Follicle Cell Proliferation Research Articles

Proliferation and differentiation of organoid hair follicle cells co-cultured with fat cells in collagen gel matrix culture.

Using rat skin, we studied the influence of fat cells on the proliferation and differentiation of organoid hair follicle cells in a three-dimensional collagen gel matrix culture system. We cultured organoid hair follicles embedded in collagen gel under each of the following three conditions: cell-free collagen gel for control experiments (condition 1); co-culture with fat cells in close apposition (condition 2); and co-culture with fat cells in spatial separation (condition 3). Outgrowths of epithelial cells from the organoid hair follicles associated with perifollicular proliferation of fibroblasts were observed under conditions 1 and 3. Under condition 2, proliferation of both organoid hair follicle cells and fibroblasts was inhibited, but differentiation of the hair follicle cells appeared to be accelerated. Fat cells are considered to have an inhibitory effect on the proliferation of perifollicular fibroblasts, which might have resulted in the inhibition of hair follicle cell proliferation and also in the better maintenance of normal follicular structure and integrity, allowing for hair-type differentiation to proceed. A direct accelerating effect of fat cells on hair follicle differentiation may also have been responsible. In a physiological state (co-culture with keratinocytes on the collagen gel), similar results were observed under conditions 1 and 2. The different findings under conditions 2 and 3 may be due to either of two possibilities: either the concentration gradient of the soluble factors released from fat cells, acting on either the hair follicle cells or the perifollicular fibroblasts as an inhibitor of proliferation, caused the difference in the results, or direct contact between the organoid hair follicle cells and fat cells may have influenced the accelerating effect of fat cells on the differentiation of hair follicle cells.

From differentiation to proliferation: the secretory amyloid precursor protein as a local mediator of growth in thyroid epithelial cells.

In various species, thyrotropin (TSH) is known to stimulate both differentiation and proliferation of thyroid follicle cells. This cell type has also been shown to express members of the Alzheimer amyloid precursor (APP) protein family and to release the secretory N-terminal domain of APP (sAPP) in a TSH-dependent fashion. In this study on binding to the cell surfaces, exogenously added recombinant sAPP stimulated phosphorylation mediated by mitogen-activated protein kinase and effectively evoked proliferation in the rat thyroid epithelial cell line FRTL-5. To see whether this proliverative effect of sAPP is of physiological relevance, we used antisense techniques to selectively inhibit the expression of APP and the proteolytic release of sAPP by cells grown in the presence of TSH. The antisense-induced inhibition was detected by immunoblot, immunoprecipitation, and immunocytochemical analyses. After the reduced APP expression and sAPP secretion, we observed a strong suppression of the TSH-induced cell proliferation down to 35%. Recombinant sAPP but not TSH was able to overcome this antisense effect and to completely restore cell proliferation, indicating that sAPP acts downstream of TSH, in that it is released from thyroid epithelial cells during TSH-induced differentiation. We propose that sAPP operates as an autocrine growth factor mediating the proliferative effect of TSH on neighboring thyroid epithelial cells.

Alpha-Spectrin is required for ovarian follicle monolayer integrity in Drosophila melanogaster.

To understand the role of the spectrin-based membrane skeleton in generating epithelial polarity, we characterized the distribution of membrane skeletal components in Drosophila ovarian follicle cells and in somatic clones of mutant cells that lack alpha-spectrin. Immunolocalization data reveal that wild-type follicle cells contain two populations of spectrin heterodimers: a network of alphabeta heterodimers concentrated on the lateral plasma membrane and an alphabetaH population targeted to the apical surface. Induction of somatic clones lacking alpha-spectrin leads to follicle cell hyperplasia. Surprisingly, elimination of alpha-spectrin from follicle cells does not appear to prevent the assembly of conventional beta-spectrin and ankyrin at the lateral domain of the follicle cell plasma membrane. However, the alpha-subunit is essential for the correct localization of betaH-spectrin to the apical surface. As a consequence of disrupting the apical membrane skeleton a distinct sub population of follicle cells undergoes unregulated proliferation which leads to the loss of monolayer organization and disruption of the anterior-posterior axis of the oocyte. These results suggest that the spectrin-based membrane skeleton is required in a developmental pathway that controls follicle cell monolayer integrity and proliferation.

Effect of Melatonin on the Anuran Thyroid Gland: Follicle Cell Proliferation, Morphometry, and Subsequent Thyroid Hormone Secretionin Vitroafter Melatonin Treatmentin Vivo

The thyroid gland controls the progress of metamorphosis, although other hormones influence metamorphic rate, including melatonin, which may coordinate metamorphosis with seasonal and light conditions. Melatonin directly antagonized the action of thyroxine (T4) in promoting regression of tadpole tail tipsin vitro,and this study sought to determine if it affects the thyroid axis of tadpoles as well. In an experiment sampling at 8-hr intervals for 24 hr, after melatonin treatment (15 μg/day for 12 days) of premetamorphicRana pipienstadpoles at approximately 1100 hr on 18L:6D, thyroid follicle cell height and lumen diameter were lowered by melatonin, but follicle cell proliferation was not significantly depressed. In a second experiment conducted under the same conditions, but sampling at 3-hr intervals for 24 hr, melatonin significantly lowered follicle cell labeling index and suppressed its ultradian (7.6 hr) rhythm, while shifting the peak of follicle lumen diameter to the dark instead of the light. Thus, melatonin tended to depress the thyroid of young tadpoles and suppress or shift its rhythms. Melatonin (10 μg/day for 5 days) injected into prometamorphicRana catesbeianatadpoles at 1930 hr on 18L:6D significantly altered subsequentin vitrothyroid function as determined by radioimmunoassay of media collected at intervals for 54 hr from cultured thyroids of injected control and melatonin groups, and a noninjected control group. Melatonin decreased T4secretion during the first 30 hr, but not during the last 24 hr of culture, suppressed 3,5,3‘-triiodothyronine (T3) secretion for 12 hr, and then raised T3output into the media above the control for the remainder of the culture period, increasing the T3:T4ratio. Injection alone increased both T3and T4secretion for the first 30 hr, but did not change the T3:T4ratio. The findings show that exogenous melatonin administeredin vivosignificantly modulated thyroid activity and morphometry directly and/or indirectly and comprise the first demonstration of an ef-fect of melatonin on the amphibian thyroid gland.

Differential effects of insulin-like growth factor-I and follicle-stimulating hormone on proliferation and differentiation of bovine cumulus cells and granulosa cells.

Effects of gonadotropins and peptide growth factors on 3H-thymidine incorporation, as an indicator of proliferation of granulosa cells and cumulus cells from bovine ovarian follicles during in vitro culture, were determined. Incorporation of 3H-thymidine in cumulus cells during 24-h culture in protein-free medium was about 100-fold greater than in granulosa cells from small follicles. Small but significant (p < 0.05) increases in incorporation of 3H-thymidine in cumulus cells (2.5-fold), but not in granulosa cells, resulted from addition of FSH, LH, or epidermal growth factor to culture media. Much larger, highly significant (p < 0.01) increases in 3H-thymidine incorporation resulted from exposure of both cumulus cells (18-fold) and granulosa cells (6-fold) to insulin-like growth factor-I (IGF-I). Addition of IGF-I together with FSH resulted in additive increases in 3H-thymidine incorporation in granulosa cells over a wide range of each agonist. In contrast, addition of FSH markedly decreased the stimulatory effect of a maximally effective concentration of IGF-I on incorporation in cumulus cells. Addition of estradiol, either alone or with IGF-I, had no consistent effect on 3H-thymidine incorporation in either cumulus cells or granulosa cells. Differentiated functions of cumulus and granulosa cells, including cumulus expansion (an indicator of hyaluronic acid secretion) and progesterone secretion, were investigated under the same culture conditions. FSH was highly effective in stimulation of cumulus cell expansion, with maximal expansion occurring at the lowest concentration tested (0.04 micrograms/ml). LH was effective only at considerably higher concentrations consistent with degree of contamination with FSH. IGF-I was ineffective in inducing cumulus expansion, either alone or together with FSH. FSH and IGF-I by themselves each stimulated progesterone secretion by both cumulus and granulosa cells, with further additive stimulatory effects by the two agents in combination. On a per cell basis, cumulus cells produced considerably more progesterone than granulosa cells under both basal and hormone-stimulated conditions. The results suggest that IGF-I has a dual role in follicle regulation--that it acts additively with FSH as an autocrine regulator of granulosa cell growth and, in the absence of FSH, as a paracrine regulator of cumulus cell proliferation in small antral follicles. The effect of FSH, by inducing cumulus expansion, may terminate further cumulus cell proliferation before ovulation.

Effects of various types of extracellular matrices on adhesion, proliferation, differentiation, and c-fos protein expression of porcine thyroid follicle cells.

Thyroid follicles in vivo are embedded in extracellular matrix (ECM). The composing epithelial cells are in close contact with ECM at the basal side. To examine cell-to-ECM interactions, we studied adhesion, proliferation and differentiation of porcine follicle cells monolayer-cultured on type I and IV collagen, fibronectin or laminin. At 3 h in culture, laminin had the lowest rate of cell adhesion. In proliferation, type IV collagen induced the highest level of nuclear bromodeoxyuridine intake. In a functional differentiation, laminin had about 3 times as much triiodothyronine production as the other ECM molecules. In confluent culture cells, we also examined an expression of c-fos protein, a transcription factor that plays crucial roles in signal transduction. Immunocytochemistry detected the protein mainly in the nuclei. Western blot showed that laminin induced the highest level of its expression. Thyrotropin (TSH, 10 mU/ml) did not affect adhesion of the cells on any of the substrata or proliferation of the cells on fibronectin; nor did TSH affect c-fos protein expression of the cells on the substrata except for fibronectin. Our results suggest that type IV collagen and laminin, major components of basement membrane, play positive roles in proliferation and differentiation of follicle cells, respectively, while laminin has no positive effect on adhesion of the cells at early culture; that the cells express c-fos protein even in contact inhibition of growth and its expression is regulated in part by ECM; and that ECM controls some behaviors of the cells in a TSH-dependent or TSH-independent manner.

Anterior pituitary and adrenal cortical hormones accelerate or inhibit tadpole hindlimb growth and development depending on stage of spontaneous development or thyroxine concentration in induced metamorphosis

The effect of prolactin, growth hormone, and various adrenal corticoids on hindlimb growth, development, and differentiation was studied in Rana pipiens larvae. Experiments were performed at different stages of spontaneous development and during metamorphosis induced in premetamorphic tadpoles by various concentrations of exogenous T4. Prolactin at 10 micrograms/day inhibited the limb at spontaneous premetamorphosis, had no effect at prometamorphosis or when administered with 3.8 nM T4, and synergized with T4 at 63 nM T4 and above. Growth hormone (10 or 20 micrograms/day) promoted limb growth and development during premetamorphosis but had no effect on spontaneous or induced metamorphosis thereafter, nor did it stimulate limb epidermal differentiation. The adrenal corticoids inhibited limb growth and epidermal cell proliferation during pre- and prometamorphosis but had no effect on limb morphogenesis or differentiation. The depressive effect of corticoids during spontaneous metamorphosis is at least partly through thyroid inhibition since hydrocortisone significantly reduced follicle cell height, lumen diameter, and cell proliferation in the thyroid. During induced metamorphosis, steroids (0.29 microM), especially corticosterone and aldosterone, antagonized the effect of 0.38 to 1.2 nM T4 on the limb. All steroids except deoxycorticosterone synergized with 3.8 nM T4, and at 31 nM T4, approximating the climax level with permeability factors taken into account, all corticoids synergized with T4 to promote limb growth and development. Aldosterone antagonized T4 at a higher T4 level than the other corticoids. The effect of all steroids except corticosterone was also corticoid dose-dependent. The results show the importance of the T4 concentrations in interactions of T4 with other hormones and suggest a scheme for hormonal control of limb growth and morphogenesis during metamorphosis. During premetamorphosis growth hormone synergizes with low endogenous T4 to promote initial limb growth and development while prolactin opposes this action. During prometamorphosis, as growth hormone and prolactin become ineffective corticosteroids begin to synergize with the rising level of endogenous T4. At climax, prolactin also augments the action of T4 to bring about rapid hindlimb growth.

Wool follicle morphology and cell proliferation in New Zealand Romney sheep: a seasonal comparison of fleeceweight-selected and control rams

Effects of selection for high fleeceweight in the New Zealand Romney sheep were investigated in relation to the morphology of individual follicles and changes in the germinative cell population of the follicle bulb. Two-year-old Romney rams, 10 from each of two selection lines (Massey University fleeceweight-selected (FWT) and control (CLT) flock), were run together on pasture for a period from June to early December. At three times during this observation period (June, August and November) skin samples were taken from their midside flanks after local injection of bromodeoxyuridine (BrdU), to assess proliferation of bulb cells and several dimensional measurements of the follicle bulb and dermal papilla. FWT sheep had larger follicle dimensions than CLT sheep during winter and summer, with a greater number of proliferating bulb cells. Both flocks showed a seasonal change in follicle size, with a decline during winter, but the size of the dermal papilla was less affected than the germinative tissue area. Measurements of proliferation density (number of proliferating cells per area/volume of bulb tissue) suggest that changes in proliferation density do not contribute to flock differences in fleece production. However, during summer, FWT showed a 40% advantage over CLT sheep in hourly cell production based on data from three dimensional follicle bulb extrapolation. The different genotypes showed variations in width, as well as area of cortex and inner root sheath (IRS), measured across the top of the dermal papilla. The expression of these differences was further enhanced through seasonal influences, suggesting that there is an interaction between genetic/flock influences and seasonal influences on cell distribution to cortex and inner root sheath.

Regulation of hair follicle development: an in vitro model for hair follicle invasion of dermis and associated connective tissue remodeling.

During embryonic development presumptive hair follicle cells of epithelial and mesenchymal origin are determined in defined body locations. This is followed by rapid proliferation of epithelial cells and associated penetration into the dermis in response to as yet undetermined signals. A collagen matrix culture system, which maintains the three-dimensional relationships of hair follicle cells to each other, was developed to study the regulation of the enlargement of immature hair follicles and the accompanying remodeling of the dermis. In studies with a heterogeneous dermis-derived preparation of murine hair follicles, ranging in size from the earliest down-growing budding cell mass to hair-forming follicles, we had previously shown that cell proliferation was stimulated by cholera toxin and epidermal growth factor, but only the epidermal growth factor-stimulated proliferation was accompanied by digestion of the collagen matrix due to release of collagenolytic enzymes. Further studies revealed that transforming growth factor-alpha also stimulated hair follicle cell proliferation and collagenase release. However, although transforming growth factor-beta inhibited the transforming growth factor-alpha-stimulated proliferation, it enhanced the release and activation of collagenases and other gelatin-degrading enzymes detectable by gelatin zymography. Stimulation of collagenolytic activity depended on the three-dimensional hair follicle structure and did not occur in monolayer cultures of hair follicle cells. Comparison of hair follicle buds with more developed dermis-derived hair follicles, plated at the same cell density (based on DNA content), suggested that a greater fraction of cells in the bud-stage follicle responded to the growth factors by release of collagenases. Possibly only the cells in the advancing portion of growing hair follicles that are closest to the dermal papilla cell cluster produce the collagenases in response to growth factors. To examine the participation of dermal papilla cells in collagenase release and activation, several immortalized rat whisker dermal papilla cell lines were co-cultured with mouse hair follicle buds. Co-culture resulted in a marked enlargement of follicles as well as activation of the 92-kDa type IV collagenase, produced by hair follicle buds, that correlated with ability of the dermal papilla cells to stimulate hair formation in grafts of hair follicle buds on nude mice. Dermal papilla cells cultured alone produced the 72-kDa type IV collagenase, which was also activated during co-culture with hair follicle buds. Thus, two activities, both relevant for hair follicle development, namely, cell proliferation and release and activation of collagenases, have been stimulated in immature hair follicle buds by either growth-factor supplementation or interaction with dermal papilla cells.(ABSTRACT TRUNCATED AT 400 WORDS)

Regulation of hair follicle development: An in vitro model for hair follicle invasion of dermis and associated connective tissue remodeling

During embryonic development presumptive hair follicle cells of epithelial and mesenchymal origin are determined in defined body locations. This is followed by rapid proliferation of epithelial cells and associated penetration into the dermis in response to as yet undetermined signals. A collagen matrix culture system, which maintains the three-dimensional relationships of hair follicle cells to each other, was developed to study the regulation of the enlargement of immature hair follicles and the accompanying remodeling of the dermis. In studies with a heterogeneous dermis-derived preparation of murine hair follicles, ranging in size from the earliest down-growing budding cell mass to hair-forming follicles, we had previously shown that cell proliferation was stimulated by cholera toxin and epidermal growth factor, but only the epidermal growth factor-stimulated proliferation was accompanied by digestion of the collagen matrix due to release of collagenolytic enzymes. Further studies revealed that transforming growth factor-α also stimulated hair follicle cell proliferation and collagenase release. However, although transforming growth factor-β inhibited the transforming growth factor-α-stimulated proliferation, it enhanced the release and activation of collagenases and other gelatin-degrading enzymes detectable by gelatin zymography. Stimulation of collagenolytic activity depended on the three-dimensional hair follicle structure and did not occur in monolayer cultures of hair follicle cells. Comparison of hair follicle buds with more developed dermis-derived hair follicles, plated at the same cell density (based on DNA content), suggested that a greater fraction of cells in the bud-stage follicle responded to the growth factors by release of collagenases. Possibly only the cells in the advancing portion of growing hair follicles that are closest to the dermal papilla cell cluster produce the collagenases in response to growth factors. To examine the participation of dermal papilla cells in collagenase release and activation, several immortalized rat whisker dermal papilla cell lines were co-cultured with mouse hair follicle buds. Co-culture resulted in a marked enlargement of follicles as well as activation of the 92-kDa type IV collagenase, produced by hair follicle buds, that correlated with ability of the dermal papilla cells to stimulate hair formation in grafts of hair follicle buds on nude mice. Dermal papilla cells cultured alone produced the 72-kDa type IV collagenase, which was also activated during co-culture with hair follicle buds. Thus, two activities, both relevant for hair follicle development, namely, cell proliferation and release and activation of collagenases, have been stimulated in immature hair follicle buds by either growth-factor supplementation or interaction with dermal papilla cells. The collagen matrix culture system allows investigation of the mechanism by which these activities are controlled under defined in vitro conditions.

Cell proliferation in the wool follicles of fleeceweight selected and control Romney rams

Two year old Romney rams from the Massey University fleeceweight-selected (FW) and control (C) lines, five from each line, were given arterial catheters into a branch of the deep circumflex artery on each side of the sheep, to permit local infusion into patches of skin on each lateral abdominal flank. One side of each sheep was infused with saline to give a direct FW v. C comparison, while the other side was infused with low levels of either growth hormone, thyroxine, prolactin or insulin for 4 days. At the end of the infusion period, biopsy samples were taken from each flank for measurement of follicle activity, particularly bulb cell proliferation using intracutaneous injections of 5-bromo-2'-deoxyuridine (BrDU). After a period of recovery, the saline and treated sides were reversed and another series of infusions were performed and biopsies undertaken. Wool from the FW sheep had greater fibre length growth rate and fibre diameter than the C wool (P &lt; 0.05). This was associated with larger follicle bulbs (P &lt; 0.05) and greater numbers of BrDU labelled cells (P &lt; 0.05) in the bulbs of the FW skin. In a restricted number of samples from two sheep, where BrDU was successfully given as repeated intracutaneous injections into the same site (one at 72 h and one at 6 h prior to biopsy), 55-60% of the numbers of BrDU cells in a section of bulb appeared in a section of the shaft of the same follicle. When converted to three dimensions, the efficiency of labelled bulb cell movement into the shaft was 30-40%. Hormonal infusions showed few significant effects with the restricted numbers of animals in each treatment. Thyroxine reduced the size of follicle bulbs (P &lt;0.05) and the numbers of labelled bulb cells in skin from the infused area.

Modulation of Hair Follicle Cell Proliferation and Collagenolytic Activity by Specific Growth Factorsa

Modulation of Hair Follicle Cell Proliferation and Collagenolytic Activity by Specific Growth Factors^a

Hair Growth and Hair Follicle Cell Proliferation in Histocultured Mouse Skin

Hair Growth and Hair Follicle Cell Proliferation in Histocultured Mouse Skin

Negative signaling by surface IgM on B cells isolated from ileal Peyer's patch follicles of sheep

Lymphoid follicles from the sheep ileal Peyer's patch (PP) were used to prepare a cell suspension consisting of 98% surface IgM-positive (sIgM+) B cells and 1% T cells. Co-stimulation of follicular cells with pokeweed mitogen and either recombinant bovine interleukin 1 (IL 1) or IL 2 resulted in a marked proliferative response. In contrast, the addition of soluble F(ab')2 rabbit anti-sheep Ig completely inhibited the proliferative response induced by pokeweed mitogen and IL 1 or IL 2 co-stimulation. Anti-Ig inhibition of B cell proliferation was specific for ileal PP follicular cells and was not observed with mesenteric lymph node cells or splenocytes. Furthermore, suppression of ileal PP follicular B cell proliferation required at most divalent cross-linking of sIg was independent of Fc receptors, but was dependent on the concentration of anti-Ig and required 48 h for maximal effect. Negative signaling by sIgM indicates that ileal PP follicular B cells are functionally distinct from B cells in other secondary lymphoid tissues. Also, the present observations are consistent with previous reports indicating that B cell proliferation in ileal PP follicles is antigen independent.

Growth factors specifically alter hair follicle cell proliferation and collagenolytic activity alone or in combination

Abstract A three-dimensional culture model for isolated murine pelage hair follicles in a type I collagen gel has been utilized to study the effects of selected growth factors on follicle cell proliferation and release of collagenolytic factors. Cultured follicle organoids differentially express cytokeratins 6 and 14 in a pattern suggesting they contain cells of the outer root sheath, inner root sheath and follicle matrix. Using incorporation of [ 3H]thymidine as a measure of proliferation, follicle organoids show a peak of DNA synthesis between day 1 and 5 of culture, depending on plating density, and then have a low rate of DNA synthesis. Thymidine incorporation is stimulated by transforming growth factor-alpha (TGF-α) in a dose-dependent response. Only peripheral cells presumably of the outer root sheath, incorporate thymidine in basal or stimulated conditions. TGF-β1 and TGF-β2 inhibit constitutive cell proliferation and oppose growth stimulation by TGF-α. Hair follicles lyse the collagen gel matrix when exposed to certain cytokines. Epidermal growth factor (EGF) and TGF-α stimulate gel lysis, but TGF-βl, TGF-β2 and cholera toxin do not. Other skin-derived cells, such as interfollicular epidermal cells, dermal fibroblasts, or combinations thereof, do not lyse gels in this culture model even when exposed to growth factors. Combinations of EGF or TGF-α with TGF-β1 or TGF-β2 are synergistic for collagenase release. These cytokines stimulate release of multiple species of matrix metalloproteinases, but the 92-kDa and 72 kDa type IV procollagenases and their activated derivatives predominate on zymograms. In cytokine-stimulated follicles, both peripheral and centrally located cells in the organoids express the 72-kDa type IV collagenase and a similar immunostaining pattern is present in developing follicles in vivo. Thus growth factors appear to work in concert for certain hair follicle responses and in opposition for others. These combined actions may play a role in different phases of hair follicle development that require cell replication and invasion into the deeper dermis.

Effects of Dietary Iodine on Chemical Induction of Thyroid Carcinoma

Effects of dietary iodine on the induction of thyroid carcinoma using N-nitrosobis(2-hydroxypropyl)amine (BHP) were studied. Male Wistar rats were fed with an iodine-adequate diet (IAD group), an iodine-rich diet (IRD group) and an iodine-deficient diet (IDD group), respectively, until the time of sacrifice. From the 2nd experimental month, animals were injected with BHP once a week for 10 weeks. In the IAD and IRD groups, benign nodules and papillary carcinoma were found. The incidence of rats with benign nodules was 100% in both groups and animals with papillary carcinoma in the IAD and IRD groups comprised 33% and 29%, respectively. The area of the thyroid gland occupied by nodular lesions was much narrower in the IRD group than in the IAD group. In the IDD group, the thyroid showed marked enlargement due to multiple nodular proliferation of follicle cells. The incidence of rats with carcinoma was 100%, and not only papillary but also follicular carcinoma and one pulmonary metastasis were found. As the iodine content of the diet decreased, the nodular lesions increased in width and number, and the incidence of carcinoma in rats became higher. These effects of dietary iodine are probably related to the goitrogenic and/or promoting effects of TSH.

Granulosa cell proliferation in very small follicles of cycling rats studied by long-term continuous tritiated-thymidine infusion.

It is generally believed that in adult rodents the vast majority of very small follicles (less than 20 granulosa cells in cross section) are not growing. However, the only data to support this assumption were collected with methods that may not be sufficiently sensitive to distinguish between nongrowing follicles and slowly growing follicles. In this study, the method of long-term continuous [3H]thymidine (3H-TdR) infusion was used to examine growth of very small follicles. Young adult rats were given continuous infusions of 3H-TdR for up to 7 days. Autoradiographs were prepared from 2-microns-thick sections of the ovaries. The proportion of labeled very small follicles increased as the duration of the infusion increased. After 7 days of continuous 3H-TdR infusion, 37% of follicles with 4 or fewer granulosa cells had at least one labeled granulosa cell, as did 68% of follicles with 5 8 granulosa cells, 86% of follicles with 9 12 granulosa cells, and 100% of follicles with 13 or more granulosa cells. The number of labeled cells per labeled follicle (the labeling index) also increased with increasing infusion time. However, few follicles had labeling indices of 100%, even after 7 days of continuous 3H-TdR infusion. These results suggest that a substantial fraction of very small follicles is growing in adult cycling rats; however, the rate of growth appears to be quite slow.

Growth factors in ovarian function.

Medical Research Centre, Prince Henry's Hospital, St Kilda Road, Melbourne, Victoria 3004, Australia Keywords: ovary; granulosa; theca; growth factors The studies of the effects of epidermal growth factor (EGF) and fibroblast growth factor (FGF) on bovine granulosa cells under chemically defined conditions in vitro first indicated that these growth factors have a role in stimulation of follicle cell proliferation (Gospodarowicz et al., 1977). Even now, however, relatively few data in respect of the mitogenic action of these growth factors on follicle cells are available and most studies have concentrated on the role of growth factors in control of functional differentiation of follicle cells. This probably reflects the technical and interpretive difficulties associated with stimulation of follicle cell mitosis under defined conditions. It is now evident that a range of growth factors influence not only proliferation but also functional differentiation of ovarian follicle cells. The growth factors of specific interest are

B cell proliferation in follicles, germinal centre formation and the site of neoplastic transformation in Burkitt's lymphoma.

Both the nature of germinal centres and the origin of Burkitt lymphoma have given rise to an exceptional level of divergent speculation. The histological similarities between this tumor and germinal centres was recognised as long ago as 1961 by O’Conor. Mann et al (1976) noted that several American patients with Burkitt lymphoma had tumors which appeared to arise in germinal centres in lymph nodes or Peyer’s patches. In a careful review of the histopathological evidence for this relationship Lennert (1978) concluded that on morphological grounds the Burkitt lymphoma cell most closely resembled an intermediate between a true centroblast and a B blast cell. This paper reports the findings of a study of synchronised germinal centre formation in rats. It shows that germinal centre formation is most apparent in primary B cell responses; secondary responses being associated with massive extrafollicular B cell responses. Finally the phenotype of germinal centre cells is compared with that of cells derived from Burkitt lymphoma. It is concluded that there is an extraordinary concordance between the cells found in normal germinal centres and the neoplastic cells of Burkitt lymphoma.

The differentiation and proliferation of follicle cells during oocyte growth in Lacerta sicula

The follicular epithelium of the lizard oocytes undergoes structural and morphological modifications throughout oocyte growth. During this process the number of follicle cells increases and the epithelium acquires a multilayered and polymorphic organization which is characterized by the appearance of large follicle cells (intermediate and pyriform cells). The number of large cells also increases during oocyte growth and this increase parallels that of small cells. However, only the small cells become labelled one hour after [3H-]thymidine administration. Large cells have been found labelled after a longer period of time, i.e. 4--5 months after isotope injection. All these results together indicate that large follicle cells arise from the differentiation of small cells.