Surgical management of congenital tracheal stenosis

Long-segment tracheal stenosis in infants and children is difficult to manage and can be life-threatening. Patients frequently have associated cardiac, other respiratory, or gastrointestinal anomalies that may confuse the diagnosis at initial presentation. The rarity of congenital tracheal stenosis has not allowed sufficient experience for the development of standard treatment protocol. Several surgical techniques have been described but have varying results. This article reviews the diagnosis and different surgical options for congenital tracheal stenosis and their outcomes.

Arabidopsis intron mutations and pre-mRNA splicing

Arabidopsis intron mutants provide and will continue to provide a valuable source of information on in vivo plant intron splicing. All of the characterized mutants discussed here contain base substitutions in either the 5' splice site :GU or 3' splice site AG: dinucleotides or broader splice site consensus sequences. Many of these mutations lead to the activation of cryptic splice sites, usually upstream or downstream of the authentic 5' and 3' splice sites respectively, often with reduced efficiency. This splicing behaviour is in agreement with detailed splicing analyses of test plant introns. However, some of the Arabidopsis mutations lead to more complex splicing patterns often involving exon skipping. These mutations illustrate the complexity of the splicing reaction (where the final splicing event reflects the characteristics such as splice site sequence, intron size and composition, and their interactions with spliceosomal components) and how single nucleotide mutations can affect the strength and balance of interactions to alter splicing patterns. The splicing patterns observed in the Arabidopsis mutants parallel those seen in mutations causing some human genetic disorders underlining the emerging similarities in mechanisms of splice site selection and intron/exon definition between plant and vertebrate systems. Analysis of the Arabidopsis intron mutations exhibiting complex splicing patterns will help to address fundamental questions in plant splicing, such as splice site selection and exon scanning. This information will be important in understanding the mechanisms by which gene expression is regulated post-transcriptionally in the ever-increasing number of alternatively spliced plant gene systems.

Surgical management of total anomalous pulmonary venous connection. Thirty-year trends

BACKGROUND

Reports of surgical correction of total anomalous pulmonary venous connection (TAPVC) over the past 30 years indicate a general improvement in operative survival. However, prevention of late pulmonary venous obstruction continues to be a cornerstone of successful repair. The purpose of the study was to identify factors associated with improvement in perioperative mortality and to determine risk factors for death and reoperation due to pulmonary vein stenosis after repair of TAPVC.

METHODS AND RESULTS

Using univariate and multiple regression analysis, we analyzed risk of early and late mortality and need for reoperation in 105 patients operated on between April 1966 and June 1995. Despite increased frequency of neonatal repair in the most recent time period (29% in 1966 through 1985; 55% in 1991 through 1995, P < .05), operative mortality declined (13% in 1966 through 1985; 0% in 1991 through 1995). The incidence of postoperative pulmonary hypertensive episodes and death related to pulmonary hypertension decreased significantly over the study period (P < .001). Aggressive preoperative elective medical stabilization and prophylaxis of postoperative pulmonary hypertensive episodes may have contributed to this improvement. By univariate analysis, preoperative pulmonary hypertension (P < .02) and preoperative pulmonary vein obstruction (P < .01) correlated with early mortality up to 1990 but not in the past 5 years. Multiple logistic regression analysis showed that only a small pulmonary confluence associated with diffuse pulmonary vein stenosis was an independent risk factor for early (P < .001) and late (P = .01) death as well as need for reoperation (P = .007). Type of TAPVC was not a significant risk factor throughout the three decades of our experience. At a median follow-up of 87 months, late survival was 98% (93 of 95 operative survivors), and all are NYHA class I.

CONCLUSIONS

Improvements on surgical technique as well as preoperative and postoperative management account for the reduction in mortality and need for reoperation for most types of TAPVC. However, the presence of a small venous confluence and diffuse pulmonary vein stenosis remains a risk factor for adverse outcome.

Anterior pericardial tracheoplasty for congenital tracheal stenosis: intermediate to long-term outcomes

BACKGROUND

Although several techniques for the treatment of long-segment stenosis of the trachea have been reported, including slide tracheoplasty, rib grafting, and use of a pericardial patch, the optimal repair remains controversial because of a lack of midterm to long-term follow-up data.

METHODS

To assess the intermediate and long-term outcomes of patients having repair with anterior pericardial tracheoplasty, we reviewed case histories of 12 patients (1984 to present). The median age was 6.7 months (range, 1 to 98 months), and the median weight was 6.0 kg (range, 0.97 to 42 kg). All patients underwent anterior pericardial tracheoplasty through a median sternotomy during partial normothermic cardiopulmonary bypass. An average of 13 tracheal rings (range, five to 23) were divided anteriorly, and a patch of fresh autologous pericardium was used to enlarge the trachea by 1.5 times the predicted diameter for patient age and weight.

RESULTS

There was one hospital death, and all but 2 patients are long-term survivors. All but 1 current survivor remain asymptomatic, with no bronchoscopic evidence of airway obstruction or granulation on the pericardial patch. All survivors examined have normal tracheal growth and development, with a median follow-up of 5.5 years (range, 1 to 11 years).

CONCLUSIONS

Anterior pericardial tracheoplasty for congenital tracheal stenosis provides excellent results at intermediate to long-term follow-up.

Tyrosine hydroxylase gene expression in varying forms of human pheochromocytoma

We performed a comparative study of catecholamine content, tyrosine hydroxylase (TH) activity, and TH mRNA levels in normal human adrenals and various clinical forms of human pheochromocytoma. We studied sporadic, benign intra-adrenal chromaffin tumors and other non-malignant intra-adrenal tumors associated with multiple endocrine neoplasia type 2B (MEN 2B) and von Hippel-Lindau disease along with one extra-adrenal malignant pheochromocytoma. Our findings suggest substantial differences in TH transcriptional rates or the stability of TH mRNA or both may contribute to altered TH expression in human chromaffin cells associated with "normal" adrenal tissues and various forms of pheochromocytoma and distinctive patterns of expression in the different settings in which these tumors arise.

Effect of cAMP binding site mutations on the interaction of cAMP receptor protein with cyclic nucleoside monophosphate ligands and DNA

Although cAMP binding to wild type cAMP receptor protein (CRP) induces specific DNA binding and activates transcription, cyclic nucleoside monophosphate (cNMP) binding to the CRP mutant Ser128 --> Ala does not, whereas the double CRP mutant Thr127 --> Leu/Ser128 --> Ala activates transcription even in the absence of cNMP. Isothermal titration calorimetry measurements on the cNMP binding reactions to the S128A and T127L/S128A mutants show that the reactions are mainly entropically driven as is cAMP binding to CRP. In contrast to cAMP binding to CRP, the binding reactions are noncooperative and exothermic with binding enthalpies (DeltaHb) ranging from -23.4 +/- 0.9 kJ mol-1 for cAMP binding to S128A at 39 degrees C to -4.1 +/- 0.6 kJ mol-1 for cAMP binding to T127L/S128A at 24 degrees C and exhibit enthalpy-entropy compensation. To account for the inactivity of the S128A mutant, in vitro and in vivo DNA binding experiments were performed on the cAMP-ligated S128A mutant. The cAMP-ligated S128A mutant binds to the consensus DNA binding site with approximately the same affinity as that of cAMP-ligated CRP but forms a different type of complex, which may account for loss of transcriptional activity by the mutant. Energy minimization computations on the cAMP-ligated S128A mutant show that amino acid conformational differences between S128A and CRP occur at Ser179, Glu181, and Thr182 in the center of the DNA binding site, implying that these conformational changes may account for the difference in DNA binding.

Selective management of embolized intracardiac missiles

Intracardiac projectiles are occasionally found in stable patients who have sustained penetrating trauma. These missiles may arise from embolization from a peripheral injury site. We describe 3 patients with embolized intracardiac projectiles. The diagnosis was suggested by the presence of a foreign body within the cardiac silhouette on chest roentgenograms and was confirmed using fluoroscopy, echocardiography, or computed tomography. The management of embolized intracardiac missiles should be individualized to each patient. All of our patients had fixed intracavitary right-sided missiles and were successfully managed expectantly.

Surgical management of hypoplastic left heart syndrome

BACKGROUND

The treatment of infants with hypoplastic left heart syndrome has been challenging and controversial.

METHODS

To assess the operative management and intermediate-term outcome, we retrospectively analyzed our surgical experience with 50 newborns with hypoplastic left heart syndrome operated on between January 1989 and June 1995.

RESULTS

Surgical palliation with a first-stage Norwood operation was offered to 28 patients. The remaining 22 infants were initially listed for heart transplantation, and 15 underwent the operation. Ten of the 15 recipients are alive, and all are in New York Heart Association class I. Seven infants underwent a Norwood procedure after being on the list for transplantation for 12 to 42 days. A total of 34 patients underwent Norwood procedures with one operation aborted because of inoperable anatomy. Two infants who survived the first-stage Norwood operation underwent subsequent heart transplantation and are currently doing well. The 1-year mortality rate for heart transplantation was 18% (3/17) versus 50% (17/34) for the Norwood procedure. Risk factors for early mortality after a Norwood procedure include longer circulatory arrest time (> 50 minutes), preoperative acidosis (pH < 7.20), larger systemic-pulmonary artery shunt (> or = 4 mm), diminutive ascending aorta (< or = 2.0 mm), and anatomic subtype of aortic and mitral atresia. The 1-year survival rate for the Norwood procedure improved from 36% for the patients operated on during 1989 through 1992 to 75% during 1993 to mid-1995 (p = 0.005). Of the 17 survivors of a first-stage Norwood operation, 10 have undergone the second stage (bidirectional Glenn procedure), and 7 have completed a Fontan procedure. Heart transplantation results have also improved, with no deaths since 1992.

CONCLUSIONS

Both the Norwood procedure and heart transplantation have encouraging early to intermediate results in infants with hypoplastic left heart syndrome. Hypoplastic left heart syndrome should be managed selectively on the basis of cardiac morphology, donor availability, and family wishes. Development of a flexible program involving the use of both procedures may aid in the successful management of infants with hypoplastic left heart syndrome.

The organization of ribosomal RNA processing correlates with the distribution of nucleolar snRNAs

We have analyzed the organization of pre-rRNA processing by confocal microscopy in pea root cell nucleoli using a variety of probes for fluorescence in situ hybridization and immunofluorescence. Our results show that transcript processing within the nucleolus is spatially highly organized. Probes to the 5' external transcribed spacer (ETS) and first internal transcribed spacer (ITS1) showed that the excision of the ETS occurred in a sub-region of the dense fibrillar component (DFC), whereas the excision of ITS1 occurred in the surrounding region, broadly corresponding to the granular component. In situ labelling with probes to the snoRNAs U3 and U14, and immunofluorescence labelling with antibodies to fibrillarin and SSB1 showed a high degree of coincidence with the ETS pattern, confirming that ETS cleavage and 18 S rRNA production occur in the DFC. ETS, U14, fibrillarin and SSB1 showed a fine substructure within the DFC comprising closely packed small foci, whereas U3 appeared more diffuse throughout the DFC. A third snoRNA, 7-2/MRP, was localised to the region surrounding the ETS, in agreement with its suggested role in ITS1 cleavage. All three snoRNAs were also frequently observed in numerous small foci in the nucleolar vacuoles, but none was detectable in coiled bodies. Antibodies to fibrillarin and SSB1 labelled coiled bodies strongly, though neither protein was detected in the nucleolar vacuoles. During mitosis, all the components analyzed, including pre-rRNA, were dispersed through the cell at metaphase, then became concentrated around the periphery of all the chromosomes at anaphase, before being localized to the developing nucleoli at late telophase. Pre-rRNA (ETS and ITS1 probes), U3 and U14 were also concentrated into small bodies, presumed to be pre-nucleolar bodies at anaphase.

Ventricular septal aneurysm after atrioventricular septal repair with pericardium

A 2-month-old infant underwent a two-patch repair of a type C atrioventricular septal defect using autologous pericardium. Several months later a large, symptomatic aneurysm of the ventricular septal patch developed, requiring resection. The use of untreated autologous pericardium for large, congenital ventricular septal defects is unpredictable and should be avoided.

Mycoplasma fermentans simplifies our view of the catalytic core of ribonuclease P RNA

The catalytic RNA moiety of (eu)bacterial RNase P is responsible for cleavage of the 5' leader sequence from precursor tRNAs. We report the sequence, the catalytic properties, and a phylogenetic-comparative structural analysis of the RNase P RNA from Mycoplasma fermentans, at 276 nt the smallest known RNase P RNA. This RNA is noteworthy in that it lacks a stem-loop structure (helix P12) that was thought previously to be universally present in bacterial RNase P RNAs. This finding suggests that helix P12 is not required for catalytic activity in vivo. In order to test this possibility in vitro, the kinetic properties of M. fermentans RNase P RNA and a mutant Escherichia coli RNase P RNA that was engineered to lack helix P12 were determined. These RNase P RNAs are catalytically active with efficiencies (Kcat/Km) comparable to that of native E. coli RNase P RNA. These results show that helix P12 is dispensable in vivo in some organisms, and therefore is unlikely to be essential for the mechanism of RNase P action. The notion that all phylogenetically volatile structures in RNase P RNA are dispensable for the catalytic mechanism was tested. A synthetic RNA representing the phylogenetic minimum RNase P RNA was constructed by deleting all evolutionarily variable structures from the M. fermentans RNA. This simplified RNA (Micro P RNA) was catalytically active in vitro with approximately 600-fold decrease in catalytic efficiency relative to the native RNA.

Comparative analysis of ribonuclease P RNA using gene sequences from natural microbial populations reveals tertiary structural elements

PCR amplification of template DNAs extracted from mixed, naturally occurring microbial populations, using oligonucleotide primers complementary to highly conserved sequences, was used to obtain a large collection of diverse RNase P RNA-encoding genes. An alignment of these sequences was used in a comparative analysis of RNase P RNA secondary and tertiary structure. The new sequences confirm the secondary structure model based on sequences from cultivated organisms (with minor alterations in helices P12 and P18), providing additional support for nearly every base pair. Analysis of sequence covariation using the entire RNase P RNA data set reveals elements of tertiary structure in the RNA; the third nucleotides (underlined) of the GNRA tetraloops L14 and L18 are seen to interact with adjacent Watson-Crick base pairs in helix P8, forming A:G/C or G:A/U base triples. These experiments demonstrate one way in which the enormous diversity of natural microbial populations can be used to elucidate molecular structure through comparative analysis.

Comparative analysis of ribonuclease P RNA structure in Archaea

Although the structure of the catalytic RNA component of ribonuclease P has been well characterized in Bacteria, it has been little studied in other organisms, such as the Archaea. We have determined the sequences encoding RNase P RNA in eight euryarchaeal species: Halococcus morrhuae, Natronobacterium gregoryi, Halobacterium cutirubrum, Halobacteriurn trapanicum, Methanobacterium thermoautotrophicum strains deltaH and Marburg, Methanothermus fervidus and Thermococcus celer strain AL-1. On the basis of these and previously available sequences from Sulfolobus acidocaldarius, Haloferax volcanii and Methanosarcina barkeri the secondary structure of RNase P RNA in Archaea has been analyzed by phylogenetic comparative analysis. The archaeal RNAs are similar in both primary and secondary structure to bacterial RNase P RNAs, but unlike their bacterial counterparts these archaeal RNase P RNAs are not by themselves catalytically proficient in vitro.

Ultrastructural dynamics of mitochondrial morphology in varying functional forms of human adrenal cortical adenoma

Adrenal cortical mitochondria display an extensive capacity to adapt morphologically to the functional state of the adrenal cortical cell. In the present study, we have used transmission electron microscopy to analyze cortical tissues from 3 normal human adrenal glands (zona fasciculata and zona glomerulosa), and from 8 steroid-secreting adrenal cortical adenomas (3 cortisol-producing, 4 aldosterone-producing, and 1 progesterone-producing tumor), correlating both clinical and biochemical features with cellular ultrastructure. The morphology of mitochondria was related to the enzyme activity and steroid-biosynthetic capacity of each tumor. Cells from aldosterone-producing adenomas demonstrated a large number of elongated tubular mitochondria with characteristic bridging of inner membranes, producing a lamellar-type pattern. Cells from cortisol-producing adenomas showed large round mitochondria with vesicular or tubulovesicular inner membranes surrounded by a characteristic dilated smooth endoplasmic reticulum. A highly unusual progesterone-producing adenoma, in which a deficiency of 21 alpha-hydroxylase activity was demonstrated, showed a peculiar type of enlarged lamellar mitochondria with bright inner matrix and a reduced number of inner membranes. Therefore, the ultrastructural characteristics of adrenal cortical mitochondria appear to be potential markers for the differentiation of steroid-producing adenomas. These studies point to the possibility of a broader use of electron microscopy in the study of adrenal tumors.

Mutation of putative branchpoint consensus sequences in plant introns reduces splicing efficiency

Intron lariat formation between the 5' end of an intron and a branchpoint adenosine is a fundamental aspect of the first step in animal and yeast nuclear pre-mRNA splicing. Despite similarities in intron sequence requirements and the components of splicing, differences exist between the splicing of plant and vertebrate introns. The identification of AU-rich sequences as major functional elements in plant introns and the demonstration that a branchpoint consensus sequence was not required for splicing have led to the suggestion that the transition from AU-rich intron to GC-rich exon is a major potential signal by which plant pre-mRNA splice sites are recognized. The role of putative branchpoint sequences as an internal signal in plant intron recognition/definition has been re-examined. Single nucleotide mutations in putative branchpoint adenosines contained within CUNAN sequences in four different plant introns all significantly reduced splicing efficiency. These results provide the most direct evidence to date for preferred branchpoint sequences being required for the efficient splicing of at least some plant introns in addition to the important role played by AU sequences in dicot intron recognition. The observed patterns of 3' splice site selection in the introns studied are consistent with the scanning model described for animal intron 3' splice site selection. It is suggested that, despite the clear importance of AU sequences for plant intron splicing, the fundamental processes of splice site selection and splicing in plants are similar to those in animals.

Ribonuclease P structure and function in Archaea

An important approach to understanding RNA-based catalytic function by ribonuclease P is the investigation of its evolutionary diversity in structure and function. Because RNase P enzymes from all organisms are thought to share common ancestry, the fundamental features of structure and biochemistry should be conserved in all of its modern forms. In contrast to the bacterial enzyme, the RNase P enzymes from Eucarya, organelles, and Archaea are poorly understood. This review describes our nascent understanding of the structure and function of RNase P in Archaea, and how this enzyme compares to its homologs in the other evolutionary Domains.

The Ribonuclease P Database

Ribonuclease P is the endoribonuclease responsible for the removal of leader sequences from tRNA precursors. Ribonuclease P is a ribonucleoprotein, and in bacteria the RNA alone is capable of pre-tRNA processing in vitro, i.e. it is a catalytic RNA. The Ribonuclease P Database is a compilation of ribonuclease P sequences, sequence alignments, secondary structures, three-dimensional models and accessory information, in the form of a hypertext document available via the Worldwide Web.