Central projections of the nervus terminalis in the bichir,Polypterus palmas

Summary Central pathways of the nervus terminalis (n.t.) in the bichir, Polypterus palmas, were studied with the use of tracing techniques. After application of horseradish peroxidase to the unilateral olfactory mucosa labeled n.t. fibers were traced in seven distinct bundles through the subpallium. Projection areas are found in the precommissural ventral nucleus of the area ventralis telencephali ipsilaterally, the anterior commissure and commissural parts of the periventricular preoptic nucleus bilaterally; few n.t.-fibers cross via the anterior commissure to the contralateral side; no fibers were observed to turn rostrally to the contralateral olfactory bulb. Major targets of the n.t. include a restricted ventral part of the periventricular preoptic nucleus at the level of the optic chiasma bilaterally, and the periventricular nuclei located between the thalamic nuclei and the hypothalamus bilaterally. N.t. fibers continue their course through the ipsilateral hypothalamus and are traced as far as the mesencephalic tegmentum ipsilaterally. N.t. terminations are found consistently within the boundaries of periventricular cell nuclei, suggesting axosomatic synaptic contacts. We propose a differentiation of the n.t. ganglion cells into a distal (mucosal) and proximal (bulbar) type regarding the peripheral cell processes. Our findings are compared with those of other reports on the n.t. system.     

Central connections of the olfactory bulb in the bichir,Polypterus palmas,reexamined

Summary Central connections of the olfactory bulb of Polypterus palmas were studied with the use of horseradish peroxidase and cobalt-tracing techniques. The olfactory bulb projects to subpallial and palliai areas in the ipsilateral telencephalon; a projection to the contralateral subpallium is noted via the habenular commissure. A further target of secondary olfactory fibers is a caudal olfactory projection area in the ipsilateral hypothalamus. No labeling was seen in the anterior commissure and in the contralateral olfactory bulb. The medial and the lateral pallium receive secondary olfactory fibers in distinct areas. Neurons projecting to the bulb are found in the ipsilateral subpallium, mainly in one dorsal longitudinal nucleus. The main connection with the tel- and diencephalon is mediated via the medial olfactory tract. This tract also contains fibers to the contralateral telencephalon, and to the hypothalamus. The smaller lateral olfactory tract mediates fibers to the lateral pallium. The organization of pathways of secondary olfactory fibers in the telencephalon is described. The present findings are compared to those obtained in species possessing an inverted forebrain.This investigation was supported by grants from the Deutsche Forschungsgemeinschaft to DLM     

Hox clusters of the bichir (Actinopterygii, Polypterus senegalus) highlight unique patterns of sequence evolution in gnathostome phylogeny

Teleost fishes have extra Hox gene clusters owing to shared or lineage-specific genome duplication events in rayfinned fish (actinopterygian) phylogeny. Hence, extrapolating between genome function of teleosts and human or even between different fish species is difficult. We have sequenced and analyzed Hox gene clusters of the Senegal bichir (Polypterus senegalus), an extant representative of the most basal actinopterygian lineage. Bichir possesses four Hox gene clusters (A, B, C, D); phylogenetic analysis supports their orthology to the four Hox gene clusters of the gnathostome ancestor. We have generated a comprehensive database of conserved Hox noncoding sequences that include cartilaginous, lobe-finned, and ray-finned fishes (bichir and teleosts). Our analysis identified putative and known Hox cis-regulatory sequences with differing depths of conservation in Gnathostoma. We found that although bichir possesses four Hox gene clusters, its pattern of conservation of noncoding sequences is mosaic between outgroups, such as human, coelacanth, and shark, with four Hox gene clusters and teleosts, such as zebrafish and pufferfish, with seven or eight Hox gene clusters. Notably, bichir Hox gene clusters have been invaded by DNA transposons and this trend is further exemplified in teleosts, suggesting an as yet unrecognized mechanism of genome evolution that may explain Hox cluster plasticity in actinopterygians. Taken together, our results suggest that actinopterygian Hox gene clusters experienced a reduction in selective constraints that surprisingly predates the teleost-specific genome duplication.     

Distribution and Structure of the Adrenocortical Homolog in Polypterus palmas Ayres

The identity, distribution and structure of the adrenocortical homolog (AH) was made in Polypterus palmas Ayres using routine light and electron microscopy and histochemistry for the enzyme δ⁵-3β-hydroxysteroid dehydrogenase (3β-HSD). The AH is confined to yellow corpuscles which are positioned near the posterior cardinal and renal veins in the anterior two-thirds of each kidney. The 46–57 spherial to cigar-shaped corpuscles are placed end to end and are equally distributed in the kidneys. The tortuous cords of epithelial cells of each corpuscle are surrounded by sinusoids and are completely delimited from the haemopoietic and renal tissue of the kidneys. The steroidogenic nature of the cells is demonstrated by their 3β-HSD activity and their ultrastructure, namely lipid droplets, tubular smooth endoplasmic reticulum and mitochondria with tubulovesicular cristae. Giant mitochondria and gap junctions are notable features of AH cells in this fish. The yellow corpuscles of the kidneys in P. palmas represent the AH and this tissue has a distribution which is in accordance with the taxonomic position of Polypteriformes.     

Polymorphous granular cells in the lung of the primitive fish,the bichir Polypterus senegalus

This study describes the distribution and the coexpression of specific neurochemical markers in both neuroendocrine‐like cells (NEC‐like) and polymorphous granular cells (PGCs) that populate the mucociliated epithelium of the lung in the air‐breathing fish Polypterus senegalus, using confocal immunohistochemistry. Using confocal immunohistochemistry, we determined the coexpression of specific neurochemical markers. Colocalization studies showed that 5HT is coexpressed with calbindin and nNOS and choline acetyltransferase (ChAT) is coexpressed with nNOS in the PGCs. This study also shows for the first time the simultaneous occurrence of piscidin 1 and 5HT in the PGCs. The function of these cells being equivalent to ones found in fish gill subepithelial parenchyma is still not known. Due to the importance of piscidin 1 in local immune defence, more research is to be useful to understand a possible interaction of PGCs with immune response in the bichir lung. In fact, the capacity of PGCs to produce NO and other neuroactive substances found in immune cells of fish may represent a primitive form of immunoregulation of innate immunity and specifically antimicrobial function as NO induction and respiratory burst activity are correlated with immune response.     

Development of cranial muscles in the actinopterygian fish Senegal bichir,Polypterus senegalus Cuvier, 1829

Polypterus senegalus Cuvier, 1829 is one of the most basal living actinopterygian fish and a member of the Actinopterygii. We analyzed the spatial and temporal pattern of cranial muscle development of P. senegalus using whole‐mount immunostaining and serial sectioning. We described the detailed structure of the external gill muscles which divided into dorsal and ventral parts after yolk exhaustion. The pattern of the division is similar to that of urodeles. We suggest that, the external gill muscles of P. senegalus are involved in spreading and folding of the external gill stem and the branches. The fibers of the external gill muscles appear postero‐lateral to the auditory capsule. In addition, the facial nerve passes through the external gills. Therefore, the external gill muscles are probably derived from the m. constrictor hyoideus dorsalis. In contrast to previous studies, we described the mm. interhyoideus and hyohyoideus fibers as independent components in the yolk‐sac larvae. The m. hyohyoideus fibers appear lateral to the edge of the ventral portion of the external gill muscles, which are probably derived from the m. constrictor hyoideus dorsalis. These findings suggest that the m. hyohyoidues is derived from the m. constrictor hyoideus dorsalis in P. senegalus . In other actinopterygians, the m. hyohyoideus is derived from the m. constrictor hyoideus ventralis; therefore, the homology of the m. hyohyoidues of P. senegalus and other actinopterygians remains unclear. J. Morphol. 278:450–463, 2017. © 2017 Wiley Periodicals, Inc.     

Prolactin-producing Cells in Clupea harengus membras,Polypterus palmas and Calamoichthys calabaricus Studied by Immuno-histochemical Methods

The prolactin-producing cells in Clupea harengus membras, Polypterus palmas and Calamoichthys calabaricus have been localized by fluores-ceinlabelled antibodies to ovine prolactin. Pituitary sections were cut in a cryostat and both direct and indirect protein tracing methods have been used. As an additional method the paraffin embedding technique was carried out with Polypterus palmas. The prolactin-producing cells in Clupea harengus membras were localized to the follicle epithelium in the rostral pars distalis. In Polypterus palmas and Calamoichthys calabaricus the prolactin producing cells were scattered all over the pars distalis. A possible relationship between the erythrosinophilic prolactin cells and the epithelium cells in the buccohypophyseal canal is discussed.     

Aerial and aquatic visual acuity of the grey bichir Polypterus senegalus,as estimated by optokinetic response

The present study assessed the aerial and aquatic visual abilities of juvenile grey bichir Polypterus senegalus, fish capable of terrestrial locomotion, by measuring the optokinetic response to stimuli of varying speed and spatial frequency. In water, fish tracked slow-moving (2° s⁻¹) stimuli moderately well and fast-moving stimuli very poorly. Spatial acuity was very low compared with many other species, with maximum response observed at 0.05–0.075 stimulus cycles per degree of visual arc; however, it should be noted that adult fish, with their larger eyes, are likely to have somewhat improved spatial acuity. Low spatial acuity and limited stimulus tracking ability might be expected in a nocturnal ambush predator such as P. senegalus, where gaze stabilization may be less crucial and other sensory inputs may have greater importance in perception of the environment. In air, spatial and temporal acuity were both poorer by every measure, but some visual ability persisted. As the eye shows no anatomical specialization for aerial vision, poor vision was expected; however, the large decrease in saccade velocity observed in air trials was unexpected. Stimulus parameters typically have little effect on the characteristics of the saccade, so this finding may suggest that the function of the reflex system itself could be compromised in the aerial vision of some fishes capable of terrestrial locomotion.     

The anatomical components of the cardiac outflow tract of the gray bichir,Polypterus senegalus: their evolutionary significance

It has been reported that in chondrichthyans the cardiac outflow tract is composed of the myocardial conus arteriosus, while in most teleosteans it consists of the nonmyocardial bulbus arteriosus. Classical studies already indicated that a conus and a bulbus coexist in several ancient actinopterygian and teleost groups. Recent work has shown that a cardiac outflow tract consisting of a conus and a bulbus is common to both cartilaginous and bony fishes. Nonetheless and despite their position at the base of the actinopterygian phylogenetic lineage, the anatomical arrangement of the cardiac outflow tract of the Polypteriformes remained uncertain. The present study of hearts from gray bichirs was intended to fill this gap. The cardiac outflow tract of the bichir consists of two main components, namely a very long conus arteriosus, furnished with valves, and a short, intrapericardial, arterial-like bulbus arteriosus, which differs from the ventral aorta because it is covered by epicardium, shows a slightly different spatial arrangement of the histological elements and is crossed by coronary arteries. Histomorphologically, the outflow tract consists of three longitudinal regions, distal, middle and proximal, an arrangement which has been suggested to be common to all vertebrates. The distal region corresponds to the bulbus, while the conus comprises the middle and proximal regions. The present findings reinforce the notion that the bulbus arteriosus of fish has played an essential role in vertebrate heart evolution as it is the precursor of the intrapericardial trunks of the aorta and pulmonary artery of birds and mammals.     

Molecular evolution of the neurohypophysial hormones: The active peptides of a primitive bony fish Polypterus bichir

Neurohypophysial hormones have been so far identified in Neopterygii and Crossopterygii but not in species of the bird sub-class of bony fishes, the Palaeopterygii. Isolation and chemical characterization of the active principles of a primitive bony fish, Polypterus bichir, have been performed. Isotocin (Ser(4)-Ile(8)-oxytocin) and arginine vasotocin (Arg(8)-oxytocin) have been identified. Because the same peptides were found in the recent Neopterygii, it can be deduced that neurohypophysial hormones have displayed a peculiar stability in the course of the evolution of bony fishes. However isotocin and vasotocin are replaced by oxytocin and vasopressins in mammals and therefore might be regarded as "old" molecules.     

家蚕Hox基因研究进展

Hox基因（homeobox genes）在昆虫躯体模式（body plan）的发育调控机制中扮演着重要角色,其表达具有严格的组织特异性和胚胎发育的程序性。家蚕Bombyx mori作为鳞翅目昆虫的代表,其Hox基因也陆续得到鉴定。在家蚕中存在一个拟复等位基因群--E群基因,其突变表型均与过剩斑纹和过剩附肢有关,这可能与Hox基因有着密切联系。家蚕全基因组测序完成后,发现其Hox基因簇中存在12个特有的homeobox基因（Bmshx1~Bmshx12）, 说明家蚕Hox基因可能具有独特的生物学意义。我们还利用家蚕基因芯片数据分析了Bmlab与Bmpb基因的组织表达特征。通过对家蚕Hox基因的研究,探索家蚕躯体模式建立机制,可望为解析其他鳞翅目昆虫的躯体模式的建立机制提供理论依据。本文就家蚕Hox基因的表达、功能及其与E群突变的关系等方面进行了综述。     

Isolation of Hox and Parahox genes in the hemichordate Ptychodera flava and the evolution of deuterostome Hox genes

Because of their importance for proper development of the bilaterian embryo, Hox genes have taken center stage for investigations into the evolution of bilaterian metazoans. Taxonomic surveys of major protostome taxa have shown that Hox genes are also excellent phylogenetic markers, as specific Hox genes are restricted to one of the two great protostome clades, the Lophotrochozoa or the Ecdysozoa, and thus support the phylogenetic relationships as originally deduced by 18S rDNA studies. Deuterostomes are the third major group of bilaterians and consist of three major phyla, the echinoderms, the hemichordates, and the chordates. Most morphological studies have supported Hemichordata+Chordata, whereas molecular studies support Echinodermata+Hemichordata, a clade known as Ambulacraria. To test these competing hypotheses, complete or near complete cDNAs of eight Hox genes and four Parahox genes were isolated from the enteropneust hemichordate Ptychodera flava. Only one copy of each Hox gene was isolated suggesting that the Hox genes of P. flava are arranged in a single cluster. Of particular importance is the isolation of three posterior or Abd-B Hox genes; these genes are only shared with echinoderms, and thus support the monophyly of Ambulacraria.     

Hox genes in the echiuroid Urechis unicinctus

An echiuroid species, Urechis unicinctus, was surveyed for Hox genes using polymerase chain reaction with homeobox-specific degenerate primers. We identified nine distinct homeodomain-containing gene fragments. These nine fragments were classified by comparative analysis. This analysis revealed that this echiuroid possessed at least three Hox genes from the anterior group, five from the central group, and one from the posterior group.     

Additional duplicated Hox genes in the earthworm: Perionyx excavatus Hox genes consist of eleven paralog groups

Annelida is a lophotrochozoan phylum whose members have a high degree of diversity in body plan morphology, reproductive strategies and ecological niches among others.Of the two traditional classes pertaining to the phylum Annelida (Polychaete and Clitellata), the structure and function of the Hox genes has not been clearly defined within the Oligochaeta class. Using a PCR-based survey, we were able to identify five new Hox genes from the earthworm Perionyx excavatus: a Hox3 gene (Pex-Hox3b), two Dfd genes (Pex-Lox6 and Pex-Lox18), and two posterior genes (Pex-post1 and -post2a). Our result suggests that the eleven earthworm Hox genes contain at least four paralog groups (PG) that have duplicated. We found the clitellates-diagnostic signature residues and annelid signature motif. Also, we show by semi-quantitative RT-PCR that duplicated Hox gene orthologs are differentially expressed in six different anterior-posterior body regions. These results provide essential data for comparative evolution of the Hox cluster within the Annelida.     

Fast sequence evolution of Hox and Hox -derived genes in the genus Drosophila

Background  

It is expected that genes that are expressed early in development and have a complex expression pattern are under strong purifying selection and thus evolve slowly. Hox genes fulfill these criteria and thus, should have a low evolutionary rate. However, some observations point to a completely different scenario. Hox genes are usually highly conserved inside the homeobox, but very variable outside it.     

Sea urchin Hox genes: insights into the ancestral Hox cluster

We describe the Hox cluster in the radially symmetric sea urchin and compare our findings to what is known from clusters in bilaterally symmetric animals. Several Hox genes from the direct-developing sea urchin Heliocidaris erythrogramma are described. CHEF gel analysis shows that the Hox genes are clustered on a < or = 300 kilobase (kb) fragment of DNA, and only a single cluster is present, as in lower chordates and other nonvertebrate metazoans. Phylogenetic analyses of sea urchin, amphioxus, Drosophila, and selected vertebrate Hox genes confirm that the H. erythrogramma genes, and others previously cloned from other sea urchins, belong to anterior, central, and posterior groups. Despite their radial body plan and lack of cephalization, echinoderms retain at least one of the anterior group Hox genes, an orthologue of Hox3. The structure of the echinoderm Hox cluster suggests that the ancestral deuterostome had a Hox cluster more similar to the current chordate cluster than was expected Sea urchins have at least three Abd-B type genes, suggesting that Abd-B expansion began before the radiation of deuterostomes.      

Two more Posterior Hox genes and Hox cluster dispersal in echinoderms

Background

Hox genes are key elements in patterning animal development. They are renowned for their, often, clustered organisation in the genome, with supposed mechanistic links between the organisation of the genes and their expression. The widespread distribution and comparable functions of Hox genes across the animals has led to them being a major study system for comparing the molecular bases for construction and divergence of animal morphologies. Echinoderms (including sea urchins, sea stars, sea cucumbers, feather stars and brittle stars) possess one of the most unusual body plans in the animal kingdom with pronounced pentameral symmetry in the adults. Consequently, much interest has focused on their development, evolution and the role of the Hox genes in these processes. In this context, the organisation of echinoderm Hox gene clusters is distinctive. Within the classificatory system of Duboule, echinoderms constitute one of the clearest examples of Disorganized (D) clusters (i.e. intact clusters but with a gene order or orientation rearranged relative to the ancestral state).

Results

Here we describe two Hox genes (Hox11/13d and e) that have been overlooked in most previous work and have not been considered in reconstructions of echinoderm Hox complements and cluster organisation. The two genes are related to Posterior Hox genes and are present in all classes of echinoderm. Importantly, they do not reside in the Hox cluster of any species for which genomic linkage data is available.

Conclusion

Incorporating the two neglected Posterior Hox genes into assessments of echinoderm Hox gene complements and organisation shows that these animals in fact have Split (S) Hox clusters rather than simply Disorganized (D) clusters within the Duboule classification scheme. This then has implications for how these genes are likely regulated, with them no longer covered by any potential long-range Hox cluster-wide, or multigenic sub-cluster, regulatory mechanisms.