Appearance Of Primordial Germ Cells Research Articles

JAK-STAT signaling regulation of chicken embryonic stem cell differentiation into male germ cells.

The Janus kinase-signal transducer and activator of transcription (JAK-STAT) signaling is crucial in chicken germ stem cell differentiation, but its role in the regulation of germ cell differentiation is unknown. To address this, cucurbitacin I or interleukin 6 was used to inhibit or activate JAK-STAT signaling during embryonic stem cells (ESCs) differentiation. The expression of downstream JAK-STAT signaling molecules was assessed by Western blotting and quantitative real-time polymerase chain reaction (qRT-PCR). PAS, and immunohistochemical staining of frozen sections was used to determine the appearance of primordial germ cells (PGCs) and, later, spermatogonial stem cells (SSCs) during gonadal development. Inhibition of the JAK-STAT signaling resulted in decreased expression of JAK2 and STAT3 as well as of PGCs markers; moreover, the proportion of CVH and C-KIT positive cells as well as the yield of PGCs were remarkably decreased, and the gonad was smaller than that of control samples. Conversely, activation of JAK-STAT resulted in increased expression of JAK2 and STAT3 as well as that of PGC marker CVH. In addition, the proportion of CVH and C-KIT-positive cells as well as the PGC yield was increased, and the gonad was significantly larger than that from control samples. Collectively, our results suggested that JAK-STAT effectively promoted the formation of PGCs in the genital ridge during early embryogenesis in vivo and played a positive role in the regulation of ESC to SSC differentiation in vitro, with JAK2 and STAT3 functioning as pivotal factors for intracellular signal transduction.

Cancer metastasis: enactment of the script for human reproductive drama

Based on compelling evidence from many biological disciplines, we put forth a hypothesis for cancer metastasis. In the hypothesis, the metastatic cascade is depicted as human reproduction in miniature. Illustrated in a reproductive light, the staggering resemblance of cancer metastasis to human reproduction becomes evident despite some ostensible dis-similarities. In parallel to the appearance of primordial germ cells during early embryogenesis, the cancer reproductive saga starts with the separation of metastasis initiating cells (MICs) from cancer initiating cells when the primary cancer is still in its infancy. Prime MICs embark on a journey to the host bone marrow where they undergo further development and regulation. Migrating MICs are guided by the same CXCR4/CYCL12 axis as used in the migration of primordial germ cells to the genital ridge. Like the ovary, the host bone marrow features immune privileges, coolness, hypoxia and acidity which are essential for stemness maintenance and regulation. Opportune activation of the MICs via fusion with bone marrow stem cells triggers a frenzy of cellular proliferation and sets them on the move again. This scenario is akin to oocyte fertilization in the Fallopian tube and its subsequent journey towards the decidum. Just as the human reproductive process is plagued with undesirable outcomes so is the cancer metastasis highly inefficient. The climax of the cancer metastatic drama (colonization) is reached when proliferating MIC clusters attempt to settle down on decidum-like premetastatic sites. Successfully colonized clusters blossom into overt macrometastases only after the execution of sophisticated immunomodulation, angiogenesis and vascular remodeling. Similarly, the implanted blastomere needs to orchestrate these feats before flourishing into a new life. What is more, the cancer reproductive drama seems to be directed by a primordial hypothalamus–pituitary–gonad axis. Pursuing this reproductive trail could lead to new frontiers and breakthroughs in cancer research and therapeutics.

The role of germ cell loss during primordial follicle assembly: a review of current advances.

In most female mammals, early germline development begins with the appearance of primordial germ cells (PGCs), and develops to form mature oocytes following several vital processes. It remains well accepted that significant germ cell apoptosis and oocyte loss takes place around the time of birth. The transition of the ovarian environment from fetal to neonatal, coincides with the loss of germ cells and the timing of follicle formation. All told it is common to lose approximately two thirds of germ cells during this transition period. The current consensus is that germ cell loss can be attributed, at least in part, to programmed cell death (PCD). Recently, autophagy has been implicated as playing a part in germ cell loss during the time of parturition. In this review, we discuss the major opinions and mechanisms of mammalian ovarian PCD during the process of germ cell loss. We also pay close attention to the function of autophagy in germ cell loss, and speculate that autophagy may also serve as a critical and necessary process during the establishment of primordial follicle pool.

Development of testis and digestive tract in longnose gar (Lepisosteus osseus) at the onset of exogenous feeding of larvae and in juveniles

The aim of this study was to describe the ontogenetic development of the testis and the alimentary tract in longnose gar (Lepisosteus osseus) related to fish size and age at the onset of exogenous feeding and late ontogenesis. Using light microscopy, testes were first detected histologically by the appearance of primordial germ cells 9 days after the first exogenous feeding [31-31.5 mm total body length(TL)] and presumptive seminiferous tubules (maleness characteristic) in fish of 107 mm TL. The present histological studies indicated that the alimentary tract of lepisosteids is completely functional at the beginning of exogenous feeding, several days before the completion of yolk absorption. Based on these results, we have concluded that garfish larvae/juveniles can be effectively trained to consume formulated diets at early stages, after an initial feeding of live food for 2-3 days (23.5 mm TL). Our findings provide evidence of the first controlled rearing of longnose gar using live and formulated diets, providing the possibility of experimental work with this non-teleost fish.

Problems of sex determination in birds exemplified by Gallus gallus domesticus

The current views of sex determination in birds are considered mostly with the example of Gallus gallus domesticus, the species best studied in this respect. Data on the appearance of primordial germ cells, their migration to the primordial gonads, the role of hormonal factors in the regulation of sex differentiation, the sex chromosomes, putative genetic mechanisms of sex determination, and a possible contribution of dosage compensation are described. The review discusses the two best-grounded hypotheses on the roles of the Z and W chromosomes in sex determination.

Developmental origin of avian primordial germ cells and its unique differentiation in the gonads of mixed-sex chimeras.

Developmental origin of avian primordial germ cells and its unique differentiation in the gonads of mixed-sex chimeras.

A morphological study of primordial germ cells at pregastrular stages in the chick embryo

The spatial distribution, germ layer location, number and appearance of primordial germ cells (PGCs) are studied. Blastoderms from stage X (Eyal-Giladi and Kochav, 1976) to stage 2 (Hamburger and Hamilton, 1951) were serially sectioned and distribution patterns of PGCs were reconstructed. The presence of PGCs in clusters was noted at all stages examined. PGCs were found in relation to the epiblast, the primary hypoblast and in the blastocoel, during the whole period under examination. These observations show that PGCs can be directly studied at blastula stages. The results are consistent with observations on an early segregation of chick germ line that begins as early as stage X.

Appearance of Primordial Germ Cells in Young Chick Blastoderms Cultured in vitro: (primordial germ cells/blastoderms/chick).

Appearance of primordial germ cells (PGCs) in young chick blastoderms was investigated by the cultivation of only the epiblast or hypoblast. Presumptive PGCs exist in the epiblast before primitive-streak formation. They translocate gradually to the lower layer during early stages of primitive-streak formation, though substantial number of presumptive PGCs remain in the upper layer. The existing primary hypoblast under the epiblast is dispensable for the further differentiation of the PGCs.

On the Origin of Primordial Germ Cells in the Chick Embryo

An attempt was made to re-examine the location of the primordial germ cells (PGCs) in very young chick embryos. Freshly laid blastoderms, prior to hypoblast formation, of a known anterio-posterior axis, were transversely bisected and each half was separately grown in vitro. Both anterior and posterior halves were shown to be fertile and each was shown to contain roughly the same amount of PGCs as a normal control embryo. It has been concluded that in the chick as well as in the duck there is no concentration of cells containing germinal plasm in the posterior part of the blastoderm. Two other possibilities should be investigated: 1. A concentric arrangement of cells containing germinal plasm. 2. The absence of a germinal plasm and a relatively late appearance of PGCs as a result of induction.

The population of germ cells in immature male rats following irradiation at birth.

Male rats were irradiated with 19 r on the day of birth, and killed at intervals ranging from 5 to 18 days. Estimates were made of the absolute and relative numbers of germ cells at different stages of spermatogenesis in 64 irradiated and 61 untreated specimens. In the normal rat, the calculated population of germ cells increased from about 160000 at 5 days to 30 million at 18 days. Only negligible numbers of primordial germ cells (gonocytes and transitional cells) persisted beyond the age of 10 days. Small numbers of spermatogonia type A appeared at 5 days (15000) and their population rose to about 1 million at 12 days, and 2 million at 18 days (7 % of all germ cells). Intermediate spermatogonia first occurred in appreciable numbers (23000 to 55000) at 8 or 9 days, when the population of type-A spermatogonia was 360000. The subsequent rise in the population of intermediate spermatogonia was more rapid than that of type A (4 million at 18 days). Spermatogonia type B and primary spermatocytes appeared at 9 to 10 days, and their numbers rose more steeply still (6.5 and 16 million at 18 days, respectively). Irradiation at birth exerted no rapid effect on the cytological appearance of primordial germ cells. Transformation from gonocytes to transitional cells appeared to proceed normally and the estimated total population of germ cells at 5 days was no smaller than in the controls. Subsequently, however, many of the transitional cells failed to divide: they enlarged to form giant cells, acquired bizarre nuclear outlines, and persisted for unusually long periods. Some degenerated at mitotic prophase or metaphase, while a few seemed to die at interphase, without entering division. The calculated total population of germ cells in irradiated rats rose from 160000 at 5 days to 9.4 million at 18 days. Small numbers of spermatogonia type A, presumably derived from such primordial germ cells as were able to complete mitosis, appeared some 2 to 3 days later than in controls. The number of type-A spermatogonia in 7-day-old irradiated rats was 44000, cf. 215000 in controls; the difference became less pronounced with time, and by the age of 18 days, the population of 1.9 million was comparable to that estimated for the controls. Small numbers of intermediate spermatogonia appeared on the 9th (8000) and 10th day (35000), when the population of type-A spermatogonia was about 110000 and 260000 respectively. By the 18th day, intermediate spermatogonia numbered 2 million. The populations of type-B spermatogonia and primary spermatocytes rose from 11000 to 13000 at 10 days to 1.6 and 3.4 million, respectively, at 18 days. The difference in the absolute and relative numbers of germ cells between normal and irradiated testes widened progressively with advance in the developmental stage of the germ cells. Analysis of the results indicates that in the reduced population of spermatogonia type A after irradiation, the pattern of spermatogonial mitoses is modified so as to favour the formation of more type-A, in preference to intermediate, spermatogonia.