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A contribution to the embryology of Limeum indicum
Abstract
The embryology of Limeum indicum of the Phytolaccaceae has been studied in detail. The anther is quadrilocular and consists of five wall layers. The endothecium is fibrous. The middle layer is soon obliterated. The cells of glandular tapetum are two- to three-nucleate. Microsporogenesis is normal. The microspores are tetrahedral or decussate in arrangement. Both the types of arrangement are common. The pollen grains are spherical, tricolporate and three-celled when shed. The ovule is bitegmic, campylotropous and crassinucellate. There is a funicular obturator. The development of the embryo sac is of the polygonum type. The antipodals persists up to the 32-nucleate stage of the endosperm. The endosperm is nuclear. The embryogeny is of the drosera variation, caryophyllad type. The seed is albuminous and campylotropous with a persistent massive perisperm. The entire outer integument and the inner layer of the inner integument form the seed coat. There is a distinct hypostase. The embryological evidence supports the position of Limeum in the Phytolaccaceae.
... Hindbrain segmentation has been investigated in reptiles other than Alligator. These include studies in lizards (McClure, 1890; Orr, 1887), snakes (Herrick, 1892), and Sphenodon (Wyeth, 1924). The most detailed descriptions have been made in Anolis where five (Orr, 1887) and six (McClure, 1890 ) rhombomeres have been identified. ...
... The most detailed descriptions have been made in Anolis where five (Orr, 1887) and six (McClure, 1890 ) rhombomeres have been identified. Furthermore , the relationship between rhombomeres and cranial nerves have been described (McClure, 1890; Orr, 1887 ). Nevertheless, considerable details are lacking, making comparisons difficult between individual rhombomeres identified in the present study and those identified by others (McClure, 1890; Orr, 1887). ...
... Furthermore , the relationship between rhombomeres and cranial nerves have been described (McClure, 1890; Orr, 1887 ). Nevertheless, considerable details are lacking, making comparisons difficult between individual rhombomeres identified in the present study and those identified by others (McClure, 1890; Orr, 1887). ...
Rhombomere development was investigated in a reptile, Alligator mississippiensis, using a variety of methodologies: cytoarchitecture (cresyl violet), histochemistry (peanut agglutinin), immunocytochemistry (antibodies to acetylated tubulin, vimentin, calretinin, and acetylcholinesterase), and external and internal morphology of wholemount embryos. Rhombomere boundaries form sequentially until 8 rhombomeres are present at stage 8. From stage 11 onwards, rhombomere borders fade. When present, boundaries of rhombomeres 2 through 5 were distinct. In all embryos, except the earliest stages, neural tissue was divided between the caudal end of the mesencephalon and the rostral end of the rhombencephalon. This area of transection was designated as the isthmus. For these technical reasons, a distinct border between the midbrain and the first rhombomere was not seen and the isthmic rhombomere could not be identified. The interrhombomeric boundary between rhombomere 7 and rhombomere 8 and between the most caudal rhombomere and the spinal cord was not nearly as clear as were the boundaries of rhombomeres 2 through 5. Development of rhombomeres 2 through 5 was investigated in wholemount preparations between stages 5/6 and 11. Qualitative and quantitative observations were made. In these rhombomeres, r2 through r5, rostrocaudal caudal expansion occurs at a slower rate than mediolateral development. This differential growth sculpts the morphology of rhombomeres 2 through 5.
Rhombomere development in Alligator shares several features in common with hindbrain segmentation in chick. The identification of rhombomeres in a multitude of vertebrates from a variety of classes suggests that segmentation is a feature common to hindbrain development in all vertebrates. J. Comp. Neurol. 411:317–326, 1999.
... Rhombomeres had been discovered and histologically characterized in the last century (e.g. von Baer, 1828; Remak, 1855; Orr, 1887). Only recently, however, have molecular and cell biological studies shed light on the role of rhombomeres in development . ...
... For example, motoneurons of nerve V derive from r2 and r3, those of nerve VII+VIII arise in r4 and r5. Cephalic neural crest populations, sensory ganglion primordia, and pharyngeal arches exhibit a similar periodicity (Remak, 1855; Beranek, 1884; Orr, 1887; His, 1887; Kuhlenbeck, 1935; Wen, 1928; Bartelmez and Dekaban, 1962; Kuratani and Tanaka, 1990). Grafting an even (odd) numbered rhombomere next to another even (odd) numbered rhombomere, results in a single enlarged rhombomere that lacks the interrhombomeric boundary (Guthrie and Lumsden, 1991). ...
The developing vertebrate hindbrain consists of segmental units known as rhombomeres. Hindbrain neuroectoderm expresses 3 Hox 1 and 2 cluster genes in characteristic patterns whose anterior limit of expression coincides with rhombomere boundaries. One particular Hox gene, referred to as Ghox 2.9, is initially expressed throughout the hindbrain up to the anterior border of rhombomere 4 (r4). Later, Ghox 2.9 is strongly upregulated in r4 and Ghox 2.9 protein is found in all neuroectodermal cells of r4 and in the hyoid crest cell population derived from this rhombomere. Using a polyclonal antibody, Ghox 2.9 was immunolocalized after transplanting r4 within the hindbrain. Wherever r4 was transplanted, Ghox 2.9 expression was cell-autonomous, both in the neuroectoderm of the graft and in the hyoid crest cell population originating from the graft.
In all vertebrates, rhombomeres and cranial nerves (nerves V, VII+VIII, IX, X) exhibit a stereotypic relationship: nerve V arises at the level of r2, nerve VII+VIII at r4 and nerves IX-X extend caudal to r6. To examine how rhombomere transplantation affects this pattern, operated embryos were stained with monoclonal antibodies E/C8 (for visualization of the PNS and of even-numbered rhombomeres) and HNK-1 (to detect crest cells and odd-numbered rhombomeres). Upon transplantation, rhombomeres did not change E/C8 or HNK-1 expression or their ability to produce crest cells. For example, transplanted r4 generated a lateral stream of crest cells irrespective of the site into which it was grafted. Moreover, later in development, ectopic r4 formed an additional cranial nerve root. In contrast, transplantation of r3 (lacks crest cells) into the region of r7 led to inhibition of nerve root formation in the host.
These findings emphasize that in contrast to spinal nerve segmentation, which entirely depends on the pattern of somites, cranial nerve patterning is brought about by factors intrinsic to rhombomeres and to the attached neural crest cell populations. The patterns of the neuroectoderm and of the PNS are specified early in hindbrain development and cannot be influenced by tissue transplantation. The observed cell-autonomous expression of Ghox 2.9 (and possibly also of other Hox genes) provides further evidence for the view that Hox gene expression underlies, at least in part, the segmental specification within the hindbrain neuroectoderm.
... Limits habitually appear as constrictions (transversal neuroepithelial microzones with slower proliferation) that separate bulging neural wall domains of various sizes, depending on the embryonic stage. These bulges are called successively primary brain vesicles (i.e., forebrain (F), midbrain (M), hindbrain (H), see alsoFig. 1, second column on the left), proneuromeres (secondary vesicles that will later subdivide, particularly in the hindbrain), and neuromeres (the smallest outpouchings;[59,64]). The number of transverse proliferative minimal and maximal thus increases over time, but in a spatially disjoint pattern[75]. ...
... Vaage[75]revised previous data regarding the morphological segmentation of the developing neural tube and discussed them in the context of his own observations in whole mounts and sectioned material. He used the morphological criteria of Orr[59]to define gradual appearance of neuromeres from stage HH8+ to HH27 (Figs. 1A, E, I, M, Q, and T;[75]) and later complemented this with a detailed analysis of isthmomesencephalic histogenesis extending into adult stages[76]. These two papers must be regarded as masterpieces of descriptive neuroembryology, irrespective of the faulty interpretation of the isthmomesencephalic boundary (IMB). ...
The vertebrate brain is progressively regionalized during development in a process whereby a precise spatio-temporal arrangement of gene expression patterns and resulting intercellular and intracellular signals drive patterning, growth, morphogenesis, and final fates, thus producing ordered species-specific differentiation of each territory within a shared morphotype. Before genetic and molecular biology tools started to be used to uncover the underlying mechanisms that control morphogenesis, knowledge on brain development largely depended on descriptive analysis and experimental embryology. The first approach allowed us to know how the brain develops but not why. The second provided insights into inductive and field histogenetic phenomena, requiring causal explanation. In this review, we focused on the regionalization of the rostral hindbrain, defined as isthmus plus rhombomere 1, which is the least understood part of the hindbrain. We addressed what is known about the formation of boundaries in this area and the fate of diverse neuroepithelial portions. We introduced to this end some fate-mapping data recently obtained in our laboratory. Starting from the background of pioneering morphological studies and available fate mapping data, we establish correlation with current knowledge about how morphogens, transcription factors, or other signaling molecules map onto particular territories, from where they may drive morphogenetic interactions that generate final fates step by step.
... The reproductive structures, especially the stamens and one-seeded locules, of the Limeum species differ markedly from those of Molluginaceae and other members of the "globular inclusion" clade (cf. Narayana & Jain 1962, Endress & Bittrich 1993, Sukhorukov et al. 2015. ...
The distribution of Limeum, the single genus in Limeaceae, has been considered limited to continental Africa, SW Asia and India. Limeum madagascariense Sukhor., a new species described here, is the first member of the genus reported from Madagascar. It was recorded from the area surrounding Mahajanga in the northwest of the island. The species can be easily distinguished from all congeners by its twining habit, unique within the genus, and long-attenuate leaves.
... Hunziker and Coccaci [14] studied the pollen morphology of the genus Trianthema L. The pollen morphology of few genera of the family Molluginaceae and Aizoaceae from America has been examined by Bogner [15]. Narayana [16] studied the embryology of Limeum indicum Stocks. Mitroiu-Radulescu [17] examined the pollen of the family Aizoaceae. ...
The pollen morphology of 7 species belonging to the 7 genera of the family Aizoaceae was investigated by light microscope and scanning microscope. It is stenopalynous in nature. Pollen grains are usually radially symmetrical, isopolar, oblate-spheroidal to prolate-spheroidal, rarely sub-prolate, tricolpate, colpi long, with tapering ends, colpal membrane granulate. Sexine slightly thinner or thicker then nexine, rarely thicker at the polar reqion than at the equator. Tectum scabrate-punctate or spinulose. On the basis of exine ornamentation 2 distinct pollen types are recognized, namely, the Zaleya pentandra type and the Aizoon canariense type.
... The possibility that the nervous system is constructed from a segmented set of repeated units has become an issue of intense interest in recent years (see Lumsden, 1990; Keynes and Lumsden, 1990; Fraser, 1993). A series of undulations of the neural tube, termed neuromeres (Orr, 1887 ), have been documented for over a century (for review, see Vaage, 1969; Bergquist, 1952). Because the neuromeres represent a transient organization during the development of the central nervous system (Vaage, 1969), many questions about their importance have been raised. ...
Previous cell lineage studies indicate that the repeated neuromeres of the chick hindbrain, the rhombomeres, are cell lineage restriction compartments. We have extended these results and tested if the restrictions are absolute. Two different cell marking techniques were used to label cells shortly after rhombomeres form (stage 9+ to 13) so that the resultant clones could be followed up to stage 25. Either small groups of cells were labelled with the lipophilic dye DiI or single cells were injected intracellularly with fluorescent dextran. The majority of the descendants labelled by either technique were restricted to within a single rhombomere. However, in a small but reproducible proportion of the cases (greater than 5%), the clones expanded across a rhombomere boundary. Neither the stage of injection, the stage of analysis, the dorsoventral position, nor the rhombomere identity correlated with the boundary crossing. Judging from the morphology of the cells, both neurons and non-neuronal cells were able to expand over a boundary. These results demonstrate that the rhombomere boundaries represent cell lineage restriction barriers which are not impenetrable in normal development.
... The inception of neuroembryology might be considered to be when von Baer, over 175 years ago, first observed the neural tube in a vertebrate species and described its primordial subdivisions (von Baer, 1828). In the later half of the nineteenth century, Orr continued this work and detailed the initial segmentation of the nervous system into structural subunits, coined neuromeres, during embryogenesis in reptiles (Orr, 1887). Since these initial discoveries, neuroembryologists have chronicled the remarkable anatomical and cellular changes of the brain in great detail. ...
An important component of brain mapping is an understanding of the relationships between neuroanatomic structures, as well as the nature of shared causal factors. Prior twin studies have demonstrated that much of individual differences in human anatomy are caused by genetic differences, but information is limited on whether different structures share common genetic factors. We performed a multivariate statistical genetic analysis on volumetric MRI measures (cerebrum, cerebellum, lateral ventricles, corpus callosum, thalamus, and basal ganglia) from a pediatric sample of 326 twins and 158 singletons. Our results suggest that the great majority of variability in cerebrum, cerebellum, thalamus and basal ganglia is determined by a single genetic factor. Though most (75%) of the variability in corpus callosum was explained by additive genetic effects these were largely independent of other structures. We also observed relatively small but significant environmental effects common to multiple neuroanatomic regions, particularly between thalamus, basal ganglia, and lateral ventricles. These findings are concordant with prior volumetric twin studies and support radial models of brain evolution.
During vertebrate development, the central nervous system (CNS) has stereotyped neuronal tracts (scaffolds) that include longitudinal and commissural axonal bundles, such as the medial longitudinal fascicle or the posterior commissure (PC). As these early tracts appear to guide later-developing neurons, they are thought to provide the basic framework of vertebrate neuronal circuitry. The proper construction of these neuronal circuits is thought to be a crucial step for eliciting coordinated behaviors, as these circuits transmit sensory information to the integrative center, which produces motor commands for the effective apparatus. However, the developmental plan underlying some commissures and the evolutionary transitions they have undergone remain to be elucidated. Little is known about the role of axon guidance molecules in the elicitation of early-hatched larval behavior as well.
Here, we report the developmentally regulated expression pattern of axon-guidance molecules Slit2 ligand and Robo2 receptor in Xenopus laevis and show that treatment of X. laevis larvae with a slit2- or robo2-morpholino resulted in abnormal swimming behavior. We also observed an abnormal morphology of the PC, which is part of the early axonal scaffold.
Our present findings suggest that expression patterns of Slit2 and Robo2 are conserved in tetrapods, and that their signaling contributes to the construction of the PC in Xenopus. Given that the PC also includes several types of neurons stemming from various parts of the CNS, it may represent a candidate prerequisite neuronal tract in the construction of subsequent complex neuronal circuits that trigger coordinated behavior.
Maheshwari (1950) has summarized the history of development of our knowledge of embryology of angiosperms. The highlights are presented here. Sexuality in angiosperms has been known since the third century B.C. when the Arabs and Assyrians used to perform the ritual of artificial pollination of the date palm. They were not, however, aware of sexuality as such, nor what followed after dusting the female flowers with male flowers.
The pollen morphology of 7 species belonging to the 7 genera of the family Aizoaceae was investigated by light microscope and scanning microscope. It is stenopalynous in nature. Pollen grains are usually radially symmetrical, isopolar, oblate-spheroidal to prolate-spheroidal, rarely sub-prolate, tricolpate, colpi long, with tapering ends, colpal membrane granulate. Sexine slightly thinner or thicker then nexine, rarely thicker at the polar reqion than at the equator. Tectum scabrate-punctate or spinulose. On the basis of exine ornamentation 2 distinct pollen types are recognized, namely, the Zaleya pentandra type and the Aizoon canariense type.
As sturgeons are considered to represent a basal group of Osteichthyes, it is necessary to evaluate their developmental features to understand the evolution, not only of bony fishes, but also of tetrapods in general. Using Besters, commercially established hybrid sturgeons, the neural crest cell distribution pattern, mesodermal epithelium, and peripheral nerves were observed based on whole-mount immunostained and -sectioned embryos, from the pre-hatching embryonic stage to a late swimming larval stage. At the early pharyngula stage, the hindbrain exhibits at least six rhombomeres. These have a typical arrangement of neuroepithelial cells, and segmentally distributed cephalic crest cell populations associated with even-numbered rhombomeres medially, and single pharyngeal arches laterally. The head cavities first arise as a pair of epithelial primordia in the prechordal region. Secondarily, the cavity is subdivided mediolaterally into the premandibular and mandibular cavities. These mesodermal components never affect the segmental pattern of cranial nerve roots as seen in the shark embryo (Kuratani and Horigome, 2000), probably due to the early degeneration of the cavities. The hyoid cavity never appears. As observed in several teleosts, the newly hatched Bester larva possesses extensive neurites in the epidermis, originating from both trigeminal placodes and Rohon-Beard cells. This neurite network diminishes during development, in concordance with the appearance of lateral line nerves. All the epibranchial placodes are seen as focal, HNK-1-positive epidermal thickenings and give rise to inferior ganglia of the branchiomeric nerves. Metameric morphology of the branchiomeric nerve innervation is secondarily disturbed through modification of the head region, involving the expansion of the operculum and modification of the jaw.
The developing hind-brain of vertebrates consists of segmental units called rhombomeres. Although crest cells emigrate from the hind-brain, they are subsequently subdivided into several cell populations that are attached to restricted regions of the hind-brain. At the preotic level, only even-numbered rhombomeres are accompanied by crest cells, while the odd-numbered ones are not. At the postotic level, such the birhombomeric repetition becomes obscure. In order to map the origins and distributions of postotic crest cells, focal injections of Dil were made into various axial levels of the postotic neural tube. Cephalic crest cells at the postotic level first form a single cell population deposited by cells along the dorsolateral pathway. They are called the circumpharyngeal crest cells (CP cells) and are secondarily subdivided into each pharyngeal arch ectomesenchyme. The neural tube extending from r5 to the somite 3/4 boundary gave rise to CP cells. The neuraxial origins of each pharyngeal ectomesenchyme extended for more than three somite lengths, most of which overlapped with the other. Unlike in the preotic region, there is no segmental registration between neuraxial levels and pharyngeal arches. Caudal portions of the CP cell population show a characteristic distribution pattern that circumscribes the postotic pharyngeal arches caudally. Heterotopic transplantation of the Dil-labeled neural crest into the somite 3 level resulted in a distribution of labeled cells similar to that of CP cells, suggesting that the pattern of distribution depends upon dynamic modification of the body wall associated with pharyngeal arch formation.
Vertebrate brains are highly organized structures that show remarkable diversity throughout animal groups. The agnathans, which diverged from the gnathostomes early in the evolution of the vertebrates, occupy a key phylogenetic position from which to clarify the origin and evolution of the brain. We studied the developing lamprey brain and compared its developmental plan with that of the gnathostomes, in order to reconstruct the evolutionary processes of the vertebrate brain. We found that the lamprey brain has the basic molecular mechanisms necessary to form neuromeric compartments, and that its mesencephalon and diencephalon exhibit conserved morphological and molecular features. Conversely, the telencephalon and metencephalon display lamprey-specific developmental mechanisms. Thus, the molecular program of the nervous system is thought to have improved in the gnathostome lineage. Changes in the expression domains of some regulatory genes might have facilitated the evolution of the vertebrate central nervous system.
The hormone retinoic acid (RA) has been implicated in the organization of the anteroposterior (AP) body axis. In this paper, we describe the effects of RA on the activity of the RA-inducible retinoic acid receptor-beta 2 (RAR beta 2) promoter. When transgenic embryos carrying a RAR beta 2-lacZ reporter gene were exposed to a single dose of RA between gestational days 8.5 to 10.5, lacZ expression was induced in the anterior central nervous system (CNS). Strikingly, the transgene was expressed in a segmented pattern reminiscent of that of Drosophila 'pair-rule' genes. RA treatment of midgastrulation embryos at day 7.5 disturbed the segmentation and produced severe craniofacial defects. We discuss the possibility that the entire anterior CNS is segmented and that this segmentation is reflected by the RAR beta 2-lacZ induction pattern.
The segmented embryonic hindbrain of vertebrates develops by sequential constriction of the neural tube into eight metameric units known as rhombomeres. The cellular and molecular basis of this segmentation process is largely unknown. Using an antibody, we analyzed the expression pattern of the chick homeo domain-containing protein Ghox-lab in the developing chick hindbrain. At the neural plate stage, prior to the appearance of rhombomeres, Ghox-lab is expressed within a single domain that extends anteriorly up to the site where rhombomere 4 will later form. After rhombomere 4 has appeared and as hindbrain segmentation progresses, the level of Ghox-lab protein increases significantly within the fourth rhombomere. This intensification, accompanied by the elimination of Ghox-lab protein in rhombomeres 5 and 6, eventually results in the formation of a distinct island of expression in rhombomere 4. All cells in the newly formed rhombomere 4 express Ghox-lab, except for the cells of the floor plate. In addition, neural crest cells migrating from the fourth rhombomere are also Ghox-lab-positive. These data raise the possibility that Ghox-lab protein might be one of the factors involved in the specification of the metameric pattern of the vertebrate hindbrain.
We report here the histogenesis of the brainstem of the trout (Salmo trutta fario) and the medaka (Oryzias latipes) chosen as examples of teleosts with slow and fast growth, respectively. Our results reveal that the sequence of formation of brain structures is rather similar in the teleosts species examined so far, but some interspecific differences do exist in terms of brainstem maturation at particular developmental stages, such as the end of the gastrulation and hatching periods. This sequence includes the subdivision of the brainstem in different transverse segments and longitudinal zones, where morphologically discernible boundaries are observed along the caudorostral and ventrodorsal axis. The boundary formation and subsequent subdivision of the trout and medaka brainstems, together with the proliferation pattern observed by immunohistochemistry with an antibody against the proliferating cell nuclear antigen (PCNA), support a segmental model throughout the brainstem. The spatiotemporal pattern of PCNA immunoreactivity is similar in the mesencephalon and rhombencephalon of the two teleosts species studied, although proliferation centers are less clearly defined in the medaka. Moreover, the segmental appearance of the brainstem, as revealed by PCNA immunohistochemistry, is blurred earlier in the medaka than in the trout. Thus, the trout brain appears a suitable model for morphogenetic studies because it allows more gradual survey of the changes throughout development.
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