Production of duck-chicken chimeras by transferring early blastodermal cells

Duck blastodermal cells isolated from Stage X embryos of Maya ducks were injected into subgerminal cavity of recipient Stage X chicken embryos treated with gamma-irradiation or untreated. Eleven somatic chimeras were obtained based on plumage color and were raised to sexual maturity. To test for germline chimerism, progeny tests were performed by mating the chimeras with Maya ducks. A total of 622 eggs was collected and incubated. Fertility rate and hatchability were 2.9% (18/622) and 1.0% (6/622), respectively. The six duck hatchlings were from Chimera 9801 and were considered to be derived from the germ cells developed from the donor Maya blastodermal cells, indicating that Chimera 9801 is a germline chimera.

Coelom formation: binary decision of the lateral plate mesoderm is controlled by the ectoderm

Most triploblastic animals including vertebrates have a coelomic cavity that separates the outer and inner components of the body. The coelom is lined by two different tissue components, somatopleure and splanchnopleure, which are derived from the lateral plate region. Thus, the coelom is constructed as a result of a binary decision during early specification of the lateral plate. In this report we studied the molecular mechanisms of this binary decision. We first demonstrate that the splitting of the lateral plate into the two cell sheets progresses in an anteroposterior order and this progression is not coordinated with that of the somitic segmentation. By a series of embryological manipulations we found that young splanchnic mesoderm is still competent to be respecified as somatic mesoderm, and the ectoderm overlying the lateral plate is sufficient for this redirection. The lateral ectoderm is also required for maintenance of the somatic character of the mesoderm. Thus, the ectoderm plays at least two roles in the early subdivision of the lateral plate: specification and maintenance of the somatic mesoderm. We also show that the latter interactions are mediated by BMP molecules that are localized in the lateral ectoderm. Evolutionary aspects of the coelom formation are also considered.

The ability to initiate an axis in the avian blastula is concentrated mainly at a posterior site

Cell interactions during early vertebrate development are crucial for embryonic mesoderm induction and axis initiation. In the avian embryo two unique layers of cells, the epiblast and the hypoblast, constitute the blastoderm before the primitive streak develops (stage XIII). It was suggested that cells of the hypoblast have the ability to induce competent cells in the epiblast to form the mesoderm and to initiate the embryonic axis. Recent results suggest, however, that at stage XIII the hypoblast does not act by inducing the epiblast to form a primitive streak. Since the hypoblast at stage XIII does not induce the epiblast, experiments were designed in this work to examine whether other subregions of the avian blastula have the ability to initiate the embryonic axis. To distinguish the contribution of a particular fragment to the formation of the embryonic axis, cell-marking examinations with lysinated rhodamine dextran (LRD) were designed. The results of the experimental series discussed in this report suggest that at stage XIII it is mainly the posterior side of the marginal zone and/or of the posterior region of the epiblast layer which has the abilities to initiate the embryonic axis. However, the posteriolateral part of the marginal zone region also has such abilities, which are inhibited during normal development. LRD examinations have demonstrated that a graft of a particular posterior blastoderm region, or posteriolateral marginal zone, can initiate an ectopic streak, and is able to recruit other neighboring cells to the developing ectopic streak. No evidence was found that Koller's sickle itself can initiate an ectopic axis in the epiblast at stage XIII. It is proposed that the cells which are important to initiate the avian embryonic axis are concentrated mainly at the region of the posterior marginal zone including Koller's sickle and in the posterior region of the epiblast layer. The cells in this region, which also express the goosecoid and cVg1 genes, may have organizer properties which induce the mesoderm and determine the initiation site of gastrulation in the chick embryo.

The role of Engrailed in establishing the dorsoventral axis of the chick limb

Expression and mutation analyses in mice suggest that the homeobox-containing gene Engrailed (En) plays a role in dorsoventral patterning of the limb. During the initial stages of limb bud outgrowth, En-1 mRNA and protein are uniformly distributed throughout the ventral limb bud ectoderm. Limbs of En-1(−/−) mice display a double dorsal phenotype suggesting that normal expression of En-1 in the ventral ectoderm is required to establish and/or maintain ventral limb characteristics. Loss of En-1 function also results in ventral expansion of the apical ectodermal ridge (AER), suggesting that En-1 is also required for proper formation of the AER. To further investigate the role En plays in dorsoventral patterning and AER formation, we have used the replication competent retroviral vector, RCAS, to mis-express mouse En-1 in the early chick limb bud. We show that ectopic En-1 expression in dorsal ectoderm is sufficient to repress the endogenous expression of the dorsal ectodermal marker Wnt7a, with a resultant decrease in Lmx1 expression in underlying dorsal mesenchyme. Furthermore, the AER is disrupted morphologically and the expression patterns of the AER signalling molecules Fgf-8 and Fgf-4 are altered. Consistent with recent evidence that there is a reciprocal interaction between signalling molecules in the dorsal ectoderm, AER, and zone of polarising activity (ZPA), loss of Wnt7a, Fgf-8 and Fgf-4 expression leads to a decrease in expression of the signalling molecule Shh in the ZPA. These results strongly support the idea that, in its normal domain of expression, En-1 represses Wnt7a-mediated dorsal differentiation by limiting the expression of Wnt7a to the dorsal ectoderm. Furthermore, our results provide additional evidence that En-1 is involved in AER formation and suggest that En-1 may act to define ventral ectodermal identity.

Transfer of a genetic form of epilepsy in the chicken by embryonic brain grafts

The genetic photosensitive epilepsy of the Fayoumi chickens was transferred to normal chickens by grafting, in situ, on the 2nd day of incubation, the prosencephalic and mesencephalic vesicles from epileptic embryos. Such chimeras displayed typical interictal EEG and developed intermittent light stimulation-induced seizures phenotypically and electrically similar to the epileptic strain seizures.

Partial restriction in the developmental potential of late emigrating avian neural crest cells

Trunk neural crest cells migrate along two major pathways: a ventral pathway through the somites whose cells form neuronal derivatives and dorsolateral pathway underneath the ectoderm whose cells become pigmented. In avian embryos, the latest emigrating neural crest cells move only along the dorsolateral pathway. To test whether late emigrating neural crest cells are more restricted in developmental potential than early migrating cells, cultures were prepared from the neural tubes of embryos at various stages of neural crest cell migration. "Early" and "middle" aged neural crest cells differentiated into many derivatives including pigmented cells, neurofilament-immunoreactive cells, and adrenergic cells. In contrast, "late" neural crest cells differentiated into pigment cells and neurofilament-immunoreactive cells, but not into adrenergic cells even after 10-14 days. To further challenge the developmental potential of early and late emigrating neural crest cells, they were transplanted into embryos during the early phases of neural crest cell migration, known to be permissive for adrenergic neuronal differentiation. The cells were labeled with the vital dye, DiI, and injected onto the ventral pathway at stages 14-17. Two and three days after injection, some early neural crest cells were found to express catecholamines, suggesting they were adrenergic neuroblasts. In contrast, DiI-labeled late neural crest cells never became catecholamine-positive. These results suggest that the late emigrating neural crest cell population has a more restricted developmental potential than the early migrating neural crest cell population.

Implantation of chicken embryonic tissue and cells into unfertilised eggs

1. Chick embryo cells and halved embryos were successfully implanted into unfertilised eggs. Yolks containing implants were placed in recipient eggshells, covered by transparent vacuum-formed plastic cones and incubated for 72 h. 2. Dispersed cells were obtained from eggs expelled from the uterus or from eggs that had been laid. Implantation of these cells often resulted in aggregation and epithelial growth, in several cases with axial development. 3. Growth of implanted halved embryos of different ages was often observed, including one 10-somite embryo. Non-axial epithelia, sometimes with a central hole, a central fluid-filled cellular vesicle or a vesicle only, were also observed. 4. In another culture system, whole and halved embryos obtained from laid eggs were cultured on a vitelline membrane stretched across semi-solid egg albumen. During the 72 h incubation, axial development was observed only in whole embryos, while halved embryos grew either into epithelia containing fluid-filled cellular vesicles or into vesicles only. 5. It was found that daily drainage of the accumulating fluid from the embryo compartment encouraged axial development in halved embryos, and almost abolished vesicle formation. Holes were formed in half the embryos cultured on a vitelline membrane. 6. It appeared that physical and biological conditions could inflict serious malformations on the implants.

[Chick embryo culture using duck egg shell--first successful hatch ]

The suitability of duck egg shell (DES) for chick embryo culture was investigated. Chick embryos were transferred into DESs with all egg contents after 3 days of normal incubation and cultured. The vessels made of polyethylene cling film were used for shell-less control. Among 35 embryos cultured in DESs, 21 survived until 16 days of incubation (13 days after transfer) and finally 3 newly hatched chicks were obtained at 22 days of incubation. One of them died 4 days later, but remaining two became full-grown cocks showing normal body weight and production of fertile sperms. Among 37 embryos cultured in polyethylene vessels, none survived over the period of 19 days of incubation. It is suggested that DES culture system may be useful for the various experiments using chick embryos.

Inherited dysgammaglobulinemia of chickens: reduced incidence of disease in parabiotic chimeras

University of California, Davis (UCD) line 140 chickens develop a dysgammaglobulinemia characterized as selective 7S immunoglobulin (Ig) deficiency with elevated serum IgM levels. To study the role of bursal development on the expression of dysgammaglobulinemia in these birds, we examined the effect of bursacyte transfer to line 140 birds and parabiosis between UCD 140 and a control line of chickens on changes in serum IgM and 7S Ig levels. Bursacyte transfer was performed by injecting 18-day UCD 140 embryos (which had been cyclophosphamide treated on Day 15) with bursacytes from major histocompatibility complex B-matched control line (11 X 58) F1 birds. This transfer produced little change in the incidence of dysgammaglobulinemia in UCD 140 transfer birds (56%) compared to unmanipulated line 140 birds (60%). These data reflect a failure of line 140, rather than technique, because successful reconstitution was seen using line 11 X 58 birds injected with 11 X 58 bursacytes. In contrast, the generation of UCD 140/line 11 X 58 chimeras significantly reduced the incidence of dysgammaglobulinemia in line UCD birds. Indeed, fusion of the chorioallantoic vascular system (parabiosis) of UCD 140 and 11 X 58 embryos on Day 15 decreased the frequency of dysgammaglobulinemia of UCD 140 parabionts to 14% compared to 66% in unmanipulated line 140 controls. The success of parabiosis was 83% as determined by demonstrating chimerism with allogeneic blood groups. Moreover, the frequency of dysgammaglobulinemia in the 17% of parabionts that did not reveal chimerism was similar to unmanipulated UCD 140 chickens.

Tracing of cells of the avian thymus through embryonic life in interspecific chimeras

Differences in the structure of the interphase nucleus between two species of birds, the Japanese quail (Coturnix coturnix japonica) and the chick (Gallus gallus) has been used to distinguish cells from different origins in interspecies combinations. This biological cell marking technique was applied to thymus histogenesis. Using various combinations between components of quail and chick thymic rudiments, the respective contribution of endodermal epithelium, mesenchyme, and blood-borne extrinsic elements to the histogenesis of thymus was analyzed. It was demonstrated that the whole lymphoid population of the thymus is derived from immigrant blood-borne stem cells which are chemically attracted by the endoderm of the 3rd and 4th pharyngeal pouch. The latter is determined to differentiate into thymic epithelial reticulum as soon as the 15-somite stage, and is able to attract blood stem cells even when transplanted in an heterotopic position such as the ventral body wall of the embryo. It was shown that the thymic mesenchyme originates from the neural crest mesectoderm which colonizes early the 3rd and 4th branchial arches. It participates in the formation of perivascular mesenchyme, but does not give rise to lymphocytes. From heterospecific transplantations of quail thymuses into chick embryo (and inversely) at various stages of development is appeared that the thymic rudiment becomes attractive for lymphoid stem cells at a precise stage of its evolution for each species. The attractivity period lasts about 24 h for the quail and 36 h for the chick. Then, the inflow of stem cells becomes very low until the end of the incubation period. At this time, a second wave of lymphocytoblasts invades the thymus and the primitive embryonic lymphoid population is completely renewed around the hatching time. Competent thymic stem cells are present in the blood before and after the period of physiological thymic attractivity. The identity of basophilic cells appearing in the thymus during its histogenesis and lymphoid stem cells has been demonstrated from the analysis of quail-chick chimeric thymuses.