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Ketan Patel

Publications and source records attributed to Ketan Patel.

At least 37 records · Page 2Linked to original sources
PubMed2004

Intrinsic cartilage-forming potential of dermomyotomal cells requires ectodermal signals for the development of the scapula blade.

The avian scapula has a dual origin. The cranial part derives from the somatopleure of the forelimb field, while the caudal part, the scapula blade, originates from the dermomyotomes of the cervicothoracic transition zone. Thus, these dermomyotomes have, in addition to the well-known myogenic, angiogenic, and dermogenic potential, the ability to form cartilage. The scapula blade is therefore a derivative of dermomyotomal chondrogenesis. Although the mechanisms that direct the sclerotomal chondrogenesis are beginning to be understood, little is known about dermomyotomal chondrogenesis. Here, we address the mechanisms that control dermomyotomal cells to become chondrocytes. After heterotopic transplantation of dorsal epithelial somite halves from the scapula-forming level to the cervical level, the grafted tissue retains the capability to form cartilage, indicating that the dermomyotomal chondrogenic potential must be specified during anterior-to-posterior regionalization of the paraxial mesoderm. Furthermore, we show that signals from the ectoderm are required, allowing dermomyotome cells to express markers associated with the chondrogenic lineage.

Animals↗
PubMed2004

Sonic Hedgehog functions by localizing the region of proliferation in early developing feather buds.

Feathers are formed following a series of reciprocal signals between the epithelium and the mesenchyme. Initially, the formation of a dense dermis leads to the induction of a placode in the overlying ectoderm. The ectoderm subsequently signals back to the dermis to promote cell division. Sonic Hedgehog (Shh) is a secreted protein expressed in the ectoderm that has previously been implicated in mitogenic and morphogenetic processes throughout feather bud development. We therefore interfered with Shh signaling during early feather bud development and observed a dramatic change in feather form and prominence. Surprisingly, outgrowth did occur and was manifest as irregular, fused, and ectopic feather domains at both molecular and morphological levels. Experiments with Di-I and BrdU indicated that this effect was at least in part caused by the dispersal of previously aggregated proliferating dermal cells. We propose that Shh maintains bud development by localizing the dermal feather progenitors.

Animals↗
PubMed2004

Wnt 6 regulates the epithelialisation process of the segmental plate mesoderm leading to somite formation.

In higher vertebrates, the paraxial mesoderm undergoes a mesenchymal to epithelial transformation to form segmentally organised structures called somites. Experiments have shown that signals originating from the ectoderm overlying the somites or from midline structures are required for the formation of the somites, but their identity has yet to be determined. Wnt6 is a good candidate as a somite epithelialisation factor from the ectoderm since it is expressed in this tissue. In this study, we show that injection of Wnt6-producing cells beneath the ectoderm at the level of the segmental plate or lateral to the segmental plate leads to the formation of numerous small epithelial somites. Ectopic expression of Wnt6 leads to sustained expression of markers associated with the epithelial somites and reduced or delayed expression of markers associated with mesenchymally organised somitic tissue. More importantly, we show that Wnt6-producing cells are able to rescue somite formation after ectoderm ablation. Furthermore, injection of Wnt6-producing cells following the isolation of the neural tube/notochord from the segmental plate was able to rescue somite formation at both the structural (epithelialisation) and molecular level, as determined by the expression of marker genes like Paraxis or Pax-3. We show that Wnts are indeed responsible for the epithelialisation of somites by applying Wnt antagonists, which result in the segmental plate being unable to form somites. These results show that Wnt6, the only known member of this family to be localised to the chick paraxial ectoderm, is able to regulate the development of epithelial somites and that cellular organisation is pivotal in the execution of the differentiation programmes. We propose a model in which the localisation of Wnt6 and its antagonists regulates the process of epithelialisation in the paraxial mesoderm.

Animals↗
PubMed2004

Follistatin complexes Myostatin and antagonises Myostatin-mediated inhibition of myogenesis.

Follistatin is known to antagonise the function of several members of the TGF-beta family of secreted signalling factors, including Myostatin, the most powerful inhibitor of muscle growth characterised to date. In this study, we compare the expression of Myostatin and Follistatin during chick development and show that they are expressed in the vicinity or in overlapping domains to suggest possible interaction during muscle development. We performed yeast and mammalian two-hybrid studies and show that Myostatin and Follistatin interact directly. We further show that single modules of the Follistatin protein cannot associate with Myostatin suggesting that the entire protein is required for the interaction. We analysed the interaction kinetics of the two proteins and found that Follistatin binds Myostatin with a high affinity of 5.84 x 10(-10) M. We next tested whether Follistatin suppresses Myostatin activity during muscle development. We confirmed our previous observation that treatment of chick limb buds with Myostatin results in a severe decrease in the expression of two key myogenic regulatory genes Pax-3 and MyoD. However, in the presence of Follistatin, the Myostatin-mediated inhibition of Pax-3 and MyoD expression is blocked. We additionally show that Myostatin inhibits terminal differentiation of muscle cells in high-density cell cultures of limb mesenchyme (micromass) and that Follistatin rescues muscle differentiation in a concentration-dependent manner. In summary, our data suggest that Follistatin antagonises Myostatin by direct protein interaction, which prevents Myostatin from executing its inhibitory effect on muscle development.

Animals↗
PubMed2004

EphA4, RhoB and the molecular development of feather buds are maintained by the integrity of the actin cytoskeleton.

The development of feather buds is a highly ordered process involving epithelial-mesenchymal signalling. Cellular morphology is determined by the actin cytoskeleton, which is controlled by networks of regulators such as the GTPases. EphA4 belongs to a receptor tyrosine kinase family that has been consistently shown to regulate the cytoskeleton via Rho family GTPases in neural development and is expressed in early stages of feather bud development though its role has not been defined. We therefore used an in vitro skin culture system to interfere with EphA4 levels in feather buds using anti-sense oligonucleotides, demonstrating a severe effect on both their number and morphological form. Analysis of the Rho family of GTPases revealed that this effect was mediated by the GTPase RhoB, the expression of which was altered in response to altered levels of EphA4. In addition, the inhibition of RhoB mimicked the effects of reduced EphA4 levels on feather development. Significantly, manipulation of cytoskeletal dynamics revealed that those cells undergoing morphogenetic change regulate the patterning signals responsible for initiating feather development. We propose that this molecular maintenance mechanism between EphA4-RhoB and the actin cytoskeleton converges or coordinates with other morphogenic signalling systems to control feather bud development.

Actins↗
PubMed2004

Decamethonium bromide-mediated inhibition of embryonic muscle development.

This study determined the effect of decamethonium bromide (DMBr), a non-competitive blocker of the neuromuscular junction, on skeletal muscle development during chick embryogenesis. Decamethonium bromide caused generalized edema and high mortality with treated embryos rarely surviving beyond day 16 of incubation. Muscle degeneration was grossly evident on the muscles of abdomen, pectoral girdle, and leg. Semi-thin sections showed a high infiltration of macrophages in treated embryos and a massive degenerative process. Electron microscopy showed that both fast and slow fibers formed in the control and treated embryos, but those of the treated embryos failed to form myofibrils. Other organ systems, such as the heart and the gut, appeared histologically normal throughout the course of treatment. To investigate possible nerve independent action of DMBr on muscle development we determined the effect of this compound on the growth and differentiation of the C2C12 skeletal muscle cell line. DMBr treatment of C2C12 cell cultures did not affect the growth or survival of the cells, even at a tenfold higher concentration than that used in ovo, but myosin heavy chain expression was dramatically inhibited. We conclude that DMBr has a nerve independent blocking inhibition effect on myosin heavy chain synthesis in the developing avian embryo besides the recognized role as a non-competitive post-synaptic blocker of the neuromuscular junction.

Animals↗
PubMed2004

Relationship of GnRH-stimulated LH release to episodic LH secretion and baseline endocrine-metabolic measures in women with polycystic ovary syndrome.

BACKGROUND AND OBJECTIVE: In polycystic ovary syndrome (PCOS) inappropriate gonadotrophin secretion is characterized by increased pulse frequency and amplitude, elevated 24-h mean serum concentrations, and greater responses to GnRH. While the mechanism(s) responsible for this increased release of LH are not well understood, enhanced LH secretion has been attributed to increased pituitary sensitivity to GnRH and feedback influences from circulating steroid hormones. To address these considerations, we conducted a study to examine the relationships between GnRH-stimulated LH responses, episodic gonadotrophin secretion, and baseline measurements of endocrine-metabolic function in PCOS. PATIENTS: Serum LH responses to sequential multidose GnRH administration and pulsatile gonadotrophin secretion were examined in 13 PCOS and 13 normal women. MEASUREMENTS: Serum LH, steroid hormone, insulin and glucose levels were determined in blood samples obtained during assessment of episodic gonadotrophin secretion and LH responses to GnRH stimulation. DESIGN: Each subject was studied on two consecutive days. On study day 1 each subject underwent frequent blood sampling every 10 min for 12 h. On study day 2 each received sequential doses of GnRH, 2 microg, 10 microg and 20 microg, administered intravenously at 4-h intervals over a continuous 12-h period. RESULTS: Serum LH responses following GnRH were markedly greater in PCOS compared to normal women, as expected. In individual PCOS, peak LH responses to GnRH were significantly correlated with corresponding basal LH and LH pulse amplitude, but not LH pulse frequency. In the PCOS group, LH responses were positively correlated with serum oestradiol (E2) and inversely related to body mass index (BMI). Between-group differences in LH responsiveness disappeared when controlling for serum testosterone (T) levels. CONCLUSIONS: These results indicate that the absolute LH increment following GnRH is largely dependent on baseline LH levels and may account for the well-documented difference in LH responsiveness between PCOS and normal women. That neither LH responses to GnRH nor LH pulse amplitude were correlated to LH pulse frequency suggests involvement of other factors along with GnRH to account for increased LH secretion in PCOS. In addition to E2 and BMI, serum testosterone appears to be, at least in part, responsible for differences in LH secretion and release between PCOS and normal women.

Adult↗
PubMed2004

Factors in the interictal record predicting an ictal episode: a case study.

This report deals with a patient with intractable seizures, who had 64 subdural electrodes implanted onto the left frontal and temporal cerebral cortex in anticipation of probable seizure surgery. One specific region on the left frontal lobe proved to be the focus for both the interictal spikes and also for the ictal activity. Our goal was to determine what electrical characteristics in the interictal record predicted the ictal episodes. The number of interictal spikes and also the amount of fast activity (15-128/sec) progressively increased before each of the 5 ictal episodes; an analysis showed that the number of spikes and their frequency proved the more significant variable. One other characteristic that changed before the ictal episodes was a great decrease in the interval between spikes as an example of a diminishing variability or increasing periodicity. Thus, the important factors in the interictal record that lead to an ictal event are the number of spikes, the amount of fast activity and the decreasing variability between the spikes.

Adult↗
PubMed2003

Major components of the insulin-like growth factor axis are expressed early in chicken embryogenesis, with IGF binding protein ( IGFBP) -5 expression subject to regulation by Sonic Hedgehog.

Using whole-mount in situ hybridisation techniques, we have examined the expression of major components of the insulin-like growth factor (IGF) axis in early development of the chicken embryo, including both IGF-I and -II, the type 1 IGF receptor ( IGFR), and two of the IGF binding proteins, ( IGFBP) -2 and -5. We report that these genes fall into two distinct groups with respect to expression pattern, with IGFBP-2 displaying broad overlap of mRNA expression with IGFR and IGF-I during early development, whereas the expression profile of IGFBP-5 most closely resembled that of IGF-II. Comparison between different stages revealed IGFBP-2 mRNA was detected as early as stage 3, whereas IGFBP-5 was first seen at stage 4. In addition, we detected expression domains of IGFBP-5, and to a lesser extent IGFBP-2, which did not overlap with either IGFR or IGF expression patterns. This could indicate IGF independent actions of the IGFBPs during early embryonic development. A striking observation concerning the expression profiles of both IGF-II and IGFBP-5 at early stages of chick embryogenesis is that both these genes are expressed asymmetrically in a pattern similar to that of Sonic Hedgehog (Shh). Furthermore, using cyclopamine, we have demonstrated that IGFBP-5 expression in the early embryo is regulated by Shh. Taken together, these results describe an important role for the IGF system in the very early stages of the developing chicken embryo, and imply that IGFBP-2 and -5 are fundamental developmental factors, with the latter involved in Shh signalling pathways.

Animals↗
PubMed2003

Ventral axial organs regulate expression of myotomal Fgf-8 that influences rib development.

Fgf-8 encodes a secreted signaling molecule mediating key roles in embryonic patterning. This study analyzes the expression pattern, regulation, and function of this growth factor in the paraxial mesoderm of the avian embryo. In the mature somite, expression of Fgf-8 is restricted to a subpopulation of myotome cells, comprising most, but not all, epaxial and hypaxial muscle precursors. Following ablation of the notochord and floor plate, Fgf-8 expression is not activated in the somites, in either the epaxial or the hypaxial domain, while ablation of the dorsal neural tube does not affect Fgf-8 expression in paraxial mesoderm. Contrary to the view that hypaxial muscle precursors are independent of regulatory influences from axial structures, these findings provide the first evidence for a regulatory influence of ventral, but not dorsal axial structures on the hypaxial muscle domain. Sonic hedgehog can substitute for the ventral neural tube and notochord in the initiation of Fgf-8 expression in the myotome. It is also shown that Fgf-8 protein leads to an increase in sclerotomal cell proliferation and enhances rib cartilage development in mature somites, whereas inhibition of Fgf signaling by SU 5402 causes deletions in developing ribs. These observations demonstrate: (1) a regulatory influence of the ventral axial organs on the hypaxial muscle compartment; (2) regulation of epaxial and hypaxial expression of Fgf-8 by Sonic hedgehog; and (3) independent regulation of Fgf-8 and MyoD in the hypaxial myotome by ventral axial organs. It is postulated that the notochord and ventral neural tube influence hypaxial expression of Fgf-8 in the myotome and that, in turn, Fgf-8 has a functional role in rib formation.

Animals↗
PubMed2003

The water load test: observations from healthy controls and patients with functional dyspepsia.

Gastric sensation and accommodation are studied by barostat, but this is invasive. The drink test is noninvasive and may provide similar information. We evaluated relationships between drink test, gastric function, symptoms, and psychiatric distress. Controls (73) and functional dyspeptics (FD) (92) were studied using a 5-min water load test (WL5), gastric emptying, and electrogastrography (EGG). Symptoms, quality of life, and psychiatric distress were measured using standardized measures. Controls underwent test-retest of WL5 and comparison of WL5 with 100 ml/min water-based drink test (WL100) or nutrient drink. Controls, FD, and gastroparetics estimated drinking capacity before WL5 using a visual analog scale. WL5 correlated with WL100 (r = 0.7929) but not nutrient drink test (r = 0.1995). WL5 was significantly less in FD than controls, and abnormal WL5 was seen in 46%. In FD, volume to fullness inversely correlated with symptom severity (r =-0.29; P = 0.0154) and WL5 produced more symptoms, particularly nausea. Gastric function was not different between FD with normal or abnormal WL5. Symptoms and psychiatric distress were similar between normal and abnormal WL5 groups, but the abnormal group had significantly poorer quality of life. Controls and gastroparetics had good correlation of estimated and ingested volumes, but FD did not. Versus FD with normal WL5 capacity, FD with impaired drinking capacity have normal gastric function and similar symptoms but poorer quality of life. FD are less able to predict drinking capacity. These data suggest that WL5 identifies FD with intact gastric function but abnormal visceral perception.

Adult↗
PubMed2003

Evidence for abnormal granulosa cell responsiveness to follicle-stimulating hormone in women with polycystic ovary syndrome.

Women with polycystic ovary syndrome (PCOS) undergoing ovulation induction appear to be extremely sensitive to gonadotropin stimulation and at increased risk for ovarian hyperstimulation syndrome. To determine granulosa cell responsiveness to recombinant human FSH (r-hFSH), dose-response studies were conducted in 16 individual PCOS patients and 7 normal women. Each subject received an iv injection of r-hFSH at doses of 0, 37.5, 75, or 150 IU in a randomized fashion on four separate occasions. Blood samples were obtained at frequent intervals before and for 24 h after r-hFSH administration for measurement of gonadotropins and steroid hormones. Our results showed that administration of r-hFSH produced instantaneous and equivalent dose-related increases in serum FSH in PCOS and normal women, which were followed by similar exponential decreases to baseline levels within 24 h in both groups. In PCOS subjects, the peak mean incremental response of serum estradiol (E(2)) to 150 IU of r-hFSH was 1.8-fold greater (P < 0.0001) and considerably accelerated compared with that found in normal women. In contrast, E(2) responses to 37.5 IU and 75 IU were similar between groups. Regression analysis of maximal E(2) concentrations in response to r-hFSH in each individual subject revealed that the slope of the linear trend line in the group of women with PCOS (r = 0.82) was significantly greater (P < 0.01) than that of normal controls (r = 0.71). The time-course of response revealed that in PCOS women, increases of E(2) were not sustained, compared with those of normal controls, because peak concentrations were followed by an estimated 40% decrement in circulating levels, whereas E(2) levels in normal women persisted for 24 h after reaching maximal values. These findings indicate that women with PCOS exhibit a significantly greater capacity for E(2) production in response to iv r-hFSH, compared with normal women. In PCOS, E(2) production was relatively transient because after peak concentrations a marked decline was detected at each dose, unlike normal women who exhibited persistent elevations of E(2) for up to 24 h. That this distinction was dose-dependent supports the concept of an FSH dose-response threshold, beyond which PCOS but not normal women are susceptible to ovarian hyperresponsiveness.

Dose-Response Relationship, Drug↗
PubMed2003

Enhanced granulosa cell responsiveness to follicle-stimulating hormone during insulin infusion in women with polycystic ovary syndrome treated with pioglitazone.

Women with polycystic ovary syndrome (PCOS) are known to exhibit insulin resistance with compensatory hyperinsulinemia. To determine the role of hyperinsulinemia on follicle function in PCOS, we examined 24-h estradiol (E(2)) responses to recombinant human FSH (r-hFSH), 75 IU, before and during insulin infusion both before and after administration of pioglitazone (30 mg/d) in seven PCOS women. Each subject underwent two 10-h hyperinsulinemic-euglycemic clamps at rates of 30 (low dose) and 200 (high dose) mU/m(2).min, respectively. During both low- and high-dose insulin infusions, E(2) responses to r-hFSH were unaltered compared with that observed in the absence of insulin. Pioglitazone administration for 5 months improved insulin sensitivity as indicated by significantly (P < 0.05) increased glucose infusion rates during the clamp studies. At 3 months of treatment, r-hFSH-stimulated E(2) responses were not different from those observed before treatment. With pioglitazone treatment, E(2) responses to r-hFSH remained unchanged during low-dose insulin infusion, whereas a highly significant (P < 0.02) increased response was noted with the high-dose hyperinsulinemic-euglycemic clamp. In addition to a greater magnitude of response, peak levels of E(2) were sustained longer compared with that seen before treatment. The data indicate that granulosa cell responsiveness to FSH was enhanced by insulin after improved insulin sensitivity induced by pioglitazone. These findings are consistent with the possibility that PCOS granulosa cells are insulin resistant.

Adult↗
PubMed2003

Increased luteinizing hormone secretion in women with polycystic ovary syndrome is unaltered by prolonged insulin infusion.

In PCOS women with insulin resistance, hyperinsulinemia may contribute to inappropriate gonadotropin secretion. To determine whether insulin influences gonadotropin release in PCOS, pulsatile LH secretion and gonadotropin responses to GnRH were evaluated before (phase 1) and during (phase 2) insulin infusion. In phase 1, 11 PCOS and 9 normal women on separate days underwent 1) frequent blood sampling (q 10 min) for 12 h and 2) gonadotropin stimulation by successive doses of GnRH, 2 microg, 10 microg, and 20 microg, administered i.v. at 4 h intervals over a continuous 12 h. In phase 2, studies were repeated 2 h after initiation of a 12-h hyperinsulinemic-euglycemic clamp (80 mU/m(2).min). Administration of insulin to both groups failed to alter mean serum gonadotropin concentrations, LH pulse frequency, or LH pulse amplitude. Moreover, gonadotropin responses to GnRH were unchanged by insulin infusion. In PCOS and normal women, a significant reduction of serum androstenedione was associated with insulin administration, whereas no differences were noted for the remaining androgens and estrogens measured. These findings demonstrated that in PCOS women, LH secretion and gonadotropin responses to GnRH were not influenced by insulin administration. Insulin infusion had little effect on steroid hormone production with the possible exception of androstenedione. These results suggest that inappropriate LH secretion in PCOS is not a direct consequence of insulin resistance and compensatory hyperinsulinemia.

Adult↗
PubMed2002

The regulation and action of myostatin as a negative regulator of muscle development during avian embryogenesis.

Myostatin is a potent inhibitor of muscle growth. Genetic deletion of Myostatin leads to massive hyperplasia and hypertrophy of skeletal muscle. However, the overall muscle pattern is preserved. We show that, during chick embryonic development, Myostatin is expressed at stages and positions unlikely to influence qualitative muscle development. In the somites, Myostatin is predominantly expressed in a central domain of the dermomyotome but not at the dorsomedial and ventrolateral lips, where most cells for myotomal elongation are recruited. During limb bud development, Myostatin is transiently expressed at early stages in both myogenic and nonmyogenic regions. Myostatin is reexpressed during limb bud development at a time when splitting of muscle is underway. Heterotopically developed wing buds that fail to form muscle still express Myostatin. This demonstrates that, in the limb, not all Myostatin-expressing cells are of myogenic origin. Ectoderm and Sonic hedgehog have different effects on the expression of Myostatin dependent on stages at which the operation was performed and the length of the postoperative period. Finally, we show that application of Myostatin protein into the developing limb bud results in a down-regulation of Pax-3 and Myf-5, both genes associated with proliferation of myogenic cells; and, furthermore, Myostatin also prevents the expression of MyoD, a gene associated with muscle differentiation. The long-term effect of Myostatin treatment leads to a deficiency of limb muscle. Therefore, Myostatin negatively affects gene expression of transcription factors, which are necessary for establishing myogenic cell identity.

Animals↗
PubMed2002

Development of an arterial tree in C6 gliomas but not in A375 melanomas.

The microcirculation of tumors is severely disturbed. Tumors are usually supplied by fragile capillaries and do not possess the natural hierarchy of blood vessels. The detection of specific markers for arterial and venous endothelial cells (ECs) now enables us to study the vascular tree in tumors. We have injected rat C6 glioma and human A375 melanoma cells into 3.5- to 4-day-old avian embryos. After 10-12 days of reincubation the tumor cells formed solid tumors vascularized by host ECs. In contrast to the melanomas, the gliomas induced an almost normal vascular tree with arterial and venous vessels. The arterial vessels express the arterial EC marker ephrin-B2, and possess a media of smooth muscle alpha-actin (alphaSMA)-positive cells. Venular vessels in the gliomas are ephrin-B2-negative/alphaSMA-positive. Although the gliomas may represent a rare case of vascular tree induction in tumors, the results underline the heterogeneity of tumor-induced angiogenesis. This has an impact on tumor blood flow and thereby also on the efficacy of chemotherapy and radiotherapy.

Actins↗
PubMed2002

Follistatin regulates bone morphogenetic protein-7 (BMP-7) activity to stimulate embryonic muscle growth.

Bone morphogenetic proteins (BMPs) can either promote growth of embryonic muscle by expanding the Pax-3-expressing muscle precursor population or restrict its development by inducing apoptosis. Follistatin, a proposed BMP antagonist, is expressed in embryonic muscle. Deficiency in Follistatin results in muscle defects and postnatal asphyxia. Here, we report that during chick limb development Follistatin enhances BMP-7 action to induce muscle growth but prevents the ability of BMP-7 to induce apoptosis and muscle loss. Follistatin, unlike another BMP-binding protein, Noggin, promotes Pax-3 expression and transiently delays muscle differentiation and thus exerts proliferative signalling during muscle development. We provide data which show that Follistatin binds BMP-7 and BMP-2 at low affinities and that the binding is reversible. These data suggest that Follistatin acts to present BMPs to myogenic cells at a concentration that permits stimulation of embryonic muscle growth.

Activins↗