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Featured researches published by M.M. Ali.


Developmental Dynamics | 1999

VENTRALLY EMIGRATING NEURAL TUBE CELLS CONTRIBUTE TO THE FORMATION OF MECKEL'S AND QUADRATE CARTILAGE

G.S. Sohal; M.M. Ali; A.A. Ali; Donghai Dai

A population of multipotential neuroepithelial cells originating in the ventral portion of the hindbrain neural tube has been shown recently to emigrate at the site of attachment of the trigeminal nerve. These ventrally emigrating neural tube cells populate the mesenchyme of the first pharyngeal (branchial) arch. Because the Meckels and the quadrate cartilage develop from this mesenchyme, we sought to determine whether these ventrally emigrating neural tube cells contributed to their development. The ventral neural tube cells were tagged with a replication‐deficient retroviral vector containing the LacZ gene. This method permanently labels the descendents of the neural tube cells; thus, they can be subsequently tracked during development. The viral concentrate was microinjected into the lumen of the rostral hindbrain of chick embryos, after the emigration of neural crest is finished, on embryonic day 2 (stage 14). In control embryos, the virus was placed on top of the neural tube. Embryos were killed on days 3, 4, and 7 and processed for the detection of LacZ‐positive cells. By day 7, the Meckels and the quadrate cartilage can be easily recognized. LacZ‐positive cells were seen in both cartilages. They were located in perichondrium and in the cartilage. Immunostaining with the neural crest cell marker HNK‐1 indicated that the LacZ‐positive cells were HNK‐1 negative. The HNK‐1‐positive neural crest–derived cells were located in the cartilage but not in the perichondrium. These results indicate that the chondrocytes in the Meckels and the quadrate cartilage differentiate from two sources of cells; the ventrally emigrating neural tube cells and the neural crest. The developmental significance of differentiation of cartilage from the ventral neural tube cells and of the heterogeneous origin of chondrocytes in morphogenesis remains to be established. Dev Dyn 1999;216:37–44.


International Journal of Developmental Neuroscience | 1996

DiI labeling and homeobox gene Islet-1 expression reveal the contribution of ventral neural tube cells to the formation of the avian trigeminal ganglion

G.S. Sohal; D.E. Bockman; M.M. Ali; N.T. Tsai

Cells of the neural tube are thought to be committed to form only the central nervous system, whereas the peripheral nervous system is believed to be derived from neural crest cells and from placodes, which are specialized regions of the surface ectoderm. Neural crest cells arise early from the dorsal part of the neural tube. The possibility that after emigration of the neural crest cells, another population of cells arising from the ventral part of the neural tube also emigrates via a different route was examined. Here we report that, after labeling cells of the ventral neural tube in the rostral hindbrain of E3 duck embryos with DiI, they were later found in the trigeminal ganglion of the fifth cranial nerve. A trail of labeled cells could be traced from the ventral part of the neural tube to the peripheral ganglion. Further, expression of the homeobox gene Islet‐1 in cells of the neural tube and the ganglion also indicated that some ventral neural tube cells may normally emigrate to the trigeminal ganglion. It is concluded that not all neural tube cells are committed to form the central nervous system; the ventral part of the neural tube also provides cells for the formation of the trigeminal ganglion. These results raise the possibility that the ventral neural tube may serve as an additional source of cells for the formation of various other components of the peripheral nervous system.


International Journal of Developmental Neuroscience | 2002

A second source of precursor cells for the developing enteric nervous system and interstitial cells of Cajal.

G.S. Sohal; M.M. Ali; F.A. Farooqui

The enteric nervous system is believed to be derived solely from the neural crest cells. This is partly based on the belief that the neural crest cells are the sole neural tube‐derived cells colonizing the gastrointestinal tract. However, recent studies have shown that after the emigration of neural crest cells an additional population of cells emigrates from the cranial neural tube. These cells originate in the ventral part of the hindbrain, emigrate through the site of attachment of the cranial nerves, and colonize a variety of developing structures including the gastrointestinal tract. This cell population has been named the ventrally emigrating neural tube (VENT) cells. We followed the fate of these cells in the gastrointestinal tract. Ventral hindbrain neural tube cells of chick embryos were tagged with replication‐deficient retroviral vectors containing the LacZ gene, after the emigration of neural crest from this region. In control embryos, the viral concentrate was dropped on the dorsal part of the neural tube. Embryos were sacrificed from embryonic days 3–12 and processed for the detection of LacZ positive ventrally emigrating neural tube cells. These cells colonized only the foregut, specifically the duodenum and stomach. Immunostaining with the neural crest cell marker HNK‐1 showed that they were HNK‐1 negative, indicating that they were not derived from neural crest. Cells were detected in three locations: (1) the myenteric and submucosal plexus of the enteric nervous system; (2) circular smooth muscle cell layer; and (3) mucosal lining of the lumen. A variety of specific markers were used to identify their fate. Some ventrally emigrating neural tube cells differentiated into neurons and glial cells, indicating that the enteric nervous system in the foregut develops from an additional source of precursor cells. It was also found that some of these cells differentiated into interstitial cells of Cajal, which mediate impulses between the enteric nervous system and smooth muscle cells, whereas others differentiated into epithelium. Altogether, these results indicate that the ventrally emigrating neural tube cells are multipotential. More importantly, they reveal a novel source of precursor cells for the neurons and glial cells of the enteric nervous system. The developmental and functional significance of the heterogeneous origin of the cell types remains to be established.


General Pharmacology-the Vascular System | 1999

Ventrally emigrating neural tube cells differentiate into vascular smooth muscle cells

A.A. Ali; M.M. Ali; Donghai Dai; G.S. Sohal

A multipotential cell population originating in the ventral part of the hindbrain neural tube, the ventrally emigrating neural tube cells (VENT cells), has recently been shown to migrate into the craniofacial mesenchyme. Because vascular smooth muscle cells develop from this mesenchyme, we sought to determine if the VENT cells contributed to their differentiation. VENT cells were tagged with replication-deficient retroviral vector with LacZ by microinjection into the lumen of the rostral hindbrain of chick embryos on day 2. Embryos were processed for the detection of LacZ positive cells on day 7. LacZ-positive cells were present in the wall of craniofacial arteries and veins. Immunostaining with the smooth muscle alpha-actin confirmed the labeled cells to be smooth muscle cells. It is concluded that some vascular smooth muscle cells differentiate from neural tube cells. the developmental and functional significance of which remains to be established.


International Journal of Developmental Neuroscience | 1998

Emigration of neuroepithelial cells from the hindbrain neural tube in the chick embryo

G.S. Sohal; M.M. Ali; Deni S. Galileo; A.A. Ali

It is generally believed that after the emigration of neural crest, the neuroepithelial cells of the neural tube are committed to differentiate only as neurons and supporting cells of the central nervous system. Neural crest cells arise from the dorsal portion of the developing neural tube and contribute to the formation of the peripheral nervous system and a variety of non‐neural structures. In contrast to this view we have recently shown, by focal application of the vital dye Dil in duck embryos, that an additional population of cells emigrates from the neural tube. By using an entirely different technique we confirm and extend these observations in the chick embryo. Replication‐deficient retroviral vector LZ12 containing the gene LacZ was utilized to label the neural tube cells. The viral concentrate was microinjected into the lumen of the rostral hind‐brain neural tube, considerably after the completion of emigration of neural crest cells. The labeled cells were monitored in whole mounts and histological sections. Initially, the labeled cells were restricted to the neuroepithelium of the hindbrain neural tube. Subsequently, they were seen in the neural tube and in the ganglion of the fifth cranial nerve (trigeminal ganglion). Later, they migrated beyond the trigeminal ganglion, i.e., into the mesenchyme of the first pharyngeal arch. Immunostaining with the neural crest cell marker, HNK‐1, indicated that the emigrated neuroepithelial cells were HNK‐1 negative. It is concluded that in the chick embryo some neuroepithelial cells emigrate at the site of attachment of the trigeminal nerve, migrate into the ganglion and then into the mesenchyme of the first arch. This cell population differs antigenically from the neural crest cells.


Cellular and Molecular Life Sciences | 1999

Ventral neural tube cells differentiate into hepatocytes in the chick embryo

G.S. Sohal; M.M. Ali; A.A. Ali; D.E. Bockman

Abstract. A population of ventral neural tube cells has recently been shown to migrate out of the hind brain neural tube via the vagus nerve and contribute to the developing gastrointestinal tract. Since liver is also innervated by the vagus nerve, we sought to determine if these cells also migrate into the liver. Ventral neural tube cells in the caudal hindbrain of chick embryos were tagged with a replication-deficient retroviral vector containing the LacZ gene on embryonic day 2. Embryos were processed for detection of labeled cells on embryonic day 5 and 11. Labeled cells were seen in the liver on both days and identified as hepatocytes. Previously, it was believed that all hepatocytes develop from the gut endoderm. Results of the present study show an additional source for the formation of liver cells.


Vascular Pharmacology | 2003

Ventrally emigrating neural tube cells contribute to the normal development of heart and great vessels

M.M. Ali; F.A. Farooqui; G.S. Sohal

We investigated the contributions of a recently described population of neural tube cells, which participates in the development of a variety of tissues, to the development of the heart and great vessels. These cells, termed as the ventrally emigrating neural tube (VENT) cells, originate in the ventral part of the hindbrain neural tube, emigrate at the site of attachment of the cranial nerves, and populate their respective target tissues. VENT cells of the caudal hindbrain neural tube at the level of the vagus nerve, which were previously reported to migrate into the heart, were tagged with replication-deficient retroviruses containing the LacZ gene in chick embryos, after the emigration of neural crest from this region. In older embryos, VENT cells were detected in a variety of locations including the ventricles, atria, their septa, aorticopulmonary septum, and great vessels of the heart. Immunostaining with a specific marker revealed that VENT cells differentiated into smooth muscle cells of great vessels. Differentiation of VENT cells into cardiac muscle cells was reported previously. Extirpation of the VENT cells prior to their departure from the neural tube resulted in some common cardiovascular malformations: thin-walled ventricles and atria, ventricular and atrial septal defects, persistent truncus arteriosus, and stenosis of the great vessels. These results suggest that a novel population of neural tube cells also contributes to the normal development of the heart and great vessels. Thus, the heart and great vessels develop from three sources of cells: mesoderm, neural crest, and VENT cells.


International Journal of Developmental Neuroscience | 1991

Synapse formation on trochlear motor neurons under conditions of increased and decreased cell death during development

G.S. Sohal; K. Kumaresan; S Hirano; M.M. Ali

There is a normally occurring death of about half of the trochlear motor neurons during development. Early removal of the target muscle results in death of almost all neurons whereas neuromuscular blockade prevents neuron death. The present investigation was undertaken to determine whether the number of central afferent synapses on motor neurons is altered under conditions which either accentuate cell loss or rescue neurons. The sole peripheral target of innervation of the trochlear motor neurons, the superior oblique muscle, was extirpated in duck embryos before the motor axon out‐growth begins. The neuromuscular blockade was achieved by application of paralyzing dosages of alpha bungarotoxin on to the vascularized chorioallantoic membrane. This treatment began prior to the onset of cell death and embryos were treated daily throughout the period of cell death. Brains were processed for electron microscopy and quantitative observations were made on synapses at the onset, during the period of, and at the end of cell death. It was found that there was no significant difference in the number of synapses on neurons following target removal, following neuromuscular blockade, and those developing normally. This observation indicates that the number of central afferent synapses on cell soma is not altered under conditions which either decrease or increase neuron survival. These results suggest that the synapse number per se may not be directly involved in the process of naturally occurring cell death. The results also suggest that the number of synapses on trochlear motor neurons is independent of interactions with the target.


International Journal of Developmental Neuroscience | 1991

Synapse formation on trochlear motor neurons in relation to naturally occurring cell death during development.

S Hirano; K. Kumaresan; M.M. Ali; G.S. Sohal

About half of the trochlear motor neurons die during the course of normal development. The present study was undertaken to determine whether the afferent synapses form before the onset of motor neuron death and also to determine whether the number of synapses differs between the healthy and degenerating trochlear motor neurons. Brains of duck embryos from days 10 to 20 were prepared for quantitative electron microscopical observations on synaptogenesis. Results indicate that synapses form on the trochlear motor neuron soma before cell death begins suggesting that afferent input is in a position to exert an influence on survival or death of motor neurons. There were no significant differences in the number of synapses between the healthy and dying neurons during the period of cell death. This observation suggests that the mechanism by which afferent synapses could be involved in neuron survival or death is not related to the number of synapses on the cell soma. The number of synapses on the cell process, synaptic transmission and/or molecules released at the synapses are likely candidates for the mechanism of action of afferent input.


International Journal of Developmental Neuroscience | 1995

Formation of the cranial motor neurons in the absence of the floor plate

G.S. Sohal; M.M. Ali; N.T. Tsai

The inductive signals for the differentiation of motor neurons in the spinal cord have been experimentally shown to arise from cells in the midventral region of the neural tube, often referred to as the floor plate, and from the notochord. Although the prevailing view is that a similar mechanism accounts for the differentiation of motor neurons in the brain stem, supporting experimental evidence is lacking. Here, using the formation of the trochlear nucleus in the midbrain of duck embryos as a model system, we report that the floor plate and the notochord are not necessary for the development of these motor neurons in the brain stem. Early damage to the floor plate or extirpation of the floor plate and notochord does not prevent the development of these cranial motor neurons. Thus, either the inductive signals for the formation of these cranial motor neurons arise from some other structure or the germinal epithelium of the cranial neural tube is intrinsically programmed to form specific cranial motor nuclei.

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G.S. Sohal

Georgia Regents University

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A.A. Ali

Georgia Regents University

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K. Kumaresan

Georgia Regents University

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N.T. Tsai

Georgia Regents University

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S Hirano

Georgia Regents University

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D.E. Bockman

Georgia Regents University

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F.A. Farooqui

Georgia Regents University

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