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PubMed1990

Neurogenesis and development of callosal and intracortical connections in the hamster.

The developmental time-course of callosal and ipsilateral corticocortical projections was studied in embryonic and postnatal hamsters, from the time of neurogenesis until the appearance of adult patterns. Callosal neurogenesis was determined by combining the incorporation of [3H]thymidine injected on specific embryonic days with retrograde labelling of callosal neurons in the adult animal. The development of both callosal and corticocortical projections was studied by the transport of wheat germ agglutinin conjugated to horseradish peroxidase. Despite a significant radial disperson of postmigratory neurons born on the same day, it was found that the birthdates of callosally-projecting neurons in the frontal cortex were not restricted to a short period of time, but extended between embryonic days 13 and 15. This period covers the neurogenesis of cells in cortical layers III-V. Elongation of callosal axons (and possibly also of corticocortical fibres) started a couple of days before birth in the frontal cortex, and continued through the first postnatal days. After a "waiting period" of a few days, axons from both sets of projections were seen innervating restricted target sectors of the cortex. The zones of origin of these projections were initially exuberant, but were subsequently trimmed to overlap completely with the corresponding terminal fields. It is concluded that callosal and ipsilateral corticocortical projections undergo similar sequences of ontogenetic stages, suggesting that the development of neocortical connectivity as a whole may be governed by one and the same set of rules.

Animals↗
PubMed2006

Ca2+ signaling and early embryonic patterning during the blastula and gastrula periods of zebrafish and Xenopus development.

It has been proposed that Ca(2+) signaling, in the form of pulses, waves and steady gradients, may play a crucial role in key pattern forming events during early vertebrate development [L.F. Jaffe, Organization of early development by calcium patterns, BioEssays 21 (1999) 657-667; M.J. Berridge, P. Lipp, M.D. Bootman, The versatility and universality of calcium signaling, Nat. Rev. Mol. Cell Biol. 1 (2000) 11-21; S.E. Webb, A.L. Miller, Calcium signalling during embryonic development, Nat. Rev. Mol. Cell Biol. 4 (2003) 539-551]. With reference to the embryos of zebrafish (Danio rerio) and the frog, Xenopus laevis, we review the Ca(2+) signals reported during the Blastula and Gastrula Periods. This developmental window encompasses the major pattern forming events of epiboly, involution, and convergent extension, which result in the establishment of the basic germ layers and body axes [C.B. Kimmel, W.W. Ballard, S.R. Kimmel, B. Ullmann, T.F. Schilling, Stages of embryonic development of the zebrafish, Dev. Dyn. 203 (1995) 253-310]. Data will be presented to support the suggestion that propagating waves (both long and short range) of Ca(2+) release, followed by sequestration, may play a crucial role in: (1) Coordinating cell movements during these pattern forming events and (2) Contributing to the establishment of the basic embryonic axes, as well as (3) Helping to define the morphological boundaries of specific tissue domains and embryonic structures, including future organ anlagen [E. Gilland, A.L. Miller, E. Karplus, R. Baker, S.E. Webb, Imaging of multicellular large-scale rhythmic calcium waves during zebrafish gastrulation, Proc. Natl. Acad. Sci. USA 96 (1999) 157-161; J.B. Wallingford, A.J. Ewald, R.M. Harland, S.E. Fraser, Calcium signaling during convergent extension in Xenopus, Curr. Biol. 11 (2001) 652-661]. The various potential targets of these Ca(2+) transients will also be discussed, as well as how they might integrate with other known pattern forming pathways known to modulate early developmental events (such as the Wnt/Ca(2+)pathway; [T.A. Westfall, B. Hjertos, D.C. Slusarski, Requirement for intracellular calcium modulation in zebrafish dorsal-ventral patterning, Dev. Biol. 259 (2003) 380-391]).

Animals↗
PubMed2002

Molecular patterning along the sea urchin animal-vegetal axis.

The molecular regulatory mechanisms underlying primary axis formation during sea urchin development have recently been identified. Two opposing maternally inherited systems, one animalizing and one vegetalizing, set up the animal-vegetal (A-V) axis. The vegetal system relies in part on the Wnt-beta-catenin-Tcf/Lef signaling pathway and the animal system is based on a cohort of animalizing transcription factors that includes members of the Ets and Sox classes. The two systems autonomously define three zones of cell-type specification along the A-V axis. The vegetalmost zone gives rise to the skeletogenic mesenchyme lineage; the animalmost zone gives rise to ectoderm; and the zone in which the two systems overlap generates endoderm, secondary mesenchyme, and ectoderm. Patterning along the A-V also depends on cellular interactions involving Wnt, Notch, and BMP signaling. We discuss how these systems impact the formation of the second axis, the oral-aboral axis; how they connect to later developmental events; and how they lead to cell-type-specific gene expression via cis-regulatory networks associated with transcriptional control regions. We also discuss how these systems may confer on the embryo its spectacular regulatory capacity to replace missing parts.

Animals↗
PubMed1991

Evidence for expression of the C3d receptor of Candida albicans in vitro and in vivo obtained by immunofluorescence and immunoelectron microscopy.

The complement conversion product C3d binds to a receptor on the cell surface of Candida albicans. While the function of this receptor is still uncertain, we investigated whether it is expressed during a murine infection. Rabbit antiserum raised against purified receptor was used in conjunction with immunofluorescence microscopy and immunocolloidal gold electron microscopy to examine kidney tissue and peritoneal lavages from infected mice for receptor expression by C. albicans in vivo. Specificity of the antiserum was indicated by reactivity with purified receptor (55 to 60 kDa) and with a protein of similar molecular mass from whole hyphal extracts in Western blots (immunoblots). In vitro analysis by immunofluorescence microscopy showed that the antiserum reacted with both yeast and pseudohyphal forms of the organism, but reactivity was strongest with pseudohyphae. Immunocolloidal gold electron microscopy of fungal cells from peritoneal lavages revealed intense staining of mother cells of germinative forms, germ tubes, and pseudohyphae. Staining of the mother cells was heaviest at the innermost layers of the cell wall but only scant on the cell surface. In contrast, staining was observed throughout the cell walls of germ tubes and pseudohyphae. In kidney, expression of the C3d receptor was found primarily on the cell walls of hyphae and pseudohyphae, although some staining was observed in the cytoplasm. These data support that the C3d receptor of C. albicans is expressed in vivo.

Animals↗
PubMed1992

The afferent and efferent connections of the nucleus submedius in the rat.

The afferent and efferent connections of the nucleus submedius (Sm) in the medial thalamus of the rat were examined. Injections of wheat-germ agglutinin conjugated horseradish peroxidase (WGA-HRP) into the Sm resulted in dense terminal labeling in the middle layers of the ipsilateral ventrolateral orbital cortex (VLO). Less dense labeling was also observed in the superficial and deep layers of VLO and in the medial part of the lateral orbital cortex (LO) and in the contralateral VLO. Retrogradely labeled neurons were observed primarily in the deep layers of VLO and the dorsal peduncular cortex (DP). Labeled neurons were also observed bilaterally, in the nucleus of the horizontal limb of the diagonal band, the lateral hypothalamus, the thalamic reticular nucleus (Rt), medial parabrachial nucleus (MPB), and the laterodorsal tegmental nucleus (LDT). Many labeled neurons were also observed in the trigeminal brain-stem complex. Injections of Fluoro-Gold (FG) into Sm resulted in a very similar distribution of retrogradely labeled neurons. Injections of WGA-HRP and FG in the orbital cortex confirmed the ipsilateral Sm projection to VLO and suggested that the middle and deep layers of VLO receive a specific ipsilateral projection from the dorsal Sm and that the superficial layers receive a projection primarily from the ventral Sm. Injections of WGA-HRP into the lateral hypothalamus, LDT, and MPB confirmed the retrograde labeling findings; the lateral hypothalamus was found to send a projection to the medial Sm, the LDT region to the ventromedial Sm and the MPB to the medial and dorsal Sm. These findings confirm and extend the results of previous studies in cat and rat indicating that Sm has a major and specific reciprocal connection with VLO. This finding, in conjunction with previous studies showing direct spinal and trigeminal inputs and the existence of nociceptive neurons in Sm and VLO, provides further support for a role of Sm in nociception.

Afferent Pathways↗
PubMed1982

Experimental fetal infection with bovine viral diarrhea virus. II. Morphological reactions and distribution of viral antigen.

The effect of an infection with bovine viral diarrhea virus on fetal bovine tissues as well as the tissue-localization of viral antigen are described. Four bovine fetuses, 120-165 days of gestation, were inoculated in utero with a second passage virus strain. Lymphoid tissues were studied by light and electron microscopy. The infection induced precocious development of the secondary lymphoid organs. Characteristic changes were seen in postcapillary venules, cells of the mononuclear phagocyte system and lymphoid follicles. In all four fetuses the thymus was hypoplastic. In three fetuses this implicated a morphological immaturity, but no actual pathological alterations. In the fourth fetus, the hypoplasia was caused by necrosis and depletion of lymphocytes, attended by infiltration of macrophages. Histopathological changes were also noted in the cerebellum of three fetuses, consisting of necrosis in and depletion of the external germ layer and in the skin and mucous membranes of all four fetuses. The viral antigen was present in cells of the mononuclear phagocyte system, primarily in the lymphoid tissues. The infection was further demonstrated in the affected cerebelli.

Animals↗
PubMed1990

Development of cortical vesicles in Sicyonia ingentis ova: their heterogeneity and role in elaboration of the hatching envelope.

In the marine shrimp Sicyonia ingentis, ova lack cortical vesicles at spawning. Previous ultrastructural studies suggested that two different populations of cortical vesicles (dense vesicles and the ring vesicles) appear within 30 min post-spawning. These vesicles undergo sequential exocytosis (exocytosis of the dense vesicles followed by exocytosis of the ring vesicles) that leads to the formation of a hatching envelope around the ovum (see Pillai and Clark: Tissue & Cell 20:941-52, 1988). In the present study, lectins were used as molecular probes to study the development of cortical vesicles subsequent to spawning and the role of these vesicles in formation and elaboration of the hatching envelope. Isolated envelopes were screened with 11 different lectins to determine what group(s) were specific to the envelope glycoconjugates; Concanavalin A (Con A), Griffonia simplicifolia (GS II), Lens culinaris (LCA), and wheat germ agglutinin (WGA) bound to the envelopes. FITC-lectin studies of sectioned ova (fixed at various time points after spawning) utilizing WGA and LCA showed different labelling patterns. Data obtained at the light microscopical level indicated that WGA was specific to the dense vesicles and the outer portion of the envelope, while LCA exhibited specificity for the ring vesicles and the inner portion of the envelope. At the ultrastructural level, gold-LCA labelling was seen associated with the cisternal elements (containing ring-shaped structures), ring vesicles, and the inner layer of the fully formed envelope. These data demonstrated that 1) the ring vesicles are formed by fusion of cisternal elements containing ring-shaped structures; 2) the two species of cortical vesicles are chemically heterogeneous; and 3) the components of each type of vesicle contribute to different integral parts (the outer and inner layers) of the hatching envelope.

Animals↗
PubMed1994

Essential role of Mash-2 in extraembryonic development.

The outer layer of the blastocyst, or trophectoderm, is the first cell lineage to differentiate in the mouse embryo, but little is known about the genetic control of its development. Lineage-specific transcription factors may be important in lineage specification, and the product of the Mash-2 gene fulfils the criteria for such a factor. Mash-2 is a mammalian member of the achaete-scute family which encodes basic-helix-loop-helix transcription factors and is strongly expressed in the extraembryonic trophoblast lineage. Mash-2 transcripts are found in the female germ line and in the embryo throughout preimplantation development, but are highly expressed later only in the ectoplacental cone, the chorion and their derivatives in the placenta. Mash-2 transcripts are not found in primary and secondary giant cells, yolk sac or allantois at any post-implantation stage, and are present only transiently and at low levels in the embryo during gastrulation. To analyse the role of Mash-2 in development, we have used gene targeting to generate mice having no Mash-2 function. We report here that Mash-2-/- embryos die from placental failure at 10 days postcoitum. In mutant placentas, spongiotrophoblast cells and their precursors are absent and chorionic ectoderm is reduced. We have rescued this placental mutant phenotype by constructing chimaeras with tetraploid wild-type embryos which contribute almost exclusively to extraembryonic tissues. Mash-2-/- embryos developed normally and adult Mash-2-/- mice were viable, demonstrating that Mash-2 has no major role in the embryo itself. Mash-2 is the first transcription factor shown to play a critical part in the development of the mammalian trophoblast lineage.

Animals↗
PubMed1987

Development of brainstem and cerebellar projections to the diencephalon with notes on thalamocortical projections: studies in the North American opossum.

The North American opossum is born in a very immature state, 12 days after conception, and climbs into an external pouch where it remains attached to a nipple for an extended period of time. We have taken advantage of the opossum's embryology to study the development of brainstem and cerebellar projections to the diencephalon as well as the timing of diencephalic projections to somatosensory motor areas of neocortex. The techniques employed included immunocytochemistry for serotonin, the retrograde and orthograde transport of wheat germ agglutinin conjugated to horseradish peroxidase, and the selective impregnation of degenerating axons. Our results suggest that serotoninergic axons, presumably from the dorsal raphe and superior central nuclei, are present in the diencephalon at birth. Axons from the bulbar reticular formation, the vestibular complex, the trigeminal sensory nuclei, and the dorsal column nuclei reach at least mesencephalic (and probably diencephalic) levels by postnatal day (PND) 3, whereas those from the cerebellar nuclei may not grow into comparable levels until PND 5. The dorsal column and cerebellar nuclei innervate the ventral nuclei of the thalamus by estimated postnatal day (EPND) 17 and all of the diencephalic nuclei supplied in the adult animal by EPND 26. Diencephalic axons enter ventrolateral (face) areas of presumptive somatosensory motor cortex by PND 12, but do not reach dorsomedial (limb) regions until EPND 21. At both ages, diencephalic axons are limited to the cortical subplate and marginal zone; they do not innervate an identifiable internal granular layer until considerably later. Our results suggest that axons from the brainstem and cerebellum grow into the diencephalon early in development, but that they do not influence the cerebral cortex until relatively late. When the results of the present study are compared with those reported previously on the development of ascending spinal (Martin et al., '83) and corticofugal (Martin et al., '80; Cabana and Martin, '85b,c) projections, it appears that specific components of major somatosensory and motor circuits develop according to different timetables.

Animals↗
PubMed2005

Late type of daughter cell wall synthesis in one of the Chlorellaceae, Parachlorella kessleri (Chlorophyta, Trebouxiophyceae).

Autosporulation is a common mode of propagation for unicellular algae. Autospore-forming species of Chlorellaceae, Chlorella vulgaris Beijerinck, C. sorokiniana Shihira et Krauss, C. lobophora Andreyeva, and Parachlorella kessleri (Fott et Nováková) Krienitz et al. have glucosamine as the main constituent of their rigid cell wall. Recent phylogenetic analyses have showed that the Chlorellaceae divided into two sister groups: the Chlorella-clade and the Parachlorella-clade. We compared the cell wall structure and synthesis of the daughter cell wall in the four species by electron microscopy using rapid freezing and freeze substitution methods. The cell wall of C. vulgaris, C. sorokiniana, and C. lobophora consisted of an electron-dense thin layer with an average thickness of 17-20, 22, and 19 nm, respectively. In these three species, daughter cell wall synthesis occurred on the outer surface of the plasma membrane in the early cell-growth phase. The cell wall of P. kessleri, however, was electron-transparent and 54-59 nm in thickness. Ruthenium red staining of P. kessleri indicated that ruthenium-red-specific polysaccharides accumulated over the outer surface of the plasma membrane. Immunoelectron microscopic observation with an anti-beta-1, 3-glucan antibody and staining with wheat germ agglutinin (WGA) indicated that the cell wall contained beta-1, 3-glucan and WGA specific N-acetyl-beta-D-glucosamine. In P. kessleri, daughter cell wall synthesis began after successive protoplast division. The daughter cell wall synthesis during autosporulation in the four species of Chlorellaceae can be classified into two types-the early and the late types.

Cell Cycle↗
PubMed2006

Retinoids and nonvertebrate chordate development.

Retinoic acid (RA) is required for the differentiation and morphogenesis of chordate-specific features, such as the antero-posterior regionalization of the dorsal hollow nerve cord and neural crest cells. RA receptors (RARs) have been reported exclusively in chordates, suggesting that the acquisition of the RAR gene was important for chordate evolution. A scenario is presented here for the establishment of an RAR-mediated developmental regulatory system during the course of chordate evolution. In the common chordate ancestor, RAR came to control the spatial expression pattern of Hox genes in the ectoderm and endoderm along the antero-posterior axis. In these germ layers, RA was required for the differentiation of epidermal sensory neurons and the morphogenesis of pharyngeal gill slits, respectively. As the diffuse epidermal nerve net in the chordate ancestor became centralized to form the dorsal nerve cord, the epidermal Hox expression pattern was carried into the central nervous system. Because the Hox code here came to specify neuronal identity along the antero-posterior axis, RA became inextricably linked to the antero-posterior patterning of the chordate central nervous system.

Animals↗
PubMed2006

Site-specific recombination in human embryonic stem cells induced by cell-permeant Cre recombinase.

The biomedical application of human embryonic stem (hES) cells will increasingly depend on the availability of technologies for highly controlled genetic modification. In mouse genetics, conditional mutagenesis using site-specific recombinases has become an invaluable tool for gain- and loss-of-function studies. Here we report highly efficient Cre-mediated recombination of a chromosomally integrated loxP-modified allele in hES cells and hES cell-derived neural precursors by protein transduction. Recombinant modified Cre recombinase protein translocates into the cytoplasm and nucleus of hES cells and subsequently induces recombination in virtually 100% of the cells. Cre-transduced hES cells maintain the expression of pluripotency markers as well as the capability of differentiating into derivatives of all three germ layers in vitro and in vivo. We expect this technology to provide an important technical basis for analyzing complex genetic networks underlying human development as well as generating highly purified, transplantable hES cell-derived cells for regenerative medicine.

Cells, Cultured↗
PubMed1991

Cyclic localization change of Golgi apparatus in Sertoli cells induced by mature spermatids in rats.

Previously we reported that the intracellular localization of the Golgi apparatus of rat Sertoli cells changes during the seminiferous epithelial cycle, and that the cyclic changes seem to be correlated to specific generations of germ cells. To ascertain which generations of germ cells are responsible for the cyclic changes, we determined the relative volume of the Golgi apparatus within the basal, mid, and apical cytoplasm of Sertoli cells in testes with and without mature spermatids. In normal adult rats, the Golgi apparatus was usually localized exclusively in the basal cytoplasm, whereas at stages VII-IX it increased remarkably in mid and apical cytoplasm, with a concomitant decrease in the basal cytoplasm. In young adult testes without spermatids at steps 15-19 of spermiogenesis (2nd layer spermatids), the Golgi apparatus was localized in the basal cytoplasm throughout the seminiferous epithelial cycle. Orchiopexy maintained for 35 days following 60 days of cryptorchidism allowed germ cells to regenerate to spermatids at steps 1-14 of sperminogenesis (1st layer spermatids), but failed to change the intracellular localization of the Golgi apparatus in Sertoli cells. At 50 days after orchiopexy, when all generations of germ cells appeared in the tubules, the cyclic changes in localization of the Golgi apparatus were restored similar to those in normal adult testes. These findings indicate that the cyclic change in localization of the Golgi apparatus in Sertoli cells is evoked by the presence of 2nd layer spermatids.

Animals↗
PubMed1997

Localization of the steroidogenic acute regulatory protein in human tissues.

The rate-limiting step in steroid hormone production in the adrenal cortex and gonads, the translocation of cholesterol from the outer to the inner mitochondrial membranes, is mediated by the steroidogenic acute regulatory protein (StAR). Heretofore, the localization of StAR in human adult and fetal tissues has not been defined. To this end, expression of StAR was detected in formalin-fixed, paraffin-embedded specimens using a polyclonal antiserum raised against recombinant human StAR. Primordial follicles of adult ovaries did not contain StAR, whereas antral follicles stained intensely in the thecal layer, with occasional staining of granulosa cells. Corpora lutea were intensely stained, but with a patchy distribution. Corpora albicantia did not stain. A luteoma of pregnancy stained with patches of moderate intensity. Ovaries with hyperthecosis contained areas of intense thecal staining. An ovarian Leydig cell tumor stained intensely, whereas granulosa cell tumors were negative. Ovarian adenocarcinomas, borderline tumors, teratomas, cystadenomas, and a Brenner tumor displayed no specific StAR immunostaining. Testicular Leydig cells stained moderately to intensely, as did a testicular Leydig cell tumor. Sertoli cells stained weakly in some specimens. Seminomas and testicular germ cell tumors were negative. There was minimal to moderate staining in the adrenal glomerulosa and faciculata and minimal staining in the reticularis, while the medulla was negative. Adrenal cortical adenomas, hyperplasias, and carcinomas all contained areas of StAR staining. The renal distal tubules stained with moderate to marked intensity. Renal carcinomas had occasional modest staining. No immunostaining was found in the placenta. Fetal ovaries contained sporadic stromal cells displaying intense StAR staining, particularly in the hilar region. Oocytes from a 32-week fetal ovary showed moderate to intense staining. Fetal testes displayed intense Leydig cell staining. The neocortex of the fetal adrenal glands displayed only minimal StAR staining, whereas moderate to intense staining was found in the fetal zone. The fetal kidneys had moderate StAR staining of the distal convoluted tubules. We conclude that StAR is localized to normal and neoplastic cells in the gonads and adrenal cortex, which produce large amounts of pregnenolone. StAR protein was not detected in the placenta, documenting that placental progestin synthesis occurs through StAR-independent mechanisms. The presence of StAR in cells that do not express cholesterol side-chain cleavage enzyme cytochrome P450, including renal distal tubules, Sertoli cells, and fetal oocytes, suggests that StAR has roles in metabolic processes in addition to stimulating pregnenolone synthesis.

Adrenal Gland Diseases↗
PubMed2006

Generation and characterization of rabbit embryonic stem cells.

We described the derivation of four stable pluripotent rabbit embryonic stem cell (ESC) lines, one (RF) from blastocysts fertilized in vivo and cultured in vitro and three (RP01, RP02, and RP03) from parthenogenetic blastocysts. These ESC lines have been cultivated for extended periods (RF >1 year, RP01 >8 months, RP02 >8 months, and RP03 >6 months) in vitro while maintaining expression of pluripotent ESC markers and a normal XY or XX karyotype. The ESCs from all lines expressed alkaline phosphatase, transcription factor Oct-4, stage-specific embryonic antigens (SSEA-1, SSEA-3, and SSEA-4), and the tumor-related antigens (TRA-1-60 and TRA-1-81). Similar to human and mouse ESCs, rabbit ESCs expressed pluripotency (Oct-4, Nanog, SOX2, and UTF-1) and signaling pathway genes (fibroblast growth factor, WNT, and transforming growth factor pathway). Morphologically, rabbit ESCs resembled primate ESCs, whereas their proliferation characteristics were more like those seen in mouse ESCs. Rabbit ESCs were induced to differentiate into many cell types in vitro and formed teratomas with derivatives of the three major germ layers in vivo when injected into severe combined immunodeficient mice. Our results showed that pluripotent, stable ESC lines could be derived from fertilized and parthenote-derived rabbit embryos.

Animals↗
PubMedDate not supplied

Immunomagnetic isolation and long-term culture of mouse type A spermatogonia.

In the mammalian testis, type A spermatogonia proliferate and differentiate into sperm under the tight control of both endocrine and paracrine factors. In order to study the complex process of spermatogenesis at the molecular level, an in vitro system must be devised in which type A spermatogonia can be cultured for a prolonged period of time. Therefore, cocultures including type A spermatogonia and Sertoli cells, which act as nurse cells to the developing germ cells, are desirable. We have developed a method for the specific isolation of type A spermatogonia using magnetic beads and antibodies that recognize the c-kit receptor or the homophilic adhesion molecule, Ep-CAM. Purified spermatogonia could survive for a period of 25 days when cocultivated on Sertoli cell monolayers. Moreover, we recently established Sertoli cell lines that produce growth factors that are essential for the maintenance of spermatogonia in a proliferative state. Some of these Sertoli cell lines are able to reorganize into tubular structures when cultivated on a layer of Matrigel as extracellular matrix. We show here that type A spermatogonia associate specifically with the Sertoli cell tubules, and are able to replicate their DNA in this environment. Thus, these in vitro culture systems could be used for the long-term culture of primary, nonimmortalized type A spermatogonia.

Animals↗
PubMed1992

Innervation from the claustrum of the frontal association and motor areas: axonal transport studies in the cat.

The anatomical organization of the projections from the claustrum to the motor and prefrontal cortical areas of the cat's brain was investigated. Both retrograde (single horseradish peroxidase or double fluorochrome deposits in the cortex) and anterograde (peroxidase-labeled wheat germ agglutinin deposits in the claustrum) tracing techniques were used. Within the claustrum, the neurons projecting to each sector of the frontal cortex were found to be distributed according to specific patterns of segregation and overlap. Spatial segregation was particularly marked between the cell populations projecting to the various sectors of area 4. The cells projecting to the subareas of area 6 and prefrontal cortex displayed a less marked but definite segregation. The neuronal populations projecting to some sectors of areas 4, 5, and the primary somatosensory cortex known to contain homotopical representations of the body map were found intermingled in the same small claustral portions. The few double-labeled neurons found after closely adjacent fluorochrome injections indicates that, in spite of their profuse intracortical branching, claustral axons spread little within the boundaries of a single architectonic area. Anterograde transport experiments showed that claustral fibers end primarily in layers IIIb/IV, VI, and I, whereas layer V is spared. This pattern is homogeneous throughout the frontal cortex. The possible role of the claustrum as a subcortical site for organized interactions amongst wide arrays of functionally related zones of the cerebral cortex is thereby suggested.

Animals↗
PubMed1995

Nuclear translocation of a maternal CCAAT factor at the start of gastrulation activates Xenopus GATA-2 transcription.

The transcription factor GATA-2 is present in blood cell precursors and plays a pivotal role in the control of erythroid differentiation. In Xenopus embryos, low levels of GATA-2 mRNA are maternally derived, while the onset of zygotic GATA-2 expression coincides with commitment to haematopoietic lineages. However, its initial transcriptional activation is not restricted to the presumptive blood islands, but occurs throughout ventral and lateral regions, in all three germ layers. In order to determine how this expression pattern is controlled, we have isolated and characterized the Xenopus GATA-2 gene. We show that 1.65 kb of 5' flanking sequences are sufficient to direct both correct transcriptional initiation in oocytes and appropriate temporal and spatial gene expression in early embryos. The transgene is activated during gastrulation and by neurula stages in predominantly expressed in the ventral hemisphere. We demonstrate that a CCAAT element is necessary for gene activity in both systems and that extracts prepared from oocytes and embryos contain a factor which specifically recognizes this element. We also show that cytoplasmic localization inhibits the function of this CCAAT factor until the beginning of gastrulation, when the zygotic GATA-2 gene is activated. These observations extend our understanding of the mechanisms by which maternal factors control the temporal activation of transcription in early vertebrate embryos.

Alternative Splicing↗