The development of inducibility for glutamine synthetase in embryonic neural retina: inhibition by BrdU.

The hydrocortisone-mediated induction of glutamine synthetase (GS) in the neural retina of the chick embryo is a characteristic and unique feature of differentiation of this tissue. The induction involves genomic activity elicited by the inducer resulting in synthesis and accumulation of the enzyme. We describe correlations between the growth of embryonic retina tissue in vivo and in vitro and the development of its inducibility for GS, and demonstrate that this development proceeds through two phases: competence-acquisition phase (before the 7th day of development), and maturation phase. BrdU applied for 24 h to retinas of 5-day embryos irreversibly suppresses the development of induction-competence. However, BrdU does not affect the progressive maturation of inducibility when applied to retinas that already are fully induction-competent (8 days and older). The short treatment with BrdU of 5-day retinas also causes defective histogenesis resulting in drastic malformation of the tissue. The nature of the processes involved in competence-acquisition and in the maturation of inducibility for GS are examined. Possible mechanisms by which BrdU prevents the development of induction-competence for GS in the early embryonic retina and elicits defective histogenesis are discussed.

Embryonic cell recognition: uncoupling tissue-specific affinities from cell-type specificities.

We have experimentally defined the two major aspects of embryonic cell recognition-adhesion (ReAd), tissue type-specific ReAd and cell type-specific ReAd; we showed that they arise consecutively during cell differentiation, and that the former can function in the absence of the latter. Embryonic chick cells (retina and chondroblasts) in which differentiation was arrested by BrdU at an early stage, failed to express cell-type ReAd, yet they continued to display tissue-type ReAd: they distinguished tissue-self from non-self and selectively cohered with self. Our results indicate that tissue-type and cell-type ReAd represent distinct, separately controlled mechanisms. BrdU appears to be useful as a probe for investigating the regulation of these mechanisms, and as an experimental effector of differentiation abnormalities associated with defects in cell recognition.

Effect of embryonic age on aggregability, histogenesis and biochemical differentiation in the embryonic chick and quail neural retina.

In this paper, the different ages of the chicken and quail embryonic retina cell aggregates are used to examine the aggregation, histogenesis, and the induction of glutamine synthetase (GS) elicited by hydrocortisone. The results show that the GS inducibility in the retina cells increases at a slow rate, then rises sharply on the 9th day, and after 9 days, the GS inducibility of aggregates decreases with the increase of embryonic age. The observed value of induced GS activity in the chick retina cells coaggregate with quail embryonic retina cells is less than the expected value. Bispecific cell coaggregates were observed when the 9-day chicken embryonic retina cells and the 71/2-day quail embryonic retina cells were combined and coaggregated, the chicken and quail cells formed three retinal rosettes. When the 9-day chicken embryonic retina cells were commingled with the 13-day quail embryonic retina cells, in the coaggregates, only one retinal rosette was formed.

Puerperal Pasteurella multocida septicemia.

A case of Pasteurella multocida infection in a puerperal healthy young women is reported. The agent was isolated from vaginal discharge and blood cultures of the patient, and also from pets and poultry with which the patient was in contact. Although Pasteurella multocida septicemia is rare, awareness of this infection and adequate intensive antibiotic therapy may improve its prognosis.

Amplification of DNA sequences during chicken cartilage and neural retina differentiation.

[3H]BrdUrd-substituted DNA probes were prepared from organ cultures of differentiating chicken neural retina and cell cultures of stage 24 chicken limb buds. Reassociation reactions using the neural retina probe demonstrated amplification of DNA sequences during differentiation of neural retina. This probe also contained sequences present in greater numbers in heart DNA than in DNA from undifferentiated neural retina. Reassociation reactions of both differentiated cartilage and differentiated neural retina DNA with both the neural retina probe and the cartilage probe demonstrated that at least part of the amplified sequences are tissue specific.

Development of differential affinities and positional information in embryonic retina cells: inhibition by BrdU.

Embryonic neural retina cells fail to develop surface properties for type-specific cell recognition if they are transiently exposed to BrdU during an early, critical age. Such cells do not proceed with histogenetic positioning, organization and differentiation and, instead, form a malformed cell mass. This effect of BrdU is correlated with BrdU incorporation into DNA, and it can be prevented by simultaneous treatment of the cells with cytosine arabinoside. The proposed working hypothesis is that, in this system, BrdU interferes with expression of genes controlling cognitive specification of the cell surface.