Biomedical subjects
H T Cho
Publications and source records attributed to H T Cho.
Altered expression of expansin modulates leaf growth and pedicel abscission in Arabidopsis thaliana.
Expansins are cell-wall-loosening proteins that induce stress relaxation and extension of plant cell walls. To evaluate their hypothesized role in cell growth, we genetically manipulated expansin gene expression in Arabidopsis thaliana and assessed the consequent changes in growth and cell-wall properties. Various combinations of promoters were used to drive antisense and sense sequences of AtEXP10, which is maximally expressed in the growing leaf and at the base of the pedicel. Compared with controls, antisense lines had smaller rosettes because of shorter petioles and leaf blades and often acquired a twisted leaf morphology. Petiole cells from antisense plants were smaller than controls and their cell walls were significantly less extensible in vitro. Sense plants had slightly longer petioles, larger leaf blades, and larger cells than controls. Abscission at the base of the pedicel, where AtEXP10 is endogenously expressed, was enhanced in sense plants but reduced in antisense lines. These results support the concept that expansins function endogenously as cell-wall-loosening agents and indicate that expansins have versatile developmental roles that include control of organ size, morphology, and abscission.
Alpha-expansins in the semiaquatic ferns Marsilea quadrifolia and Regnellidium diphyllum: evolutionary aspects and physiological role in rachis elongation.
To investigate the evolutionary history of expansins and their role in cell elongation in early land plants, we isolated two alpha-expansin genes, Mq-EXP1 and Rd-EXP1, respectively, from the semiaquatic ferns Marsilea quacdrifolia L. and Regnellidium diphyllum Lindm. The deduced amino acid sequences of the fern expansins exhibit a high degree of identity to those of seed plants, showing that expansin genes were conserved during the evolution of vascular plants. Gel-blot analysis of M. quadrifolia and R. diphyllum genomic DNA indicated that, in both ferns, alpha-expansins are encoded by multigene families. Expression of alpha-expansin genes probed with Mq-EXP1 was confined to the elongating region of the Marsilea rachis. Cell-wall proteins of M. quadrifolia induced in-vitro extension of acidified cucumber cell walls. In R. diphyllum, expression of Rd-EXP1 increased when elongation of the rachis was enhanced by submergence or ethylene. These results indicate that alpha-expansins act as wall-loosening proteins in ferns, as has been proposed for angiosperms. In addition, Rd-EXP1 may play a role in mediating elongation of the rachis in submerged plants.
Tissue localization of expansins in deepwater rice.
Expansins are a family of proteins capable of inducing stress relaxation of isolated cell walls. In earlier studies, we showed that the expression of expansin genes in deepwater rice (Oryza sativa L.) is regulated by developmental, hormonal and environmental stimuli. Here, we describe the spatial distribution pattern of expansin transcripts and proteins in tissues and organs of deepwater rice using in situ mRNA hybridization and immunohistochemical analysis. Expansin transcripts and proteins are present at high levels in the growing internodal epidermis, which has thick cell walls and acts, therefore, as a growth-limiting cell layer. Expansins are also concentrated in the differentiating vascular bundles of internodes. In the primary root, expansins are predominantly expressed in the tip region, particularly in the epidermis, differentiating vascular cylinder, and around the pericyle. Developing adventitious roots and lateral root primordia also contain high levels of expansin mRNA. In the shoot apex, expansin transcripts are abundant in the emerging leaf primordia. Our results indicate that expansins play an important role in the expansion and differentiation of plant tissues and organs.
Expansins in deepwater rice internodes.
Cell walls of deepwater rice (Oryza sativa L.) internodes undergo long-term extension (creep) when placed under tension in acidic buffers. This is indicative of the action of the cell wall-loosening protein expansin. Wall extension had a pH optimum of around 4.0 and was abolished by boiling. Acid-induced extension of boiled cell walls could be reconstituted by addition of salt-extracted rice or cucumber cell wall proteins. Cucumber expansin antibody recognized a single protein band of 24.5-kD apparent molecular mass on immunoblots of rice cell wall proteins. Expansins were partially purified by concanavalin A affinity chromatography and sulfopropyl (SP) cation-exchange chromatography. The latter yielded two peaks with extension activity (SP20 and SP29), and immunoblot analysis showed that both of these active fractions contained expansin of 24.5-kD molecular mass. The N-terminal amino acid sequence of SP20 expansin is identical to that deduced from the rice expansin cDNA Os-EXP1. The N-terminal amino acid sequence of SP29 expansin matches that deduced from the rice expansin cDNA Os-EXP2 in six of eight amino acids. Our results show that two expansins occur in the cell walls of rice internodes and that they may mediate acid-induced wall extension.
Expression of expansin genes is correlated with growth in deepwater rice.
Expansins are a family of proteins that catalyze long-term extension of isolated cell walls. Previously, two expansin proteins have been isolated from internodes of deepwater rice, and three rice expansin genes, Os-EXP1, Os-EXP2, and Os-EXP3, have been identified. We report here on the identification of a fourth rice expansin gene, Os-EXP4, and on the expression pattern of the rice expansin gene family in deepwater rice. Rice expansin genes show organ-specific differential expression in the coleoptile, root, leaf, and internode. In these organs, there is increased expression of Os-EXP1, Os-EXP3, and Os-EXP4 in developmental regions where elongation occurs. This pattern of gene expression is also correlated with acid-induced in vitro cell wall extensibility. Submergence and treatment with gibberellin, both of which promote rapid internodal elongation, induced accumulation of Os-EXP4 mRNA before the rate of growth started to increase. Our results indicate that the expression of expansin genes in deepwater rice is differentially regulated by developmental, hormonal, and environmental signals and is correlated with cell elongation.
Localization of interleukin-1 in human squamous carcinomas of the head and neck.
Recent investigations revealed that interleukin-1 can promote bone resorption by activating osteoclasts. The authors' immunocytochemical studies with monoclonal antibody against human interleukin-1 localized interleukin-1 at the bone resorption site of the squamous carcinomas as well as within the squamous carcinomas. In addition, Western blotting and dot blotting methods were used to isolate interleukin-1 from the extracts of the squamous carcinomas in the head and neck. Finding interleukin-1, a potent bone resorption-stimulating factor, in squamous carcinomas suggests that interleukin-1 might play an important role in the extensive local bone destruction seen in the head and neck patients with squamous carcinomas.
Squamous cell carcinoma of the thyroid: a diagnostic dilemma.
Four cases of primary squamous cell carcinoma of the thyroid gland are reported. Thorough evaluation confirmed these lesions to be of primary thyroid origin rather than from metastasis or direct invasion from contiguous structures. These cases illustrate the aggressive nature of the disease and the propensity for local and distant metastases. The clinicopathologic data presented here underscore the challenge in diagnosis and treatment of this rare entity.
The role of needle aspiration biopsy in the selection of patients for thyroidectomy.
Fine needle aspiration (FNA) biopsy is gaining in popularity among all diagnostic tests used in the evaluation of patients for thyroidectomy. Its safety and accuracy have been well documented, but criteria regarding when FNA is appropriate are lacking. We retrospectively reviewed our experience with 408 consecutive patients evaluated for thyroid surgery. Two hundred seventy-three ultimately underwent thyroidectomy; 100 of these had preoperative FNA. An additional 135 patients underwent FNA without surgery. Patients who benefited from FNA were those in whom cytologic findings led to surgery for otherwise unsuspected malignancy (15), and those with asymptomatic benign nodules who avoided unnecessary thyroidectomy on the basis of FNA findings (96). FNA is superfluous when clinical conditions mandate surgery. These include nodules that arouse clinical suspicion of malignancy, massive nodules that cause aerodigestive tract compression or cosmetic disfigurement, and nodules extending into the mediastinum. All patients with asymptomatic, clinically benign thyroid nodules should undergo FNA biopsy, as approximately 50% can anticipate significant benefit from the procedure.
Pseudotumor of the larynx--an unusual cause of airway obstruction.
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Management of substernal and intrathoracic goiters.
Goiters that descend into the mediastinum can cause respiratory embarrassment, dysphagia, vascular compression, vocal cord paralysis, and sudden death. Although many such goiters remain clinically silent, their ability to produce sudden and unpredictable respiratory distress is well known. The condition was not considered uncommon in the first half of the twentieth century; some authors reported series of hundreds of thyroidectomies for intrathoracic goiter. Though seen less frequently today, the only effective treatment for mediastinal goiter is surgical removal. We report our experience with the management of 70 consecutive patients with substernal or intrathoracic goiters. The clinical presentation, preoperative evaluation, operative technique, and results and complications of therapy are discussed. Consideration is also given to the pathogenesis of intrathoracic extension. The transcervical approach for resection is emphasized--even goiters extending to the aortic arch were safely removed without requiring sternotomy. A multidisciplinary team approach, including the surgeon, anesthesiologist, and endocrinologist, is essential. Because of more conservative trends in the selection of patients for thyroidectomy, the incidence of mediastinal goiter may be increasing.
Delayed failure of myocutaneous flaps in head and neck reconstruction.
Since the concept of myocutaneous flap reconstruction of the head and neck region was introduced it has opened a new approach to surgical management in this area. This flap not only reduced the number of operations as compared to "staged procedure", but also reduced the costs of medical care. We are, however, experiencing significant failures as the applications of this flap are extended. This paper reviews our experience with myocutaneous flaps in 15 partial and total failures. An evaluation of these failures reveals that most occurred 1 1/2 to 3 weeks after reconstruction. The factors predisposing to failure seem related more to technical errors rather than to general factors. Diabetes, peripheral vascular disease, malnutrition and low hemoglobin, and low blood pressure were not major contributors to the failures in our series. Local factors predisposing to failure of myocutaneous flaps can be divided into two large categories--arterial failure and venous failure. In our series of unsuccessful myocutaneous flaps, the major factors appeared to be venous stasis leading to arterial insufficiency. All failures had developed after the initial critical period of flap survival (7-10 days). The following techniques showed an especially high rate of failure: 1. SCM--myocutaneous flap to resurface floor of mouth. 2. Tubed pectoralis myocutaneous flap to reconstruct pharynx and esophagus. 3. Flaps developed with very narrow vascular pedicles. Individual cases representing delayed failure are presented.
Parotid space tumors of non-salivary origin.
A review of 700 parotidectomies showed that 98 procedures were performed for parotid space tumors of non-salivary origin. The clinical presentation in this group of patients did not differ significantly from the larger group of salivary tumors except for a higher incidence (12%) of the former in the younger age group. Of the 98 cases, 54 proved to be lymph node tumors, both neoplastic and inflammatory and 44 were tumors of various somatic origins. Among the latter group, bone and joint tumors, vascular lesions and some connective tissue tumors may be recognized preoperatively. Generally, however, the entire group of non-salivary tumors can be distinguished only intra-operatively, if at all. Correct recognition may lead to variations in operative techniques and extent of resection.