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Biomedical subjects

C A Koch

Publications and source records attributed to C A Koch.

81 records · Page 5Linked to original sources
PubMed1985

Freeze fracture morphology of thyroid tight junctions in goats with different thyrotropin stimulation.

In the thyroid follicles and blood of goats with congenital hypothyroidism and goiter, abnormal iodoproteins (e.g. iodoalbumin) are found. To study the mechanism involved in the passage of these proteins between the follicles and the blood, the morphology of tight junctions in goiters and normal thyroids of goats was studied by means of freeze fracturing. The T4 and TSH levels of 16 goats were measured by RIA. Based on the TSH levels, the goats could be divided into three groups: a euthyroid group of eight goats with TSH levels between 28 and 55 mU/liter, a hypothyroid group of six goats with TSH levels higher than 199 mU/liter, and an intermediary group of two goats with TSH levels of 120 and 124 mU/liter, respectively. The euthyroid and intermediate animals had normal T4 levels (less than 49 nmol/liter), except for three newborn goats, which had T4 levels above 250 nmol/liter. The hypothyroid goats had T4 levels below 43 nmol/liter. The mean numbers of strands composing the tight junctions were negatively correlated with TSH levels. Hence, the tight junctions of the glands of hypothyroid goats are narrower and are composed of fewer strands than those of normal thyroids. This reduction in tight junction complexity may provide an explanation for the leakage of proteins into the follicles of goitrous glands.

Animals↗
PubMed1981

Nonfunctional thyroglobulin messenger RNA in goats with hereditary congenital goiter.

A goat strain with congenital goiter was studied as a model for human thyroid disoders. These goats were deficient in thyroglobulin (Tg), the precursor protein of the thyroid hormones T3 and T4. RNA coding for Tg (Tg-RNA) was detected in reduced amounts in the goiters and was almost absent from the membranes, where Tg is normally synthesized. This paper describes the preparation and characterization of a goat Tg cDNA plasmid and its use in the study of thyroglobulin gene expression in the goiter. We found that the goiter Tg-RNA is polyadenylated and has the same size as normal 33S goat TG mRNA. Thus, there are no major defects in the mRNA processing. However, in contrast to normal Tg mRNA, the goiter Tg-RNA was not translated into immunoprecipitable Tg subunits when injected into Xenopus oocytes. We conclude therefore that the goiter Tg-RNA has one or more alterations causing a lack of proper translation and/or a decreased cytoplasmic stability.

Animals↗
PubMed1969

Chromosome micromanipulation. 3. Spindle fiber tension and the reorientation of mal-oriented chromosomes.

Kinetochore reorientation is the critical process ensuring normal chromosome distribution. Reorientation has been studied in living grasshopper spermatocytes, in which bivalents with both chromosomes oriented to the same pole (unipolar orientation) occur but are unstable: sooner or later one chromosome reorients, the stable, bipolar orientation results, and normal anaphase segregation to opposite poles follows. One possible source of stability in bipolar orientations is the normal spindle forces toward opposite poles, which slightly stretch the bivalent. This tension is lacking in unipolar orientations because all the chromosomal spindle fibers and spindle forces are directed toward one pole. The possible role of tension has been tested directly by micromanipulation of bivalents in unipolar orientation to artificially create the missing tension. Without exception, such bivalents never reorient before the tension is released; a total time "under tension" of over 5 hr has been accumulated in experiments on eight bivalents in eight cells. In control experiments these same bivalents reoriented from a unipolar orientation within 16 min, on the average, in the absence of tension. Controlled reorientation and chromosome segregation can be explained from the results of these and related experiments.

Animals↗
PubMedDate not supplied

The exchange factor Ras-GRF2 activates Ras-dependent and Rac-dependent mitogen-activated protein kinase pathways.

Ras and Rac are membrane-associated GTPases that function as molecular switches activating intracellular mitogen-activated protein kinase (MAPK) cascades and other effector pathways in response to extracellular signals [1]. Activation of Ras and Rac into their GTP-bound conformations is directly controlled by specific guanine-nucleotide exchange factors (GEFs), which catalyze GDP release. Several Ras-specific GEFs that are related to the budding yeast protein Cdc25p have been described, whereas GEFs for Rac-related GTPases contain a region that is homologous to the oncoprotein DbI [2-3]. The Ras-GRF1 and Ras-GRF2 proteins, which couple Ras activation to serpentine receptors and calcium signals, contain both Cdc25 and DbI homology (DH) regions [3-4]. Here, we demonstrate that Ras-GRF2 is a bifunctional signaling protein that is able to bind and activate Ras and Rac, and thereby coordinate the activation of the extracellular-signal-regulated kinase (ERK) and stress-activated protein kinase (SAPK) pathways.

Anisomycin↗