Parthenogenetic Cells Research Articles

Prenatal fate of parthenogenetic cells in mouse aggregation chimaeras

Parthenogenetically activated BCF1 and fertilized BALB/c embryos were aggregated to form chimaeras. The fate of the parthenogenetic component was followed in the conceptus during the second half of gestation. The results indicate an early strong selection against parthenogenetic cells in the extra-embryonal part, which is presumably complete by term, and a weaker selective process in the embryo. During early development, parthenogenetic cells have nearly normal developmental potency in the embryo, which allows their balanced contribution in the chimaeras on day 12. Later, this contribution declines significantly resulting in an unbalanced relation to the advantage of the fertilized counterpart. From the results, we suggest that gametic imprinting may play a role not only in the key steps of preimplantation and early postimplantation development, but later in cell and tissue differentiation.

Influence of parental chromosomes on spatial specificity in androgenetic----parthenogenetic chimaeras in the mouse.

The presence of both parental genomes is essential for development to term in the mouse embryo probably because of germline-specific modifications of homologous chromosomes. Neither androgenetic nor parthenogenetic embryos can by themselves develop to term; any post-implantation embryos they produce have opposite phenotypes, which reflects the presence of complementary information in parental chromosomes. The development of androgenetic----parthenogenetic chimaeras is of considerable interest because in this case both parental chromosomes are available even though they are in separate cells. We demonstrate here that in post-implantation chimaeric fetuses, the expression of parental information results in spatial specificity so that parthenogenetic cells are confined to the embryo but the trophoblast consists almost entirely of androgenetic cells. The yolk sac contains both cell types. However, there is incomplete functional complementation because the chimaeras do not reach term. Although failure to reach term may occur partly because of inadequate intermingling and interactions between embryonic cells, it is more likely that further control of mouse development depends on the presence of both sets of chromosomes within the same cells.

Turkey-chicken hybrids: a cytological study of early development.

Reciprocal hybridization experiments were performed between the line of Beltsville Small White turkeys that has been selected for high incidence of parthenogenesis and two strains of chickens. The eggs were examined cytologically at early stages of development. In the cross of turkey females X chicken males, it was found that both male (2A-ZZ) and female (2A-ZW) zygotes are formed, but the latter are much less viable and usually die in a very early stage of development. Besides the hybrid embryos, parthenogenetic-type embryos also were found. In the cross of chicken females X turkey males, no evidence of successful hybridization was obtained. However, cell division was initiated in 100 percent of the chicken eggs. This fact suggests that turkey sperm had some enhancing effect on parthenogenetic cell division in chicken eggs.

Totipotent cells of parthenogenetic origin in a chimaeric mouse.

IN strain LT/Sv mice, eggs often begin to develop parthenogenetically in the ovary after the first meiotic division1–3. They undergo apparently normal cleavage and blastocyst formation, but at the egg cylinder stage they become disorganised and form teratomas. They persist as tumours composed of many kinds of tissue, indicating that cells of parthenogenetic origin are viable. Spontaneous parthenogenesis is also common in ovulated strain LT eggs. They cleave, form blastocysts and implant in the uterus, but die shortly afterwards, in the same way that embryos derived from experimentally induced parthenogenesis die early4–7. However, parthenogenetic cells have been ‘rescued’ by removing embryos from the oviducts of virgin females and grafting them to extrauterine sites such as testis1 and kidney8. Those embryos become disorganised and can survive as teratomas composed of many kinds of viable tissues. Why, then, do cells of parthenogenetic origin fail to survive in utero? To investigate this problem we are using chimaeras derived from aggregates of eight-cell parthenogenetic and normal embryos2, transferred to the uteri of pseudopregnant females. We report here that early embryonic parthenogenetic cells are totipotent. They can give rise to fully functional ova which, when fertilised by sperm, develop into normal individuals.

Development to term of chimaeras between diploid parthenogenetic and fertilised embryos.

PARTHENOGENETIC mouse embryos have the potential for extensive cellular proliferation as well as differentiation into various cell types1–3. But this potential has been realised only when parthenogenetic embryos have been transferred to extrauterine sites1, and in spontaneously occurring ovarian teratomas and teratocarcinomas of parthenogenetic origin2,3. The development of mammalian parthenogenetic embryos in utero is restricted, with no conclusive evidence that they can develop to term4,5. Several hypotheses have been proposed to account for their poor development. For example, deleterious recessive genes may affect the viability of their cells, possibly because of their extensive homozygosity2,5, or disorganised growth and limited life span may result from anomalies of cellular interactions5. But the extensive cellular proliferation and differentiation of parthenogenetically derived cells which occurs in extrauterine sites is not entirely consistent with these explanations, and indicates that parthenogenones probably have a relatively stable genetic constitution. Indeed, these studies stress the likely importance of cellular environment for cytodifferentiation, provided in this instance by the extrauterine host tissue. There is a precedent for supposing that if the environment is critical for cytodifferentiation, parthenogenetic cells should be able to form chimaeras with cells derived from fertilised embryos6. Teratocarcinoma cells7,8 and cells carrying known lethal alleles9,10 can develop into viable chimaeras when aggregated with cells from normal embryos. Previous attempts to achieve development to term of aggregation chimaeras between parthenogenetic and fertilised embryos were apparently unsuccessful11. We have introduced inner cell masses (ICMs) from diploid ,parthenogenetic embryos into intact fertilised mouse blastocysts, and we report here the development of a chimaera to term.

Formwechsel, sippenspezifischer Paarungsmodus und Systematik bei einigen pennaten Diatomeen

Cymbella cesatii var.paradoxa, var. nova, is significantly characterized by its total variation of size, by the size of gamete mother cells and auxospores; moreover its particular mode of pairing is significant too. Whilst in var.cesatii, in connection with its naviculoid cell shape, the combinations ventral-ventral, dorsal-dorsal, ventral-dorsal are realized haphazardly, in var.paradoxa, which is naviculoid-shaped just the same, regularly only the combination dorsal-dorsal is practicable. With regard to the naviculoid shape of the cells it is concluded that not space-mechanical causes alone are involved, but that a factor controlling the mode of pairing is at work. In comparison with the twocesatii sibs it is remarkable that inCymbella microcephala, although its cells are more strongly dorsiventrally organized, nevertheless the three combinations are realized haphazardly. On the contrary, inC. delicatula, whilst its cells are not more dorsiventrally organized, pairing always is accomplished at the ventral sides. This comparison also shows the effectiveness of factors other than the form of the partner cells. Some specific peculiarities of pairing behavior in other allogamous diatoms are compared and discussed. — In both sibs ofC. cesatii ± deformed parthenogenetic primary cells exceptionally arise. A survey demonstrates the common occurence of clearly separable infraspecific sibs and aggregates in diatoms.