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PubMed1993

Melanoma recurrence after excision. Is a wide margin justified?

Through retrospective analysis of patient records for 187 patients with melanoma seen between 1975 and 1989, the aim of this study was to determine whether outcome varied according to degrees of surgical intervention in the primary treatment of stage I disease for thin, intermediate, and thick lesions. There were no significant differences in recurrence rate associated with an excision margin of 15 mm or less compared with wider excision margins; with initial excision compared with wider re-excision after excision biopsy; or for primary closure as compared with closure with a graft. There was, however, a significant difference in wound complication rate between wounds closed primarily (6%) and those closed by grafting (31%) (p < 0.01). The authors advocate the more conservative excision margin of 1.00 cm to 1.50 cm in the treatment of stage I melanoma with primary closure of the wound where possible.

Adolescent↗

PubMed2002

Long-term results of local excision for rectal cancer.

OBJECTIVE: To review the authors' experience with local excision of early rectal cancers to assess the effectiveness of initial treatment and of salvage surgery. SUMMARY BACKGROUND DATA: Local excision for rectal cancer is appealing for its low morbidity and excellent functional results. However, its use is limited by inability to assess regional lymph nodes and uncertainty of oncologic outcome. METHODS: Patients with T1 and T2 adenocarcinomas of the rectum treated by local excision as definitive surgery between 1969 to 1996 at the authors' institution were reviewed. Pathology slides were reviewed. Among 125 assessable patients, 74 were T1 and 51 were T2. Thirty-one patients (25%) were selected to receive adjuvant radiation therapy. Fifteen of these 31 patients received adjuvant radiation in combination with 5-fluorouracil chemotherapy. Median follow-up was 6.7 years. One hundred fifteen patients (92%) were followed until death or for greater than 5 years, and 69 patients (55%) were followed until death or for greater than 10 years. Recurrence was recorded as local, distant, and overall. Survival was disease-specific. RESULTS: Ten-year local recurrence and survival rates were 17% and 74% for T1 rectal cancers and 26% and 72% for T2 cancers. Median time to relapse was 1.4 years (range 0.4-7.0) for local recurrence and 2.5 years (0.8-7.5) for distant recurrence. In patients receiving radiotherapy, local recurrence was delayed (median 2.1 years vs. 1.1 years), but overall rates of local and overall recurrence and survival rates were similar to patients not receiving radiotherapy. Among 26 cancer deaths, 8 (28%) occurred more than 5 years after local excision. On multivariate analysis, no clinical or pathologic features were predictive of local recurrence. Intratumoral vascular invasion was the only significant predictor of survival. Among 34 patients who developed tumor recurrence, the pattern of first clinical recurrence was predominantly local: 50% local only, 18% local and distant, and 32% distant only. Among the 17 patients with isolated local recurrence, 14 underwent salvage resection. Actuarial survival among these surgically salvaged patients was 30% at 6 years after salvage. CONCLUSIONS The long-term risk of recurrence after local excision of T1 and T2 rectal cancers is substantial. Two thirds of patients with tumor recurrence have local failure, implicating inadequate resection in treatment failure. In this study, neither adjuvant radiotherapy nor salvage surgery was reliable in preventing or controlling local recurrence. The postoperative interval to cancer death is as long as 10 years, raising concern that cancer mortality may be higher than is generally appreciated. Additional treatment strategies are needed to improve the outcome of local excision.

Adenocarcinoma↗

PubMed2002

Management of periocular basal cell carcinoma with modified en face frozen section controlled excision.

PURPOSE: To determine the rate of recurrence of basal cell carcinomas (BCCs) after modified en face frozen section-controlled excision in a high-risk population in Queensland, Australia. METHODS: Retrospective, noncomparative interventional case series. A review was conducted of all patients with periocular BCCs examined between 1992 to 2001 in a tertiary oculoplastics practice. Basal cell carcinomas were surgically excised, and the recurrence rates under modified en face frozen section control, Mohs micrographic surgery, and no frozen section control were documented. Epidemiologic aspects of periocular BCC in Queensland, Australia were also studied. RESULTS: In patients with primary BCCs, 0.71% (3 of 423 lesions) recurred when excised under frozen section control (mean follow-up, 2.6 years). At 5-year follow-up, the recurrence rate was 2.1% (2 of 97 lesions). Excision without frozen section control yielded a recurrence rate of 1.8% (2 of 113 lesions; mean follow-up, 2.6 years). There were 6 additional lesions, however, that were incompletely excised. At 5 years, the recurrence rate was 5%. Six patients had lesions removed with Mohs micrographic surgery. There were no recurrences after a mean follow-up of 1.7 years. Of 653 total lesions, 361 involved the right eye (55%). Most BCCs were on the lower eyelid (53%) and inner canthus (29%). Solid BCCs were the most common type (54%), followed by the infiltrative type (15%). The majority of complications were minor and caused no ocular damage. CONCLUSIONS: Carefully performed, modified en face frozen section controlled excision of periocular BCCs yields cure rates comparable to Mohs micrographic surgery at 5-year follow-up. Close communication with a skilled pathologist is essential to achieve these low recurrence rates. The fact that lesions involved the right periocular region more than the left may reflect greater sun exposure on that side from driving.

Aged↗

PubMedDate not supplied

Sequential excision and grafting of the burn injuries of 1507 patients treated between 1967 and 1986: end results and the determinants of death.

The development of a more aggressive approach to burn wound management, leading to complete excision within 72 hours after burn, has led some to conclude that total early excision is a major force behind improved survival rates. We have summarized the results of treatment of 1507 patients with burn injuries treated between 1967 and 1986. Wounds were managed with use of standard topical therapy, occlusive dressings, and staged excision and grafting of full-thickness injury or deep dermal injury (not healed by 21 days). Data were analyzed with use of a logistic-regression model because, with the exception of older patient cohorts, the data did not fit the probit model. The major determinants predicting death were the percentage of body surface area burned, age, smoke inhalation, and the percentage of full-thickness burn. Concordance was 97%. These data show that aggressive sequential wound excision and grafting produces end results comparable with those achieved with complete early burn wound excision for similar age ranges and injury. Early harvest of available donor sites in patients with large burns may be more important to survival than complete early wound excision.

Adolescent↗

PubMed1975

Clinical evaluation of the carbon dioxide laser for burn wound excisions: a comparison of the laser, scalpel, and electrocautery.

The use of a 100 watt carbon dioxide laser for surgical excisions of burn eschar was evaluated in 13 patients with symmetrical burns. In each patient, laser excision was compared with either scalpel or electrocautery excision of a comparable area. Graft "take," blood loss, and operative speed were measured. Graft "take" following laser excisions was comparable to that obtained when either scalpel or electrocautery was used. Regression analysis indicates that laser excisions involved 29% of the blood loss encountered with scalpel excisions and that laser speed was 1.49 times scalpel speed. Although laser blood loss was 60% of electrocautery blood loss, laser speed was significantly slower: 73% of electrocautery speed. These differences, however, were of small clinical consequence. It is felt that the surgical arm of this laser is at present quite awkward and is in need of technological refinement if the full potential of the laser is to be realized.

Burns↗

PubMed1986

Reduction of blood loss using tourniquets and 'compression' dressings in excising limb burns.

Excessive blood loss can limit the area of burn excised per sitting, lead to selection of en bloc rather than tangential excision, and increase the number of surgical procedures required per patient. Twenty-four burned extremities were studied to measure blood loss, complications, and effectiveness of a technique for tangentially excising burns of extremities using tourniquet hemostasis followed by application of steel-wool-pad 'compression' dressings before tourniquet release. An average of 7.3 days postburn (PB), a mean of 7% body surface area (BSA) burn was excised per extremity with a mean blood loss of 29 ml/% BSA burn excised (less than one fifth of recently published values). Graft take averaged 91%. There was no evidence of neurocirculatory injury or other complications. When applied as described and carefully monitored, hemostatic tourniquets followed by 'compression' dressings can safely reduce blood loss associated with the exclision of limb burns and allow larger areas to be excised at each operation.

Bandages↗

PubMed1987

Shave excision of superficial solar skin lesions.

Shave excision is a useful technique for the treatment of superficial solar lesions. The most common of these is the solar keratosis, which can be a red or gray scaling lesion. This can at times be difficult to differentiate from the superficial basal cell carcinoma or squamous cell carcinoma or their more infiltrating types. Shave excision gives the advantage of a histopathologic report. Lesions found to be infiltrating or in danger of recurrence can then be further excised. The cosmetic appearance of the healed shave excision site is generally quite good, although it can be paler than the surrounding skin. If this is likely to be a problem, the shave graft can be applied, as with deeper shave excisions. A thin shave graft also can be used to repigment pale scarred areas. A series of 1313 shave excised lesions is analyzed.

Basal Cell Carcinoma↗

PubMed1998

The excised preauricular sinus in 14 years of experience: is there a problem?

The congenital preauricular sinus is usually asymptomatic. However, if recurrent infection occurs, complete surgical excision of the sinus is required. If the sinus tracts are not entirely removed, recurrence is likely to follow. A retrospective study of the surgical results at The Hospital for Sick Children in Toronto, Ontario, was completed. One-hundred sixty-five primary preauricular excision procedures, performed in 146 patients between the years 1982 and 1996, were reviewed. All clinical, operative, and postoperative data were gathered. Patient outcome and epidemiologic issues were addressed. The overall recurrence rate of this series was 9.09 percent (15 of 165 sinuses). For the group of patients with active infection present at surgery, the recurrence rate was 15.79 percent, and when no infection was present, recurrence rate was 8.22 percent (p value = 0.32, odds ratio = 2.09). Moreover, in patients who underwent surgical drainage of an abscess before the procedure, 16.7 percent of the sinuses recurred, whereas in the patients who did not have an abscess, only 8.16 percent recurred (p value = 0.25, odds ratio = 2.25). In the group of patients in whom auricular cartilage was not excised from the base of the tract, 18.52 percent of the sinuses recurred; when cartilage was excised, the recurrence rate was 4.5 percent (p value = 0.006). A very high recurrence rate of 21.95 percent was found in the group of patients in whom no modality was used to demonstrate the sinus tract at surgery. A high recurrence rate of 10.87 percent was found in the group for whom probing with a cannula was used to identify the tract (p value = 0.17); a low recurrence rate of 2 percent was found in a group with dye injection only (p value = 0.015). In those patients in whom sinus probing and dye injection were used simultaneously, there were no recurrences (0 percent, p value < 0.05). In conclusion, a patient with an actively infected preauricular sinus or one with a previous abscess may have a tendency to experience a higher recurrence rate after excisional surgery. Excising a cartilage piece at the base of the tract and demonstrating the sinus with dye injection or with dye injection and probing at the time of surgery will reduce recurrence rates. In conclusion, we advise the excision of cartilage in the base of the tract as well as the use of methylene blue injection and probing of the sinus at surgery.

Adolescent↗

PubMed2002

Comparison of partial excision with simple section of the transverse carpal ligament in the treatment of carpal tunnel syndrome.

In the surgical treatment of carpal tunnel syndrome, debate has commonly focused on whether decompression should be performed by open or blind techniques. Contrarily, the goal of the present study was to determine whether instead of simple section, partial excision of the transverse carpal ligament has contributed to better results. Because complete healing of the transverse carpal ligament observed during reoperations has been reported elsewhere, the charts of 75 carpal tunnel syndrome patients who had been treated with open technique at Dokuz Eylül University were reviewed. Statistical analysis was performed using the Fisher's exact test and Student's t test when appropriate. Thirty-five patients had been treated with simple section of the transverse carpal ligament, whereas 40 had been treated with partial excision. Internal neurolysis was also performed in 19 of the patients, 11 of whom were treated with partial excision. The average follow-up time was 3.8 years. The comparisons regarding the overall operative outcomes did not show any significant difference between the two different techniques of releasing the transverse carpal ligament. In patients treated without neurolysis, results of partial excision of the transverse carpal ligament improved when compared with those of simple section, but this superiority was not statistically significant. There seemed to be statistically higher reoperation rates and worse outcomes after neurolysis (p < 0.05). Reoperation was required in eight patients (11 percent). Five of the patients who underwent reoperation had initially been treated with partial excision and neurolysis, whereas two had been treated with simple section and neurolysis. Another patient who had undergone reoperation had initially undergone only simple section. The mean time to return to work or daily activities did not differ between the types of applied technique for releasing the transverse carpal ligament. However, neurolysis lengthened these periods significantly when performed (p < 0.05). In the present study, partial excision of the transverse carpal ligament without adding neurolysis offered relatively better results than simple section. Verification of this finding endoscopically, if applicable, may improve the success rate of surgical therapy in patients with carpal tunnel syndrome.

Adult↗

PubMed2000

Clinical and radiographic evaluation of disc excision for lumbar disc herniation with and without posterolateral fusion.

STUDY DESIGN: A prospective study evaluating the clinical and radiographic results in 95 patients with lumbar disc herniation. OBJECTIVES: To evaluate the results of disc excision, with and without posterolateral fusion. SUMMARY OF BACKGROUND DATA: The effect of posterolateral fusion on the outcomes and radiologic changes in patients with lumbar disc herniation has rarely been reported. METHODS: Forty-four patients underwent disc excision, and 51 patients underwent disc excision and fusion. Clinical symptoms were evaluated using the Japanese Orthopaedic Association Back scores. All medical and surgical records were examined with regard to intraoperative blood loss, operation time, and other data. Preoperative and follow-up radiographs were analyzed to determine the spinal motion and disc height. RESULTS: Clinical outcome was excellent or good in 73% of the nonfusion group and in 82% of the fusion group (P = 0.31). The reduction in lower back pain after surgery was greater in the fusion group. The rate of recurrent disc herniation at the surgical level in the nonfusion group increased, but intraoperative blood loss, operation time, length of hospital stay, and total cost of procedure were all significantly less in the patients undergoing disc excision alone than in the fusion group. The radiologic analysis provided evidence that the disc height at the level of disc excision and posterolateral fusion in the fusion group decreased with time, as in the nonfusion group. The changes in disc height and spinal motion were not related to the clinical results. CONCLUSIONS: Although there is still controversy regarding the pros and cons of fusion in association with disc excision, there is seldom an indication for primary fusion for lumbar disc herniation.

Adolescent↗

PubMed2005

T1 adenocarcinoma of the rectum: transanal excision or radical surgery?

BACKGROUND: Recent studies suggest local excision may be acceptable treatment of T1 adenocarcinoma of the rectum, but there is little comparative data with radical surgery to assess outcomes and quantify risk. We performed a retrospective evaluation of patients with T1 rectal cancers treated by either transanal excision or radical resection at our institution to assess patient selection, cancer recurrence, and survival. METHODS: All patients who underwent surgery for T1 adenocarcinomas of the rectum (0-15 cm from anal verge) by either transanal excision (TAE) or radical resection (RAD) between January 1987 and January 2004 were identified from a prospective database. Data were analyzed using Fisher exact test, Kaplan-Meier method, and log-rank test. RESULTS: Three hundred nineteen consecutive patients with T1 lesions were treated by transanal excision (n = 151) or radical surgery (n = 168) over the 17-year period. RAD surgery was associated with higher tumor location in the rectum, slightly larger tumor size, a similar rate of adverse histology, and a lymph node metastasis rate of 18%. Despite these features, patients who underwent RAD surgery had fewer local recurrences, fewer distant recurrences, and significantly better recurrence-free survival (P = 0.0001). Overall and disease-specific survival was similar for RAD and TAE groups. CONCLUSION: Despite a similar risk profile in the 2 surgical groups, patients with T1 rectal cancer treated by local excision were observed to have a 3- to 5-fold higher risk of tumor recurrence compared with patients treated by radical surgery. Local excision should be reserved for low-risk cancers in patients who will accept an increased risk of tumor recurrence, prolonged surveillance, and possible need for aggressive salvage surgery. Radical resection is the more definitive surgical treatment of T1 rectal cancers.

Adenocarcinoma↗

PubMed1990

Precise excision and instability of the transposon Tn5 in Pseudomonas aeruginosa.

Excision of the transposon Tn5 from sites of insertion in plasmid DNA was shown to occur at high frequency in Pseudomonas aeruginosa. Plasmids with Tn5 insertions conjugated poorly into P. aeruginosa and adversely affected growth compared to the respective parental plasmids. The kanamycin-resistance phenotype of Tn5 was expressed poorly in P. aeruginosa and kanamycin-sensitive strains were common during the manipulation of the P. aeruginosa transconjugants. Examination of plasmid DNA isolated from kanamycin-sensitive P. aeruginosa transconjugants revealed excision of Tn5 sequences. A plasmid containing a selectable marker (mercury resistance) inactivated by a Tn5 insertion was constructed, and Tn5 excised precisely, permitting the expression of the mercury-resistance marker at high frequency (10(-3) in P. aeruginosa and at the expected low frequency (10(-7] in Escherichia coli. The recombinational mechanism that promotes frequent Tn5 excision in P. aeruginosa operated in the absence of the P. aeruginosa recA gene product. Fragments of Tn5 were also examined for excision and instability in P. aeruginosa. A plasmid containing the terminal 485 bp of inverted repeat sequences from Tn5, but lacking the transposase or kanamycin-resistance genes, also showed precise excision of Tn5 DNA at high frequency (10(-2] in P. aeruginosa. Unlike plasmids containing a complete Tn5 insertion, this plasmid transferred to P. aeruginosa at normal frequencies and growth of the host was not severely impaired. In contrast, plasmids containing either IS50 element transferred to P. aeruginosa at greatly reduced frequencies, and transconjugants containing the IS50R element (which contains the active transposase gene) were small and especially difficult to maintain. P. aeruginosa transconjugants harbouring a plasmid containing only the DNA between the IS50 elements (which included the kanamycin-resistance gene) were of normal size and stably maintained.(ABSTRACT TRUNCATED AT 250 WORDS)

Alleles↗

PubMed1995

Epigenetic self-regulation of developmental excision of an internal eliminated sequence on Paramecium tetraurelia.

Differentiation of the somatic macronucleus of ciliates after sexual events involves the programmed excision of thousands of single-copy internal eliminated sequences (IESs) from the germ-line genome. We have studied two cell lines of Paramecium tetraurelia that have identical germ-line genomes but differ in their macronuclear genomes. In the IES- cell line, a 222-bp IES interrupting a coding sequence is reproducibly excised during macronuclear differentiation, whereas it is not in the IES+ cell line. In a cross between the two lines, the developmental alternative in maternally inherited, suggesting that it is epigenetically controlled by the old (prezygotic) macronucleus in each cell. Transformation of the macronucleus of both lines with plasmids carrying fragments of either version of the gene shows that the presence of the IES sequence in the old macronucleus results in retention of the IES in the new macronuclear genome of sexual progeny. This could be attributable to (1) inhibition of excision, or (2) repair of a double-strand gap left in the genomic sequence after constitutive excision of the IES, by a polymerization mechanism using a homologous IES+ template from the old macronucleus. The latter possibility is ruled out by experiments showing that modified IESs can inhibit excision without being copied in the new macronuclear genome. Possible mechanisms are discussed in the light of a quantitative analysis of excision inhibition by the maternal IES sequence.

Animals↗

PubMed1978

Influence of Excision and Aging upon K Influx into Barley Roots: Recovery or Enhancement?

The influx of K(+) from (86)Rb-labeled solutions in the concentration range 0.008 to 0.2 mm into roots of intact plants and excised roots of barley plants (Hordeum vulgare [L.]) previously grown in 5 mm CaSO(4) (low K(+) roots) or 0.5 mm CaSO(4) plus 5 mm KCl (high K(+) roots) was measured. A consistent observation of these experiments was a substantial reduction of influx (usually by about 50%) following excision. The possible leakage of K(+) into the medium and subsequent dilution of specific activity of labeled solutions was eliminated as an explanation for influx reduction in excised low K(+) roots. Reduction of transpirational rates was also without effect upon influx into low K(+) roots. Excision followed by 2 hours aging in 0.5 mm CaSO(4) solution revealed that influx values recovered within the 2 hours to the values obtained in intact roots. It is concluded that much of the literature which describes the enhancement of ion uptake following excision actually describes excision damage followed by recovery.

Journal Article↗

PubMed1988

Root excision decreases nutrient absorption and gas fluxes.

The roots of barley plants (Hordeum vulgare L. cv Steptoe) were monitored before and after excision for net uptake of carbon dioxide, oxygen, ammonium, potassium, nitrate, and chloride and for their content of sucrose, glucose, fructose, and malic acid. All fluxes began to attenuate within 2 hours after excision. Net potassium uptake returned to control levels 6 hours after excision, but carbon dioxide, oxygen, ammonium, and nitrate fluxes continued to diminish for the remainder of the observation period. The addition of 0.1 molar glucose or 0.1 molar sucrose to excision medium had no significant effect on these changes in ion and gas fluxes. Net chloride uptake was negligible for all treatments. Sugar and malic acid content of the root declined after excision. Sucrose and glucose levels remained depressed for the entire observation period, whereas fructose and malic acid returned to control levels after 9 hours. These results indicate that excision has profound, adverse effects on root respiration and the absorption of mineral nitrogen.

Journal Article↗

PubMed1991

Abscisic Acid accumulates at positive turgor potential in excised soybean seedling growing zones.

Abscisic acid (ABA) accumulated in soybean (Glycine max [L.] Merr. cv Williams) hypocotyl elongating regions when seedlings were transferred to low water potential vermiculite (Psi = -0.3 megapascals) even though positive turgor is retained in this tissue. Accumulation of ABA in growing zones could occur from de novo biosynthesis within this tissue or transport from adjacent nongrowing zones. Both growing and nongrowing hypocotyl and root tissues accumulated significant levels of ABA when excised and dehydrated to reduce turgor. Surprisingly, excised growing zones (which experienced no water loss) also accumulated ABA when incubated in darkness for 4 hours at 100% relative humidity and 29 degrees C. Induction of ABA accumulation in the excised elongating region of the hypocotyl was not caused by disruption of root pressure or wounding. While excision of hypocotyl elongating regions induced ABA accumulation, no change in either extensin or p33 mRNA levels was observed. Accumulation of extensin or p33 mRNA required more severe wounding. This suggests that ABA is not involved in the response of these genes in wounded tissue and that wound signals are not causing ABA accumulation in excised tissue. Accumulation of ABA in excised elongating regions was correlated with growth inhibition and a decline in turgor to the yield threshold (Psi;(p) = 0.37 megapascals; R Matyssek, S Maruyama, JS Boyer [1988] Plant Physiol 86: 1163-1167). Inhibiting hypocotyl growth by transferring seedlings to lower temperatures or light did not cause ABA accumulation. We conclude that induction of ABA accumulation in growing zones is more sensitive to changes in turgor than the induction which occurs in mature tissues.

Journal Article↗

PubMed1992

Promoter fusions to the Activator transposase gene cause distinct patterns of Dissociation excision in tobacco cotyledons.

To explore the effects of altering the level of Activator (Ac) transposase (TPase) expression, a series of plasmids was constructed in which heterologous promoters were fused to the TPase gene. Promoters for the cauliflower mosaic virus (CaMV) 35S transcript and the octopine synthase (ocs) and nopaline synthase (nos) genes were tested. These fusions, and constructs expressing TPase from the wild-type Ac promoter, were introduced into tobacco, and their activity was monitored by crossing to a line carrying Dissociation (Ds) in a streptomycin phosphotransferase gene (Ds::SPT). The SPT marker provides a record of somatic excisions of Ds that occur during embryo development. The patterns of somatic variegation that resulted from transactivation by each fusion were distinct and strikingly different from the pattern triggered by the wild-type Ac constructs. Unlike wild-type Ac, which caused transposition throughout embryo development, each fusion gave rise to sectors of discrete size. Sectors triggered by the CaMV 35S fusion were largest, ocs sectors were intermediate, and nos were smallest. These patterns appear to indicate differential timing of the activation of these promoters during embryogeny. Measurement of transcript abundance for each transformant indicated that the CaMV 35S-transformed plants accumulated approximately 1000-fold more TPase mRNA than plants containing wild-type Ac, whereas ocs- and nos-transformed lines accumulated about 100-fold and 20-fold higher levels, respectively. Measurements of germinal excision frequencies driven by the chimeric TPase fusions, however, indicated that increasing transcription does not necessarily result in an increase in germinal excision. These measurements showed that the ocs and nos fusions have very low rates of germinal excision. Only the CaMV 35S fusion transformants were found to have higher rates than the Ac constructs, although significant pod-to-pod variation was observed. Gel blot analysis of DNA from progeny carrying germinal excision events resulting from the CaMV 35S fusion showed that excision is associated with reinsertion and that siblings sometimes carry the same transposition events. These findings suggest that in tobacco there is no direct proportionality between TPase expression and Ac-Ds transposition activity. This possibility has important implications for understanding the regulation of Ac transposition and for designing efficient gene tagging systems.

Base Sequence↗

PubMed1997

Tag1 is an autonomous transposable element that shows somatic excision in both Arabidopsis and tobacco.

Tag1 is a transposable element first identified as an insertion in the CHL1 gene of Arabidopsis. The chl1::Tag1 mutant originated from a plant (ecotype Landsberg erecta) that had been transformed with the maize transposon Activator (Ac), which is distantly related to Tag1. Genomic analysis of untransformed Landsberg erecta plants demonstrated that two identical Tag1 elements are present in the Landsberg erecta genome. To determine what provides transposase function for Tag1 transposition, we examined Tag1 excision in different genetic backgrounds. First, the chl1::Tag1 mutant was backcrossed to untransformed wild-type Arabidopsis plants to remove the Ac element(s) from the genome. F2 progeny that had no Ac elements but still retained Tag1 in the CHL1 gene were identified. Tag1 still excised in these Ac-minus progeny producing CHL1 revertants; therefore, Ac is not required for Tag1 excision. Next, Tag1 was inserted between a cauliflower mosaic virus 35S promoter and a beta-glucuronidase (GUS) marker gene and transformed into tobacco. Transformants showed blue-staining sectors indicative of Tag1 excision. Transgenic tobacco containing a defective Tag1 element, which was constructed in vitro by deleting an internal 1.4-kb EcoRI fragment, did not show blue-staining sectors. We conclude that Tag1 is an autonomous element capable of independent excision. The 35S-GUS::Tag1 construct was then introduced into Arabidopsis. Blue-staining sectors were found in cotyledons, leaves, and roots, showing that Tag1 undergoes somatic excision during vegetative development in its native host.

Arabidopsis↗