Embryonic Disc Research Articles

Yolk distribution and utililization during early development of a teleost embryo (Brachydanio rerio)

ABSTRACT The work of Oppenheimer (1934, 1936) and Tung (1955, see also Devillers, 1961) suggests that an embryo such as Fundulus, a marine teleost, explanted at early cleavage (two-cell stage) is more dependent upon the amount of periblast yolk included in an explant than is an embryo that is more advanced prior to explanation. In other words, ‘if it (the embryo) is explanted before a so-called critical stage, the blastoderm turns into a hyperblastula (a non-differentiated mass of cells); if it is explanted after that, it undergoes differentiation. The critical stage corresponds to eight blastomeres in Carassius, thirty-two in Fundulus, and a young blastula in Salmo’ (Devillers, 1961, p. 391). The zebrafish, Brachydanio rerio, with a smaller egg than these fish, has not been characterized by explantation. Devillers, in summary, states that ‘these results mean that a substance indispensable for differentiation exists in the yolk sphere’ (p. 392). He continues, ‘On the other hand, how this hypothetical material may reach the blastoderm needs to be explained. The base of the blastoderm is in direct contact with the periblast in the early stages; later on, this syncytium ‘buds’ off blastomeres that add themselves to the embryonic disc’ (p. 397). He then asks the question ‘but then how can one explain that in later stages the syncytium can still impose an orientation on the germ? Are diffusing organizing substances involved?’ (p. 397).

Effect of steroid hormones on biochemical characteristics of blastocysts in ovariectomized rabbits.

AbstractGroups of nulliparous pregnant rabbits were bilaterally ovariectomized on the third, fifth, sixth or seventh days of gestation; some groups were then treated daily with 40 mg of progesterone alone or with 4 mg progesterone alone or in combination with estradiol at a ratio of 1:400 or 1:4000. Animals ovariectomized 3 days post coitum (p.c.) were autopsied four days later; those ovariectomized five, six, or seven days p.c. were autopsied 24 hours later. The number of viable blastocysts per doe was greatly decreased following ovariectomy; however, the number was increased by treatment with progesterone alone or in combination with estradiol (1:400 or 1:4000). The weight of blastocyst and embryonic matter (trophoblast and embryonic disc), and the volume of blastocoelic fluid in the blastocyst at six or seven days p.c. were neither affected by ovariectomy nor by injection of 4 mg of progesterone. The weight of the blastocysts was significantly reduced when ovariectomy was performed seven days p.c. The concentration of the biochemical compounds in the blastocoelic fluid was not altered by ovariectomy at five or seven days p.c. In contrast, the concentration of glucose, lactic acid, protein N and nonprotein in the blastocyst was greatly lowered by ovariectomy at six days p.c., being partly alleviated by daily injections of progesterone, alone or in combination with estradiol. Ovariectomy at three days p.c. was no more detrimental than later ovariectomy if steroids were administrated.

Cytodifferentiation and embryogenesis in cell colonies and tissue cultures derived from ova and blastocysts of the rabbit

The ability of cells from various stages of preimplantation rabbit embryos to form colonies in vitro has been studied, with a view to obtaining large populations of embryonic cells which retain a capacity for further differentiation in response to specific stimuli. When the zona pellucida was left intact, all cleavage stages developed to blastocysts. After enzymatic removal of the zona pellucida several cleavages occurred, the number increasing with the age of the embryo. In colonies derived from morulae, differentiation of trophoblastic cells which attached to the substratum occurred, and embryonic cells formed a small mass on top of these. Cleavage also continued in blastomeres of embryos disaggregated with trypsin. Colonies of unattached cells were formed, or spontaneous reaggregation into morulae and subsequent blastocyst formation occurred. When, after enzymatic removal of the zona pellucida, adhesion of blastocysts to the substratum was encouraged, the trophoblast cells spread out in a flat sheet leaving the embryonic disc on the upper surface. The embryonic cells multiplied and migrated over the trophoblastic layer and differentiation of cell types occurred. These cell were unable to migrate beyond the trophoblast and none became permanently established in culture. Cells from the embryonic disc were shown to be unable to attach to inorganic substrata but able to attach to and multiply on reconstituted collagen. When embryonic discs were freed from trophoblast and explanted onto this surface, dense homogeneous masses of cells developed, from which in a few instances monolayers of cells migrated out. After trypsinization some of these outgrowths have given rise to primary cell cultures which can be maintained and serially transferred in vitro. Primary cell strains have also been established from single cell suspensions obtained by disaggregating isolated embryonic discs and plating onto collagen coated surfaces. Several primary cell strains differing in both morphological appearance and some biochemical features were derived in these ways and are being kept in continuous culture. Some have continued to divide rapidly and have remained euploid after many months in culture.

GROWTH AND SURVIVAL OF BLASTOCYSTS IN THE DOMESTIC RABBIT

Summary. A total of 180 nulliparous rabbits was bred, bilaterally ovariectomized 2 or 4 days post coitum, and injected daily with 0·5, 0·75, 1, 4 or 40 mg of progesterone alone or in combination with oestradiol at a ratio of 1 : 400 or 1 : 4000. Uninjected, unilaterally and subtotally ovariectomized rabbits and progesterone-treated intact animals served as controls. The animals were autopsied at 6 days post coitum and 1111 blastocysts were recovered, examined for their normality and their diameters measured. The length and weight of uterus were affected neither by ovariectomy nor by the dose of injected progesterone. Intact does had an average of 6·6 to 9·0 viable blastocysts and 0·3 to 0·6 degenerating blastocysts. Ovariectomized does had an average of 4·1 to 10·2 viable blastocysts and 0 to 2·2 degenerating blastocysts. In ovariectomized does the percentage of viable blastocysts, the size of blastocysts and diameter of embryonic disc were decreased when the daily dose of progesterone was less than 1 mg and when oestradiol was combined with progesterone at a ratio of 1 : 400. There was no quantitative relationship between dosage of progesterone on one hand and percentage of viable blastocysts, size of blastocysts and diameter of embryonic disc on the other hand. Salpingectomy, unilateral ovariectomy, subtotal ovariectomy or administration of progesterone in intact rabbits had no significant effect on viability and size of blastocyst or diameter of embryonic disc.

GESTATION IN SALPINGECTOMIZED-OVARIECTOMIZED PROGESTERONE-TREATED RABBITS.

SummaryNulliparous rabbits were bred, ovariectomized and salpingectomized bilaterally at 3 1/2 days post coitum, injected daily with 4 mg of progesterone and autopsied at 6 days post coitum. The blastocysts were recovered, examined for their normality and their diameters measured. Some salpingectomized-ovariectomized animals that were allowed to term were laparotomized at 9 days post coitum, to count and measure implantation swellings. Control groups were subjected to sham operations. The percentage of viable blastocysts to the total number of corpora lutea varied from 52 to 90. The percentage of viable blastocysts varied from 89 to 100. The viability of blastocysts was not affected by ovariectomy with or without salpingectomy. Ovariectomy with or without salpingectomy reduced the percentage of viable blastocysts expressed to number of corpora lutea. Groups did not differ significantly in the outer diameter of blastocysts and in the diameter of embryonic disc. There was great variability within group and ...

Effect on the Early Embryo of Agents Administered to the Mother

A relatively simple and rapid histological technique for studying the action upon the pre-implantation rabbit embryo (blastocyst) of maternally transmitted agents has been developed. Flat-mounts are prepared from rabbit blastocysts recovered from pregnant animals that have received various treatments and are compared with embryos from normal untreated rabbits. Photomicrographs show the changes in the embryonic disk as produced by the treatment of pregnant animals with doses of 6-mercaptopurine E39 soluble thalidomide and phthaloyl-DL-isoglutamine that were incapable of affecting maternal health. The possibility of the flat-mount technique as an additional and promising test-object for the study of growth-modifying and chemotherapeutic substances is easily envisaged.

Luteal Function as Related to Pituitary and Ovarian Cytology and Embryo Development in the Bovine

Summary Embryos recovered 15 days after insemination from 20 of 27 untreated Holstein heifers and those recovered from 18 of 43 heifers treated daily with 7 U.S.P. units of oxytocin per hundredweight per day did not differ in total length, embryonic disc size, or mesodermal development attained. No embryos were recovered from animals with less than 100 µg. of total progesterone in their corpora lutea; normal embryo development appeared possible when the level of luteal progesterone was above this figure. The weights of the corpora lutea of the 15 oxytocin-treated heifers which had precocious ovulations were significantly (P

The Action of Various Agents upon the Rabbit Embryo

ABSTRACT A study was made of the action upon the rabbit embryo of various agents administered to pregnant animals in doses which did not seriously upset maternal health. The pre-implantation blastocyst, examined as a flat mount, was the principal object of study, but observations were also made on ovulation, fertilization, cleavage, nidation, and subsequent phases of pregnancy. To facilitate comparison between embryos from normal and treated animals 5-to 7-day-old blastocysts from untreated animals, grouped according to size, were classified into 6 developmental stages, depending upon the degree of maturity of the embryonic disc. Additional procedures which served to evaluate the condition of blastocysts and their uterine environment were: mitotic counts made in the abembryonic part of the trophoblast, chemical determinations of certain characteristic constituents of blastocyst fluid, and measurement of carbonic anhydrase activity in the endometrium. . The experimental agents comprised hormones, colchicine derivatives, several polyfunctional alkylating compounds, metabolic analogues, a sulphonamide inhibitor of carbonic anhydrase, and substances endowed with teratogenic, hepatotoxic, radiation-protective, and hypoglycaemia-inducing properties; total body exposure to X-rays was also investigated. Results obtained at various stages of pregnancy with the different treatments are described and discussed; several results relating to blastocysts are illustrated by photomicrographs. Among significant general findings emerging from the study are: the speed with which exogenous agents are transmitted to embryos even before uterine attachment; differential drug sensitivity, frequently evident in the pre-implantation blastocysts, as between the embryonic disc and trophoblast, the former usually being more susceptible; and variability in response, both individual and between litters, of the embryos to parenterally administered agents. It is suggested that the blastocyst flat mount preparation could be adapted as a conveniently rapid and simple procedure for the screening of cytostatic and other growth-modifying agents.

Development of the embryonic covernings in the scorpion Buthus quinquestriatus (H.E.).

DURING the period of proliferation of the embryonic disk of the scorpion (Buthus quinquestriatus (H.E.)), an amnio-serosal fold appears at the anterior periphery (Fig. 1). The posterior margin of the embryonic disk up to this stage does not show any trace of either the serosa or the amnion. This is contrary to the findings of Kowalevsky and Schulgin1, who claimed that the amnio-serosal fold, in Androctonus ornatus, arises simultaneously around the whole margin of the embryonic disk.

Cranial chordoma.

CHORDOMA is a fairly rare tumor derived from notochordal remnants, which are found along the craniosacrococcygeal axis. It is locally malignant. Most frequently it is found originating in the sacrum or cranium.¹Its consideration in differential diagnosis of intracranial and nasopharyngeal tumors is sufficient reason to report a new case together with a brief outline of the nature of the tumor and the disease. <h3>EMBRYOLOGY</h3> A proper understanding of the nature of the tumor necessitates a brief discussion of the embryology of the notochord.² The notochord has as its anlage a rodlike mesodermal structure, growing forward from a knob of cells at the head end of the primitive streak. This is a thickened band of ectoderm, which occupies the midplane of the embryonic disk. The latter is present at the end of the second week and is the result of the apposition of the floor of the early amnion sac

A series of potentially abortive ova recovered from fertile women prior to the first missed menstrual period

Over a period of ten years, twenty-eight early conceptuses have been found in a group of 136 potentially pregnant women of known fertility who submitted to hysterectomy for a variety of therapeutic reasons. Twelve of these early human ova were abnormal and of these seven were certainly destined to abort. Four of the latter might not even have caused clinical evidence of pregnancy because of their extreme abnormality.The ova destined to abort, either with or without evidence of their ability to produce clinical pregnancy, showed such fundamental defects as multinucleated blastomeres, absence of embryonic disc and/or chorionic cavity, or profound hypoplasia of the future placental tissue. None of these patients in whom abnormal ova were found showed any clinical or pathological evidence that maternal environment per se played any part in the production of the abnormal ovum. In other words, the endometrium was normal in all cases. The evidence, such as it is, indicates that the defective fertilized ovum is due to intrinsic “ “germ plasm” quality rather than to its environment and is the main factor in the production of spontaneous abortion.

Effects of the flexed‐tailed gene on the development of the house mouse

AbstractThe flexures in the flexed‐tailed mouse consist of unilateral fusions of adjacent vertebrae. Fusions, if complete, produce straight stiff segments.In normal mouse embryogeny, the precartilage cells surrounding the developing nucleus pulposus of the embryonic intervertebral disk in the proximal tail region begin to elongate and become fiber‐like at about 14 days after fertilization. In the flexed mouse, such differentiation fails to take place on one side of an affected disk, and these cells develop through cartilage to bone. At such a point there is frequently a bend in the notochordal axis. Other abnormalities of the notochord have been observed. These are not the cause of the flexures.The gene for flexed tail also produces two effects more general in their expression. First, it slows the growth of the vertebral column as indicated by the shorter vertebrae of the proximal tail region. This is observable 13 days after fertilization. Second, it produces an embryonic anemia which is already in existence at 14 days after fertilization. It is postulated that the flexures are due to the retardation of growth at a time which is critical for the intervertebral disks. Whether this retardation is the primary effect of the gene and produces the anemia, or whether the anemia is primary and produces the retardation, the data do not show.

On the Phenomenon of the Fusion of the Epiblastic Layers in the Rabbit and in the Frog.

ABSTRACT In my paper upon the early stages of the development of the rabbit I have given evidence in support of the views held by Balfour and Heape concerning the fate of the outer layer of epiblast over the embryonic disc of the rabbit embryo of the seventh day. The two layers of epiblast gradually fuse together, and cells from each take part in the formation of the permanent epiblast.

A Rare Form of the Blastoderm of the Chick, and its Bearing on the Question of the Formation of the Vertebrate Embryo

ABSTRACT In the summer of 1878, while in Leipsic, I obtained a blastoderm of the chick, which presented at least one unusual and very remarkable feature. The egg had been kept in an incubator, at a temperature of 37° to 38° C., for eighteen hours. After cutting away a portion of the shell and removing as much of the white of the egg as could be done without injury to the embryonic disc, the remainder of the egg, while still in the shell, was carefully dropped into a bowel of nitric acid (10%). The embryonic portion was then freed from the coagulated white by the aid of a feather, and, after fifteen minutes’ immersion, was carefully cut around by sharp scissors and floated into a watch-glass. The vitelline membrane was then removed by the aid of pincers, and the yolk detached by gently shaking the blastoderm in the watch-glass. The acid was next turned off and replaced with distilled water, several times renewed. After being thus thoroughly washed from the acid it was stained in an aqueous solution of carmine, then passed through several grades of alcohol, and finally mounted in balsam. The whole process was accomplished without causing any distortion or wrinkle, and without the loss of any portion of the blastoderm, as the preparation still shows.

On the Growth, Development, and Situation of the Human Fœtal Heart

The earliest condition of the embryonic vascular system, as described by Wagner and other embryologists, consists of a venovascular chain of sinuses along the ventral surface of the serous or animal lamina of the embryonic germ disc, which, being suddenly arrested by a large projection of the germ vesicle at the anterior part beyond the vascular and mucous lamina, causes a stagnation in the form of a conical sac, whose apex points forward below the head of the embryo at that time consisting of the mesocrane and procrane, with the visceral segments of the face-kist, and exhibiting three facial clefts.