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Y Rao

Publications and source records attributed to Y Rao.

52 records · Page 3Linked to original sources
PubMed1994

The homophilic binding site of the neural cell adhesion molecule NCAM is directly involved in promoting neurite outgrowth from cultured neural retinal cells.

The neural cell adhesion molecule NCAM mediates intercellular adhesion by homophilic binding and its homophilic binding site has been mapped to a decapeptide sequence 243-KYSFNYDGSE-252 located within the third immunoglobulin-like domain of chick NCAM. To investigate the relationship between homophilic binding and NCAM-dependent neurite outgrowth, mutations were created in the binding site of NCAM-140 cDNA. Mutant NCAMs were expressed in L cells, and their ability to promote neurite outgrowth from chick retinal ganglion cells was assayed in coculture systems. Mutations that resulted in the loss of NCAM homophilic binding failed to promote neurite outgrowth from retinal cells. Alternatively, synthetic peptides containing the decapeptide sequence of the homophilic binding site were used to block NCAM homophilic interaction. Peptides that inhibited NCAM-NCAM binding also blocked neurite elongation. However, the peptide P5 (243-KYSFNYDGSELIIKKVDKSDE-263), despite being an inhibitor of NCAM-NCAM binding, induced the sprouting of multiple neurites. Moreover, peptide P5 stimulated a 2-fold increase in neurite-bearing cells, suggesting that P5 is a potent inducer of neurite outgrowth. Only E4-E6 retinal cells could be induced by P5, corresponding closely to their NCAM-responsive embryonic stages. The P5 effects were inhibited by pertussis toxin, indicating the involvement of a G-protein-dependent pathway. Taken together, these results provide evidence for a direct role of the NCAM homophilic binding site in the regulation of neurite outgrowth.

Amino Acid Sequence↗
PubMed1994

Conversion of a mesodermalizing molecule, the Xenopus Brachyury gene, into a neuralizing factor.

It has been shown previously that a Xenopus homolog of the mouse gene Brachyury, Xbra, can initiate mesodermal differentiation. Here, I report that a Xbra mutant truncated at the carboxyl terminus, B304, has lost the mesodermalizing activity and can block the activity of the wild-type Xbra. Injection of B304 mRNA led to formation of neural structures in animal cap explants. Examination of molecular markers in B304-injected explants shows expression of anterior neural markers in the absence of mesodermal markers, indicating that B304 can cause neuralization without the mediation of mesoderm. Implications of these findings on intracellular mechanisms underlying the initiation of neural differentiation in the ectodermal cells are discussed.

Activins↗
PubMed1993

Structural characterization of a homophilic binding site in the neural cell adhesion molecule.

We have previously used synthetic peptides to identify a homophilic binding site between Lys-243 and Glu-252 (KYSFNYDGSE) in the third immunoglobulin-like domain of the chick neural cell adhesion molecule (NCAM). In this report, we show that the deletion of this decapeptide sequence from chick NCAM or the scrambling of the first 5 amino acid residues led to the abolition of the homophilic binding activity of NCAM, thus confirming the role of this sequence in NCAM-NCAM binding. To investigate the involvement of individual residues of this decapeptide in NCAM binding, competition experiments were carried out using peptide analogues with various amino acid substitutions. Substitution of both Lys-243 and Asp-249 with Ala or of the 3 aromatic residues with Ala led to a total loss of activity, highlighting the importance of these residues in NCAM binding. Site-directed mutagenesis was then employed to substitute individual amino acids within the decapeptide sequence with Ala. The homophilic binding activity of mutant NCAMs transiently expressed in COS-1 cells was determined using the NCAM-Covasphere binding assay. Substitution of the charged residues with alanine decreased NCAM binding activity, implicating electrostatic interactions in NCAM binding activity. Substitution of the aromatic residues Tyr-244 and Phe-246 with Ala abolished NCAM binding activity, suggesting that hydrophobic and/or aromatic interactions may play an important role in NCAM homophilic binding. Substitution of amino acids in the predicted beta-strand portion of the decapeptide with Pro, which would tend to disrupt beta-strand conformation, led to a substantial loss of activity. Thus, NCAM-NCAM binding may also depend on the beta-backbone structure of this site. These results are consistent with the involvement of multiple amino acids within the decapeptide sequence in NCAM homophilic interaction.

Amino Acid Sequence↗
PubMed1992

Identification of a peptide sequence involved in homophilic binding in the neural cell adhesion molecule NCAM.

The neural cell adhesion molecule NCAM is capable of mediating cell-cell adhesion via homophilic interactions. In this study, three strategies have been combined to identify regions of NCAM that participate directly in NCAM-NCAM binding: analysis of domain deletion mutations, mapping of epitopes of monoclonal antibodies, and use of synthetic peptides to inhibit NCAM activity. Studies on L cells transfected with NCAM mutant cDNAs using cell aggregation and NCAM-covasphere binding assays indicate that the third immunoglobulin-like domain is involved in homophilic binding. The epitopes of four monoclonal antibodies that have been previously shown to affect cell-cell adhesion mediated by NCAM were also mapped to domain 3. Overlapping hexapeptides were synthesized on plastic pins and assayed for binding with these monoclonal antibodies. One of them (PP) reacted specifically with the sequence KYSFNY. Synthetic oligopeptides containing the PP epitope were potent and specific inhibitors of NCAM binding activity. A substratum containing immobilized peptide conjugates also exhibited adhesiveness for neural retinal cells. Cell attachment was specifically inhibited by peptides that contained the PP-epitope and by anti-NCAM univalent antibodies. The shortest active peptide has the sequence KYSFNYDGSE, suggesting that this site is directly involved in NCAM homophilic interaction.

Amino Acid Sequence↗
PubMed1992

The big brain gene of Drosophila functions to control the number of neuronal precursors in the peripheral nervous system.

big brain (bib) is one of the six known zygotic neurogenic genes involved in the decision of an ectodermal cell to take on the neurogenic or the epidermogenic cell fate. Previous studies suggest that bib functions in a pathway separate from the one involving Notch and other known neurogenic genes. For a better understanding of the bib function, it is essential first to characterize the mutant phenotype in detail. Our mutant analyses show that loss of bib function approximately doubles the number of neuronal precursors and their progeny cells in the embryonic peripheral nervous system. Mosaic studies reveal a hypertrophy of sensory bristles in bib mutant patches in adult flies. Our observations are compatible with a function of bib in specifying neuronal precursors of both the embryonic and adult sensory nervous system. This is in contrast to the function of Notch, which continues to be required at multiple stages of neural development subsequent to this initial determination event.

Animals↗
PubMed1991

Neuroectoderm in Drosophila embryos is dependent on the mesoderm for positioning but not for formation.

By studying neuroectoderm formation in the absence of mesoderm and mesectoderm in mutants of the zygotic genes snail and twist, we have found that the number of neuroblasts is not reduced in these mutants, suggesting that mesoderm and mesectoderm are not essential for the initiation of neural development. The position of the neuroectoderm, however, is ventrally shifted: Neuroectoderm takes over the presumptive peripheral mesoderm domain in single mutants, whereas the entire presumptive mesoderm domain in double mutants takes on the neuroectodermal fate. The shifted neuroectoderm still requires the proneural genes and the neurogenic genes. This shift is unlikely to be due to any shift in the nuclear localization gradient of the maternally supplied dorsal protein. A model for cell fate determination of the neuroectoderm, mesectoderm, and mesoderm will be discussed.

Animals↗
PubMed1990

Similarity of the product of the Drosophila neurogenic gene big brain to transmembrane channel proteins.

Cells in the neurogenic region of Drosophila embryos are initially bipotential; they can become either neuroblasts or epidermoblasts. Cell-cell interaction seems to play an important part in this developmental decision, which involves the function of a group of genes (the neurogenic genes). Loss-of-function mutations in any of the neurogenic genes result in nervous system hyperplasia and epidermal hypoplasia. Of the six known zygotic neurogenic genes, big brain (bib) is unique in several aspects. Most notably, all the other known neurogenic genes seem to fit into a cascade defined by genetic interactions, whereas bib does not show any detectable interaction with them. To understand how bib functions, we have now cloned the bib genomic and complementary DNAs. The predicted bib product shows significant sequence similarity to a family of transmembrane proteins, some of which form channels permeable to small molecules. Together with genetic studies, our results indicate that the bib product may mediate intercellular communication in a pathway separate from the one involving the products of the other neurogenic genes.

Amino Acid Sequence↗
PubMed1990

Urinary red cell size: diagnostic value and determinants.

Urinary red blood cells (RBC) are usually small and morphologically abnormal in glomerular (GN) hematuria, and slightly enlarged and morphologically normal in nonglomerular (NG) hematuria. This study was performed to evaluate the diagnostic value of urinary red cell size and morphology and to investigate the mechanism of the alteration in cell size. In 34 consecutive patients with hematuria we examined the urinary RBC size distribution and mean corpuscular volume (MCV) by electronic sizing of suspensions of RBC in an isotonic medium and, in 28 cases, compared it with the presence of 50% or greater dysmorphia. In 15 consecutive cases, we correlated MCV values with urine chemistries. In two GN cases we recorded the urine MCV serially during a furosemide-induced diuresis. In vitro incubations of peripheral or urinary RBC in various electrolyte solutions prior to sizing were also performed. The MCVs were significantly lower in GN (p less than 10(-6)) and probable GN (p less than 10(-4)) than NG hematuria. A cutoff of 72 fl completely separated GN and probable GN from NG cases. Fifty percent or more 'dysmorphic' RBC were seen in 12 of 13 GN, 3 of 4 probable GN but in no NG sediments. In patients with NG hematuria, the ratio of urinary to peripheral MCV tended to be greater than unity and correlated strongly with pH (r = -0.97; p less than 0.002). The effect of pH was confirmed in vitro. Furosemide diuresis induced a partial correction of the microcytosis of GN RBC, which correlated with the changes in urine composition. Furosemide had no effect on GN cells in vitro.(ABSTRACT TRUNCATED AT 250 WORDS)

Diuresis↗
PubMed1985

Radiation therapy for advanced head and neck squamous cell carcinoma using twice-a-day fractionation. A long-term follow-up.

Twenty-one patients with massive advanced squamous cell carcinoma of the head and neck received radiation therapy under the twice-a-day fractionation regimen. One hundred ten rad tumor dose was delivered twice daily with a 4-hour gap between the fractions, 5 days/week, to a total tumor dose of 7480 rad. The purpose was to increase the therapeutic ratio by minimizing sublethal radiation damage to normal tissue while allowing reoxygenation of radioresistant hypoxic tumor cells. Fifty-three percent of the patients showed no evidence of primary tumor at the end of the therapy and 60% showed complete regression of massive cervical lymphadenopathy. The 2-year recurrent-free rates for patients with tumors of the tonsillar region were 36% of T4 (4/11) and 33% (2/6) of N3a. The experience with conventional fractionation in similar cases was previously reported by others from this institution. They reported 2-year recurrent-free rates of 0% of T4 (0/10) and 17% (1/6) of N3. The higher recurrent-free rates in our series suggests better local and regional tumor control by the twice-a-day fractionation.

Carcinoma, Squamous Cell↗
PubMed1982

Advanced carcinoma of the nasopharynx. A clinical study of 274 patients.

A total of 274 patients with a diagnosis of nasopharyngeal carcinoma was treated in eight Veterans Administration Hospitals over a period of 22 years. Of the 274 patients, 256 (93%) had squamous-cell carcinoma, while 18 (7%) had other tumors. Most of the squamous-cell carcinoma patients (82%) had Stage IV disease; cervical lymph node metastases were found in 193 (75%), and distant metastases were present in 22 (9%). The actuarial 5-, 10-, and 15-year survival rates for the 256 squamous-cell carcinoma patients were 15%, 10%, and 7%, while they were 49%, 42%, and 35% for the 18 patients with other tumors (p = 0.006). There was a progressive decrease in 5-year survival with the increase in the stage of tumor. The survival of the 63 patients without metastases was better than the survival of the 193 patients with cervical metastases (24% vs. 12% at 5 years, p = 0.03). The presence of T4 disease or Initial Performance Status of less than 80 on the Karnofsky Scale indicated a poor prognosis (p = 0.0001). Treatment failure occurred in 83% of the patients by 2 years after therapy and was due to the lack of tumor control at the primary site. Advanced (N3) cervical lymph node metastases indicated that systemic tumor dissemination of the nasopharynx is an uncommon malignancy.

Adult↗
PubMed1980

Solitary extramedullary plasmacytoma of the upper respiratory and digestive tracts.

The diagnosis, treatment and follow-up data for patients with malignant solitary extramedullary plasmacytoma of the upper respiratory and digestive tracts for the period from 1949 to 1975 are presented. The neoplasm developed in the nasal fossae in 3 patients; in the maxillary sinuses in 2; in the supraglottic region in 1; and in the tonsillar fossa in 1. Curative radiation therapy is recommended after the diagnosis is established by biopsy examination only. In the present series, this practice resulted in complete regression of the tumors in all of the patients, with restoration of functions without local recurrence. In no case did the local disease transform into systemic myeloma.

Adult↗
PubMed1980

Radiation therapy for advanced head and neck squamous-cell carcinoma using twice-a-day fractionation.

Fifteen patients with massive advanced squamous-cell carcioma of the head and neck received radiation therapy under the twice-a-day fractionation regimen. The purpose was to increase the therapeutic ratio by minimizing sublethal radiation damage to normal tissue while allowing reoxygenation of radioresistant hypoxic tumor cells. Results demonstrated better local control than can be achieved through once-a-day fractionation, with 53% of the patients showing no evidence of primary tumor at the end of therapy, and 60% showing complete regression of cervical lymphadenopathy.

Carcinoma, Squamous Cell↗
PubMedDate not supplied

Lipids in diabetic and nondiabetic hemodialysis and CAPD patients.

To examine the question of "accelerated atherogenesis" in ESRD patients, the authors conducted a lipid survey among their hemodialysis and CAPD populations and evaluated data relevant to the lipid and diabetic status of these groups. Interestingly, longer duration of hemodialysis in nondiabetic patients was associated with lower cholesterol but not HDL, which may reflect diminished cardiac risk and mortality in the long-term survivors. Diabetic patients showed lower HDL but no cholesterol change with longer duration on hemodialysis. Type I diabetics showed the highest HDL and lowest risk ratio and a strong inverse correlation between PTH and HDL. This study highlights the role of lipids in the atherogenesis of uremia and serves as a baseline for a longitudinal study.

Adult↗