The lack of genital ridge vascularization in the early chick embryo: implications in the migration of the primordial germ cells

Transfer and detection of freshly isolated or cultured chicken (Gallus gallus) and exotic species' embryonic gonadal germ stem cells in host embryos

The management of captive avian breeding programs increasingly utilizes various artificial reproductive technologies, including in ovo sexing of embryos to adjust population sex ratios. Currently, however, no attention has been given to the loss of genetic diversity following sex-selective incubation, even with respect to individuals from critically endangered species. This project evaluated the possibility of using xenotransfer of embryonic gonadal germline stem cells (GGCs) for future reintroduction of their germplasm into the gene pool. We examined and compared the host gonad colonization of freshly isolated and 3 day (3d) cultured donor GGCs from chicken and 13 species of exotic embryos. Following 3d-culture of GGCs, there was a significant increase in the percentage of stem cell marker (SSEA-1, -3, -4) positive cells. However, the percentage of positive host gonads with chicken donor-derived cells decreased from 68% (fresh) to 22% (3d), while the percentage of exotic species donor-cells positive host gonads decreased from 61% (fresh) to 49% (3d-cultured). Donor GGCs from both chicken and exotic species were localized within the caudal endoderm, including the region encompassing the gonadal ridge by 16 hours post-injection. Furthermore, donor-derived cells isolated from stage 36 host embryos were antigenic for anti SSEA-1, VASA/DDX4 and EMA-1 antibodies, presumably indicating maintenance of stem cell identity. This study demonstrates that GGCs from multiple species can migrate to the gonadal region and maintain presumed stemness following xenotransfer into a chicken host embryo, suggesting that germline stem cell migration is highly conserved in birds.

Carbohydrate characterization of quail primordial germ cells during migration and gonadal differentiation

A selection of lectins were used to study changes in the distribution of sugar residues in primordial germ cells (PGCs) during gonadal colonization and differentiation. Although the cytochemical characteristics of PGCs have been described in the chick, little is known about such characteristics in other avian species of interest to experimental biology. Therefore, we studied embryos of Japanese quail (Coturnix coturnix japonica) by light and laser confocal scanning microscopy, using the QH1 antibody as a tool to identify PGCs in both sexes and at all stages. LEA, WGA and RCA-I bound to PGCs in a similar way to QH1. LEA was the best marker for all stages. The presence of acid phosphatase and the intense reaction of LEA, WGA, RCA-I and WFA at the cell surface were shown to be a useful tool in the study of the migratory PGCs of the quail. Quails were sexed histologically in younger embryos than in chick; results were confirmed by PCR. The lectin-binding pattern changed drastically in differentiated gonads. Cell surface reactivity was almost entirely lost. Quail differentiating oogonia showed a characteristic binding pattern to QH1 and to the lectins WGA, RCA-I and WFA. Binding was observed in intense spots in the Golgi complex, and there was a specific PNA reaction. These results suggest that some selective sugar binding sites on the PGCs play a significant role in their migration, colonization and maturation.

Mesenchymal progenitor cells localize within hematopoietic sites throughout ontogeny

Mesenchymal stem cells (MSCs) have great clinical potential for the replacement and regeneration of diseased or damaged tissue. They are especially important in the production of the hematopoietic microenvironment, which regulates the maintenance and differentiation of hematopoietic stem cells (HSCs). In the adult, MSCs and their differentiating progeny are found predominantly in the bone marrow (BM). However, it is as yet unknown in which embryonic tissues MSCs reside and whether there is a localized association of these cells within hematopoietic sites during development. To investigate the embryonic origins of these cells, we performed anatomical mapping and frequency analysis of mesenchymal progenitors at several stages of mouse ontogeny. We report here the presence of mesenchymal progenitors, with the potential to differentiate into cells of the osteogenic, adipogenic and chondrogenic lineages, in most of the sites harboring hematopoietic cells. They first appear in the aorta-gonad-mesonephros (AGM) region at the time of HSC emergence. However, at this developmental stage, their presence is independent of HSC activity. They increase numerically during development to a plateau level found in adult BM. Additionally, mesenchymal progenitors are found in the embryonic circulation. Taken together, these data show a co-localization of mesenchymal progenitor/stem cells to the major hematopoietic territories, suggesting that, as development proceeds, mesenchymal progenitors expand within these potent hematopoietic sites.

Germ cells

Recently, cell signaling has been shown to be required for the formation of germ cells in the mouse embryo, direct observation of germ cell migration in living mouse embryos has been achieved, novel genes that control germ-cell migration have been identified in Drosophila, and the roles of many components of germ plasm in several species have become clearer.

Definitive hematopoietic stem cells first develop within the major arterial regions of the mouse embryo

The aorta-gonad-mesonephros (AGM) region is a potent hematopoietic site within the mammalian embryo body, and the first place from which hematopoietic stem cells (HSCs) emerge. Within the complex embryonic vascular, excretory and reproductive tissues of the AGM region, the precise location of HSC development is unknown. To determine where HSCs develop, we subdissected the AGM into aorta and urogenital ridge segments and transplanted the cells into irradiated adult recipients. We demonstrate that HSCs first appear in the dorsal aorta area. Furthermore, we show that vitelline and umbilical arteries contain high frequencies of HSCs coincident with HSC appearance in the AGM. While later in development and after organ explant culture we find HSCs in the urogenital ridges, our results strongly suggest that the major arteries of the embryo are the most important sites from which definitive HSCs first emerge.