Mature T cells are derived from prethymic stem cells, which arise at one or more extrathymic sites and enter and differentiate in the thymus. The nature of these prethymic stem cells is a critical factor for the formation of the T-cell repertoire. Although the bone marrow of adult mice can provide such stem cells, their origin during murine embryogenesis is still undetermined. Among potential s...

AIMS The present study aimed to determine whether yolk sacs with abnormal sonographic appearance are associated with adverse perinatal outcomes in both early and late gestation. MATERIAL AND METHODS A total of 305 viable singleton pregnancies with gestational age of 6 to 9 weeks were prospectively evaluated with respect to perinatal outcomes and sonographic characteristics of the yolk sacs. ...

In order to study the bacterial flora of dead-in-shell ostrich chicks, twelve unhatched eggs which did nothave external pipping during the hatching period were transferred to the laboratory of microbiology. The eggshells were accurately disinfected and the embryos were removed and placed in a sterile plate. The surface of each embryo was swabbed with a sterile swab which was also plunged throug...

   Malignant germ-cell tumors (MGCT) are rare tumors of childhood accounting for less than 3% of pediatric malignancies. Endodermal sinus tumor (EST) forms the most common histologic subtype of MGCT. The vagina is an extremely rare site for GCTs. An 8-month-old female was admitted with a short history of vaginal bleeding, and a mass protruding from the vagina. She was pale and a mass was palpab...

Studies were conducted to explore in rats the role of retinol in the regulation of the synthesis and secretion of retinol-binding protein (RBP) by the visceral yolk sac compared to the liver. Previous studies have shown that in retinol deficiency, hepatic RBP secretion is specifically inhibited, whereas hepatic RBP synthesis rate is unchanged. Retinol-depleted, retinoic acid-supplemented female...

Lymphocyte development and ontogenetic changes in erythroid cells have been studied in chick-chick yolk-sac-embryo chimeras differing at the B locus antigens. Erythroid cells derived from the yolk sac or from the intraembryonic mesenchyme were demonstrated by indirect immunofluorescence in the peripheral blood of these allogenic chimeras. At 7 days of incubation, yolk-sac-derived red cells repr...

The capacity of the yolk sac to generate multilineage, adult-type hematopoiesis was investigated in vivo using vascular endothelial-cadherin deficient embryos. In these mutants, the yolk sac is not connected to the vasculature of the embryo and therefore all hematopoietic activity detected therein is intrinsic to the yolk sac and not derived from intraembryonic sources. At embryonic days 9.5 an...

The potential absorptive role of the yolk sac membrane was evaluated by examining protein and enzyme patterns in embryonic fluids and by comparing the synthetic capacity of the secondary yolk sac, fetal liver and placenta for human chorionic gonadotrophin (HCG) and alpha-fetoprotein (alphaFP). In yolk sac fluid samples, protein electrophoresis showed two main electrophoretic bands with mobiliti...