In vitro development of the mammalian embryo

Synchronization of the factors critical for diabetic teratogenesis: an in vitro model

OBJECTIVE

Our goal was to determine the relationship between critical factors and conditions such as gestational age and exposure time to elevated glucose levels in diabetic embryopathy.

STUDY DESIGN

A postimplantation rat embryo culture was used as a model for investigation. The effect of various factors on embryonic development was studied. Experiments were conducted with increasing glucose concentrations (150 to 905 mg/dl, n = 186), at various gestational ages (10 to 12 days, n = 169), and for varying durations of exposure (30 to 180 minutes, n = 169). Gross morphologic characteristics of the yolk sac and embryo were assessed.

RESULTS

Embryopathy was induced by hyperglycemia in a dose-related fashion: a 20% rate at two times control glucose concentration, almost a 50% rate at four times control, and approximately a 100% abnormality rate at more than six times control. A critical window in gestational age, days 10 to 11, and a minimum exposure time to hyperglycemia of 2 hours were necessary to induce teratogenesis.

CONCLUSIONS

Diabetic teratogenesis occurs in a dose-related fashion and requires a minimum exposure time and critical gestational age. Only synchronization of these critical conditions induces embryonic maldevelopment. Furthermore, nonsynchronized aberrant conditions may result in apparently normal embryonic development.

In vitro culture of postimplantation hamster embryos

In vitro culture of intact rat and mouse embryos has been described extensively, but information on the culture of other species is sparse. The present study examined some culture requirements of early somite stage hamster embryos and assessed the embryotoxic effects of sodium salicylate (SS), a direct acting chemical and cyclophosphamide (CP), a proteratogen, on these embryos. Hamster embryos explanted on gestation days (GD) 8 and 9 were cultured in Waymouth's embryo-hepatocyte co-cultivation medium (WEHC), 70% McCoy's 5A medium-30% male rat serum (MMRS) or 100% male rat serum (MRS) for 24 hours under various oxygen concentrations. Embryos cultured GD 8 to 9 in the various media grew and differentiated much as they did in vivo, while embryos cultured GD 9 to 10 grew best in MMRS as compared to embryos at the same stage in vivo. Embryos exposed to SS in MMRS at concentrations of 250, 300, or 400 micrograms/ml showed dose related embryotoxicity which included CNS defects, absence of hind limb bud formation, and lack of axial rotation. Hamster embryos co-cultivated with pregnant hamster hepatocytes and treated with 2.5, 6.25 and 12.5 micrograms/ml of CP, showed dose-dependent toxicity when compared to co-cultivated controls. Hamster embryos develop extensively in culture over a 24 hour period. This system may therefore provide a valuable tool for evaluating the species differences of a variety of potential teratogens and embryotoxins and allow the comparison of these embryotoxic effects between rat, mouse and hamster during similar stages of organogenesis.

Anomalous neural differentiation induced by 5-bromo-2'-deoxyuridine during organogenesis in the rat

The influence of 5-bromo-2'-deoxyuridine (BrdU) on rat embryo development and neurogenesis was investigated using a rat conceptus culture system during organogenesis (pregnancy days 10-13). The embryos and visceral yolk sacs of conceptuses cultured with BrdU were examined for overall growth, morphological anomalies, incorporation of radiolabeled BrdU into DNA, and neurotransmitter enzyme activities in embryos. In addition, neural tubes from cultured whole embryos were isolated and mechanically dissociated into fragments and cultured again to assess neural cell differentiation into neuron-like cells. BrdU was found to incorporate differentially into embryonic and visceral yolk sac DNA with simultaneous stage-specific retardation and anomalous organogenesis in proportion to the increasing concentrations used. Neural tube differentiation of cultured embryos was markedly altered, and there were morphologically distinct neural anomalies. The neurite outgrowth from neuroblast cells (type 1) of explanted spinal neural tube fragments from BrdU-treated embryos was markedly reduced in length and number compared to those from similar areas of embryos grown without BrdU. In contrast, BrdU at the same doses did not affect differentiation of a number of neural tissue-related enzymes. These results indicate that BrdU incorporation into DNA of primordial embryonic cells significantly affects neurogenesis and differentiation of neurites from neuroblasts, which is a specific neural cytodifferentiation characteristic of neuronal cells.

Yolk sac failure in embryopathy due to hyperglycemia: ultrastructural analysis of yolk sac differentiation associated with embryopathy in rat conceptuses under hyperglycemic conditions

Diabetes mellitus in pregnancy is associated with an increased incidence of various congenital anomalies that occur during organogenesis. Because a well functioning yolk sac is crucial to embryonic growth and development during this period, we performed an ultrastructural study of the effects of excess glucose (total glucose 750 mg/dl, osmolality 305 mOsm/kg) on pregnancy day 10 (Witschi stage 13) rat conceptuses cultured for 48 hr in heat-inactivated male rat serum with and without added d- or l-glucose. Embryos exposed to excess d-glucose demonstrated decreased conceptus size (P less than 0.001), and gross malformations in a dose-related fashion. The visceral yolk sac capillaries and vitelline vessels of conceptuses in excess d-glucose were sparse, patchy, and nonuniformly located. Ultrastructurally, the visceral yolk sac endodermal cells had reduced numbers of rough endoplasmic reticulum, ribosomes, and mitochondria. These obvious defects in yolk sac structure suggest that hyperglycemia during organogenesis has a primary deleterious effect on yolk sac function with resultant embryopathy.

Ultrastructural analysis of malformations of the embryonic neural axis induced by in vitro hyperglycemic conditions

Neural tube defects are the most common malformations associated with diabetic pregnancies. Although the teratogenic effects of excess glucose have been investigated in in vivo and in vivo studies, a cellular basis for neural tube defects has not been elucidated. We used rat embryo culture to study the organogenesis period of development, with excess d-glucose added to the serum medium to induce neural tube anomalies. Light and electron microscopic examination of control 12-day-old embryos grown 48 hours in culture revealed blastlike cells with few organelles or cellular processes. Twelve-day-old embryos cultured in excess d-glucose had advanced cellular maturation with differentiation, including the presence of free polysomes and copious cell processes, regardless of whether they had an open neural tube. Cytoarchitectural changes such as decreased numbers of mitotic figures with mitotic cells in the mantle layer were focally distributed throughout the neural epithelium but with predominance at the site of failed closure. In vivo studies failed to demonstrate neural processes in day 12 normal embryos. Fourteen-day-old embryos grown in utero also had foci of cell processes in the neural tube but to a much lesser degree than that observed in the in vitro day 12 glucose-exposed embryos. The cellular aberrations in the excess d-glucose-treated embryos are characteristic of a premature maturational change. Since they are present in excess d-glucose-exposed embryos with or without failure of neural tube closure, these maturational and cytoarchitectural changes may contribute to the cellular basis for neural tube defects.

Differential dysmorphogenesis induced by microinjection of an alkylating agent into rat conceptuses cultured in vitro

A technique of microinjection of small quantities of teratogens into extraembryonic compartments or specific organ primordium of rat conceptuses of pregnancy day 11 is described. Conceptuses microinjected with 50 nl tissue culture medium developed normally for 44-45 hr when cultured in homologous rat serum, indicating that the microinjection procedure itself did not produce any deleterious effects on growth and differentiation of embryos. Microinjection of an alkylating agent, phosphoramide mustard dissolved in tissue culture medium, into the exocoelom produced anomalous embryogenesis, consisting of retarded embryonic growth, anomalies of the neural tube, and general necrosis of various organ primordia. In contrast, the embryonic development remained relatively unaffected by microinjection of identical amounts of this alkylating agent into the amniotic cavity. However, neural-tube differentiation was markedly affected when phosphoramide mustard was injected into anterior neural-tube fluid, producing anencephalic or microcephalic embryos without significant effect on postcephalic organ differentiation. The morphogenesis of the anterior limb was unaffected by local injection of the agent into somitic tissues adjacent to the presumptive limb-bud region. Therefore, it appears that differential dysmorphogenesis could be induced by microinjection of an alkylating agent into different conceptus compartments. These results indicate that even during early embryogenesis various cell types are not equally susceptible to a given teratogen, and that the differential cytotoxicity of the teratogen toward specific embryonic or extraembryonic cells and tissues may account for embryonic anomalies characteristically produced by that agent.

Serum is not necessary in human in vitro fertilization, early embryo culture, and transfer

Human in vitro fertilization (IVF), embryo culture (EC), and embryo transfer (ET) are commonly performed in various media supplemented with blood serum. To determine whether serum is really necessary, the results of IVF, EC, and ET were compared by using two types of media: B2 medium supplemented with human cord serum and B3 medium without any serum. B3 medium is similar to B2, except that it contains 1% pure controlled human serum albumin in place of 1% bovine serum albumin. We did not observe any difference between the results obtained by using B2 or B3 at any phase of IVF, EC, and ET processes. Both media give an overall evolutive pregnancy rate of about 16%. B3 medium with serum seems to increase slightly the cleavage speed. Our results indicate that there are no positive effects when serum is used for human IVF-ET. To avoid serum supplementation is of evident interest for the homogeneity of the results. This will also lead to a better understanding of human early development and control of the egg quality by metabolic analysis of the media following in vitro EC.