Biomedical subjects

Mark D Kirk

Publications and source records attributed to Mark D Kirk.

10 recordsLinked to original sources

PubMed2006

Selective migration of neuralized embryonic stem cells to stem cell factor and media conditioned by glioma cell lines.

BACKGROUND: Pluripotent mouse embryonic stem (ES) cells can be induced in vitro to become neural progenitors. Upon transplantation, neural progenitors migrate toward areas of damage and inflammation in the CNS. We tested whether undifferentiated and neuralized mouse ES cells migrate toward media conditioned by glioma cell lines (C6, U87 & N1321) or Stem Cell Factor (SCF). RESULTS: Cell migration assays revealed selective migration by neuralized ES cells to conditioned media as well as to synthetic SCF. Migration of undifferentiated ES cells was extensive, but not significantly different from that of controls (Unconditioned Medium). RT-PCR analysis revealed that all the three tumor cell lines tested synthesized SCF and that both undifferentiated and neuralized ES cells expressed c-kit, the receptor for SCF. CONCLUSION: Our results demonstrate that undifferentiated ES cells are highly mobile and that neural progenitors derived from ES cells are selectively attracted toward factors produced by gliomas. Given that the glioma cell lines synthesize SCF, SCF may be one of several factors that contribute to the selective migration observed.

Journal Article↗

PubMed2006

Identification and characterization of homologues of vertebrate beta-thymosin in the marine mollusk Aplysia californica.

The beta-thymosins have been known as actin-sequestering proteins, but now are recognized as molecules with multiple and diverse intracellular and extracellular functions. Two closely related proteins, beta-thymosin(His) and beta-thymosin(Gln), have been de novo sequenced by top-down mass spectrometry in the common neurobiology model, Aplysia californica. As determined by nanoelectrospray quadrupole-enhanced Fourier-Transform mass spectrometry with collisionally activated and electron-capture dissociations, both of these Aplysia beta-thymosins are acetylated and differ by a single residue in the central actin-binding domain. Profiling of individual cells and tissue by matrix-assisted laser desorption/ionization mass spectrometry reveals that these proteins are widely expressed in the Aplysia central nervous system, including in individual identified neurons, neuronal clusters, nerves and connective tissues. Newly identified beta-thymosin(His) and beta-thymosin(Gln) are also detected by mass spectrometry in hemolymph, and in releasates collected from whole ganglia. When applied exogenously, beta-thymosin proteins, purified from nerve cell extract, support the anchoring of neurons, and increase neurite sprouting and total neurite outgrowth in culture. These positive effects on neurite regeneration in cell culture suggest that the beta-thymosin proteins have an extracellular function in the central nervous system of Aplysia californica.

Amino Acid Sequence↗

PubMed2006

Ocular phenotype in a mouse gene knockout model for infantile neuronal ceroid lipofuscinosis.

Mutations in the human protein palmitoyl thioesterase-1 (PPT-1) gene result in an autosomal recessive neurodegenerative disorder designated neuronal ceroid lipofuscinosis (NCL), type CLN1, or infantile NCL. Among the symptoms of the CLN1 disease are accumulation of autofluorescent lysosomal storage bodies in neurons and other cell types, seizures, motor and cognitive decline, blindness, and premature death. Development of an effective therapy for this disorder will be greatly assisted by the availability of suitable animal models. A mouse PPT-1 gene knockout model has recently been generated. Studies were performed to determine whether the mouse model exhibits ocular features of the human CLN1 disorder. A progressive accumulation of autofluorescent storage material in all layers of the retina was observed in the PPT-1 knockout mice. Accompanying the storage body accumulation was a modest loss of cells with nuclei in the outer and inner nuclear layers. As indicated by electroretinogram (ERG) responses, retinal function was only mildly impaired at 4 months of age but was severely impaired by 8 months, despite only modest changes in retinal morphology. The pupillary light reflex (PLR), on the other hand, was exaggerated in the knockout mice. The apparent anomaly between the ERG and the PLR findings suggests that disease-related PLR changes may be due to changes in extraocular signal processing. The pronounced ocular phenotype in the PPT-1 knockout mice makes these animals a good model for testing therapeutic interventions for treatment of the human CLN1 disorder.

Adaptor Proteins, Signal Transducing↗

PubMed2006

Neural crest as the source of adult stem cells.

Recent studies suggest that adult stem cells can cross germ layer boundaries. For example, bone marrow-derived stem cells appear to differentiate into neurons and glial cells, as well as other types of cells. How can stem cells from bone marrow, pancreas, skin, or fat become neurons and glia; in other words, what molecular and cellular events direct mesodermal cells to a neural fate? Transdifferentiation, dediffereniation, and fusion of donor adult stem cells with fully differentiated host cells have been proposed to explain the plasticity of adult stem cells. Here we review the origin of select adult stem cell populations and propose a unifying hypothesis to explain adult stem cell plasticity. In addition, we outline specific experiments to test our hypothesis. We propose that peripheral, tissue-derived, or adult stem cells are all progeny of the neural crest.

Adult↗

PubMed2005

Embryonic stem cell-derived neural progenitors incorporate into degenerating retina and enhance survival of host photoreceptors.

Embryonic stem (ES) cells differentiate into all cell types of the body during development, including those of the central nervous system (CNS). After transplantation, stem cells have the potential to replace host cells lost due to injury or disease or to supply host tissues with therapeutic factors and thus provide a functional benefit. In the current study, we assessed whether mouse neuralized ES cells can incorporate into retinal tissue and prevent retinal degeneration in mnd mice. These mice have an inherited lysosomal storage disease characterized by retinal and CNS degeneration. Sixteen weeks after intravitreal transplantation into adult mice, donor cells had incorporated into most layers of the retina, where they resembled retinal neurons in terms of morphology, location in the retina, and expression of cell type-specific marker proteins. Presence of these donor cells was correlated with a reduction in the sizes and numbers of lysosomal storage bodies in host retinal cells. The presence of transplanted donor cells was also accompanied by enhanced survival of host retinal neurons, particularly photoreceptors. These results demonstrate that neuralized ES cells protect host neurons from degeneration and appear to replace at least some types of lost neurons.

Animals↗

PubMed2005

Stem cells for retinal degenerative disorders.

Many systemic and eye-specific genetic disorders are accompanied by retinal degenerations that lead to blindness. In some of these diseases retinal degeneration occurs early in life and is quite rapid, whereas in other disorders, retinal degeneration starts later and progresses very slowly. At present, no therapies are available to patients for preventing or reversing the retinal degeneration that occurs in these diseases. Implantation of neural progenitor cells into the eye may be a means by which to retard or even reverse degeneration of the retina. To evaluate the potential of neural precursor cell implantation for treating retinal degenerative disorders, neuralized mouse embryonic stem cells from green fluorescent protein (GFP) transgenic mice were administered intravitreally to normal mice, mice with early retinal degeneration, and mice with slowly progressing retinal degeneration. In normal mice, the donor cells remained in the vitreous cavity and did not associate with the host retina. In mice with early retinal degeneration, implantation of the neural precursors was performed after the degeneration was almost complete. In these animals, the donor cells primarily associated closely with the inner surface of the retina, although a small fraction of donor cells did integrate into the host retina. Donor cells implanted in mice with slowly progressing retinal degeneration also associated with the inner retinal surface, but many more of the cells integrated into the retina. These findings indicate the importance of host tissue-donor cell interactions in determining the fate of implanted neural precursor cells. These interactions will be a major consideration when devising strategies for using cell implantation therapies for neurodegenerative disorders.

Animals↗

PubMed2004

Neural differentiation of mouse embryonic stem cells in vitro and after transplantation into eyes of mutant mice with rapid retinal degeneration.

Embryonic stem (ES) cells can differentiate into many specialized cell types, including those of the nervous system. We evaluated the differentiation of enhanced green fluorescent protein (EGFP)-expressing B5 mouse ES cells in vitro and in vivo after transplantation into the eyes of mice with hereditary retinal degeneration. After neural induction with retinoic acid, the majority of cells in embryoid bodies expressed markers for neural progenitors as well as for immature and mature neurons and glial cells. When induced ES cells were plated in vitro, further differentiation was observed and the majority of cells expressed beta-III Tubulin, a marker for immature neurons. In addition, many plated cells expressed markers for mature neurons or glial cells. Four days after intravitreal transplantation into the eyes of rd1 mice (a model of rapid retinal degeneration), donor cells appeared attached to the vitreal surface of the retina. After 6 weeks in vivo, most transplanted cells remained adherent to the inner retinal surface, and some donor cells had integrated into the retina. Transplanted cells exhibited some properties typical of neurons, including extensive process outgrowth with numerous varicosities and expression of neuronal and synaptic markers. Therefore, after induction B5 ES cells can acquire the morphologies of neural cells and display markers for neuronal and glial cells in vitro and in vivo. Furthermore, when placed in the proper microenvironment ES-derived neural precursors can associate closely with or migrate into nervous tissue where differentiation appears to be determined by cues provided by the local environment, in this case the degenerating neural retina.

Animals↗

PubMed2003

Endogenous neurotrophic factors enhance neurite growth by bag cell neurons of Aplysia.

Mechanisms that regulate neurite outgrowth are phylogenetically conserved, including the signaling molecules involved. Here, we describe neurotrophic effects on isolated bag cell neurons (BCNs) of substrate-bound growth factors endogenous to the sea slug Aplysia californica. Sheath cells dissociated from the pleural-visceral connectives of the Aplysia CNS and arterial cells dissociated from the anterior aorta enhance neurite outgrowth when compared to controls, i.e., BCNs grown in defined medium alone. In addition, the substrate remaining after sheath cells or arterial cells are killed significantly enhances growth, relative to all other conditions tested. For instance, primary neurites are more numerous and greater in length for BCNs cultured on substrate produced by arterial cells. These results suggest that sheath and arterial cells produce growth-promoting factors, some of which are found in the substrates produced by these cell types. Using matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), we found that Aplysia collagen-like peptides are produced by dissociated arterial cells, and therefore likely contribute to the observed growth effects. Collagen-like peptides and other factors produced by sheath and arterial cells likely influence neurite growth in the Aplysia CNS during development, learning and memory, and regeneration after injury.

Animals↗

PubMed2002

Ingestion motor programs of Aplysia are modulated by short-term synaptic enhancement in cerebral-buccal interneuron pathways.

In the sea slug Aplysia, buccal synapses of cerebral-buccal interneurons (CBIs) CBI-2 and CBI-12 exhibit short-term synaptic enhancement (STE), including frequency-dependent facilitation and augmentation/post-tetanic potentiation (AUG/PTP). The STE that results from driving CBI-2 or CBI-12 is associated with significantly decreased latency to burst onset in buccal premotor neurons and motor neurons, increased cycle frequency of ingestion buccal motor programs (iBMPs) and increased intraburst firing frequency of buccal neurons during iBMPs. Tests of paired-pulse facilitation during AUG/PTP suggest that the locus for this plasticity is presynaptic. The AUG/PTP is not elicited by heterosynaptic pathways, indicating that its origin is homosynaptic. At low CBI-2 and CBI-12 firing frequencies, STE is likely to contribute to iBMP initiation, while at higher firing frequencies, STE is correlated with increased cycle frequency of iBMPs. Thus, STE is an important component of the mechanisms whereby cerebral neurons regulate cyclic feeding programs and likely contributes to observed variations in behavioral responses, including feeding arousal.

Animals↗

PubMed2002

Arterial cells and CNS sheath cells from Aplysia californica produce factors that enhance neurite outgrowth in co-cultured neurons.

Substrate-bound and soluble factors regulate neurite outgrowth and synapse formation during development, regeneration, and learning and memory. We report that sheath cells from CNS connectives and arterial cells from the anterior aorta of the sea slug, Aplysia californica, enhance neurite outgrowth from co-cultured Aplysia neurons. Sheath and arterial cell cultures contain several cell types, including fibrocytes, myocytes, and amoebocytes. When compared to controls (neurons with defined growth medium alone), the percentage of neurons with growth and the average neurite lengths are significantly enhanced by sheath and arterial cells at 48 h after plating of the neurons; these parameters are comparable to those of neurons cultured in medium containing hemolymph. Our results indicate that sheath cells produce substrate-bound factor(s) and arterial cells produce diffusible factor(s) that promote growth. These growth factors likely promote neuron survival and neurite outgrowth during neural plasticity exhibited in the adult CNS.

Animals↗