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PubMed1977

Induction of the rat prostate gland by androgens in organ culture.

The induction of the prostate gland by testosterone or dihydrotestosterone was studied in urogenital sinuses from Wistar rat embryos explanted in organ culture. In normal development, prostatic rudiments appeared in the urogenital sinuses of 18-19 day male foetuses as epithelial buds projecting into the mesenchyme. Male urogenital sinuses from 17-5 and 18-5 day foetuses formed buds in control medium, and addition of testosterone or dihydrotestosterone increased their number and size. In contrast, sinuses from 15-5 and 16-5 day male foetuses did not form buds in the absence of androgens, while exposure to the hormones induced them de novo. A concentration of 0-0015 microgram testosterone/ml was sufficient to elicit prostatic buds. The same effect was seen after continuous treatment with testosterone or brief exposure to the hormone followed by cultivation in control medium. The development of the buds followed the same time sequence as in the organ in situ. Testosterone and dihydrotestosterone elicited prostatic buds in female sinuses from 15-5 to 18-5 day foetuses, but their response to androgens decreased with advancing foetal age. Male and female sinuses from 15-5 day foetuses did not respond to testosterone but formed buds after exposure to dihydrotestosterone. This difference was considered to be due to a low content or absence of 5alpha-reductase at this stage. Testes from 15-5 to 18-5 day foetuses grown in close contact with urogenital sinuses or explants of mature prostate glands induced prostatic buds or augmented the height of the prostatic epithelium. It was concluded that androgens are necessary for the initiation of the rat prostate gland and that the effect of testosterone is mediated via 5alpha-dihydrotestosterone. The onset of 5alpha-reductase synthesis is likely to occur between days 14 and 15 of foetal life. The early androgenic activity of the testes suggests that bud formation in the older male sinuses in the absence of androgens is due to exposure to endogenous testosterone before explanation.

Animals↗

PubMed1999

Gap junction-mediated transfer of left-right patterning signals in the early chick blastoderm is upstream of Shh asymmetry in the node.

Invariant patterning of left-right asymmetry during embryogenesis depends upon a cascade of inductive and repressive interactions between asymmetrically expressed genes. Different cascades of asymmetric genes distinguish the left and right sides of the embryo and are maintained by a midline barrier. As such, the left and right sides of an embryo can be viewed as distinct and autonomous fields. Here we describe a series of experiments that indicate that the initiation of these programs requires communication between the two sides of the blastoderm. When deprived of either the left or the right lateral halves of the blastoderm, embryos are incapable of patterning normal left-right gene expression at Hensen's node. Not only are both flanks required, suggesting that there is no single signaling source for LR pattern, but the blastoderm must be intact. These results are consistent with our previously proposed model in which the orientation of LR asymmetry in the frog, Xenopus laevis, depends on large-scale partitioning of LR determinants through intercellular gap junction channels (M. Levin and M. Mercola (1998) Developmental Biology 203, 90-105). Here we evaluate whether gap junctional communication is required for the LR asymmetry in the chick, where it is possible to order early events relative to the well-characterized left and right hierarchies of gene expression. Treatment of cultured chick embryos with lindane, which diminishes gap junctional communication, frequently unbiased normal LR asymmetry of Shh and Nodal gene expression, causing the normally left-sided program to be recapitulated symmetrically on the right side of the embryo. A survey of early expression of connexin mRNAs revealed that Cx43 is present throughout the blastoderm at Hamburger-Hamilton stage 2-3, prior to known asymmetric gene expression. Application of antisense oligodeoxynucleotides or blocking antibody to cultured embryos also resulted in bilateral expression of Shh and Nodal transcripts. Importantly, the node and primitive streak at these stages lack Cx43 mRNA. This result, together with the requirement for an intact blastoderm, suggests that the path of communication through gap junction channels circumvents the node and streak. We propose that left-right information is transferred unidirectionally throughout the epiblast by gap junction channels in order to pattern left-sided Shh expression at Hensen's node.

Animals↗

PubMed2003

Competitive inhibition by Rauber's sickle of the primitive streak and/or (pre)neural plate inducing effects of sickle endoblast in avian blastoderms.

When in unincubated chicken blastoderms the Rauber's sickle is (sub)totally mechanically removed by selective scraping, the further evolution of the blastoderm in culture is often profoundly disturbed, going from only expansion of the upper layer and preneural plate formation to the development of a slowly growing miniature embryo. Our results suggest that the developmental potencies of the embryo are related to the presence or absence of Rauber's sickle material left after its removal. This can be checked after culture by the presence or nonpresence of junctional endoblast (derived from Rauber's sickle) and the concomitant induction of blood islands in the immediate neighborhood. Our study thus indicates that without Rauber's sickle (in the cases of successful total selective removal), an avian blastoderm cannot develop normally, even in the presence of an intact caudal marginal zone. After placing a fragment of quail sickle endoblast on the anti-sickle region of unincubated chicken blastoderms from which the Rauber's sickle was (sub)totally removed, different developmental scenarios were seen, according to the degree of removal, both in the anti-sickle as in the sickle regions. 1) If Rauber's sickle activity is strongly reduced, then besides a centripetally directed miniature embryo, induced by the remnants of the autochthonous Rauber's sickle, an additional centripetally directed embryo or preneural plate (without accompanying blood islands) develops in the anti-sickle region under inductory influence of the apposed quail sickle endoblast. We make a distinction between a neural plate and a preneural plate. The latter consists of a thickening of the upper layer (with the same initial aspect as a neural plate) adjacent to endophyll or sickle endoblast in the absence of chordomesoblast and gastrulation phenomena. 2) If Rauber's sickle activity is totally absent, then the inducing power of the sickle endoblast fragment becomes maximal and, starting from the anti-sickle region, one single embryo (without blood islands) extending over the whole area centralis appears. 3) If much of the Rauber's sickle material has been left in the blastoderm, then the inducing activity of the sickle endoblast, placed on the anti-sickle region, will be totally suppressed (although the sickle endoblast remains intact) and neither a preneural plate nor a primitive streak was induced. After placing a fragment of quail sickle endoblast on the anti-sickle region of an unincubated chicken blastoderm from which the Rauber's sickle and surrounding tissues were completely excised, an embryo was always induced by the sickle endoblast in the adjacent upper layer of this anti-sickle region. In the absence of sickle endoblast, this never occurred. Thus, our experiments demonstrate that in the absence of the Rauber's sickle, a parent tissue (sickle endoblast) induces both gastrulation and neurulation phenomena, while in the full presence of Rauber's sickle these functions are totally suppressed. Moreover, Rauber's sickle not only organizes gastrulation and blood island formation by itself but also influences neurulation at a distance (in space and time) by part of its cell lineage (i.e., sickle endoblast). Our study suggests that the inhibitory effect of Rauber's sickle on its parent tissue (sickle endoblast) represents an early mechanism impairing polyembryony, so that only a single primary major organizer (Rauber's sickle) remains active in the young avian germinal disc.

Animals↗

PubMed2000

delta Ca(2+)/Calmodulin-dependent protein kinase II isozyme-specific induction of neurite outgrowth in P19 embryonal carcinoma cells.

Ca(2+)/calmodulin-dependent protein kinase II (CaMK-II) has been linked to the induction of differentiation in preneuronal cells. In these cells, delta isozymes represent the majority of CaMK-IIs expressed and are activated by differentiation stimuli. To determine whether delta CaMK-IIs are causative or coincident with in vitro differentiation, we overexpressed wild-type, constitutively active, and C-terminal domains of delta and gamma CaMK-II isozymes in mouse P19 and NIH/3T3 cells using high-efficiency transfections. At 1-2 days after transfection, only constitutively active delta CaMK-II isozymes induced branched cellular extensions in both cell types. In P19 cells, retinoic acid induced neurite extensions after 3-4 days; these extensions were coincident with a fourfold increase in endogenous CaMK-II activity. Extensions induced by both retinoic acid and delta CaMK-IIs contained class III beta-tubulin in a discontinuous or beaded pattern. C-terminal CaMK-II constructs disrupted the ability of endogenous CaMK-II to autophosphorylate and blocked retinoic acid-induced differentiation. delta CaMK-II was found along extensions, whereas gamma CaMK-II exhibited a more diffuse, cytosolic localization. These data not only support an extranuclear role for CaMK-II in promoting neurite outgrowth, but also demonstrate CaMK-II isozyme specificity in these early steps of neuronal differentiation.

3T3 Cells↗

PubMed1997

Classifying sex biased congenital anomalies.

The reasons for sex biases in congenital anomalies that arise before structural or hormonal dimorphisms are established has long been unclear. A review of such disorders shows that patterning and tissue anomalies are female biased, and structural findings are more common in males. This suggests different gender dependent susceptibilities to developmental disturbances, with female vulnerabilities focused on early blastogenesis/determination, while males are more likely to involve later organogenesis/morphogenesis. A dual origin for some anomalies explains paradoxical reductions of sex biases with greater severity (i.e., multiple rather than single malformations), presumably as more severe events increase the involvement of an otherwise minor process with opposite biases to those of the primary mechanism. The cause for these sex differences is unknown, but early dimorphisms, such as differences in growth or presence of H-Y antigen, may be responsible. This model provides a useful rationale for understanding and classifying sex-biased congenital anomalies.

Congenital Abnormalities↗

PubMed1998

De novo 7q36 deletion: breakpoint analysis and types of holoprosencephaly.

We report on a de novo 7q36 deletion in a 3-month-old girl with manifestations of the 7q terminal deletion syndrome. Only minimal findings of holoprosencephaly (HPE) were present since only a partial corpus callosum hypoplasia was seen on a magnetic resonance imaging scan of the brain. Extensive fluorescence in situ hybridization analysis showed that the HPE3 critical gene region, inclusive Sonic hedgehog (SHH), En2 (HOX1), and HTR5A, was deleted. A review of 33 other patients with a de novo terminal 7q deletion and the different types of HPE manifestations within these patients will be presented.

Brain↗

PubMed1997

Development of differential preganglionic projections to pre- and paravertebral sympathetic ganglia.

Sympathetic preganglionic axons project to spatially distinct targets in the periphery. A precise topographic pattern exists within the thoracic preganglionic cell column relative to the direction of axonal projections within the sympathetic chain. In this study, the time course and pattern of axonal outgrowth from different populations of preganglionic neurons in the chicken embryo is examined in detail to clarify the origin of the topography in this system. Projections to prevertebral targets are established by development of the splanchnic nerves by stage 25, well after the earliest somatic motor projections at stage 19 but at least two stages before the reported onset of paravertebral projections. Further, preganglionic axons that project rostrally into the sympathetic chain may do so earlier than those that project caudally in the chain. The separation of preganglionic axons into prevertebral, rostral paravertebral or caudal paravertebral directions occurs at a common site in the ventral mesenchyme, established by the initial ventromedial projection of the splanchnic nerves. Analysis of the axonal trajectories of rostrally and caudally projecting cells reveals that preganglionic axons are not selectively fasciculated before their point of separation at the sympathetic chain. The patterning of the preganglionic cell column is specified before the establishment of functional connections within the chain, indicating that target contact is not a determinant of the segmental pattern. We suggest that the differential outgrowth of preganglionic axons to peripheral targets is determined by the unique identities of underlying subpopulations of preganglionic axons.

Acetylcholinesterase↗

PubMed1997

Distribution of radial glia in the developing telencephalon of chicks.

Radial glia are known to have a sparse and uneven distribution in the telencephalon of adult birds. The present study utilizes antibodies against vimentin to reveal a more extensive, and more clearly radial, set of radial glia in the chicken telencephalon during the first half of embryogenesis. This initially extensive radial glial fiber system becomes distorted and reduced between 10 and 14 days of incubation. This reduction coincides with the cytoarchitectural differentiation of the telencephalon into its major adult subdivisions. Because developing neurons tend to migrate along radial glial fibers in both birds and mammals, a topological projection of these major subdivisions onto the embryonic ventricular zone along the radial glial fibers suggests hypotheses about lineage relationships that can be tested by subsequent experimental methods. This analysis suggests that the major components of the avian dorsal ventricular ridge, i.e., the ventral hyperstriatum, the neostriatum with its various subdivisions, part of the archistriatum, and probably also the piriform cortex, all derive from overlapping portions of the lateral pallial ventricular zone. Staining with antibodies against neurofilament suggests that this developmental parcellation of the lateral pallial complex is associated with the development of neuronal fiber systems.

Animals↗

PubMed1999

Development and organization of a nitric-oxide-sensitive peripheral neural plexus in larvae of the moth, Manduca sexta.

Each hemisegment of the Manduca sexta larva is supplied with a subepidermal plexus of approximately 350 multidendritic neurons. An initial set of neurons, the primary plexus neurons, arise at 35-45% of embryogenesis. These neurons comprise 12-16 uniquely identifiable neurons per hemisegment that have homologues in other insect larvae. Each spreads processes across a characteristic portion of the body wall and has an axon that projects into the central nervous system. Secondary plexus neurons are born in two waves: the first between 70% and 80% of embryogenesis and the second during the molt to the second larval stage. The secondary plexus neurons are multidendritic, spread uniformly across the body wall, and appear to make contacts with the primary plexus neurons. Each secondary plexus cell arises as part of a five-cell cluster; the other cells produce a sensory bristle and socket along with the bristle sensory neuron and a glial cell. Application of nitric oxide (NO) donors induces plexus neurons to produce cyclic 3',5' guanosine monophosphate (cGMP), suggesting the presence of soluble guanylate cyclase. With few exceptions, plexus neurons become sensitive to NO stimulation approximately 10 hours after their birth and remain so throughout larval life. Cyclic GMP is detected primarily in the cytoplasm of plexus neurons and extends into the finest peripheral dendrites. Our results suggest that cGMP participates in the development and/or physiology of this peripheral neural plexus.

Animals↗

PubMed1999