Follicle cells

No spermatozoa are seen on the egg surface or on the vitelline coat. After 5 h of treatment with 10 M TBTCl, a few spermatozoa, with very anomalous heads, have been detected. The absence of spermatozoa on the egg surface or on the vitelline coat could be explained by the absence of the follicle cells, which, in S. plicata, primarily play an attracting function. It was previously shown that TBTCl solution, either 10 or 10 M, induces anomalies in spermatozoa, unfertilized, and fertilized eggs of Ascidia malaca. In particular, the follicle cells detach from eggs and the test cells show anomalies in their nucleus and granules. Moreover, damaged spermatozoa are observed in the vitelline coat, but never in... 

Villa, L. Patricolo, E. Follicle cells of Styela plicata eggs (Ascidiacea), In Sawada, H. Yokosawa, H. Lambert, C. C. (Eds.), The Biology of Ascidians, Springer-Verlag, Tokyo, 2001. 

Lohka MJ, Hayes MK, Mailer JL 1988 Purification of maturation-promoting factor, an intracellular regulator of early mitotic events. Proc Natl Acad Sci USA 85 3009—3013 Mailer JL, Butcher FR, Krebs EG 1979 Early effects of progesterone on levels of cyclic adenosine 3 5 -monophosphate in Xenopus oocytes. J Biol Chem 254 579-582 Masui Y 1967 Relative roles of the pituitary, follicle cells, and progesterone in the induction of oocyte maturation in Ranapipiens. J Exp Zool 166 365-375 Masui Y, Markert CL 1971 Cytoplasmic control of nuclear behavior during meiotic maturation of frog oocytes. J Exp Zool 177 129-145... 

Thyroxine synthesis begins when iodide (I-) is transferred from the blood stream to the thyroid follicle cell by an active ATP-driven membrane pump mechanism this process is stimulated by cAMP following TSH stimulation of the gland. Iodide is transported through the follicular cell and secreted into the lumen of the follicle where it is oxidized to iodine and incorporated in to tyrosine residues by the enzyme thyroid peroxidase (TPO). 

Aggarwal BD, Calvi BR (2004) Chromatin regulates origin activity in Drosophila follicle cells. Nature 430 372-376... 

In some cases it is recommended to take radioactive iodine drugs such as iodotop (NaT ). It accumulates in the thyroid gland along with L-thyroxine and L-triiodothyronin, where radioactive decay takes place—weak 8-radiation destroys thyroid gland follicle cells, which leads to a gradual decline in thyroid hormone secretion. 

Once taken up by the thyroid gland, iodide undergoes a series of enzymatic reactions that incorporate it into active thyroid hormone (Figure 38-1). The first step is the transport of iodide into the thyroid gland by an intrinsic follicle cell basement... 

Development in Drosophila and other insects follows a somewhat different pathway, as is indicated in Fig. 32-6B. The egg, which is surrounded by follicle cells and 16 nurse cells, does not divide. However, its nucleus divides repeatedly, about once every nine minutes, to form -6000 nuclei. Only then do separating membranes form to give individual cells.9,285 316 317 During the first two hours the nuclei form a syncytium, in which they are embedded in a common cytoplasm, that allows free diffusion of signaling compounds. At first the nuclei are in the center, but later most migrate to the periphery and form a single layer of cells comparable to the blastoderm of amphibian cells. A few nuclei remain in the central cavity to become yolk cells, and some at the posterior pole become separated into pole cells. 

Rothnagel, J. A., and Rogers, G. E. (1986). Trichohyalin, an intermediate filament-associated protein of the hair follicle./. Cell Biol. 102, 1419-1429. 

The primary steps in thyroid hormone biosynthesis are shown schematically in Figure 31-2. Thyroid follicle cells take up and concentrate iodide from the bloodstream—this is significant because there must be a sufficient amount of iodine in the diet to provide what is needed for thyroid hormone production.55 Thyroid cells also manufacture a protein known as thy-... 

FIGURE 31-2 Thyroid hormone biosynthesis. Iodide is taken into the follicle cell, where it is converted by thyroid peroxidase to an oxidized form of iodine (Ip). h is transported to the follicle lumen, where it is bonded to tyrosine residues of the thyroglobulin [TGB] molecule. Iodinated TGB is incorporated back into the cell, where it undergoes lysis to yield the thyroid hormones T3 and T4. See text for further discussion. 

Iodide. Relatively large dosages of iodide (exceeding 6 mg/d) cause a rapid and dramatic decrease in thyroid function.35 In sufficient amounts, iodide inhibits virtually all the steps involved in thyroid hormone biosynthesis. For instance, high iodide levels limit the uptake of iodide into thyroid follicle cells, inhibit the formation of T4 and T3, and decrease the secretion of the completed hormones from the thyroid cell. 

Sevala V. L. and Davey K. G. (1993) Juvenile hormone dependent phosphorylation of a 100 kDa polypeptide is mediated by protein kinase C in the follicle cells of Rhodnius prolixus. Invert. Reprod. Dev. 23, 189-193. 

Sevala V. L., Davey K. G. and Prestwich G. D. (1995) Photoaffinity labeling and characterization of a juvenile hormone binding protein in the membranes of follicle cells of Locusta migratoria. Insect Biochem. Molec. Biol. 25, 267-273. 

Nilsson M, Engstrom G, Ericson LE (1986) Graded response in the individual thyroid follicle cell to increasing doses of TSH. Mol Cell Endocrinol 44 165-9 O Connor JC, Frame SR, Davis LG, Cook JC (1999) Detection of thyroid toxicants in a tier I screening battery and alterations in thyroid endpoints over 28 days of exposure. Toxicol Sci 51 54-70... 

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