Early stages in development of the Escherichia coli cell-division site

Development of the Escherichia coli cell division site was studied in wild-type cells and in non-septate filaments of ftsZ null and ftsZTs mutant cells. Localized regions of plasmolysis were used as markers for the positions of annular structures that are thought to be related to the periseptal annuli that flank the ingrowing septum during cytokinesis. The results show that these structures are localized at potential division sites in non-septate filaments of FtsZ^- cells, contrary to previous reports. The positions of the structures along the long axis of the cells in both wild-type cells and FtsZ^- filaments were unaffected by the presence of plasmolysis bays at the cell poles. These results do not agree with a previous suggestion that the apparent association of plasmolysis bays with future division sites was artefactual. They support the view that division sites begin to differentiate before the initiation of septal ingrowth and that plasmolysis bays and the annular attachments that define them, mark the locations of these early events in the division process.     

Gas tensions within the egg of the quail (Coturnix c. Japonica) during the closing stages of embryonic development

• 1.1. The respiratory status of the embryonic quail during the two days prior to hatching was assessed by measuring the gas tensions within the air space of the egg and of blood collected from the chorioallantois.
• 2.2. When the lungs became inflated there was a significant decrease in the pO₂ of the gas in the air space.
• 3.3. After pipping, there was a rise in the pO₂ and fall in the pCO₂ within the air space, together with corresponding changes in the blood.
• 4.4. The outer shell membrane remained intact until the onset of hatching.
• 5.5. These results were compared with those obtained by other workers using the domestic fowl.

     

Effects of conditioned media on porcine embryos at different stages of development

The objective of our study was to determine the effect of conditioning media with homologous porcine uterine cells on the developmental rate of porcine embryos. Cell monolayers were prepared by selective dissection and digestion of sections from the uterus of prepuberal gilts that were primed with PMSG and hCG. Conditioned media were used with 2 type of embryos: 4-cell stage (Experiment 1) or blastocyst stage (Experiment 2). In Experiment 1, embryos were collected surgically by flushing the oviducts, 36 to 48 h following the first of 2 inseminations. Embryos were cultured in Whitten's medium containing 1.5% BSA as a protein source until they attained the 4-cell stage. Embryos at the 4-cell stage were cultured randomly in either Whitten's medium with 1.5% BSA or Whitten's medium with 1.5% BSA that was previously conditioned for 24 h with an endometrial epithelial cell monolayer. Embryos were cultured in 50-microl drops covered with oil in a 38.5 degrees C, 5% CO(2) in air incubator. There was no advantage to using the conditioned media with the 4-cell stage embryos. The embryos were less developed than those cultured in nonconditioned Whitten's medium (P <0.001). In Experiment 2, embryos were cultured at the blastocyst stage. They were recovered the same way as in Experiment 1 and then cultured in Whitten's medium containing 1.5% BSA until they reached the blastocyst stage. At the blastocyst stage (Day 6), embryos were randomly assigned to 1 of the 6 following treatments: Whitten's with 1.5% BSA or Whitten's plus 1.5% BSA that was previously conditioned with endometrial epithelial cell monolayer, TCM-199 containing 0.4% BSA or TCM-199 plus 0.4% BSA that was previously conditioned with endometrial epithelial cell monolayer, finally, TCM-199 containing 10% serum or TCM-199 plus 10% serum that was previously conditioned with endometrial epithelial cell monolayer. Results show that initiation of hatching was significantly enhanced by conditioning the Whitten's media.     

Early stages of development of the Taenia solium metacestode in pigs

In order to identify the early stages of Taenia solium metacestodes, 12 pigs were each fed 100,000 viable eggs and later killed and necropsied at different times after infection. Hematoxylin-eosin (HE) and immunohistochemical techniques (IHCs) were used to identify onchospheres and cysticerci in different tissues. At 2 days postinfection (dpi) structures compatible with onchospheres were found in the lumen of the small intestine, and in the mesenteric blood vessels and lymph nodes. At 4 dpi, these same structures were observed in the small intestine, the liver, and skeletal muscles. Between 6 and 39 dpi, they were found only in skeletal muscles. Between 2 and 6 dpi the postonchospheres were circular and oval shaped and measured between 6 and 34 x 27 microm. From 14 to 39 dpi, well-developed metacestodes 550 x 750 microm were observed. IHCs support the identification of early stages of T. solium.     

Early embryo development of the bird egg subjected to a magnetic field

Chick and quail eggs exposed during the first 4 or 7 days of incubation to 50 Hertz and 5 Gauss sinusoidal magnetic fields developed normally. The percentages of dead and abnormal embryos observed in such conditions are identical to those arising spontaneously in control eggs.     

Heat production during early development of frog egg

The production of heat in the fertilized eggs, during the early development of the Japanese pond frog, Rana brevipoda porosa, was measured using a pyroelectric detector constructed with a polyvinylidene fluoride film. One and 2 μW of heat production was detected during the cleavage periods in the embryogenesis of the 2-cell embryo and the 4-cell embryo, respectively. The heat production increased stepwise with the cleavage in the embryogenesis of each stage. In comparison with the heat production during the inter-cleavage periods, a larger amount was noted at the cleavage periods in the two embryonic stages.     

Early stages in biofilm development in methanogenic fluidized-bed reactors

Summary Biofilm development in methanogenic fluidized-bed reactors with sand as the carrier was studied on a laboratory scale. The microorganisms present in consecutive layers of the biofilm of mature sludge granules were preliminarily characterized on the basis of their morphology, element composition and adhesion capacity and were compared to bacteria which take part in the initial colonization of sand. The early phase of biofilm development was monitored with reactors receiving waste-waters containing different mixtures of volatile fatty acids and inoculated with fluidized-bed reactor effluent for different lengths of time. The results obtained indicate that facultative anaerobic bacteria abundantly present in the outermost biofilm layers of mature sludge granules are probably the main primary colonizers of the sand. Methanothrix spp. or other methanogens were rarely observed among the primary colonizers. The course of biofilm formation was comparable under the various start-up conditions employed including variations in waste-water composition, inoculation and anaerobicity. However, omission of waste-water and thus of substrate resulted in rapid wash-out of the attached biomass. Offprint requests to: W. Heinen     

Early morphogenesis in the platyhelminthes with special reference to egg development and development of cestode larvae

Early development of fertilized eggs is reviewed for the main groups within the phylum Platyhelminthes (Turbellaria, Temnocephaloidea, Monogenea, Digenea, Cestodaria and Cestoda). The Turbellaria show two different patterns of embryological development consequent on whether yolk material is contained within the ovum membrane (endolecithal) or whether yolk is added to the outside of the ovum (ectolecithal). In the parasitic groups, those that are oviparous or ovoviviparous produce shelled eggs of the ectolecithal type and, in addition, there are viviparous forms in which egg development shows variations and the amount of yolk, where present, is reduced. In every case examined, however, cleavage is of the spiral type. Within the Cestoda, clear distinction is made between those groups (orders) of worms which are oviparous as compared to those which are viviparous. It is suggested that oviparity is more primitive (ancestral) than viviparity based on adult morphology and on the evidence of life-cycle studies.The continued, post-oncospheral development of cestodes is described as is the ultrastructure of various representative cercoid larval forms. These include: the procercoid of Pseudophyllidea and Haplobothrioidea; the cercoid of Tetraphyllidea; and, within the Cyclophyllidea, the cercoscolex of the Dilepididae, the cysticercoid of the Hymenolepidae, and the cysticercus of the Taeniidae. During post-oncospheral development, in every case examined the posterior part of the developing larva, the cercomer, can be characterized by a microvillar tegument (at least during early development) whereas the more anterior larval body itself, destined to develop in the definitive host, develops microtriches. Modifications to the cercomer, and its microvilli, in the later stages of post-oncospheral development, occur particularly in the more advanced Cyclophyllidea such as the Taeniidae and in some Hymenolepididae.     

Changes in membrane potential during mouse egg development

The electrical membrane potential (E_m) was measured in the developing mouse egg with intracellular microelectrodes. The oocyte had a low negative E_m of ?8.3 ± 0.8 mV (mean ± SE) when immature, which decreased and reversed polarity to a small positive value (+1.9 ± 0.2 mV) in the mature ovulated oocyte. After fertilization E_m returned to a negative value (?9.2 ± 0.5 mV) similar in magnitude to that observed in immature oocytes and then increased significantly (P < 0.01) at both the two-cell (?10.7 ± 0.3 mV) and morula stage (?12.8 ± 0.7 mV) and leveled out at the blastocyst stage (?12.9 ± 0.7 mV). Average potential difference recorded across the blastocoele wall of not fully expanded blastocysts was ?5.0 ± 0.5 mV. These data represent the first report on membrane potentials of the mammalian egg during development. A striking similarity is seen in the relative changes in E_m throughout development of the mouse egg in comparison to those seen in other invertebrate and vertebrate eggs.     

Histogenesis of the rat thymic medulla during first stages of development

We investigated first stages of thymic medulla organisation in foetuses of Wistar strain rats. between 13th and 17th days of foetal life (GD). Medullary cells were identified by immunocytochemical localisation of neuron-specific enolase (NSE) as well as by traits of ultrastructure. The first thymic medullary precursor cells which were reactive for NSE were at first spread all over the thymic primordium. In the period of thymus colonisation by lymphoid cells, the following stages were distinguished in medulla organisation: (1) migration of NSE+ cells to the central portion of the thymus (GD 14-15), (2) small medullary epithelial patches, distributed within the thymus (GD 16), and (3) expansion of medullary patches into medullary compartment (GD 17). At the second and third stages of the medulla organisation, an increase in the number of NSE+ cells, followed by differentiation of their ultrastructure and increase in their biological activity were observed. We conclude that formation of medullary architectural pattern is controlled by interactions between maturing epithelial cells and developing lymphoid cells and by angiogenesis in the region.