Sohail Ahmed - Academia.edu (original) (raw)

Papers by Sohail Ahmed

Molecular and Cellular Biology, 1997

Rho family GTPases have been assigned important roles in the formation of actin-based morphologie... more Rho family GTPases have been assigned important roles in the formation of actin-based morphologies in nonneuronal cells. Here we show that microinjection of Cdc42Hs and Rac1 promoted formation of filopodia and lamellipodia in N1E-115 neuroblastoma growth cones and along neurites. These actin-containing structures were also induced by injection of Clostridium botulinum C3 exoenzyme, which abolishes RhoA-mediated functions such as neurite retraction. The C3 response was inhibited by coinjection with the dominant negative mutant Cdc42Hs(T17N), while the Cdc42Hs response could be competed by coinjection with RhoA. We also demonstrate that the neurotransmitter acetylcholine (ACh) can induce filopodia and lamellipodia on neuroblastoma growth cones via muscarinic ACh receptor activation, but only when applied in a concentration gradient. ACh-induced formation of filopodia and lamellipodia was inhibited by preinjection with the dominant negative mutants Cdc42Hs(T17N) and Rac1(T17N), respect...

2006 IEEE 63rd Vehicular Technology Conference

In this contribution, we propose two successive interference cancellation (SIC) schemes for a fas... more In this contribution, we propose two successive interference cancellation (SIC) schemes for a fast frequency hopping (FFH) multiple access (MA) system using M-ary frequency shift keying (MFSK) and invoking multiuser detection (MUD). One of the proposed schemes invokes clipped combining, while the other scheme employs both product combining and clipped combining. The SIC schemes are adapted from a scheme proposed by U.-C. Fiebig in 1996. The basic principle of the SIC schemes is that detection is carried out in multiple stages and during each stage, only the most reliable symbols are detected. In subsequent stages, the interference contributed by the already detected symbols may be removed. The performance of the proposed schemes is evaluated and compared to that of Fiebig's scheme, when the FFH-MFSK system operates in a Nakagamim fading MA channel. The simulation results demonstrate that the proposed schemes attain a better bit error rate performance than Fiebig's scheme.

1998 URSI International Symposium on Signals, Systems, and Electronics. Conference Proceedings (Cat. No.98EX167)

Iterative decoding (ID) aided fast frequency hopping (FFH), M-ary frequency shift keying (MFSK) u... more Iterative decoding (ID) aided fast frequency hopping (FFH), M-ary frequency shift keying (MFSK) using clipped combining in multiple access (MA) channels is investigated. All users' data are convolutionally encoded and the encoded bits are interleaved and converted to M-ary symbols, which are transmitted using FFH-MFSK modulation. The soft metrics to be passed from the demodulator to the decoder are derived assuming a Rayleigh fading channel. We also propose a novel multiuser detection (MUD) scheme which employs joint soft decoding as well as successive interference cancellation (SIC), the receiver exploiting the soft information fed back by the decoder to the demodulator in order to cancel the interference imposed by reliable symbols. Our simulation results show that the proposed scheme is capable of combatting multiuser interference and outperforms the conventional ID by about 3dB.

Lecture Notes in Computer Science, 2009

A new method is proposed for joint tracking of cell morphology and motion from 3D temporal cellul... more A new method is proposed for joint tracking of cell morphology and motion from 3D temporal cellular images. We adopt the framework of region-based active contours for segmentation, which is able to cope with objects having blurred boundaries. Motion estimation is performed by optical flow to increase the robustness and accuracy. Cell morphology and motion are modelled via a unified energy formulation and estimated iteratively searching for the minimum energy configuration. Experiments are carried out on synthetic and real cellular images to demonstrate the performance of the method.

Saudi medical journal, 2011

Toxicology, 2006

Fig. 1. Molecular beacon-FRET induction following incubation with complementary oligonucleotide (... more Fig. 1. Molecular beacon-FRET induction following incubation with complementary oligonucleotide (n = 3 ± S.E.M.). and appears to be maximal within 60 min. The limit of detection achieved with 200 nM molecular beacon lies between 10 and 20 nM complementary oligonucleotide (Fig. 1). In the presence of target (ratio 1:1) and excess non-hybridising DNA (equivalent to that of 10,000 cells), FRET is induced by up to 12-fold. The molecular beacon approach has been used to detect RAD52 mRNA in living cells. We have optimised molecular beacon transfection in human cells, confirmed stability and demonstrated a response to double strand break inducing agents. These preliminary studies suggest that the RAD52 molecular beacon may be useful in understanding the dynamics of double strand breaks and provide the opportunity to follow DNA damage in real-time.

Communicative & Integrative Biology, 2012

2011 IEEE International Conference on Communications (ICC), 2011

ABSTRACT In this contribution, we employ the Mellin transform to derive the expressions for proba... more ABSTRACT In this contribution, we employ the Mellin transform to derive the expressions for probability density function (PDF) of the product of Nakagami-m and Gamma distributed random variables. As the special cases of the Nakagami-m and Gamma family, the PDF of the product of Rayleigh distributed random variables and that of the product of exponentially distributed Random variables are also derived. We exploit the fact that the Mellin transform of a product of independent and identically distributed random variables is the product of the Mellin transforms of the individual random variables. Using this approach, the PDF of the product of random variables is expressed in the form of an easily computable infinite series. Furthermore, application of the PDFs in digital communications using M-ary orthogonal modulation is illustrated.

BioArchitecture, 2011

I t was light microscopy that first revealed the hidden world of bacteria and the unit of life th... more I t was light microscopy that first revealed the hidden world of bacteria and the unit of life the "cell." From these first observations, made in the late 1600s, it has been clear that seeing is an important tool in biology. The merging of the fields of fluorescence and microscopy created the possibility to see subcellular structures and proteins. In the 1990s the use of the confocal microscopes, where cells/tissue could be optically sectioned, further improved the resolution of object visualization. From this microworld view we now move forward to the exciting prospects of the nanoworld view of biology. In this review I propose a nanoimaging approach, nanoscopy, which could be used to reveal cell architecture at the level of proteins and protein complexes. Nanoscopy includes, the F-techniques, superresolution microscopy, correlative light and electron microscopy and atomic force microscopy. To illustrate the biology that could be investigated by nanoscopy we focus on structures formed at the actin-membrane interface. In particular, focal adhesions and stress fibres have been analyzed using nanoscopy. Many of the proteins present in focal adhesions and stress fibres are shared with structures such as filopodia, lamellipodia, endocytic vesicles, actin pedestals and invadopodia. It is likely that nanoscopy of cells will reveal mechanistic details of biology at the level of individual proteins and protein complexes and importantly in a physiological context.

Proceedings of 2014 11th International Bhurban Conference on Applied Sciences & Technology (IBCAST) Islamabad, Pakistan, 14th - 18th January, 2014, 2014

The design and development of small scale aerial robots has been currently hindered by the lack o... more The design and development of small scale aerial robots has been currently hindered by the lack of applicability of conventional aerodynamics equations/principles to the small size vehicles flying at extremely low Reynolds number. Also conventional optimization techniques and algorithms have shown very limited success in these applications. Trial and error has been the most effective design tool in many cases often leading to computationally intensive and expensive design processes with longer iteration time. The non-availability of physics based analytical tools and the computational expense of numerical methods makes an empirical design optimization approach a practical alternative. This current research effort has been based on identification & application of physics based tools to evolve a Modeling & Simulation environment, in which such a design effort is possible.

Trends in Endocrinology & Metabolism, 2008

Recent developments in advanced microscopy techniques, the so-called F-techniques, including Fö r... more Recent developments in advanced microscopy techniques, the so-called F-techniques, including Fö rster resonance energy transfer, fluorescence correlation spectroscopy and fluorescence lifetime imaging, have led to a wide range of novel applications in biology. The F-techniques provide quantitative information on biomolecules and their interactions and give high spatial and temporal resolution. In particular, their application to receptor protein studies has led to new insights into receptor localization, oligomerization, activation and function in vivo. This review focuses on the application of the Ftechniques to the study of receptor molecules and mechanisms in the last three years and provides information on new modalities that will further improve their applicability and widen the range of biological questions that can be addressed. Receptor dimerization and oligomerization studies using FRET FRET has been applied to study homodimerization, heterodimerization and oligomerization of a wide range of receptors, including scavenger receptor [6], growth hormone receptor (GHR) [7,8] and G-protein-coupled receptors (GPCRs), in recent years [9-12]. To address the question of the 'when' and 'where' of receptor dimerization, Herrick-Davis and his colleagues examined serotonin 5-hydroxy-tryptamine2C (5-HT 2C) receptor dimerization biogenesis by using time-lapse confocal imaging and acceptor photobleaching FRET (apFRET) [13]. They monitored the proximity between cyan fluorescent protein (CFP)-and yellow fluorescent protein (YFP)-tagged 5-HT 2C receptors at different subcellular locations. The FRET efficiencies detected at different intracellular compartments indicated that homodimerization of 5-HT 2C receptors occurs in the endoplasmic reticulum (ER) and Golgi apparatus, which suggests that receptor dimerization could occur during receptor maturation.

Phytoparasitica, 2006

Insecticides which were environmentally friendly and the least toxic, were screened against a lab... more Insecticides which were environmentally friendly and the least toxic, were screened against a laboratory strain of Bracon hebetor (Say) (Hymenoptera: Braconidae) for their suitability for release in IPM of cotton. Concentrations ranging from 1 to 1000 ppm of the formulated insecticides in acetone were applied in glass vials and also by a leaf method, whereby cotton leaves were dipped in aqueous solutions of the same concentrations of insecticides. Adult parasitoids were exposed in both methods. According to the LCso at 24 h exposure, Acyhalothrin and spinosad were the most (7 and 5 ppm) and least (263 and 225 ppm) toxic in the vial and the leaf method, respectively, to B. hebetor. The possible use of the parasitoid for IPM of cotton is discussed.

Journal of Neurochemistry, 2004

Myelin-derived proteins, such as tenascin-R (TN-R), myelin associate glycoprotein (MAG), and Nogo... more Myelin-derived proteins, such as tenascin-R (TN-R), myelin associate glycoprotein (MAG), and Nogo-A, inhibit the CNS regeneration. By targeting specifically the inhibitory epitopes, we have investigated whether vaccination with a recombinant DNA molecule encoding multiple domains of myelin inhibitors may be useful in CNS repair. We show here that the recombinant DNA vaccine is able to activate the immune system but does not induce experimental autoimmune encephalomyelitis (EAE) in Lewis rats. Importantly, it promotes axonal regeneration in a spinal cord injury model. Thus, the application of DNA vaccine, encoding multiple specific domains of major inhibitory proteins and/or their receptors, provides another promising approach to overcome the inhibitory barriers during CNS regeneration.

Journal of Cellular Biochemistry, 2009

A stem cell has three important features. Firstly, the ability of self-renewal: making identical ... more A stem cell has three important features. Firstly, the ability of self-renewal: making identical copies of itself. Secondly, multipotency, generating all the major cell lineages of the host tissue (in the case of embryonic stem cells-pluripotency). Thirdly, the ability to generate/ regenerate tissues. Thus, the study of stem cells will help unravel the complexity of tissue development and organisation, and will also have important clinical applications. Neural stem cells (NSCs) are present during embryonic development and in certain regions of the adult central nervous system (CNS). Mobilizing adult NSCs to promote repair of injured or diseased CNS is a promising approach. Since NSCs may give rise to brain tumor, they represent in vitro models for anti-cancer drug screening. To facilitate the use of NSCs in clinical scenarios, we need to explore the biology of these cells in greater details. One clear goal is to be able to definitively identify and purify NSCs. The neurosphereforming assay is robust and reflects the behavior of NSCs. Clonal analysis where single cells give rise to neurospheres need to be used to follow the self-renewal and multipotency characteristics of NSCs. Neurosphere formation in combination with other markers of NSC behavior such as active Notch signaling represents the state of the art to follow these cells. Many issues connected with NSC biology need to be explored to provide a platform for clinical applications. Important future directions that are highlighted in this review are; identification of markers for NSCs, the use of NSCs in high-throughput screens and the modelling of the central nervous development. There is no doubt that the study of NSCs is crucial if we are to tackle the diseases of the CNS such as Parkinson's and Alzheimer's.

Journal of Cataract and Refractive Surgery, 2007

We report an unusual case of unilateral spontaneous lens dislocation in a 52-year-old woman with ... more We report an unusual case of unilateral spontaneous lens dislocation in a 52-year-old woman with a posterior polar cataract. We postulate that the increasing lens size secondary to nuclear sclerosis may have exerted pressure on a thinned posterior capsule, causing the capsule to rupture spontaneously. The unusual weak posterior capsule in posterior polar cataract is a well-recognized risk factor in phacoemulsification surgery. We believe this is the first report case of spontaneous lens dislocation secondary to posterior capsule rupture in posterior polar cataract.

IEEE Transactions on Vehicular Technology, 2008

We employ the Mellin transform to facilitate the bit error ratio (BER) analysis of a fast frequen... more We employ the Mellin transform to facilitate the bit error ratio (BER) analysis of a fast frequency hopping (FFH)-assisted, M-ary frequency-shift keying (MFSK) using product combining (PC) when the transmitted signal is subjected to both Rayleigh fading and partial-band noise jamming. Exploiting the fact that the Mellin transform of the product of independent random variables is the product of their Mellin transforms, we derive the probability density function (PDF) of the PC's output. The derivation of the PDF then allows the computation of the system's BER. It is shown that the Mellin transform substantially simplifies the analysis of the PC receiver and hence facilitates, for the first time, the analysis of the FFH-MFSK PC receiver for modulation orders of M > 2.

PloS one, Jan 2, 2011

Adenomatous Polyposis Coli (APC) is a tumor suppressor gene product involved in colon cancer. APC... more Adenomatous Polyposis Coli (APC) is a tumor suppressor gene product involved in colon cancer. APC is a large multidomain molecule of 2843 amino acid residues and connects cell-cell adhesion, the F-actin/microtubule cytoskeleton and the nucleus. Here we show that Cdc42 interacts directly with the first three armadillo repeats of APC by yeast two-hybrid screens. We confirm the Cdc42-APC interaction using pulldown assays in vitro and FRET assays in vivo. Interestingly, Cdc42 interacts with APC at leading edge sites where F-actin is enriched. In contrast, Cdc42 interacts with the truncated mutant APC¹⁻¹⁶³⁸ in cellular puncta associated with the golgi-lysozome pathway in transfected CHO cells. In HCT116 and SW480 cells, Cdc42 induces the relocalization of endogenous APC and the mutant APC¹⁻¹³³⁸ to the plasma membrane and cellular puncta, respectively. Taken together, these data indicate that the Cdc42-APC interaction induces localization of both APC and mutant APC and may thus play a dir...

Experimental Cell Research, 2011

Cytokinesis in mammalian cells requires actin assembly at the equatorial region. Although functio... more Cytokinesis in mammalian cells requires actin assembly at the equatorial region. Although functions of RhoA in this process have been well established, additional mechanisms are likely involved. We have examined if Cdc42 is involved in actin assembly during cytokinesis. Depletion of Cdc42 had no apparent effects on the duration of cytokinesis, while overexpression of constitutively active Cdc42 (CACdc42) caused cytokinesis failure in normal rat kidney epithelial cells. Cells depleted of Cdc42 displayed abnormal cell morphology and caused a failure of tight accumulation of actin and RhoA at the equator. In contrast, in cells overexpressing CACdc42, actin formed abnormal bundles and RhoA was largely eliminated from the equator. Our results suggest that accurate regulation of Cdc42 activity is crucial for proper equatorial actin assembly and RhoA localization during cytokinesis. Notably, our observations also suggest that tight actin concentration is not essential for cytokinesis in adherent mammalian cells.

Dalton Trans., 2014

Y2CuO4–5CuO composite thin films having a band gap of 1.82 eV and a photocurrent density of 9.85 ... more Y2CuO4–5CuO composite thin films having a band gap of 1.82 eV and a photocurrent density of 9.85 μA cm−2 at 0.8 V have been deposited from a solution of precursor 1 by AACVD.

Coloration Technology, 2008

An 80:20 polyester ⁄ viscose blended woven fabric was subjected to different softening and sanfor... more An 80:20 polyester ⁄ viscose blended woven fabric was subjected to different softening and sanforising treatments. The effect of different softeners and sanforising treatments on the pilling propensity of the fabric was investigated. It was found that, while some types of softeners had no effect on pilling, the others may result in extreme deterioration of the pilling performance of polyester ⁄ viscose blended fabrics. It was further found that, in all cases, sanforising after softening adversely affects the fabric pilling performance.