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PubMed2004

An fMRI investigation of speech and tone segmentation.

Recent research strongly indicates that phonological tasks activate a subregion of the inferior frontal gyrus. The purpose of the present fMRI study was to investigate the extent to which activation of this region during phonological processing is due to speech processes per se such as articulatory recoding or to other cognitive task demands such as working memory. Thus, we compared activation patterns during segmentation of speech and tone sequences to a tone discrimination task. In particular, participants performed same/different judgments on pairs of words, pseudowords, and tone sequences that required segmentation of a continuous acoustic signal as well as tone pairs that did not require segmentation. Accuracy and reaction time data showed that speech and tone sequence segmentation conditions patterned more similarly to each other than to tone discrimination pairs. Analyses of group data revealed strong activation of the region at the border of the left inferior and middle frontal gyrus for all three segmentation conditions compared to tone discrimination, but no consistent differences were observed when word and pseudoword segmentation were directly contrasted. Analyses of individual subjects indicated that a large number of participants activated a small area of the middle frontal gyrus during the speech conditions compared to the sequences. These results suggest that a significant portion of active frontal areas is recruited for extracting acoustic information and maintaining it in memory for decision. However, some regions at the border of the inferior/middle frontal gyrus may be unique to speech segmentation.

Adult↗
PubMed1996

Displacement field estimation and image segmentation using block matching enhanced by a neural network.

The block-matching method plays an important role in displacement field estimation due to its simplicity, achievement of long-range motion, and robustness to noise. In this paper, a single-layer feedback neural network model is proposed that enhances block matching, estimates the displacement field, and simultaneously performs image segmentation from consecutive images. In this paper, image segmentation is defined as partitioning each image into a set of moving objects and the background. For any two consecutive images, a neural network is created that learns the connection relationship of the pixels in an object from the displacement field and stores the relationship in the network. A modified block matching is used to compute a more accurate displacement field by utilizing the segmentation information embedded in the neural network. The displacement vector at the edge of an object or occluding boundary is hard to estimate, but the proposed model performs satisfactorily because it learns and uses the connection information. Furthermore, a flood-fill algorithm is used to compute the dense displacement field more efficiently and correctly than the exhaustive search does. The most important aspect of this paper is that image segmentation is performed simultaneously with the displacement-field estimation by the neural-network model. The novel idea of the work is to embed the segmentation information (connection relations) in the neural network and to perform the displacement-field estimation and image segmentation simultaneously. Two methods for retrieving segmentation information from the neural network with any two consecutive images are also presented.

Algorithms↗
PubMed1994

Soluble intracellular adhesion molecule 1 in bronchoalveolar lavage fluid of allergic subjects following segmental antigen challenge.

This study was undertaken to determine the relationship of soluble intercellular adhesion molecule 1 (sICAM-1) levels in bronchoalveolar lavage (BAL) fluid during allergic airway inflammation to those in the vascular compartment and to cellular components in the BAL fluids. A group of 11 allergic subjects underwent initial bronchoscopy during which a control BAL was performed and normal saline (NS) and specific antigen (Ag) were administered to two sublobar segments. A second bronchoscopy was performed 17 to 21 h later, and the NS and Ag segments were lavaged. Blood was drawn before each bronchoscopic procedure. The mean concentration of sICAM-1 in BAL fluid from NS-challenged segments was 59.2 +/- 7.6 ng/ml and was not different from that in unchallenged segments (51.5 +/- 5.6 ng/ml). In BAL fluid from Ag-challenged segments, mean concentrations of sICAM-1 increased significantly to 97.5 +/- 12.5 ng/ml. Segmental antigen challenge was associated with a small but statistically significant increase in sICAM-1 concentrations in serum. The concentrations of sICAM-1 in BAL fluid after antigen challenge exceeded levels that could be accounted for by passive transudation from the circulation, based upon the magnitude of increases in BAL albumin concentrations. The levels of sICAM-1 in BAL from Ag-challenged segments were correlated significantly with the total white cell, lymphocyte, neutrophil, and eosinophil counts in BAL fluids. These results are supportive of the notion that the local release of sICAM-1 may play a role in allergen-induced inflammatory processes in the airways.

Adult↗
PubMed2006

Bone morphogenetic protein 7 increases chick photoreceptor outer segment initiation.

PURPOSE: The purpose of this study was to investigate the regulation of photoreceptor differentiation and outer segment elongation by the growth factor BMP7. METHODS: Dissociated low-density embryonic day 6 (E6) chick retinal cultures were grown for 6 days in the presence of BMP7, other members of the TGF-beta family of growth factors, or control vehicle. Cultured cells were characterized using microscopy, immunocytochemistry, and RT-PCR. Antibodies against visinin and GABA were used to distinguish photoreceptors from nonphotoreceptor cells, and monoclonal antibodies rhodopsin (rho) 4D2, OS-2, and COS-1 were used to distinguish subpopulations of cones and rods. RT-PCR was used to investigate mRNAs encoding visual pigments. RESULTS: Photoreceptors treated with BMP7 initiated outer segment elongation more frequently than photoreceptors in control cultures. The effect on outer segment initiation was confined to rods and to green opsin-expressing cones and appeared not to involve an increase in outer segment length. BMP7 did not appear to affect the survival, proliferation, or differentiation of progenitors or the fate of photoreceptors or amacrine cells in vitro. BMP5 and GDF5 showed weaker stimulatory effects than BMP7 on outer segment formation, whereas activin, BMP2, and BMP4 inhibited visual pigment expression and outer segment formation, and BMP6 had no detectable effects. CONCLUSIONS: BMP7 must be added to the list of candidate molecules capable of stimulating outer segment formation.

Animals↗
PubMed1975

Characteristics of salt and water transport in superficial and juxtamedullary straight segments of proximal tubules.

The purpose of the present studies was to characterize the nature of salt and water transport out of the superficial (SF) and juxtamedullary (JM) straight segments of rabbit proximal tubules as examined by in vitro microperfusion techniques. When the perfusate consisted of a solution simulating ultrafiltrate of plasma, there were no differences between SF and JM straight tubules in either net reabsorption of fluid (SF=0.47 nl/mm per min; JM=0.56 nl/mm per min) or in transtubular potential difference (PD) (SF=-2.1 mV; JM=-1.8 mV). Removal of glucose and alanine from the perfusate had no effect on the magnitude of the PD in either straight segment. Ouabain decreased both the net reabsorptive rates and the PD. Isosmolal replacement of NaCL by Na-cyclamate (a presumed impermeant anion) in the perfusate and the bath caused an increase in luminal negativity in both segments wheras similar substitution of NaCL by choline-CL (nontransported cation) changed the PD TO NEAR ZERO. These studies, therefore, suggest that sodium is transported out of the proximal straight tubules by an active noncoupled process that generates a PD (electrogenic process). When the perfusate consisted of a solution with a high chloride concentration (resulting from greater HCO3 than CI reabsorption in the proximal convoluted tubule), different PDs in SF and JM tubules were generated: SF=+1.6 plus or minus 0.2 mV; JM=-1.3 plus or minus 0.3 mV. This difference in PD was attributed to relative differences in Na and CI permeabilities in these two segments. Electrophysiological and isotopic estimates of the chloride to sodium permeability revealed that the SF tubule is about twice as permeant to chloride than to sodium whereas the JM tubules are approximately twice as permeant to sodium than to chloride. It is concluded that the mechanism of active sodium transport in the straight segment of proximal tubule differs from that of the convoluted segment and that both the SF and JM straight segments differ from each other with respect os sodium and chloride permeability.

Animals↗
PubMedDate not supplied

Semiquantitative culture of subcutaneous segment for conservative diagnosis of intravascular catheter-related infection.

BACKGROUND: Sensitivity and negative predictive values of combined surface cultures (skin and hub) are high in the presumptive diagnosis of catheter-related infection, but specificity and PPVs are poor. The purpose of the study was to evaluate the yield of the semiquantitative culture of the subcutaneous segment in the diagnosis of colonization of the catheter tip without removal of the catheter. METHODS: A prospective study was performed in 124 nontunneled central venous catheters that were removed because of suspected infection or the end of therapy. Catheter colonization was considered if >15 colony-forming units (CFU) in the roll procedure or > 1,000 CFU in the quantitative Cleri procedure were recovered from the tip cultures ("gold standard"). Before removing the catheter, a semiquantitative culture of skin surrounding the point of insertion, a semiquantitative culture of the subcutaneous segment (after removing the catheter only 2 cm), a semiquantitative cultures of the hub, and a pareated quantitative blood culture were performed. Receiver operating characteristic curves were calculated to estimate the cutoff points, and a culture was considered positive when CFUs were > or =15, > or =15, and > or =5 for skin, hub, and subcutaneous segment cultures, respectively. RESULTS: Catheter colonization was detected in 51 catheters. The mean duration of catheterization was 14 +/- 8 days, and the rates of incidence of tip colonization and bacteremia were 2.9 per 100 catheter days and 1.2 per 100 catheter days, respectively. Sensitivity of skin, subcutaneous, and hub cultures analyzed individually were < or =61%; however, specificity and positive predictive values (PPVs) of subcutaneous segment cultures were significantly higher than skin cultures (94% and 88.5% vs 71.6% (p = .001) and 62% (p = .014), respectively). Sensitivity of the combined skin and hub cultures and of the combined subcutaneous segment and hub cultures were similar: 86.2% and 84.3%, respectively; however, specificity and PPVs of this latter combination were significantly higher than former: 82% and 78.1% vs 59.7% (p = .008) and 61.9% (p = .07), respectively. The likelihood ratio of a positive test for the combined subcutaneous segment and hub culture was 4.68, and only 2.13 for the combined skin and hub culture. CONCLUSIONS: These results indicate that the combined subcutaneous segment and hub culture constitutes an easy, effective procedure for the conservative diagnosis of catheter colonization.

Bacteriological Techniques↗
PubMed1991

Intrinsic vasculature of the labyrinthine segment of the facial nerve--implications for site of lesion in Bell's palsy.

Recent studies of the intrinsic vasculature of the cat facial nerve have demonstrated relatively poor blood supply to the labyrinthine segment. In this study, the intrinsic vasculature of the human facial nerve was systematically evaluated in 25 temporal bones and three fresh cadaver nerves. Cross-sectional vessel counts were obtained for the labyrinthine, tympanic, and mastoid segments. Capillary densities for each segment were derived from these data. The labyrinthine segment of the human facial nerve, like that in the cat, contains fewer and smaller intrinsic blood vessels than do the mastoid and tympanic segments. This may indicate that the labyrinthine segment of the facial nerve may be more vulnerable to ischemic damage. In conjunction with the previously demonstrated narrowness of the labyrinthine fallopian canal, these findings support the contention that the labyrinthine segment is a likely site of lesion in Bell's palsy.

Ear, Inner↗
PubMed2001

Computer-assisted continuous ST-segment analysis for clinical research: methodological issues.

Continuous ST-segment monitoring has been used to detect acute myocardial ischemia, determine the success of the reperfusion therapy, and predict outcomes in both research and a variety of clinical settings. However, analyzing the abundant electrocardiography (ECG) data recorded using continuous multilead ST-segment monitoring techniques is time consuming and requires expertise. Experienced data interpreters in dedicated ECG core laboratories handle many continuous ECG data records from large clinical trials. Little information on measurement issues for computer-assisted ST-segment analysis is available for individual investigators. Unsupervised or inexperienced computer analysis of ST-segment deviations can, under certain circumstances, yield invalid or unreliable summary indices. The goal of this article is to discuss basic ST-segment measurement principles in evaluating acute myocardial ischemia and methodological issues surrounding the use of computer-assisted ST-segment analysis for continuous ECG data. Variables affecting ST-segment measurements will be examined. Sources and examples of variability for these potential errors will be identified.

Diagnosis, Computer-Assisted↗
PubMed2000

Vascular response in the femoropopliteal segment after implantation of an ePTFE balloon-expandable endovascular graft: an intravascular ultrasound study.

PURPOSE: To use intravascular ultrasound (IVUS) to document changes in vascular dimensions after placement of a balloon-expandable endograft. METHODS: Thirteen patients (9 men; mean age 62 years, range 47-75) treated with an investigational polytetrafluoroethylene endograft for obstructive disease of the femoropopliteal segment were studied with IVUS immediately after endograft implantation and at follow-up. Corresponding IVUS cross sections were analyzed for changes in lumen, vessel, and plaque areas seen inside the endograft, in the anastomotic segment, and in the remote arterial segment. RESULTS: A mean 6-month (range 1.5-9) follow-up was completed in 12 patients. Matched IVUS cross sections derived from within the endograft (n = 12) and at the endograft edges (n = 23) showed no change in lumen area (LA) in 17, reduction in 11, and dilatation in 7. Median changes within the endograft (+3%) were not significant (p = 0.28) and no neointima was found. Cross sections obtained at the anastomotic segment revealed a significant increase in LA (85%, p < 0.001), which was associated with a significant increase in both vessel area (VA) (42%, p < 0.001) and plaque area (PLA) (15%, p = 0.003) area. In the remote arterial segment, the change in LA was minimal (6%, p = 0.07), as were changes in the VA (9%, p = 0.04) and PLA (10%, p = 0.07). CONCLUSIONS: Following endograft placement, luminal changes within the endograft, at the endograft edges, and at the remote arterial segments were minimal. Intimal hyperplasia was not observed in the endograft. The distinct LA increase at the anastomotic segments was determined by the extent of VA and PLA change.

Aged↗
PubMed2006

Cell lineage analysis of the mandibular segment of the amphipod Orchestia cavimana reveals that the crustacean paragnaths are sternal outgrowths and not limbs.

The question of arthropod head segmentation has become one of the central issues in Evolutionary Developmental Biology. The number of theories pertaining to head segments progressively enlarges, old concepts have been revitalized, and nearly every conceivable composition of the arthropod head has at some point received discussion. One contentious issue involves a characteristic mouthpart in crustaceans--the lower lips or the so-called paragnaths. The paragnaths build the posterior border of the mouth region antagonistic to the upper lip--the labrum. We show here the development of the appendage-like structures in the mandibular region of the amphipod crustacean Orchestia cavimana at a high level of cellular resolution. The embryos are examined during development of the mouthparts using in vivo labeling. An invariant cell division pattern of the mandibular segment was detected by 4D-microscopy and a preliminary model for pattern of the first cleavages in the mandibular region created. With this indispensable precondition single ectodermal cells of the grid-like pattern were labeled with DiI--a lipophilic fluorescent dye--to trace cell lineages and determine the clonal composition of the developing mouthparts, especially the mandibular segment. From our data it is evident that the paragnaths are sternal outgrowths of the mandible segment. The assumption of the limb nature of paragnaths and the presence of an additional head segment between the mandibular and the second antennal segments are clearly refuted by our data. Our results show the power of cell lineage and clonal analyses for inferences on the nature, origin and thus homology of morphological structures. With this kind of investigation morphological and gene expression data can be complemented. We discuss notable similarities of paragnath anlagen to those of the hypopharynx complex in myriapods and hexapods. The fact that both structures grow out as two lateral buds in the same region of the mandibular sternite during development, and their important role in the formation of the feeding apparatus as a highly specialized chewing chamber in adults of crustaceans, myriapods, and hexapods argue for the paragnaths/hypopharynx anlagen being an additional potential apomorphy of Mandibulata.

Journal Article↗
PubMed2006

Intron gain and loss in segmentally duplicated genes in rice.

BACKGROUND: Introns are under less selection pressure than exons, and consequently, intronic sequences have a higher rate of gain and loss than exons. In a number of plant species, a large portion of the genome has been segmentally duplicated, giving rise to a large set of duplicated genes. The recent completion of the rice genome in which segmental duplication has been documented has allowed us to investigate intron evolution within rice, a diploid monocotyledonous species. RESULTS: Analysis of segmental duplication in rice revealed that 159 Mb of the 371 Mb genome and 21,570 of the 43,719 non-transposable element-related genes were contained within a duplicated region. In these duplicated regions, 3,101 collinear paired genes were present. Using this set of segmentally duplicated genes, we investigated intron evolution from full-length cDNA-supported non-transposable element-related gene models of rice. Using gene pairs that have an ortholog in the dicotyledonous model species Arabidopsis thaliana, we identified more intron loss (49 introns within 35 gene pairs) than intron gain (5 introns within 5 gene pairs) following segmental duplication. We were unable to demonstrate preferential intron loss at the 3' end of genes as previously reported in mammalian genomes. However, we did find that the four nucleotides of exons that flank lost introns had less frequently used 4-mers. CONCLUSION: We observed that intron evolution within rice following segmental duplication is largely dominated by intron loss. In two of the five cases of intron gain within segmentally duplicated genes, the gained sequences were similar to transposable elements.

Amino Acid Sequence↗
PubMed2025

Predicting host tropism in influenza a viruses: insights from multi-segment nucleotide signatures.

BACKGROUND: Influenza A virus (IAV) poses a significant public health threat due to its cross-species transmission and complex host adaptation mechanisms. This study integrated whole-genome data from avian, human, swine, and bovine IAV strains, using machine learning to predict viral host tropism based on nucleotide site features and to identify key sites driving host adaptation along with their synergistic effects. METHODS: A total of 64,000 IAV sequences from avian, human, swine, and bovine hosts were analyzed to build host-prediction models. A four-class classification framework (avian, human, swine, bovine) was constructed using nucleotide site features from all eight genomic segments (PB2, PB1, PA, HA, NP, NA, MP, NS). Eight machine learning algorithms (logistic regression, decision tree, random forest, SVM, KNN, gradient boosting, XGBoost, LightGBM) were benchmarked via 10-fold stratified cross-validation. Model performance was evaluated using accuracy, precision, recall, F1-score, AUPRC, and AUC. SHAP (SHapley Additive exPlanations) analysis prioritized critical nucleotide sites, while bivariate association tests identified synergistic/antagonistic interactions between sites. Nucleotide composition profiles were compared across host groups using hierarchical clustering and heatmap visualization. RESULTS: The XGBoost algorithm demonstrated the best and most stable performance, achieving an AUC value of over 0.95 in distinguishing human-derived sequences from non-human ones. SHAP analysis identified the top 20 critical nucleotide sites for each gene segment, such as sites 46 and 698 in the NS segment. Nucleotide composition analysis revealed high similarity between human and swine sequences in the HA and PB2 segments, and between avian and bovine sequences. The HA segment was particularly challenging in differentiating human from swine strains. Bivariate site association analysis uncovered significant synergistic or antagonistic effects between key sites within gene segments, forming complex networks. For instance, in the NS segment, a positive prediction contribution was observed when sites 371, 698, and 419 were all G. CONCLUSIONS: This study advances our mechanistic understanding of IAV host adaptation, identifies molecular determinants for zoonotic risk stratification, and establishes a scalable machine learning framework for predicting viral host tropism through nucleotide signature analysis, thereby enhancing surveillance strategies and informing preventive measures against emerging viral threats.

Influenza A virus↗
PubMed1995

The segment-specific pattern of A-raf expression in the mouse epididymis is regulated by testicular factors.

The protooncogene homolog A-raf is expressed at high levels in a variety of steroid-responsive tissues and exhibits a highly regionalized pattern of expression in morphologically and functionally distinct segments of the mouse epididymis: the highest levels occur in the proximal caput, lower levels occur in the initial segment, and intermediate levels are found in the distal caput. Castration abolished detectable A-raf expression throughout the epididymis. The administration of exogenous androgens restored expression to precastrate levels, indicating that circulating, rather than intraluminal, levels of androgens are sufficient to maintain expression. Although overall levels of A-raf were maintained in androgen-replaced animals, the segment-specific pattern of expression was altered. Elevated levels of A-raf were expressed in the initial segment relative to those in controls. Coincident with this, the morphology of the epithelial cells in the initial segment of androgen-replaced castrates was altered to more closely resemble the morphology of proximal caput epithelial cells in controls. Similar increases in A-raf expression and changes in epithelial cell morphology relative to those in controls were observed in the initial segments of the castrate-side epididymis of hemicastrate mice, in epididymis from a germ cell-deficient strain of mutant mice, and in epididymis from intact mice supplemented with exogenous testosterone. These studies indicated that testicular products, such as spermatozoa, or substances that require germ cells for their production in the testis modulate the androgen-dependent expression of A-raf in the initial segment of the caput epididymis.

Androgen-Binding Protein↗
PubMed2002

Is the middle between both halves?: midpoint location and segment size estimation in neglect.

BACKGROUND: Line bisection errors in neglect are attributed to perceptual size distortions. In order to compare the two segments of the line to determine if they are equal, one might first estimate the location of a midpoint that defines the two line segments to be compared. OBJECTIVES: The authors attempted to determine whether estimating a line's midpoint can be dissociated from comparing the two segments of this line, and if so, what the relative contribution of each of these tasks is to the perceptual bias in neglect. METHODS: The authors studied two patients with hemispatial neglect from right hemisphere lesions by asking them where bisection marks were placed on prebisected lines and whether the two adjacent line segments were equal. RESULTS: There was a stronger bias judging the position of the bisecting marks ("where" determination) than comparing the size of two adjacent line segments. CONCLUSIONS: These results suggest that perceptual size distortion of line segments alone cannot explain the subjects' line bisection bias, but postperceptual deficits in "where" computations may better account for their errors locating the midpoint. "Where" determinations might require more attentional capacity, depend more heavily on viewer-centered allocation of attention, and be mediated by the right hemisphere's "where" dorsal stream. In contrast, comparing the length of two segments might be mediated by the left hemisphere's "what" ventral stream.

Aged↗
PubMed1992

Echocardiographic analysis of dysfunctional and normal myocardial segments before and immediately after coronary artery bypass graft surgery.

Echocardiography has revealed evidence of "subnormal" regional contraction patterns that result from myocardial ischemia and are often accompanied by nonadjacent "hyperkinetic" regions. Whether these regions of hyperkinetic wall motion persist unchanged or revert to normal after coronary artery bypass graft (CABG) surgery has not been studied in humans. Using echocardiography, we evaluated both dysfunctional and normal myocardial regions for changes in segmental wall motion and percent of systolic wall thickening that occurred immediately after CABG surgery in 32 patients. Segmental wall motion analysis before CABG surgery in these patients revealed that 170 (66%) of 256 myocardial segments were subnormal, of which 115 (67%) improved and 102 (60%) returned to normal immediately after CABG surgery. Eleven myocardial segments that were hyperkinetic before CABG surgery returned to normal after CABG surgery. Preoperatively, 162 (63%) of 256 myocardial segments had systolic wall thickening less than 30%, which increased from 11.8% +/- 8.9% to 24.3% +/- 14.3% (mean +/- SD) (P less than 0.01) postoperatively. Conversely, a reverse trend was found when systolic wall thickening was greater than 30% before CABG surgery: thickening decreased from 46.2% +/- 13.8% to 33.4% +/- 14.8% after CABG surgery (P less than 0.01). Thus, we conclude that immediately after CABG surgery, there is a recovery of function in some myocardial segments and a reduction in function in others. Furthermore, we conclude that the semiquantitative assessment of percent of systolic wall thickening is a more reliable (consistent) echocardiographic index of myocardial function compared with the qualitative assessment of segmental wall motion immediately after CABG surgery.

Adult↗
PubMed2003

A distinct patterning mechanism of O and P cell fates in the development of the rostral segments of the leech Helobdella robusta: implications for the evolutionary dissociation of developmental pathway and morphological outcome.

Despite a high degree of homonomy in the segmental organization of the ectoderm, the body plan of the leech is divided into two zones based on the distinct cell lineage patterns that give rise to the O/P portion of the segmental ectoderm. In the midbody and caudal segments, each segmental repeat of ectoderm arises in part from one 'o' blast cell and one 'p' blast cell. These two blast cells are positionally specified to distinct O and P fates, and give rise to differentiated descendant cells called O and P pattern elements, respectively. In the rostral segments, each segmental repeat of O and P pattern elements arises from a single 'op' blast cell. Based on their developmental fates and their responses to the ablation of neighboring cells, the granddaughters of the primary op blast cell are categorized into two O-type cells and two P-type cells. The O-type cells do not require the presence of the rest of the op blast cell clone for their normal development. By contrast, normal development of the P-type cells depends upon interactions with the other OP sublineages. Additional experiments showed that the O-type cells are the source of a repressive signal involved in the normal fate specification of the P-type cells. Our data suggest that the cell interactions involved in fate specification differ substantially in the rostral and midbody segments, even though the set of differentiated descendants produced by the rostral OP pathway and the midbody O and P pathways are very similar.

Animals↗
PubMed2004

Segmental development of reticulospinal and branchiomotor neurons in lamprey: insights into the evolution of the vertebrate hindbrain.

During development, the vertebrate hindbrain is subdivided along its anteroposterior axis into a series of segmental bulges called rhombomeres. These segments in turn generate a repeated pattern of rhombomere-specific neurons, including reticular and branchiomotor neurons. In amphioxus (Cephalochordata), the sister group of the vertebrates, a bona fide segmented hindbrain is lacking, although the embryonic brain vesicle shows molecular anteroposterior regionalization. Therefore, evaluation of the segmental patterning of the central nervous system of agnathan embryos is relevant to our understanding of the origin of the developmental plan of the vertebrate hindbrain. To investigate the neuronal organization of the hindbrain of the Japanese lamprey, Lethenteron japonicum, we retrogradely labeled the reticulospinal and branchial motoneurons. By combining this analysis with a study of the expression patterns of genes identifying specific rhombomeric territories such as LjKrox20, LjPax6, LjEphC and LjHox3, we found that the reticular neurons in the lamprey hindbrain, including isthmic, bulbar and Mauthner cells, develop in conserved rhombomere-specific positions, similar to those in the zebrafish. By contrast, lamprey trigeminal and facial motor nuclei are not in register with rhombomere boundaries, unlike those of gnathostomes. The trigeminal-facial boundary corresponds to the rostral border of LjHox3 expression in the middle of rhombomere 4. Exogenous application of retinoic acid (RA) induced a rostral shift of both the LjHox3 expression domain and branchiomotor nuclei with no obvious repatterning of rhombomeric segmentation and reticular neurons. Therefore, whereas subtype variations of motoneuron identity along the anteroposterior axis may rely on Hox-dependent positional values, as in gnathostomes, such variations in the lamprey are not constrained by hindbrain segmentation. We hypothesize that the registering of hindbrain segmentation and neuronal patterning may have been acquired through successive and independent stepwise patterning changes during evolution.

Animals↗
PubMed1992

Development of the D. melanogaster caudal segments involves suppression of the ventral regions of A8, A9 and A10.

Whereas the segmental organization of the thorax and anterior abdomen is morphologically delineated in both the Drosophila larva and adult, segments in the head and caudal regions lack such well-defined boundaries. Consequently, the organization of these regions has been difficult to decipher. In this study, transformations caused by the bithorax-complex homeotic mutants 48, M3, Ultraabdominal-1 (Uab1) and tumorous-head-3 (tuh-3), as well as the patterns of engrailed gene expression have been analyzed to investigate the segmental organization of the caudal segments. A special emphasis was placed on sense organs appearing in abdominal segments 8, 9 and 10 (A8-A10): We find that: (1) transformations in the caudal segments obey parasegmental borders; (2) the sense organs on A8, A9, and A10 are probably homologous to the pits and hairs in anterior A1-A7; (3) except for the larval anal tuft and the anterior side of A8, all structures in larval segments A8, A9 and A10 are dorsal/lateral in origin; and (4) dorsalization of embryonic A8 and A9 cells leaves space ventrally for A10, as it follows the contracting ventral nervous system during the embryological process of germ band contraction.

Abdomen↗