Biomedical subjects

R T Ferri

Publications and source records attributed to R T Ferri.

6 recordsLinked to original sources

PubMed1997

Signaling pathways that regulate specification of neurons in developing cerebral cortex.

The expression of the limbic system-associated membrane protein (LAMP), a marker of specific functional regions of the cerebral cortex, has been used to determine the environmental signals that regulate cortical regionalization. Transplant and cell culture studies have shown previously that the fate of precursor cells, based on LAMP expression, is amenable to regulation by exposure to novel environmental stimuli. This has been demonstrated in vitro to be dependent upon exposure to transforming factor-alpha and collagen type IV. Results following exposure to the inductive signals for a specific duration indicate a cell cycle dependence on the decision to become a limbic or nonlimbic cortical neuron. It appears, therefore, that areal and laminar fates are both influenced by mechanisms that specify commitment early in cortical development.

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PubMed1996

Environmental signals influence expression of a cortical areal phenotype in vitro independent of effects on progenitor cell proliferation.

We have shown previously that, in vitro, cortical progenitor cells isolated from specific locations of the cerebral wall can adopt area-specific fates, assayed by expression of the limbic system-associated membrane protein (LAMP; R. T. Ferri and P. Levitt, Cereb. Cortex 3, 187-198, 1993). Progenitors destined to produce LAMP neurons, however, will differentiate to express the limbic molecular phenotype if grown with TGFalpha and collagen type IV (R. T. Ferri and P. Levitt, Development 121, 1151-1160, 1995), while other signals fail to induce LAMP. The present study used BrdU labeling of progenitor cells to examine whether modulation of LAMP expression was paralleled by predictable changes in cell proliferation. The general pattern of proliferation is similar under a variety of culture conditions: approximately half the cells are mitotic, and activity is always highest during the first 24 hr in vitro, with little cell division occurring by the third day. Moreover, the rate of proliferation, in the presence or absence of TGFalpha, is the same on all substrates tested, with the exception of laminin. The TGFalpha/collagen type IV signaling system that induces LAMP expression by the precursors has no modulating effect on their proliferative kinetics. Nonetheless, only progenitors that are mitotically active respond to LAMP-inducing signals; only 60% of the neurons, representing those that have divided at least once in culture, can be induced to express LAMP. The data suggest that while specific signals affect choice of area phenotype during the cell cycle, they do so in the absence of major changes in proliferative behavior.

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PubMed1995

Regulation of regional differences in the differentiation of cerebral cortical neurons by EGF family-matrix interactions.

Both lineage-based and epigenetic regulation have been postulated as mechanisms to control the formation of discrete areas in the cerebral cortex, but specific genes or signaling pathways that may be involved have yet to be defined. In this paper, we examine whether progenitors, isolated from the cerebral wall prior to neurogenesis, can respond to exogenous cues by adopting a region-specific phenotype. The expression of the limbic system-associated membrane protein (LAMP), a neuron-specific marker of limbic cortical areas, was monitored in cultured neurons arising from precursors harvested from presumptive perirhinal (limbic) and sensorimotor (nonlimbic) zones at embryonic day 12 in the rat. Neuronal phenotype in all cultures was identified by expression of microtubule-associated protein-2 (MAP2). On a substrate of poly-lysine, over 80% of the precursors from the limbic area that differentiate into neurons express a LAMP+ phenotype. Approximately 20% of the neurons generated from precursors of the sensorimotor region become LAMP+. However, modification of the microenvironment had a significant effect on the differentiation of the sensorimotor precursors. When the nonlimbic precursors are grown on Matrigel, there is a 2-fold increase in the number of MAP2+/LAMP+ double-labeled neurons. Dissection of the Matrigel components reveals that in combination with growth factor-deficient Matrigel or collagen type IV, epidermal growth factor and transforming growth factor-alpha increase LAMP expression in the sensorimotor population. Delaying the addition of growth factor until after most cell division had ceased failed to increase the number of LAMP+ neurons. Another growth factor in Matrigel, platelet-derived growth factor, does not produce the same effect. Our results indicate that local signals can regulate the differentiation of cortical progenitors, providing a potential mechanism for establishing an early commitment to specific regional phenotypes in the developing cerebral wall that relate to future functional domains in the cortex.

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PubMed1993

Progressive acquisition of cortical phenotypes as a mechanism for specifying the developing cerebral cortex.

The formation of the cerebral cortex requires the assembly of a complex array of neurons that exhibit specific patterns of laminar distribution, connectivity, and macromolecular expression. The problem of how various areas become specified relies to a large extent on the ability to assay certain characteristics of a particular cortical area during development. Certain phenotypic features appear to be acquired early in histogenesis, whereas others have a relatively late onset of expression. This pattern of progressive acquisition of traits suggests that each feature may be regulated by a different set of genomic-environmental interactions. This would lead to an early framing of cortical regions through the commitment of cells to area-specific phenotypes, but allow modifications of later developing traits through changes in certain environmental features.

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PubMedDate not supplied

Cerebral cortical progenitors are fated to produce region-specific neuronal populations.

The mammalian cerebral cortex is characterized by its organization into anatomically and functionally discrete regions. During cortical development, a homogeneous-appearing population of cells along the ventricular surface generates the neurons and glia that ultimately form these cytoarchitectonic areas. The limbic system-associated membrane protein (LAMP) is a neuronal, cell surface glycoprotein that identifies neurons restricted to limbic cerebral cortical areas (Levitt, 1984). LAMP is expressed early in development (Horton and Levitt, 1988), and transplantation studies in the rat suggest that cells in the cerebral wall are committed to a limbic or nonlimbic molecular phenotype by embryonic day 14 (E14) (Barbe and Levitt, 1991). However, at E12, cells destined for the cerebral cortex are still multipotential and presumably depend on local, extrinsic signals to adopt a limbic phenotype. We have developed an in vitro assay system for examining the fate of these multipotential progenitors and identifying potential environmental regulators of neuronal differentiation. Regions of the lateral (limbic) and dorsal (nonlimbic) cerebral wall at E12 are dissected, dissociated, and grown in low-density cultures in defined medium. The cells are examined by immunocytochemistry for expression of MAP2, a neuronal cytoskeletal protein, and LAMP to define neuronal differentiation and the expression of a limbic molecular phenotype, respectively. We find that after 4 d in culture, up to 75% of the progenitor cells from presumptive limbic cortex express LAMP upon differentiation. In contrast, only 20-30% of the differentiated cells from presumptive sensorimotor cortex express LAMP. Thus, most cortical progenitors are fated to a limbic or nonlimbic phenotype early in development, and the decision by neuronal stem cells to differentiate into neurons exhibiting this molecular phenotype occurs prior to the completion of neurogenesis, in the absence of subcortical environmental cues.

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PubMedDate not supplied

Complementary distribution of collagen type IV and the epidermal growth factor receptor in the rat embryonic telencephalon.

We previously identified an interaction between collagen type IV and the EGF receptor that regulates the differentiation of a limbic cortical phenotype in vitro (Ferri and Levitt, 1995). In the present study, we map the expression of the EGF receptor and collagen type IV in the embryonic telencephalon of the rat. At embryonic day (E) II, the earliest age examined, both proteins are coexpressed throughout the ventricular zone in the cerebral wall; this zone remains immunoreactive throughout corticogenesis (E14-E19). The cells comprising the subventricular zone are the most intensely immunoreactive for the EGF receptor, although little collage type IV is detected in this region. In contrast, postmitotic neurons that leave the proliferative zones are negative for the receptor. Moreover, during the peak of neuronal migration, the intermediate zone lacks collagen type IV immunoreactivity. Neurons that settle in the cortical plate once again exhibit EGF receptor immunoreactivity; this same zone is devoid of collagen type IV. By E19, coexpression of both proteins is evident only in the rostral extension of the subventricular zone, the pathway of migrating cells leading to the olfactory bulb. The temporal and spatial overlap of the EGF receptor and collage type IV in the cortical progenitor pool in vivo indicates that these molecules may participate in the initial decisions of neuronal differentiation. Their modified distribution during cortical maturation suggests a changing role for both proteins.

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