Follicle formation in the embryonic chick thyroid. III. Initiation of follicle formation

It has been proposed that the follicular spaces in the thyroid form by either the coalescence of intracellular droplets or by separation of cell apices by secretion into the extracellular space. On the basis of examination of thyroid primordia in early chick embryos this study provides evidence that in the chick, at least, follicle formation conforms to the second model. The first indications of change in the chick thyroid is the appearance of interdigitations of the cell apices. These interdigitations form microvilli as the two surfaces become separated and the follicular space is established. Vesicles with two types of contents can be identified in proximity with the cell surface during follicle formation, but it is not clear if either the dense particulate or the more electron-lucid materials that they contain actually enter the follicular space. Neither removal of the pituitary gland by decapitation nor inhibition of collagen synthesis and a concomitant failure of the invasion of capsular mesenchyme prevents the initiation of normal follicle formation.     

Reaginic antibody formation in the mouse. VII. Depression of the ongoing IgE antibody formation by suppressor T cells.

The ongoing IgE antibody formation against ovalbumin (OA) in high responder mice was depressed by i.v. injections of either native or urea-denatured ovalbumin (UD-OA). Adoptive transfer experiments to determine the helper function of spleen cells from the treated animals showed that helper function for both IgE and IgG antibody responses diminished after treatment. Evidence was obtained that treatment suppressed the expansion of IgE-G memory cells. When the same treatment with OA or UD-OA was given to OA-primed mice before the appearance of IgE antibody in their serum, OA-specific splenic suppressor T cells were demonstrable. Thus, the transfer of splenic T cells from treated mice into normal mice suppressed the primary IgE and IgG antibody responses of the recipeints to DNP-OA. It was also found that the transfer of the splenic T cells from UD-OA-treated mice into OA-primed mice depressed ongoing IgE antibody formation in the recipients. The results suggested strongly that the decrease of helper function and the depression of ongoing IgE antibody formation by repeated injections of UD-OA was caused by generation of antigen (OA)-specific suppressor T cells.     

Splicing and the formation of stable RNA.

To determine whether RNA splicing plays an obligatory role in gene expression, we have constructed a series of SV40-transducing viruses carrying various combinations of splice junctions derived from the viral genome and a mouse globin gene. All of the viruses that retain at least one functional splice junction, derived from either the viral or the mouse genome, encode stable hybrid RNAs. In contrast, a virus from which all the splice junctions have been removed fails to produce any detectable stable RNA. These results suggest that splicing is a prerequisite for stable RNA formation.     

Ganglia formation of the peripheral nervous system.

Embryologic studies have shown that the ganglions of the peripheral nervous system are formed by the neuroblasts from the central nervous system. The histotopography of the neurons and their segmental communications with the central nervous system are established experimentally (segmental section of the ventral roots and resection of the spinal nodes: 100 experiments). It is proved that the neurons, which communicate with the definite segment of the spinal cord, are diffusely distributed in the ganglion mass.     

Pattern formation in the cerebellar cortex.

The cerebellar cortex is subdivided rostrocaudally and mediolaterally into a reproducible array of zones and stripes. This makes the cerebellum a valuable model for studying pattern formation in the vertebrate central nervous system. The structure of the adult mouse cerebellar cortex and the series of embryological events that generate the topography are reviewed.     

Mechanics of Rouleau formation.

The formation of rouleau of red blood cells is considered from the standpoint of adhesion theory. With the use of the elastic properties of the red blood cell membrane obtained from previous work, the strain energy of the red blood cell in rouleau formation has been computed. The surface energy of adhesion for the bonding of two red blood cells is then computed from the variation of this strain energy. Computed cell shapes agree well with experiments.     

Endogenous formation of dimethylamine.

Exposure of rats to heat (39 +/- 1 degree C) decreased H2O2 generation in mitochondria of the liver, but not of the kidney or the heart. The effect was obtained with three substrates, succinate, glycerol 1-phosphate and choline, with a decrease to 50% in the first 2-3 days of exposure, and a further decrease on longer exposure. The dehydrogenase activity with only glycerol 1-phosphate decreased, which is indicative of the hypothyroid condition, whereas choline dehydrogenase activity remained unchanged and that of succinate dehydrogenase decreased on long exposure. The serum concentration of thyroxine decreased in heat-exposed rats. Thyroxine treatment of rats increased H2O2 generation. Hypothyroid conditions obtained by treatment with propylthiouracil or thyroidectomy caused a decrease in H2O2 generation and changes in dehydrogenase activities similar to those with heat exposure. Treatment of heat-exposed or thyroidectomized rats with thyroxine stimulated H2O2 generation by a mechanism apparently involving fresh protein synthesis. The results indicate that H2O2 generation in mitochondria of heat-exposed animals is determined by thyroid status.     

On the mode of formation of tetrahydro-beta carbolines.

The condensation of tetrahydro-β-carboline (TBC) takes place if serotonin is incubated with 5-MTHF and the cytosol fraction from rat brain as an enzymatic source. Such a formation occurs to a lesser extent if the enzyme(s) is omitted from the incubation mixture. The conditions of the enzymatic as well as the non-enzymatic mode of formation of TBC are investigated. It could be shown by addition of semicarbazide to the incubation medium that formaldehyde is an intermediate in the production of TBC. The biological significance of TBC will be discussed.