, and might be established in the course of development through cell-to-cell interactions, while the AV axis is established mainly according to the pre-existing egg polarity.

Pattern formation in amphibian embryos prevented from undergoing the classical "rotation response" to egg activation

Fertile Xenopus laevis eggs were immobilized so that they were prevented from undergoing the "rotation response" to activation. Many of those unrotated eggs developed through organogenesis, indicating that egg rotation is not a prerequisite for normal early embryogenesis. Various aspects of the regulation of pattern formation were analyzed in unrotated eggs: It was discovered that a substantial rearrangement of yolk platelets occurred without affecting subsequent pattern formation. The germ plasm, however, remained localized in the vegetal hemisphere in inverted eggs. Cleavage furrows and the site of involution were both often observed in novel locations in inverted eggs which were prevented from rotating during activation.

Reassortment of cells according to position in mouse morulae

Sixteen-cell mouse morulae were disaggregated and blastomeres originally occupying outer or inner positions were separated. Outer, inner, or unsorted populations of blastomeres were labeled with either trinitrobenzene sulphonic acid (TNP) or fluorescein isothiocyanate (FITC) and individual blastomeres aggregated to unlabelled partially decompact eight- to ten-cell morulae. After up to 6 h in culture, the positions of the labelled blastomeres within the aggregates were examined. The combined results demonstrated that between 86 and 92% of outer cells remained on the surface of the aggregate and flattened into extensive polygonal shapes, whereas 76-77% of the inner cells had become engulfed by the host morula cells and retained their initial spherical shape. Using unsorted cells, 33-37% were internalised, which is compatible with the most recent estimates of the presence of six to eight inner cells at the 16-cell stage. The possibility that differential adhesiveness of the outer and inner cells is involved in the allocation of cells to the trophectoderm and inner cell mass of the blastocyst is discussed.

Suppression of male pronuclear movement in frog eggs by hydrostatic pressure and deuterium oxide yields androgenetic haploids

The disruptive effects of microtubule-specific agents on pronuclear movement illustrate the requirement of an intact cytoskeletal system for movement. In this study, we investigated the effects of high hydrostatic pressure and deuterium oxide (D2O) on fertilized Rana pipiens eggs during the time of pronuclear migration. The eggs were either pulsed for six min with 3000, 5000, or 7000 psi or placed for ten min in 80% D2O between the time of second polar body emission and first cleavage. Both treatments disrupted male pronuclear migration as shown by eccentric first cleavage furrows. Treatment of eggs prior to pronuclear association resulted in haploid production. The androgenetic origin of the haploid embryos was demonstrated using morphological and isozymal markers produced by the cross Rana pipiens female x Rana utricularia male. Eggs treated with D2O also yielded embryos with neural defects identical to those following ultraviolet irradiation. This study complements the recent reports on pressure-suppression of the second polar body and of first cleavage by showing that the selective suppression of microtubular function between these two events produces an entirely different set of genetic and developmental consequences.

Observations on the development of bovine morulae on various cellular and noncellular substrata

The objective was to determine the effect of various cell types on the development of bovine embryos in vitro. Morulae were collected from beef and dairy cows 4 to 5 d after the onset of estrus (d 0). Embryos were randomly allocated to nine treatments: (1) microdrops of Ham's F-10 medium (HF-10) under paraffin oil (HF-10); (2) HF-10 over a substratum of collagen without paraffin oil (HF-10/clg); (3) HF-10 with bovine uterine fibroblasts grown on a collagen substratum (HF-10/clg-fib); (4) Minimal Essential Medium (MEM) without paraffin oil (MEM); (5) microdrops of MEM under paraffin oil (MEM/oil); (6) MEM with bovine uterine fibroblasts (MEM/Buf; (7) MEM with bovine testicular fibroblasts (MEM/Btes); (8) MEM exposed to uterine fibroblasts for 24 h to condition the medium (MEM/Con), and (9) MEM with 1 mm cubes of bovine endometrial tissue (MEM/End). In all cases, media were supplemented with 10% (v/v) heat-treated fetal calf serum. Observations were made at 24 h intervals, with the stage of embryo development recorded. Morulae developed into expanded blastocysts more frequently (P less than .05) in HF-10, MEM, MEM/oil, MEM/Buf, MEM/Btes and MEM/Con than in HF-10/clg, HF-10/clg-fib and MEM/End. More (P less than .01) blastocysts hatched in MEM/Buf and MEM/Btes than in the other media. In addition, nine of 12 (MEM/Buf), eight of 11 (MEM/Btes) and two of two (HF-10/clg-fib) hatched blastocysts attached to the fibroblast monolayers, an observation that was uncommon in treatments without cells. These data suggest that the co-culture of bovine embryos with bovine fibroblasts in a superior system for promoting embryo hatching and attachment in vitro.

The foundation of two distinct cell lineages within the mouse morula

The division of single cells, isolated from an 8-cell mouse embryo, to give 2 x 1/16 cells has been studied by sampling cells for analysis at defined stages during and after the division. Cells were analyzed for evidence of polarity in their surface organization as assessed by fluorescent ligand binding and distribution of microvilli. Individual 1/8 cells are polarized. At division, most (82%) divide such that both the pole of ligand binding and the pole of microvilli are distributed to only one of the two daughter cells. A couplet is thereby formed with a large polar cell and a small apolar cell. Some 1/8 cells divide through the pole, generating a couplet of two polar cells, the poles being contiguous at the midbody. Elements of the surface polarity observed in the 1/8 cells can be found at all stages throughout division. Analysis of couplets of cells derived from newly formed 16-cell morulae also reveals that most consist of a polar:apolar pair and some consist of a polar:polar couplet in which the poles are contiguous at the midbody. The results indicate that two distinct cell populations are generated at division. These cells are known to occupy different positions within the morula, the polar cells being peripheral and the apolar cells being central. Since peripheral and central cells give rise to trophectoderm and inner cell mass in the blastocyst, we therefore suggest that the foundation of the trophectoderm and inner cell mass lineages may occur by a process of differential inheritance. This conclusion supports the recently proposed polarization hypothesis, which is discussed.

[The first cleavage of tubal sheep eggs after fertilization with epididymal or ejaculated spermatozoa]

Prealpes ewes (N = 40) were inseminated with mature (ejaculated or epididymal cauda) or immature (epididymal corpus) spermatozoa deposited in the uterine cavity at the time of an induced ovulation (61 hrs. after PMSG injection). Intratubal eggs, recovered and examined either 38 or 48 hrs. later, showed significant differences in segmentation depending on the degree of epididymal maturation of the spermatozoa. Proportion cleaved: 85% of eggs were cleaved after insemination with mature spermatozoa and only 30% after immature spermatozoa were used. Stage of cleavage: 48 hrs. after insemination with mature spermatozoa, 87% eggs were beyond the 4-cell stage, versus 0% after immature spermatozoa.

Morphogenetic analysis of changing cell associations following release of 2-cell and 4-cell mouse embryos from cleavage arrest

Two-cell and four-cell mouse embryos were cultured in Cytochalasin D (CD) for 40-48 h. They were fixed for light and electron microscopy at various times after washing off the CD. Cleavage-arrested embryos in CD had well separated blastomeres but by 1 h from washing the embryos had compacted, in most cases without undergoing cell division. By 2 h after release from arrest one blastomere of the 2-cell arrested embryos had become crescent shaped and at 4-5 h the crescent-shaped blastomere had started to spread over the surface of the other rounded blastomere. This process continued until by 16-24 h from explantation to fresh medium one blastomere had almost completely engulfed the other. A similar process occurred in 4-cell arrested and released embryos. At this stage the embryos had accumulated fluid and become blastocyst-like vesicles. In 20% of 2-cell and 4-cell embryos one or two blastomeres underwent one cell division after release from arrest. Serial sections of these embryos lead to the conclusion that one or both progeny of the first cell to divide tended to be engulfed by the later dividing or non-dividing cell(s). These results are discussed in relation to the differentiation of ICM and trophectoderm in blastocysts.

Effects of viral exposure of the two-cell mouse embryo on cleavage and blastocyst formation in vitro

The effect of viral exposure of two-cell mouse embryos on their capacity to undergo subsequent cleavage and blastocyst formation in vitro was determined. Exposure to Coxsackie viruses B-4 and B-6, reovirus type 2, influenza virus type A, mouse cytomegalovirus, adenovirus type 5, and mouse adenovirus resulted in statistically significant inhibition of blastocyst formation. Development in vitro was unaffected by exposure to ECHO virus type 11, attenuated poliomyelitis virus type 2, parainfluenza virus type 1, mumps, rubella, and herpes simplex viruses types 1 and 2. Blastocyst formation was also unaffected by exposure of embryos to mouse interferon in a concentration 24 units/ml of culture fluid. Coxsackie virus B-4 was recovered from exposed embryos.