bluuebunny/crossref_metadata_2025 huggingface dataset:
Quelques précisions sur la cinématique de la ligne primitive chez le Poulet
Authors: Vakaet par L.
Published: April 2021

Isolated anterior and posterior fragments of very young blastoderms at the primitive-streak stage, transected in front of the streak, have been cultured for 24 hours. The posterior fragments were marked by carbon particles. Our results stress the importance, during bird gastrulation, of the transition region between the area opaca and the area pellucida, especially at the site of formation of the primitive streak. Considering this region as an extension centre, forward and backward, of the primitive streak enables us to understand the radically opposed opinions of Pasteels and Spratt by furnishing illustrations of the influence of in vitro culture circumstances. We have seen, indeed, that under Spratt’s marking conditions on whole blastoderms, absence of epiboly practically inhibits all forward movement in the blastoderm. On the contrary, however, this last tendency is seen very clearly in our experiments where, by releasing it from the hindrance formed by the anterior part of the blastoderm in vitro, we enable the streak to stretch forward. Our results, therefore, confirm the findings of Pasteels with regard to his controversy with Spratt and show that the anterior end of the very young primitive streak already contains the material of the future Hensen’s node. Using Spratt’s technique we arrive at a confirmation of Pasteels’s opinions based on in ovo staining.

It seems worth while to note that our experiments and those of our predecessors tend to localize the ‘organization centre’ in the region where earlier the formation of the endophyll started and as a consequence its contact with the ectophyll is the most precocious and the most intimate. This is stated without any implication as to the exact mode of formation of the inner germ layer. On the other hand, this point in the midst of the primitive streak is the point of convergence of Hensen’s node and the posterior node, and the place where the tail-bud will arise, as we have previously shown (Vakaet, 1960).
The Effect of Benzimidazole on the Differentiation of Ectodermal Explants from the Gastrulae of Xenopus laevis
Authors: Billett F. , Brahma S. K.
Published: April 2021

The survival of ectodermal explants taken from early to late gastrulae of Xenopus laevis does not appear to be affected by culturing them, for up to 3 days, in solutions containing 50–100 μg./ml. of benzimidazole. This compound does not prevent neural differentiation. Cell damage only becomes apparent after about 48 hours when it is confined to the differentiating neural tissues and the surrounding cells. The histological appearance of the ectoderm cells and the fact that they develop functional cilia suggest that they are not affected by the treatment. The results suggest that tissue in the process of differentiation is highly susceptible to benzimidazole. This susceptibility may be a consequence of the high rate of turnover of RNA in differentiating tissue.
Internal Factors Influencing Normal and Compensatory Growth of the Axolotl Pronephros
Authors: Fox H.
Published: April 2021

The purpose of the experiments described in this paper was to distinguish between mechanical (hydrostatic) and chemical influences upon normal or compensatory growth of the pronephros in the larval axolotl (Harrison stages 24–26). Measurements were made on pronephroi and pronephric grafts from the following groups: (a) control specimens with undisturbed pronephroi; (b) specimens with paired undisturbed pronephroi and grafts; (c) specimens unilaterally pronephrectomized; (d) specimens unilaterally pronephrectomized and containing grafts. Analysis of the measurements shows that hydrostatic pressure within pronephric tubules is the main factor responsible for maintaining size and shape in both normal and compensatory growth.
Exogenous glycosaminoglycans (GAG) are able to modulate avian skin differentiation (epithelial keratinization and feather formation)
Authors: Becchetti E. , Stabellini G. , Caruso A. , Carinci P.
Published: April 2021

Several reports have suggested that mesenchymal glycosaminoglycans (GAG) may be involved in the regulatory role of epithelial differentiation. Some researchers have pointed out that exogenous GAG affects extracellular GAG accumulation.

We have therefore examined the effect of added GAG on two typical processes of avian skin differentiation: keratinization and feather formation. Glycosaminoglycans, either obtained from fibroblasts cultures (conditioned media) or purified commercially available GAG were administered to 5/6-day chick embryo back skin explants. Control cultures were supported with 199 synthetic medium, chick embryo extract or calf serum. Explants have been examined by histological and histochemical procedures.

Skin explants maintained in vitro for 7 days exhibited an epithelial differentiation and a dermal histochemical reactivity which were related to the composition of the culture medium. In conditioned media from dermal fibroblasts, but not from heart or lung fibroblasts, explants always exhibited keratinization. In purified-GAG-containing media, keratinization was observed with condroitinsulphates and not with hyaluronic acid. Keratinization was always related to prevalent accumulation of hyaluronic acid in the underlying mesenchyme whereas feather formation was in relation to deposits of condroitinsulphates in dermis pulp.

The above findings demonstrate that exogenous GAG is able to modulate avian skin differentiation and that this regulation is linked to an influence on the mesenchymal GAG pattern.
Level of histone H4 mRNA in Xenopus laevis embryonic cells cultured in the absence of cell adhesion
Authors: Atsuchi Yasuo , Tashiro Kosuke , Yamana K. , Shiokawa Koichiro
Published: April 2021

The amount of histone H4 mRNA per embryo was followed during early development of Xenopus laevis by Northern blot analyses using a cloned histone H4 cDNA as the probe. The H4 mRNA content was nearly constant until the blastula stage, increased greatly at the gastrula stage and then decreased at the neurula stage. Experiments with actinomycin D suggested that most H4 mRNA molecules detected at the late gastrula and neurula stages were maintained depending on new transcription of H4 genes during these stages. To see if the H4 mRNA level is affected by cell adhesion, we prepared dissociated cells and measured H4 mRNA content under conditions that inhibit cellular reaggregation. It was found that the amount of H4 mRNA per embryo in dissociated and reaggregation-inhibited cells was nearly equal to that of the control embryo at the neurula stage. Therefore, we conclude that the synthetic activity of histone H4 mRNA is not dependent on the cellular adhesion during development.
Analysis of cranial neural crest cell migration and early fates in postimplantation rat chimaeras
Authors: Tan S. S. , Morriss-Kay G. M.
Published: April 2021

Rat embryos were grown in vitro during the period of cranial neural crest cell migration. In order to study the pathways and positional fates of cells from different regions of the neural crest, labelled premigratory crest cells from donor embryos were microinjected orthotopically into host embryos of the same developmental stage except for area 1 (forebrain) grafts which were, for technical reasons, injected into area 2. After various periods of time in whole embryo culture, the embryos were examined by immunohistochemical staining in order to determine the new positions of the labelled cells, and a map of their migration pathways was constructed. The observed patterns of migration were consistent with predictions from morphological studies in mammals and with extrapolations from transplantation studies in birds. However, crest cell migratory behaviour in rat and chick embryos was not identical; possible reasons for this are discussed.
The effects ofStreptomyceshyaluronidase on tissue organization and cell cycle time in rat embryos
Authors: Morriss-Kay Gillian M. , Tuckett Fiona , Solursh Michael
Published: April 2021

Day 9 rat embryos (late presomite stage with cranial neural plate or very early neural folds) were cultured for various periods of time from 6–48 h in medium containing 20TRUml-1Streptomyces hyaluronidase. Exposure to the enzyme resulted in considerable reduction of mesenchymal extracellular matrix. Access of the enzyme to the embryo was confirmed by alcian blue staining which indicated considerable reduction of extracellular and cell surface hyaluronate. Cranial neurulation was retarded, but not inhibited, and migration of both neural crest and primary mesenchyme cells occurred. In general, morphology was normal at 48 h.

The major effect was on growth: embryos were smaller, with slightly reduced neuroepithelial cell number and greatly reduced mesenchymal cell number. Neuroepithelial cell cycle time was slightly prolonged, and that of the mesenchyme more than doubled. This differential effect on the growth rates of these two tissues reflects the normal distribution of hyaluronate, which is particularly abundant in the mesenchymal extracellular matrix.
The effect of retinoic acid pretreatment on the ability of murine embryonal carcinoma and inner cell mass cells to participate in chimaera development
Authors: Waters B. K. , Rossant J.
Published: April 2021

Certain embryonal carcinoma (EC) cell lines can colonize the embryo following blastocyst injection or embryo aggregation, giving rise to EC-embryo chimaeras. However, such chimaeras often develop abnormally. For example, diploid P19 cells colonize the embryo readily but resulting chimaeras are usually abnormal, with persistence of tumour cells. Retinoic acid (RA) induces differentiation of EC cells to a variety of cell types in vitro but, in this study, it was shown that pretreatment of P19 cells with RA did not result in more normal development of P19-embryo chimaeras. The only significant effect of RA was to reduce the ability of P19 cells to participate in embryonic development at all after blastocyst injection. RA did not have a direct toxic or teratogenic effect on preimplantation mouse embryos and did not affect the ability of pluripotent embryo cells to colonize chimaeras. Therefore, RA may not be the normal inducer of differentiation in early embryogenesis.
Embryonic induction - molecular prospects
Authors: Gurdon J. B.
Published: April 2021

Embryonic induction is an interaction between one (inducing) tissue and another (responding) tissue, as a result of which the responding tissue undergoes a change in its direction of differentiation. This is probably the single most important mechanism in vertebrate development leading to differences between cells and to the organization of cells into tissues and organs.
Expression ofXenopusN-CAM RNA in ectoderm is an early response to neural induction
Authors: Kintner C. R. , Melton D. A.
Published: April 2021

We have isolated Xenopus laevis N-CAM cDNA clones and used these to study the expression of N-CAM RNA during neural induction. The results show that the first marked increase in N-CAM RNA levels occurs during gastrulation when mesoderm comes in contact with ectoderm and induces neural development. In situ hybridization results show that the early expression of N-CAM RNA is localized to the neural plate and its later expression is confined to the neural tube. Induction experiments with explanted germ layers show that N-CAM RNA is not expressed in ectoderm unless there is contact with inducing tissue. Together these results suggest an approach to studying how ectoderm is committed to form neural rather than epidermal tissue. Specifically, the data suggest that neural commitment is marked and perhaps mediated by the transcriptional activation of genes, like N-CAM, in the neural ectoderm.
Epithelial–mesenchymal interactions in the development of chick facial primordia and the target of retinoid action
Authors: Wedden S. E.
Published: April 2021

The development of the chick face involves outgrowth of buds of tissue, accompanied by the differentiation of cartilage and bone in spatially defined patterns. To investigate the role of epithelial-mesenchymal interactions in facial morphogenesis, small fragments of facial tissue have been grafted to host chick wing buds to continue their development in isolation. Fragments of the frontonasal mass give rise to typical upper-beaklike structures: a long central rod of cartilage, the prenasal cartilage and an egg tooth. Meckel’s cartilage, characteristic of the lower beak, develops from fragments of the mandible. Removal of the ectoderm prior to grafting leads to truncated development. In fragments of frontonasal mass mesenchyme only a small spur of cartilage differentiates and there is no outgrowth. The mandible is less affected; a rod of cartilage still forms but the amount of outgrowth is reduced.

Retinoid treatment of chick embryos specifically affects the development of the upper beak and outgrowth and cartilage differentiation in the frontonasal mass are inhibited. The mandibles, however, are unaffected and develop normally. In order to investigate whether the epithelium or the mesenchyme of the frontonasal mass is the target of retinoid action, recombinations of retinoid-treated and untreated facial tissue have been grafted to host wing buds. Recombinations of retinoid-treated frontonasal mass ectoderm with untreated mesenchyme develop normally whereas recombinations of untreated ectoderm with retinoid-treated mesenchyme lead to truncations. The amount of outgrowth in fragments of mandibular tissue is slightly reduced when either the ectoderm or the mesenchyme has been treated with retinoids. These recombination experiments demonstrate that the mesenchyme of the frontonasal mass is the target of retinoid action. This suggests that retinoids interfere with the reciprocal epithelial-mesenchymal interactions necessary for outgrowth and normal upper beak development.
Fibre organization and reorganization in the retinotectal projection of Xenopus
Authors: Taylor J. S. H.
Published: April 2021

This study concerns the retinotopic organization of the ganglion cell fibres in the visual system of the frog Xenopus laevis. HRP was used to trace the pathways taken by fibres from discrete retinal positions as they pass from the retina, along the optic nerve and into the chiasma. The ganglion cell fibres in the retina are arranged in fascicles which correspond with their circumferential positions of origin. Within the fascicles the fibres show little age-related layering and do not have a strict radial organization. As the fascicles of fibres pass into the optic nerve head there is some exchange of position resulting in some loss of the retinal circumferential organization. The poor radial organization of the fibres in the retinal fascicles persists as the fibres pass through the intraocular part of the nerve. At a position just behind the eye there is a major fibre reorganization in which fibres arising from cells of increasingly peripheral retinal locations are found to have passed into increasingly peripheral positions in the nerve. Thus, fibres from peripheralmost retina are located at the nerve perimeter, whilst fibres from central retina are located in the nerve core. It is at this point that the radial, chronotopic, ordering of the ganglion cell axons, found throughout the rest of the optic pathway, is established. This annular organization persists along the length of the nerve until a position just before the nerve enters the brain. Here, fibres from each annulus move to form layers as they pass into the optic chiasma. This change in the radial organization appears to be related to the pathway followed by all newly growing fibres, in the most superficial part of the optic tract, adjacent to the pia.

Just behind the eye, where fibres become radially ordered, the circumferential organization of the projection is largely lost. Fibres from every circumferential retinal position, which are of similar radial position, are distributed within the same annulus of the nerve. At the nerve-chiasma junction where each annulus forms a single layer as it enters the optic tract, there is a further mixing of fibres from all circumferential positions. However, as the fibres pass through the chiasma some active pathway selection occurs, generating the circumferential organization of the fibres in the optic tract. Additional observations of the organization of fibres in the optic nerve of Rana pipiens confirm previous reports of a dual representation of fibres within the nerve. The difference in the organization of fibres in the optic nerve of Xenopus and Rana pipiens is discussed.
The effect of the nucleocytoplasmic ratio on protein synthesis and expression of a stage-specific antigen in early cleaving mouse embryos
Authors: Petzoldt Ulrich , Muggleton-Harris Audrey
Published: April 2021

The nucleocytoplasmic ratio of fertilized mouse eggs was manipulated by removing or injecting cytoplasm by micropipette, and bisection of denuded eggs to obtain both pronuclei in one half of the eggs cytoplasm. The experimental eggs were capable of cleavage to the morula stage and, in some instances, developed to the blastocyst stage similar to unmanipulated eggs. The removal of large quantities of cyto-plasm by micropipette and injecting them into a recipient egg did not provide sufficient numbers of viable eggs, whereas transfer of smaller quantities (about a quarter of the cytoplasm) was less deleterious, at least for recipient eggs. However, the alteration of the nucleocytoplasmic ratio by this method was not of the correct magnitude for the purpose of this experiment. Therefore, bisection was the preferred method whereby the nucleocytoplasmic ratio was doubled. This resulted in both pronuclei residing in one half of the egg’s cytoplasm. Half eggs with one pronucleus (haploid) but retaining a nucleocytoplasmic ratio similar to unmanipulated control eggs served as additional controls for the bisection experiments. Protein synthesis was analysed by two-dimensional gel electrophoresis, showing that the 2-cell- and 4-cell-stage bisected embryos with double and normal nucleocytoplasmic ratio expressed equivalent protein synthesis patterns as control embryos of the same stage. Likewise, the stage-specific surface antigen SSEA-1 did not appear before the 6- to 8-cell stage. Also in cytoplasm transfer experiments, there was no indication that altering the nucleocytoplasmic ratio in either direction changed the timing of stage-specific gene expression. These results support the idea that stage-specific gene activity during early mouse cleavage might proceed in parallel to DNA replication cycles and is independent of the nucleocytoplasmic ratio.
Intercalation and the cellular origin of supernumerary limbs inXenopus
Authors: Muneoka Ken , Murad Eden H. B.
Published: April 2021

The hypothesis that a specialized polarizing zone controls the pattern of the anterior-posterior axis during limb development in Xenopus has been tested by analysing the cellular contribution to supernumerary limbs. Supernumerary limbs were generated by grafting hindlimb buds contralaterally between X. borealis and X. laevis to appose anterior and posterior limb tissues. Cells derived from these two species of Xenopus are readily identified by staining with quinacrine. The analysis of cellular contribution showed that supernumerary limbs consist of approximately half anterior-derived (57 %) and half posterior-derived (43 %) cells. These data are not consistent with the polarizing zone theory but are consistent with the hypothesis that both supernumerary limbs and normally developing limbs arise from intercalary interactions between limb bud cells with different positional values.
Pathfinding by dorsal column axons in the spinal cord of the frog tadpole
Authors: Holder Nigel , Clarke J. D. W. , Tonge David
Published: April 2021

Sensor fibres from dorsal root ganglia (DRG) enter the spinal cord and run within a clearly defined ipsilateral pathway, the dorsal column, which lies in the dorsal funiculus. We have examined the characteristics of this pathway as a defined substrate for dorsal column axons in Rana temporaria tadpoles by rotating the thoracic spinal cord through 180° from dorsal to ventral. Using HRP as a neuronal tracer we establish that many dorsal column axons from the hindlimb locate the ipsilateral or contralateral dorsal column pathway in the rotated cord. Other axons locate and grow caudally down the contralateral dorsal column returning to the lumbar region. Axons of the dorsal column never take an inappropriate pathway except at the transection sites where they negotiate abnormal routes to reach the contralateral or ipsilateral dorsal columns in normally positioned or rotated cord. The results demonstrate that the dorsal columns act as highly specific pathways for axons from DRG neurones but the axons’ interactions with the pathway do not control the craniocaudal or left-right options for growth.
The parasitophorous vacuole membrane surrounding Plasmodium and Toxoplasma: An unusual compartment in infected cells
Authors: Lingelbach Klaus , Joiner Keith A.
Published: April 2021

Plasmodium and Toxoplasma belong to a group of unicellular parasites which actively penetrate their respective mammalian host cells. During the process of invasion, they initiate the formation of a membrane, the so-called parasitophorous vacuolar membrane, which surrounds the intracellular parasite and which differs substantially from endosomal membranes or the membrane of phagolysosomes. The biogenesis and the maintenance of the vacuolar membrane are closely related to the peculiar cellular organization of these parasites and are unique phenomena in cell biology. Here we compare biological similarities and differences between the two parasites, with respect to: (i) the formation, (ii) the maintenance, and (iii) the biological role of the vacuolar membrane. We conclude that most differences between the organisms primarily reflect the different biosynthetic capacities of the host cells they invade.
The expression of an Ets1 transcription factor lacking its activation domain decreases uPA proteolytic activity and cell motility, and impairs normal tubulogenesis and cancerous scattering in mammary epithelial cells
Authors: Delannoy-Courdent A. , Mattot V. , Fafeur V. , Fauquette W. , Pollet I. , Calmels T. , Vercamer C. , Boilly B. , Vandenbunder B. , Desbiens X.
Published: April 2021

Cell migration and invasion play a crucial role during normal and pathological development. The expression of several members of the Ets family of transcription factors has been shown to correlate with the occurrence of these processes. In the present study, we investigated the effect of the expression of Ets1-DB, the DNA-binding domain of c-Ets1, on the functional properties of NMuMG and MMT epithelial cell lines, from normal and cancerous mouse mammary tissues, respectively. We found that stable expression of this Ets1-DB mutant inhibited, in both cell types, the gene expression and activity of urokinase typeplasminogen activator (uPA), a potential target of c-Ets1. uPA is a key serine proteinase in the proteolytic cascade leading to the degradation of the extracellular matrix. In two-dimensional cultures, expression of the Ets1-DB mutant resulted in a decrease in cell migration and invasion in both cell lines. In three-dimensional collagen gels, NMuMG cells underwent tubular morphogenesis, while MMT cells developed as scattered structures. The Ets1-DB mutant impaired the capacity of NMuMG cells to form tubules and reduced the ability of MMT cells to invade these gels. Similar inhibition of cell migration, invasion and morphogenesis were observed in non-infected NMuMG and MMT cell lines treated with aprotinin, a serine proteinase inhibitor, suggesting that the inhibition of the plasmin cascade mediates in part the biological effects induced by the Ets1-DB mutant. These results demonstrate that Ets family members are involved in the control of uPA activity, cell motility and invasion during normal tubular morphogenesis and cancerous scattering in mammary epithelial cells.
Spinalin, a new glycine- and histidine-rich protein in spines of Hydra nematocysts
Authors: Koch Alexander W. , Holstein Thomas W. , Mala Carola , Kurz Eva , Engel Jürgen , David Charles N.
Published: April 2021

Here we present the cloning, expression and immunocytochemical localization of a novel 24 kDa protein, designated spinalin, which is present in the spines and operculum of Hydra nematocysts. Spinalin cDNA clones were identified by in situ hybridization to differentiating nematocytes. Sequencing of a full-length clone revealed the presence of an N-terminal signal peptide, suggesting that the mature protein is sorted via the endoplasmic reticulum to the post-Golgi vacuole in which the nematocyst is formed. The N-terminal region of spinalin (154 residues) is very rich in glycines (48 residues) and histidines (33 residues). A central region of 35 residues contains 19 glycines, occurring mainly as pairs. For both regions a polyglycine-like structure is likely and this may be stabilized by hydrogen bond-mediated chain association. Similar sequences found in loricrins, cytokeratins and avian keratins are postulated to participate in formation of supramolecular structures. Spinalin is terminated by a basic region (6 lysines out of 15 residues) and an acidic region (9 glutamates and 9 aspartates out of 32 residues). Western blot analysis with a polyclonal antibody generated against a recombinant 19 kDa fragment of spinalin showed that spinalin is localized in nematocysts. Following dissociation of the nematocyst’s capsule wall with DTT, spinalin was found in the insoluble fraction containing spines and the operculum. Immunocytochemical analysis of developing nematocysts revealed that spinalin first appears in the matrix but then is transferred through the capsule wall at the end of morphogenesis to form spines on the external surface of the inverted tubule and the operculum.
The single CH domain of calponin is neither sufficient nor necessary for F-actin binding
Authors: Gimona Mario , Mital Renu
Published: April 2021

Calponins have been implicated in the regulation of actomyosin interactions in smooth muscle cells, cytoskeletal organisation in nonmuscle cells, and the control of neurite outgrowth. Domains homologous to the amino-terminal region of calponin have been identified in a variety of actin cross-linking proteins and signal transduction molecules, and by inference these ‘calponin homology (CH) domains’ have been assumed to participate in actin binding.

We here report on the actin binding activities of the subdomains of the calponin molecule. All three mammalian isoforms of calponin (basic h 1, neutral h2 and acidic) possess a single CH domain at their amino terminus as well as three tandem repeats proximal to the carboxyl terminus. Calponin h2 differs, however, from h 1 in lacking a consensus actin-binding motif in the region 142-163, between the CH domain and the tandem repeats, which in h 1 calponin can be chemically cross-linked to actin. Despite the absence of this consensus actin-binding motif, recombinant full-length h 2 calponin co-sediments in vitro with F-actin, suggesting the presence of another bindingsite in the molecule. It could be shown that this binding site resides in the C-terminal tandem repeats and not in the CH domain. Thus, constructs of h 2 calponin bearing partial or complete deletions of the triple repeated sequences failed to co-localise with actin stress fibres despite the presence of a CH domain. Deletion of the acidic carboxyl terminus, beyond the repeats, increased actin binding, suggesting that the carboxy-terminal tail may modulate actin association. Results obtained from transient transfections of amino- and carboxy-terminal truncations in h 1 calponin were consistent with the established location of the actin binding motif outside and carboxy-terminal to the CH domain, and confirm that the presence of a single CH domain alone is neither sufficient nor necessary to mediate actin binding. Instead, the carboxy-terminal tandem repeats of h 1 and h 2 calponin are shown to harbour a second, independent actin binding motif.
A rod end deletion in the intermediate filament protein nestin alters its subcellular localization in neuroepithelial cells of transgenic mice
Authors: Marvin Martha J. , Dahlstrand Jonas , Lendahl Urban , McKay Ronald D. G.
Published: April 2021

Neuroepithelial and radial glial cells span between the ventricular and the pial surfaces of the neural tube and express two intermediate filaments (IFs), nestin and vimentin, which form a filamentous network throughout the length of the cells. In this report we study the polymerization characteristics of nestin and examine how mutations affect the assembly and localization of the nestin protein in cultured cells and in the developing CNS of transgenic mice. A wild-type rat nestin gene transfected into the IF-free SW13 cell line failed to assemble into a filamentous network but was incorporated into the existing IF network of a subclone expressing vimentin, demonstrating that nestin requires vimentin for proper assembly. In transgenic mice, rat nestin formed a network indistinguishable from that formed by endogenous nestin and vimentin, but a mutant form lacking five amino acids at the carboxy terminus of the rod domain was largely restricted to the pial endfeet. Since nestin mRNA is localized to the pial endfoot region we propose that both transgenes are translated there, but that the wild-type protein is preferentially incorporated into the IF network. These observations provide evidence for hierarchical assembly and a complex organization of the IF network along the ventricular-pial axis in the early CNS.
Functional association of nuclear protein 4.1 with pre-mRNA splicing factors
Authors: Lallena Marĺa-José , Martĺnez Concepción , Valcárcel Juan , Correas Isabel
Published: April 2021

Protein 4.1 is a multifunctional polypeptide that links transmembrane proteins with the underlying spectrin/actin cytoskeleton. Recent studies have shown that protein 4.1 is also present in the nucleus, localized in domains enriched in splicing factors. Here we further analyze the relationship between protein 4.1 and components of the splicing machinery. Using HeLa nuclear extracts capable of supporting the splicing of pre-mRNAs in vitro, we show that anti-4.1 antibodies specifically immunoprecipitate pre-mRNA and splicing intermediates. Immunodepletion of protein 4.1 from HeLa nuclear extracts results in inhibition of their splicing activity, as assayed with two different pre-mRNA substrates. Coprecipitation of protein 4.1 from HeLa nuclear extracts with proteins involved in the processing of pre-mRNA further suggests an association between nuclear protein 4.1 and components of the splicing apparatus. The molecular cloning of a 4.1 cDNA encoding the isoform designated 4.1E has allowed us to show that this protein is targeted to the nucleus, that it associates with the splicing factor U2AF35, and that its overexpression induces the redistribution of the splicing factor SC35. Based on our combined biochemical and localization results, we propose that 4.1 proteins are part of nuclear structures to which splicing factors functionally associate, most likely for storage purposes.
Membrane recruitment of Rac1 triggers phagocytosis
Authors: Castellano Flavia , Montcourrier Philippe , Chavrier Philippe
Published: April 2021

Rac1 is a Rho-family GTP-binding protein that controls lamellipodia formation and membrane ruffling in fibroblasts. Recently, Rac1 and Cdc42, another member of the Rho-family, have been shown to regulate Fc receptor-mediated phagocytosis in macrophages by controlling different steps of membrane and actin dynamics leading to particle engulfment. Here, we investigated the function of Rac1 using a membrane recruitment system that mimics phagocytosis. Recruitment of an activated Rac1 protein to the cytoplasmic domain of an engineered membrane receptor by using rapamycin as a bridge induces ingestion of latex beads bound to the receptor. Rac1-mediated bead uptake depends on actin polymerisation since actin filaments accumulate at the bead/membrane binding sites and internalisation is inhibited by cytochalasin D. Internalisation is also abolished upon substitution of Phe37 to Leu in the Rac1 effector region. Our results indicate that by promoting actin polymerisation at particle attachment sites, Rac1 by acting through specific downstream effectors induces plasma membrane remodeling that allows particle internalisation in a membrane-enclosed phagosome.
Temperature Regulation Of Honey Bees (Apis Mellifera) Foraging In The Sonoran Desert
Authors: Cooper Paul D. , Schaffer William M. , Buchmann Stephen L.
Published: April 2021

A heat budget for foraging honey bees (Apis mellifera L.) indicated that at 30-35 °C all bees are in positive heat balance during flight. Observations of honey bees returning to their hives at high ambient temperatures support the conjecture that honey bees regulate head and thorax temperatures at high Ta by regurgitating droplets of honey stomach contents which are then evaporated. The proportion of returning bees with a droplet on the tongue increased with increasing shade temperature (Ts), from essentially no bees at 20°C to 40% of returning bees at 40°C. Pollen foragers carry relatively little fluid during the hottest periods, and pollen foraging decreased at high ambient temperatures. Thoracic temperatures of pollen collectors are significantly higher than thoracic temperatures of water and nectar gatherers at 40°C (46·13 vs 44°C). Additionally, water and nectar foragers with extruded droplets have slightly cooler heads and thoraces (38·94 and 43·22°C) than bees not extruding droplets (40·28 and 44·18°C). Wingloading and thoracic temperatures of bees are inversely correlated at high ambient temperatures (35 °C) and this is probably caused by a higher propensity of heavier bees to extrude fluid, thus reducing thoracic temperature.
Intrapulmonary Chemoreceptor Control of Ventilatory Movements in the Self-Ventilating Chicken
Authors: Barnas G. M. , Burger R. E.
Published: April 2021

The importance of intrapulmonary chemoreceptors (IPC), sensitive to in the lung, in the control of ventilatory movements is yet to be demonstrated in the self-ventilating bird. We distinguished between the effects of on IPC and on extrapulmonary CO2-sensitive receptors (EPC) in anaesthetized cockerels by denervating IPC in the right lung, ligating the left pulmonary artery and changing . Left IPC were thus exposed to a combination of from inspired gas and dead space, while EPC were exposed to greatly increased arterial resulting from the ventilation-perfusion inequality. At OTorr , steady state ventilatory depth and frequency did not change (P>0·5) after the ligation, although rose by 12·2 ± 1·7 Torr. After the ligation, ventilatory movements were more sensitive to increasing Pico,- Tracheostomy, which results in a greater decrease in in the innervated lung after ligation, produced greater effects. We conclude that these responses were due to the strong controlling influence of IPC on ventilatory movements in the self-ventilating cockerel.
Influence of Coxa-Thorax Joint Receptors on Retractor Motor Output During Walking in Carausius Morosus
Authors: Graham D.
Published: April 2021

The coxal leg-stump of a stick insect was rotated about the coxa-thorax joint, by means of a pen-motor, while the animal walked on a self-propelled double treadwheel. Motor activity in the retractor muscles of the legs was recorded for standing and walking animals with the stump of either the middle or hind leg moved forward and backward in a trajectory similar to that used in a walking step.

In a standing animal the movement of either leg evokes a weak resistance reflex. If the animal walks with the middle leg-stump held still, then short and weak motor bursts are generated with the periodicity of the walking legs. Front and hind legs alternate in a manner typical of the middle leg amputee and the retractor muscle of the amputated leg is most active during the power stroke of the leg behind.

When a middle leg-stump is moved at a different frequency from that of the walking legs, the motor output to the retractor is strongly modulated and depends on the relative timing of the stump and the walking legs.

Rearward movement of the hind leg-stump, during walking, is always accompanied by strong motor output in the retractor muscle. In addition, forward movement in this leg-stump produces a resistance reflex similar to that produced in the standing animal.
Oxygen Acquisition of the Reedfish, Erpetoichthys Calabaricus
Authors: Pettit Michael J. , Beitinger Thomas L.
Published: April 2021

In normoxic water at 25 °C, the reedfish (Erpetoichthys calabacicus) can breathe in both air and water, although water is the primary source of oxygen. This pattern of oxygen partitioning is altered by a number of factors. Increases in metabolic costs (e.g. locomotor activity) and decreases in aquatic oxygen concentration are met by increases in aerial oxygen uptake.

Reedfish acclimated to 33 °C have increased lung breathing compared with fish acclimated to 25°C. Also, activity stimulates lung breathing more at 33 °C than at 25 °C. Unexpectedly, weight-specific oxygen uptake rates of reedfish at these two temperatures were not significantly different. In-creased lung-breathing compensates for changes in locomotor activity, dissolved oxygen and temperature, allowing reedfish to meet their overall oxygen requirements.

Exposure of reedfish to six different combinations of oxygen and carbon dioxide indicated that lung ventilation frequencies were more labile than gill ventilation frequencies. The maximum change in lung ventilation rates was 849% above controls whereas the largest change in gill ventilation frequency was 27%. Exposure of reedfish to hyperoxia significantly de-pressed both gill and lung ventilation. Hypercapnic gases stimulated gill ventilation at both low (0·5%) and high (5%) concentrations; however, lung ventilation was only stimulated at the higher carbon dioxide concentration. The observed depression of gill ventilation frequencies in reedfish exposed to combinations of hypercapnic and hypoxic gases indicates that the inhibitory effect of low oxygen on gill ventilation dominates the stimulatory effect of hypercapnia. Overall, these data suggest that oxygen exerts a stronger influence in the control of respiration than carbon dioxide in this air-and water-breathing fish.

Reedfish survived out of water for 6 and 8 h at 25 °C without obvious ill effects. Oxygen consumption rates of these fish were significantly less than those of similar sized reedfish measured in water at either 25 or 33°C. The respiratory physiology of the reedfish frees it from aquatic oxygen constraints and allows it to tolerate at least short-term terrestrial exposures.
Coactivating Influences Between Neighbouring Legs in Walking Insects
Authors: Cruse H.
Published: April 2021

When the movement of one leg of a walking stick insect is interrupted during the power stroke, the force developed by other legs is increased. This effect is shown to occur between all orthogonal nearest-neighbour legs except for the two hind legs. Such effects do not occur between diagonal or next nearest-neighbour pairs. The possible function of these ‘coactivating’ influences is assumed to be to enable the animal to increase the total force propelling the body.
Strain Gauge Measurement Of Mesokinetic Movement In The LizardVaranusExanthematicus
Authors: Smith Kathleen K. , Hylander William L.
Published: April 2021

Single-element strain gauges were placed across the mesokinetic joint of the skull of the savanna monitor lizard, Varanus exanthematicus Bose, in order to document the extent and timing of mesokinetic movement. In addition, rosette strain gauges were placed on various points .of the palatomaxillary segment. Strain recordings and simultaneous cineradiographic films or videotapes were taken during normal feeding activities, including the strike, prey manipulation, ingestion and pharyngeal compression. Tensile strain, indicating lowering (retraction) of the palato-maxillary segment, was observed during all stages of feeding. Compressive strain, indicating lifting (protraction) of the palato-maxillary segment, generally appeared briefly in the strike and during pharyngeal compression. Maximum tensile strains were always larger than maximum compressive strains within each sequence. The highest levels of tensile strain occurred during prey manipulation periods, which were characterized by isometric biting. Strain on the palato-maxillary segment revealed a pattern of timing similar to the one at the mesokinetic joint, although strain levels were at least an order of magnitude lower. These data directly contradict conventional models of the function of the kinetic skull in lizards. We conclude that the kinetic apparatus in lizards is not a mechanism for actively moving the palato-maxillary unit and is therefore not a mechanism for increasing gape or actively controlling upper jaw movements.
Properties of the Chloride Conductance Associated with Temperature Acclimation in Muscle Fibres of Green Sunfish
Authors: Klein M.G.
Published: April 2021

Characteristics of the anion conductance of muscle fibres from green sunfish have been determined. The membrane conductance of fibres from sunfish acclimated to 25 and 7 °C was linearly related to the extracellular chloride concentration. The chloride conductance exhibited a pH dependence which was adequately described by the titration of an acidic site with a pKa of 5·3 in 25 °C-acclimated fibres and 6·4 in 7°C-acclimated fibres.

The anion current-voltage (I-V) relationship of warm-acclimated fibres exhibited constant-field rectification, while the I-V relationship of cold-acclimated fibres was linear. In Ringer solutions containing elevated calcium concentrations (33 and 115 mmol l−1), the I-V relationship of warm-acclimated fibres was similar to the control situation. However, the I-V relationship of cold-acclimated fibres showed a calcium concentration-dependent curvature in the direction expected for constant-field rectification. The voltage-dependence of the time constant of chloride current inactivation was shifted along the voltage axis by about 40 mV in the negative direction in 7°C-acclimated fibres as compared to 25°C-acclimated fibres. The results can be adequately described by a model of constant-field rectification with the inclusion of a term for the membrane surface potential. A simple hypothesis which can qualitatively account for many of these observations is that temperature acclimation alters the density of fixed negative surface charges in the vicinity of chloride channels.
An Improved Chamber for the Short-Circuiting of Epithelia
Authors: Dow Julian A. T. , Harvey William R. , Wolfersberger Michael G. , Boyes Bruce
Published: April 2021

Since the pioneering work of Ussing & Zerahn (1951), the design of short-circuit apparatus has been modified only slightly. Such chambers generally consist of two halves, between which the epithelium is stretched. The assembly is clamped together and filled with saline, which is circulated in each half chamber by gas lift pumps, usually connected to the main chamber with plastic pipes. There are two current electrodes, one at each end of the chamber, and -usually -two voltage-sensing electrodes close to the tissue. The current passed through the chamber is adjusted until the p.d. between the sensing electrodes becomes zero. Under such conditions, only actively transported ions move across the tissue, and the short-circuit current is a precise measure of the net flux of charged species. Short-circuiting is thus a method of choice for investigating transport phenomena in epithelia.
Pattern and Reset Analysis of the Gastric Mill Rhythm in a Spiny Lobster, Panulirus Interruptus
Authors: Russell David F.
Published: April 2021

The burst pattern of the gastric mill rhythm was studied by varying its cycle period in in vitro preparations comprising the stomatogastric (STG), oesophageal and (paired) commissural ganglia. Reset tests using intracellular polarization of identified STG neurones showed that the CI, LC, GP and GM cells can all strongly affect the cycle period, and therefore apparently play a role in generating the gastric rhythm. Variation in the cycle period could be obtained by: (i) cutting certain input nerves; (ii) relative coordination between the gastric and oesophageal rhythms; or (iii) intracellular polarization of identified STG cells, especially the LC motoneurone. Variation in the cycle period by any of these means showed that the gastric pattern (in such preparations) comprises two basic alternating phases: a variable-duration ‘powerstroke’ and a constant-duration ‘returnstroke’. The powerstroke is taken to include bursts in the LC, GP and GM motoneurones (since they evoke closing of the gastric mill teeth and mastication of food), along with the interburst intervals of the other cells. The durations of all these events co-varies over a large range, as a linear function of the cycle period. The activity level of neurones bursting during the powerstroke is directly proportional to their burst length, and hence appears to be a basic parameter affecting the cycle period. The returnstroke is taken to include bursts in the CP, AM and LG motoneurones (since they evoke opening and resetting of the gastric mill teeth), along with the interburst intervals of the powerstroke cells. All these events tended to assume a fixed duration. The two-part gastric mill pattern can be analogized to other two-part rhythms, e.g. for terrestrial locomotion, in which the load-bearing phase has a variable duration and accounts for most of the variation in the cycle period whereas the unloaded phase tends to assume a constant duration.
Neural Basis of Teeth Coordination During Gastric Mill Rhythms in Spiny Lobsters, Panulirus Interruptus
Authors: Russell David F.
Published: April 2021

Motoneurones that drive the closing of the lateral teeth during gastric mill rhythms in spiny lobsters start firing before the motoneurones that drive the medial tooth powerstroke. This has the expected behavioural interpretation that the lateral teeth must close on a food particle before the medial tooth is pulled across it. The neural basis of the teeth coordination was examined. Experiments were made during gastric rhythms in in vitro preparations comprising the stomatogastric, oesophageal and (paired) commissural ganglia. Identified neurones in the stomatogastric ganglion were polarized to study their functional effects on the phasing and amplitude of bursts in other cells. Evoked firing of the lateral teeth closer motoneurones (especially LC) would evoke a discharge in the medial tooth powerstroke (GM) motoneurones, and suppress the firing of the medial tooth returnstroke (CP) motoneurone. Therefore the coordination pathway starts directly with the lateral teeth closer motoneurones. 4. The CI interneurone was found to be an important link in the coordination pathway. It exerted opposite effects on the medial tooth motoneurones, suppressing firing of the powerstroke GM cells while evoking bursts in the returnstroke CP cell. CI affected other features of the pattern as well. Non-spiking inhibition from the lateral teeth closer motoneurones (LC and GP) to the lateral teeth opener motoneurones (LGs) was found to occur conjointly with spike-mediated IPSPs. Hyperpolarization of the LC, GP or CI neurones could temporarily abolish the gastric rhythm, but bursting in some or all of the other cells would eventually return, although in some cases the phase pattern was altered. It appears that no individual neurone in the gastric network is necessary for rhythm production. The coordination system can be viewed as several ‘levels’ of synaptic connections, each level being redundant and synergistic with the others.