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PubMed1999

WNT11 promotes cardiac tissue formation of early mesoderm.

Cardiac tissue in the bird is derived from paired regions of lateral mesoderm within the anterior half of the embryo (Rawles [1943] Physiol. Zool. 16:22-42; Stalsberg and DeHaan [1969] Dev. Biol. 19:128-159). Previously, we reported that WNT11 is expressed in early avian mesoderm in a pattern that overlaps with the precardiac regions. To examine whether this molecule may play a role in promoting cardiogenesis, we cultured tissue explants from microdissected HH stage 4, 5, and 6 quail embryos. The isolated tissue consisted of both the mesoderm and endoderm layers from either anterior precardiac or posterior noncardiogenic regions of the embryo. As a necessary control for examining the ability of WNT11 to convert noncardiogenic mesoderm to cardiac tissue, we compared the cardiogenic potential of anterior and posterior regions. For stages 5 and 6, our results were consistent with what has been previously reported (Rawles [1943] Physiol. Zool. 16:22-42; Sugi and Lough [1994] Dev. Dyn. 200:155-162); as anterior mesoderm becomes contractile, while posterior mesoderm does not produce cardiac tissue. Surprisingly, when we examined stage 4 embryos both anterior and posterior regions gave rise to cardiac tissue in culture. To determine whether WNT11 could promote cardiac differentiation in tissue that was noncardiogenic, this molecule was ectopically expressed or added to mesoderm/endoderm explants obtained from stage 5 or 6 posterior tissue. Transfection of stage 5 posterior tissue with a WNT11 expression plasmid provoked the appearance of cardiomyocytes in 33% of the explants; half of which were contractile. Similarly transfected stage 6 posterior explants did not demonstrate cardiac differentiation. More dramatic results were obtained when noncardiogenic tissue was exposed to conditioned media containing soluble WNT11; as 63% and 33% of posterior stage 5- or stage 6-derived explants underwent cardiac differentiation. Together, these results indicate that WNT11 can promote cardiac development within noncardiac tissue. The expression of WNT11 in anterior mesoderm of early gastrula stage embryos suggests it may play a role in the formation of the vertebrate heart. Dev Dyn 1999;216:45-58.

Animals↗
PubMed1992

Mesoderm movement and fate during avian gastrulation and neurulation.

Quail/chick transplantation chimeras were constructed during stages of gastrulation and neurulation to follow the subsequent movement and fate of cells of the primitive streak. All grafts were placed solely within the confines of the primitive streak to prevent confusion between cells that had not yet ingressed and those that had already ingressed, and transplanted cells were distinguished from host cells on the basis of a naturally occurring cell marker. Pathways of movement of ingressing cells corresponded to their level of residence within the primitive streak. Cells residing within Hensen's node (the cranial end of the primitive streak) initially migrated mainly cranially, remaining on or near the midline, and then extended caudally along the midline as regression of Hensen's node occurred. Cells residing within the nodus posterior (the caudal end of the primitive streak) migrated caudally. Cells residing at levels of the primitive streak between Hensen's node and the nodus posterior typically migrated bilaterally, confirming that such cells had not already ingressed prior to their transplantation (in which case, they would have migrated unilaterally). Subsets of these cells residing at progressively more caudal levels of the primitive streak migrated incrementally more laterally. Hensen's node contributed cells to the gut endoderm, head mesenchyme, notochord, and median hinge-point (MHP) cells of the neural tube (future floor plate). At younger stages (i.e., stages 3a, 3b) Hensen's node contributed cells to principally the foregut endoderm and head mesenchyme, whereas at older stages (i.e., stages 3c, 3d, 4), it contributed cells to principally the notochord and MHP region. The remaining segments of the cranial half of the primitive streak contributed cells to the various mesodermal subdivisions of the embryo, and the lengths of the segments forming these subdivisions were estimated. The most cranial level of the streak (directly behind Hensen's node) contributed cells to the most medial mesodermal subdivisions (head mesenchyme, somites) and consecutively more caudal levels of the streak contributed cells to sequentially more lateral mesodermal subdivisions (intermediate mesoderm, lateral plate mesoderm). The caudal half of the primitive streak contributed cells to the extraembryonic mesoderm, with the nodus posterior contributing to the most caudal extraembryonic mesoderm, including the blood islands. Our results confirm and extend the previous avian prospective fate maps, increasing our understanding of the movement and fate of cells of the gastrula and neurula stages.

Animals↗
PubMed1995

Ectodermal stimulation of the production of hyaluronan-dependent pericellular matrix by embryonic limb mesodermal cells.

Interaction of ectoderm and underlying mesoderm is essential for normal vertebrate limb morphogenesis. One of the functions of limb bud ectoderm is its influence on the composition of extracellular matrix in subectodermal mesoderm, which in turn participates in morphogenesis of this region of the limb. This matrix is highly enriched in hyaluronan, even at the time when the level of hyaluronan in the chondrogenic and myogenic regions of the limb decreases, due to secretion of a stimulatory factor by the ectoderm. In this study we show that limb bud ectoderm not only stimulates hyaluronan synthesis but induces formation of large hyaluronan-dependent, pericellular matrices around cultured limb bud mesodermal cells. The ectodermal activity is mimicked in great part by fibroblast growth factor-2 and transforming growth factor-beta, and antibodies to these proteins inhibit induction of mesodermal pericellular matrix by the ectodermal factor. It has been shown by other investigators that fibroblast growth factor-2 is produced by limb ectoderm whereas transforming growth factor-2 is produced by limb ectoderm whereas transforming growth factor-beta is present in limb mesodermal tissues. Thus we conclude that the unique properties of mesodermally produced matrix underlying limb bud ectoderm are regulated, at least in part, by ectodermal fibroblast growth factor-2, probably in concert with mesodermal transforming growth factor-beta.

Animals↗
PubMed2002

Efficient ectopic gene expression targeting chick mesoderm.

The chick model has been instrumental in illuminating genes that regulate early vertebrate development and pattern formation. Targeted ectopic gene expression is critical to dissect further the complicated gene interactions that are involved. In an effort to develop a consistent method to ectopically introduce and focally express genes in chick mesoderm, we evaluated and optimized several gene delivery methods, including implantation of 293 cells laden with viral vectors, direct adenoviral injection, and electroporation (EP). We targeted the mesoderm of chick wing buds between stages 19 and 21 (Hamburger and Hamilton stages) and used beta-galactosidase and green fluorescent protein (GFP) to document gene transfer. Expression constructs using the cytomegalovirus (CMV) promoter, the beta-actin promoter, and vectors with an internal ribosomal entry sequence linked to GFP (IRES-GFP) were also compared. After gene transfer, we monitored expression for up to 3 days. The functionality of ectopic expression was demonstrated with constructs containing the coding sequences for Shh, a secreted signaling protein, or Hoxb-8, a transcription factor, both of which can induce digit duplication when ectopically expressed in anterior limb mesoderm. We identified several factors that enhance mesodermal gene transfer. First, the use of a vector with the beta-actin promoter coupled to the 69% fragment of the bovine papilloma virus yielded superior mesodermal expression both by markers and functional results when compared with several CMV-driven vectors. Second, we found the use of mineral oil to be an important adjuvant for EP and direct viral injection to localize and contain vector within the mesoderm at the injection site. Lastly, although ectopic expression could be achieved with all three methods, we favored EP confined to the mesoderm with insulated microelectrodes (confined microelectroporation- CMEP), because vector construction is rapid, the method is efficient, and results were consistent and reproducible.

Actins↗
PubMed2005

Initiation of convergence and extension movements of lateral mesoderm during zebrafish gastrulation.

Embryonic morphogenesis is accomplished by cellular movements, rearrangements, and cell fate inductions. Vertebrate gastrulation entails morphogenetic processes that generate three germ layers, endoderm, mesoderm, and ectoderm, shaped into head, trunk, and tail. To understand how cell migration mechanistically contributes to tissue shaping during gastrulation, we examined migration of lateral mesoderm in the zebrafish. Our results illustrate that cell behaviors, different from mediolaterally oriented cell intercalation, also promote convergence and extension (C&E). During early gastrulation, upon internalization, individually migrating mesendodermal cells contribute to the elongation of the mesoderm by moving animally, without dorsal movement. Convergence toward dorsal starts later, by 70% epiboly (7.7 hpf). Depending on location along the Animal-Vegetal axis, an animal or vegetal bias is added to the dorsalward movement, so that paths fan out and the lateral mesoderm both converges and extends. Onset of convergence is independent of noncanonical Wnt signaling but is delayed when Stat3 signaling is compromised. To understand which aspects of motility are controlled by guidance cues, we measured turning behavior of lateral mesodermal cells. We show that cells exhibit directional preference, directionally-regulated speed, and turn toward dorsal when off-course. We estimate that ectoderm could supply from a fraction to all the dorsalward displacement seen in mesoderm cells. Using mathematical modeling, we demonstrate that directional preference is sufficient to account for mesoderm convergence and extension, and that, at minimum, two sources of guidance cues could orient cell paths realistically if located in the dorsal midline.

Animals↗
PubMed1994

Expression patterns of twist and snail in Tribolium (Coleoptera) suggest a homologous formation of mesoderm in long and short germ band insects.

The mesodermal region in Drosophila is determined by a maternally derived morphogenetic gradient system which specifies the different cell fates along the dorsoventral axis, including the prospective mesodermal cells at the ventral side of the embryo. There are at least two zygotic target genes, twist and snail, which are required for mesoderm formation in Drosophila. To analyze whether a similar mode of mesoderm specification might also apply to short germband insect embryos, we have cloned twist and snail-related gene fragments from the flour beetle Tribolium and have analyzed their expression pattern. Both genes are expressed in a ventral stripe at early blastoderm stage, which is restricted to the region of the developing germ rudiment. The cells expressing the two genes are those that invaginate during gastrulation, indicating that the early stages of mesoderm specification are indeed very similar between the two species. Interestingly, both genes are also expressed during germband extension in a subregion of the growth zone of the embryo which forms the mesodermal cells. This suggests that the expression of the two genes is required for mesoderm formation both at early blastoderm stage and during germband elongation until the end of the segmental growth process.

Amino Acid Sequence↗
PubMed1992

A positive correlation between permissiveness of mesoderm to neural crest migration and early DRG growth.

The microenvironment created by grafting rostral somitic halves in place of normal somites leads to the formation of nonsegmented peripheral ganglia (Kalcheim and Teillet, 1989; Goldstein and Kalcheim, 1991) and is mitogenic for neural crest (NC) cells that become dorsal root ganglia (DRG) (Goldstein et al., 1990). We have now extended these studies by using three surgical manipulations to determine how additional mesodermal tissues affected DRG growth in chick embryos. The following experimental manipulations were performed: (1) unilateral deletion of epithelial somites, similar deletions followed by replacing the somites with (2) a three-dimensional collagen matrix, or (3) fragments of quail lateral plate mesoderm. When somites were absent or replaced by collagen matrix, ganglia were unsegmented, and their volumes were decreased by 21% and 12%, respectively, compared to contralateral intact DRG. In contrast, when lateral plate mesoderm was transplanted in place of somitic mesoderm, NC cells migrated into the grafted mesoderm and formed unsegmented DRG whose volumes were increased by 62.6% compared to the contralateral ganglia. These results suggest that although DRG precursors do not require sclerotome to begin migration and condensation processes, DRG size is modulated by the properties of the mesoderm. Permissiveness to migration is positively correlated with an increase in DRG volume. This volume increase observed in grafts of lateral plate mesoderm is likely to result from enhanced proliferation of neural crest progenitors, previously demonstrated for DRG cells in rostral somitic grafts.

Animals↗
PubMed1996

Dorsal mesoderm has a dual origin and forms by a novel mechanism in Hymenochirus, a relative of Xenopus.

The dorsal mesoderm in the frog Hymenochirus forms by a mechanism not previously described in any other vertebrate. Unlike its close relative, Xenopus laevis, in which the mesoderm derives entirely from the deep mesenchymal cells of the marginal zone, Hymenochirus has "surface mesoderm" originating in the involuting marginal zone epithelium. Fluorescently labeled grafts show stage-specific invasion of deep axial tissue by cells originally located in the surface layer. These cells participate in normal mesoderm development. In video recordings, the labeled surface area shrinks as surface cells invade the deep layer. Furthermore, the mechanism of surface mesoderm morphogenesis differs from that described in other amphibians. Scanning electron microscopy at several neurula stages indicates that prospective somite cells do not individually detach from their epithelial neighbors to ingress into the deep layer, as seen in other amphibians; instead, their basal ends adhere to the somitic mesoderm as a coherent layer, taking on somitic morphology while still a part of the archenteron lining. This novel morphogenetic process we dub "relamination." Prospective notochord cells individually spread on the ventral surface of the notochord, gradually ingressing from their epithelial neighbors, but by a mechansism involving active pulling and spreading by their invasive basal ends rather than depending on apical constriction as do the corresponding "bottle cells" in other amphibians. Lateral endoderm migrates dorsally, replacing the relaminating surface mesoderm and fusing at the dorsal midline of the archenteron. These processes demonstrate the diversity of morphogenesis at the cellular, and presumably the molecular, level and shed light on the evolution of morphogenetic mechanisms.

Animals↗
PubMed1996

Fibronectin, mesoderm migration, and gastrulation in Xenopus.

The role of fibronectin in mesoderm cell migration and and the importance of mesoderm migration for gastrulation in Xenopus are examined. To allow for migration, a stable interface must exist between migrating mesoderm cells and the cells of the substrate layer, the blastocoel roof. We show that maintenance of this interface does not depend on fibronectin. We further demonstrate that fibronectin contributes to, but is not essential for, mesoderm cell adhesion to the blastocoel roof. However, interaction with fibronectin is necessary for cell spreading and the formation of lamelliform cytoplasmic protrusions. Apparently, the specific role of fibronectin in mesoderm migration is to control cell protrusive activity. Consequently, when fibronectin function is blocked by GRGDSP peptide or antibodies, mesoderm cell migration is inhibited. Nevertheless, gastrulation proceeds nearly normally in inhibitor-treated embryos. It appears that in Xenopus, mesoderm migration is not essential for gastrulation.

Animals↗
PubMed1998

A key function for alphav containing integrins in mesodermal cell migration during Pleurodeles waltl gastrulation.

During cleavage of Pleurodeles waltl amphibian embryos, inner cells of the blastocoel roof (presumptive ectodermal and mesodermal cells) organize a fibrillar extracellular matrix (ECM) containing fibronectin on their basal surface by a beta1-integrin-dependent process. This matrix is used as a migratory substrate by mesodermal cells during gastrulation. While alpha5beta1 integrin is expressed on both ectodermal and mesodermal cell surface, we have shown previously that alphav containing integrins are essentially restricted to the surface of mesodermal cells (Alfandari, D., Whittaker, C. A., DeSimone, D. W., and Darribère, T., Dev. Biol. 170, 249-261, 1995). To investigate the function of alphav integrins during gastrulation, we have generated a function blocking antibody directed against the extracellular domain of the Pleurodeles integrin alphav subunit. The antibody did not prevent fibronectin fibril formation, whereas an antibody against the alpha5beta1 integrin did. When injected into the blastocoel, the antibody against integrin alphav subunit perturbed gastrulation and further development in a stage-dependent manner. Developmental defects were correlated to an abnormal positioning of the mesoderm layer. In vitro, the antibody blocked spreading of mesodermal cell to fibronectin or blastocoel roof ECM but not their attachment. In contrast, the antibody directed against the alpha5beta1 integrin inhibited both cell attachment and spreading to the same substrates. We propose that the alpha5beta1 integrin is required for fibronectin assembly into fibrils and mesodermal cell attachment to the blastocoel roof ECM, while the alphav containing integrins are necessary for cell spreading, and possibly migration, on this complex network.

Animals↗
PubMed1998

Experimental induction of BMP-4 expression leads to apoptosis in the paraxial and lateral plate mesoderm.

In the avian embryo, epithelialization of the segmental plate and formation of an epithelial dermomyotome depend on signals from the neural tube and the ectoderm overlying the paraxial mesoderm. In this study, we report that ectoderm removal in combination with barrier insertion between the axial organs and the segmental plate leads to an induction of BMP-4 expression in the paraxial mesoderm. In the lateral plate, ectoderm removal alone leads to an increase of BMP-4 expression. Application of BMP-4 protein results in a lack of epithelialization of the paraxial mesoderm. In order to investigate whether the loss of epithelial structures after these manipulations can be attributed to a change in cell fate, a change in cell proliferation, or the induction of apoptosis, the paraxial mesoderm was tested for expression of Msx-2, BMP-2, BMP-4, and BMP-7. Moreover, BrdU and TUNEL staining were carried out. The inhibition of epithelialization after ectoderm removal alone and after segregation of the axial organs is accompanied neither by an increase in apoptosis nor by a reduction of the proliferation rate in the paraxial mesoderm. On the other hand, an ectopic BMP-4 expression in the paraxial mesoderm after ectoderm removal in combination with barrier insertion coincides with the occurrence of apoptotic cells and reduction of proliferation rate in this tissue. Increase of apoptosis and decrease in cell proliferation are observed in the paraxial and lateral plate mesoderm also after application of BMP-4 protein.

Animals↗
PubMed2000

Lim1 activity is required for intermediate mesoderm differentiation in the mouse embryo.

During gastrulation and early organogenesis, Lim1 is expressed in the visceral endoderm, the anterior mesendoderm, and the lateral mesoderm that comprises the lateral plate and intermediate mesoderm. A previous study has reported that kidneys and gonads are missing in the Lim1 null mutants (W. Shawlot and R. R. Behringer, 1995, Nature 374, 425-430). Results of the present study show that in the early organogenesis stage mutant embryo, the intermediate mesoderm that contains the urogenital precursor tissues is disorganized and displays diminished expression of PAX2 and the Hoxb6-lacZ transgene. When posterior epiblast cells of the Lim1 null mutant embryo were transplanted to the primitive streak of wild-type host embryos, they were able to colonize the lateral plate and intermediate mesoderm of the host, suggesting that Lim1 activity is not essential for the allocation of epiblast cells to these mesodermal lineages. However, most of the mutant cells that colonized the lateral and intermediate mesoderm of the host embryo did not express the Hoxb6-lacZ transgene, except for some cells that were derived from the distal part of the posterior epiblast. Lim1 activity may therefore be required for the full expression of this transgene that normally marks the differentiation of the lateral plate and intermediate mesoderm.

Animals↗
PubMed2000

IGF-II promotes mesoderm formation.

IGF-II is abundant in the nascent mesoderm of the gastrulating mouse embryo. Its function at this developmental stage is unknown. We investigated it by following the in vitro and in vivo differentiation of several androgenetic, biparental, parthenogenetic, and androgenetic Igf2 -/- murine ES cell lines; these cells differed in endogenous IGF-II levels because Igf2 is paternally expressed in the mouse embryo in most tissues. The expression of mesoderm markers and the subsequent formation of muscle structures were correlated with endogenous IGF-II level during teratoma formation and during in vitro differentiation. In addition, the absence of Igf2 in androgenetic Igf2 -/- ES cells led to a severe impairment of mesoderm development, demonstrating the dependence of the preferential mesoderm development of androgenetic ES cells upon Igf2 activity, among the numerous known imprinted genes. The addition of exogenous IGF-II to in vitro differentiation culture medium led to a specific increase in the expression of mesoderm markers. Thus, we propose a novel model in which the binding of IGF-II to its principal signaling receptor, IGF1R, at the surface of mesoderm precursor cells increases the formation of mesoderm cells.

Animals↗
PubMed2001

Expression cloning of Xenopus Os4, an evolutionarily conserved gene, which induces mesoderm and dorsal axis.

Multiple factors, including members of the FGF, TGF beta, and Wnt family of proteins, are important mediators in the regulation of dorsal-ventral pattern formation during vertebrate development. By using an expression cloning approach to identify novel factors that could regulate dorsal-ventral patterning in the Xenopus embryo, we isolated the Xenopus homologue of the human Os4 gene by virtue of its ability to induce a secondary dorsal axis. While Os4 homologues have been identified in a variety of species, and human Os4 is overexpressed in human tumors, the biological function of Os4 is unknown. To explore the mechanism by which Xenopus Os4 (XOs4) induces a secondary dorsal axis, we used Xenopus explant and whole-embryo assays. The secondary axis induced by XOs4 is distinct from that induced by activation of Wnt or FGF pathways but similar to that induced by inhibition of BMP signaling or activation of an Activin pathway. However, XOs4 did not inhibit BMP signaling in dissociated animal cap explants, indicating that XOs4 does not inhibit BMP signaling. Similar to activation of an Activin-like pathway, expression of XOs4 induces molecular markers for mesoderm in animal cap explants, although expression of gastrula-stage mesodermal markers was very weak and substantially delayed. Yet, XOs4 does not require activity of the Activin signal-transduction pathway for mesoderm induction as dominant-negative components of the Activin/Nodal/Vg1 pathway did not prevent XOs4-mediated induction of mesodermal derivatives. Finally, like Activin/Nodal/Vg1 pathways, XOs4 requires FGF signaling for expression of mesoderm markers. Results presented in this study demonstrate that XOs4 can induce mesoderm and dorsalize ventral mesoderm resulting in ectopic dorsal axis formation, suggesting a role for this large evolutionarily conserved gene family in early development.

Activins↗
PubMed2002

Urodeles remove mesoderm from the superficial layer by subduction through a bilateral primitive streak.

Urodeles begin gastrulation with much of their presumptive mesoderm in the superficial cell layer, all of which must move into the deep layers during development. We studied the morphogenesis of superficial mesoderm in the urodeles Ambystoma maculatum, Ambystoma mexicanum, and Taricha granulosa. In all three species, somitic, lateral, and ventral mesoderm move into the deep layer during gastrulation, ingressing through a "bilateral primitive streak" just inside the blastopore. The mesodermal epithelium appears to slide under the endodermal epithelium by a mechanism we term "subduction." Subduction removes the large expanse of superficial presumptive somitic and lateral-ventral mesoderm that initially separates the sub-blastoporal endoderm from the notochord, leaving the endoderm bounding the still epithelial notochord along the gastrocoel roof. Subduction may be a common feature of urodele gastrulation, differing in this regard from anurans. Subducting cells constrict their apices and become bottle-shaped as they approach the junction of the mesodermal and endodermal epithelia. Subducting bottle cells endocytose apical membrane and withdraw the tight junctional component cingulin from the contracting circumferential tight junctions. Either in conjunction with or immediately after subducting, the mesodermal cells undergo an epithelial-to-mesenchymal transition. The mechanism by which epithelial cells release their apical junctions to become mesenchymal, without disrupting the integrity of the epithelium, remains mysterious, but this system should prove useful in understanding this process in a developmental context.

Animals↗
PubMed1993

Murine stem cell factor stimulates erythropoietic differentiation of ventral mesoderm in Xenopus gastrula embryo.

We have reported that the animal pole cells stimulate the ventral mesoderm of early gastrula Xenopus embryo (stage 10) to differentiate into erythrocytes. To determine the molecular mechanism(s) involved in the stimulatory effect of the animal pole, ventral mesoderm explants were cultured in the presence of various defined cellular factors. In this study, we report that murine stem cell factor (SCF) stimulates globin expression at the optimum dose of 10 ng/ml. Globin expression was observed from the ventral mesoderm explants treated with SCF, but not from the dorsal mesoderm and the animal pole explants. Morphological studies of the ventral mesoderm treated with SCF showed that only a certain population of the ventral mesoderm differentiates into erythrocytes. On the other hand, coculture of ventral mesoderm and animal pole revealed the differentiation of the entire structures into mesenchyme, blood cells, and the overlying epidermis. These data suggest that SCF may play a role in the stimulation of erythrocytic differentiation, but the effect of the animal pole cells cannot be replaced with that of SCF.

Animals↗
PubMed1988

Transferrin and iron requirements of embryonic mesoderm cells cultured in hydrated collagen matrices.

Very early embryonic mesoderm cells were taken from the primitive streak-stage chick embryo and cultured in a matrix of type I collagen in the presence of serum. Previous work has shown that under these conditions cells do not leave the explant and move in the collagen in the absence of supplemented avian transferrin. Cells explanted onto tissue culture plastic in the presence of serum do not require this transferrin supplement. These observations were investigated further by culturing cells in collagen in the presence of the lipophilic iron chelator, ferric pyridoxal isonicotinoyl hydrazone (FePIH), which can replace transferrin as an iron-delivery agent. Under conditions in which FePIH could effectively stimulate chick embryo myoblast growth, no such long-term stimulation was obtained with the early mesoderm cells in collagen. This suggested that for mesoderm cells, FePIH could not replace transferrin. Antibody to the transferrin receptor and to transferrin itself inhibited growth of myoblasts in collagen and on plastic, and of mesoderm cells in collagen. Mesoderm cells on plastic, however, were refractory to the presence of the antibody directed to the receptor and seemed to show a low dependency on transferrin-delivered iron under these conditions, inasmuch as antiserum to transferrin itself only caused a partial inhibition of outgrowth. The results suggest that mesoderm cells in collagen require transferrin for both iron uptake and for another unspecified function. It is consistent with the results to propose that transferrin binding might modulate the cells' attachment to collagen, thus influencing outgrowth. The distribution of the actin cytoskeleton in mesoderm cells actively migrating in collagen, such as in the presence of transferrin, suggests a stronger attachment to the collagen than nonmigrating cells.

Actins↗
PubMed2004

Tribolium castaneum twist: gastrulation and mesoderm formation in a short-germ beetle.

Mesoderm formation has been extensively analyzed in the long-germ insect Drosophila melanogaster. In Drosophila, both the invagination and specification of the mesoderm is controlled by twist. Here we present a detailed description of mesoderm formation and twist regulation for the short-germ beetle Tribolium castaneum. In contrast to Drosophila, (1) the presumptive mesodermal cells of Tribolium are part of a mitotic domain and divide prior to ventral furrow formation, (2) ventral furrow formation progresses from posterior to anterior, (3) the number of cell layers within the furrow changes from multilayered in caudal to single layered in cephalic regions, and (4) there is a continuous production of mesodermal cells after gastrulation as new segments arise from the posterior growth zone. Tribolium twist (Tc-twist) is initially expressed in all presumptive mesodermal cells; however, after invagination, expression is maintained only in particular locations, which include the anterior compartments of the cephalic segments and a patch of cells at the posterior rim of the growth zone. The growth zone is multilayered with its inner cell layer being continuous with the mesoderm of the newly forming segments where twist expression is re-initiated anterior to the emerging engrailed stripes. A genomic region of Tc-twist was identified which drives ventral expression of a reporter construct in Drosophila. The expression of this Tc-twist construct in the background of Drosophila maternal mutations suggests that the dorsoventral system regulates Tc-twist, but that differences exist in regulation of the Dm-twist and Tc-twist genes by the terminal system.

Amino Acid Motifs↗