bluuebunny/crossref_metadata_2025 huggingface dataset:
Potentiation by the lithium ion of morphogenetic responses to a Xenopus inducing factor
Authors: Cooke Jonathan , Symes Karen , Smith Emma J.
Published: April 2021

We have cultured explants of Xenopus blastular animal cap tissue from embryos that had received an earlier treatment with LiCl and from their untreated siblings, in various concentrations of XTC-cell-derived mesoderm-inducing factor (XTC-MIF, Smith, 1987; Smith et al. 1988). The pretreatment with lithium that we used transforms later morphogenesis in the whole embryo to give radialized body forms with anterior/dorsal levels of structure grossly over-represented. In addition, animal caps from ‘Li+’ embryos were allowed to develop without exposure to in vitro MIF (Li+ controls) and compared with normal uninduced control explants, and explants were made from normal early blastulae but given various initial treatments with LiCl in culture.

The results confirm that the lithium ion itself will not induce mesoderm in competent, animal cap tissue of Xenopus. It does, however, enhance the responsiveness of this tissue to XTC-MIF, in a way that parallels its recently reported effect in the case of another mesoderm inducer of different character, bFGF (Slack et al. 1988). The effects observed are sufficient to imply that the altered body pattern that follows lithium treatment, in whole embryos, could be caused by modulation of the responses to an unaltered pattern of in situ inductive stimuli. We also observe evidence that appreciable inductive signals reach animal pole tissue beyond the limits of mesoderm formation in normal development.

Relatively low concentrations of MIF prevent the development of an epidermis-specific marker in dissociated blastular animal cap cells (Symes et al. 1988). When such experiments are repeated in relation to the lithium pretreatment of embryos, such treatment is seen to have sensitized the cell population, so that the MIF concentration range that assures complete suppression of the marker is reduced.

The results are discussed in relation to induction considered as pattern formation.
Expression pattern of homeobox-containing genes during chick embryogenesis
Authors: Wedden Sarah E. , PANG Kevin , Eichele Gregor
Published: April 2021

We have isolated, sequenced and examined the expression pattern of two tandemly arranged homeobox- containing genes from the chicken. The predicted amino acid sequences of the homeodomain and the adjacent carboxyterminal portion of the protein of the first gene is virtually identical (99%) to that of murine homeobox 2.1 and hence we refer to it as Ghox 2.1 (Gallus Aomeobox). The closest mouse homologue of the second homeodomain is Hox 2.2 (95% identical within the homeobox), and hence referred to as Ghox 2.2. Northern analysis of embryonic RNA reveals major transcripts of 2 kb for Ghox 2.1 and 1·7 kb for Ghox 2.2. To investigate the transcript pattern, embryos of various stages were dissected into heads, trunks and limb buds and the RNA was analysed by Northern blotting and RNase protection assays. Ghox 2.1 transcripts are present in all three regions. Ghox 2.2 RNA is found in trunks and limb buds, but it is strikingly absent from the developing head. In situ hybridization with 35S-labelled antisense riboprobes derived from Ghox 2.1 demonstrates that this gene is expressed at high levels in spinal chord, myelencephalon and mesonephros. Dorsal root ganglia and the lung rudiment also contain Ghox 2.1 message, but in somewhat lower amounts. Mid- and forebrain, the heart, presomitic mesenchyme and notochord do not contain detectable levels of Ghox 2.1 mRNA. Of particular interest is the expression of Ghox 2.1 in a well-defined patch of mesenchymal tissue situated in an anterioproximal region of the limb bud.
In situ study of c-myc protein expression during avian development
Authors: Jaffredo T. , Vandenbunder B. , Dieterlen-Lièvre F.
Published: April 2021

The distribution of the c-myc protein was studied in the developing embryo from the two-somite stage to embryonic day 17 (E17). A triple labelling method was used, with a polyclonal serum recognizing the human and avian c-myc proteins as the first marker followed by Hoechst 33258 for nuclear staining and the monoclonal antibody 13F4 which reveals the avian myogenic lineage. In situ hybridization was carried out at three selected stages (E3, E6 and E8), in order to compare the distribution of myc mRNA and myc protein. The c-myc protein signal was barely detectable in blastodisc nuclei during the period of somlte formation, after which it became ubiquitous in the embryonic body until E4. Myotomal cell nuclei displayed a strong signal until their organization Into premuscular masses.

On day 4, the level of c-myc protein decreased In all embryonic tissues. By doubling the antibody titre and amplifying the signal by means of the streptavidin-blotin method, c-myc could still be detected in nuclei of defined groups of cells. Such was the case in some mesenchyme-derived tissues at critical periods of or-ganogenesis, for instance in prechondrogenic condensations or hemopoietic cell foci at E6, the latter becoming negative at E9. The heart ventricle displayed a patchwork of positive and negative nuclei from E6 to E10. A myc signal restricted to the quail species was found In the wall of the carotid arteries. Cell nuclei in the nervous system displayed a detectable signal which became restricted to postmitotic neurones. In the ectoderm, the c-myc protein was generally not present after E4, except In presumptive feather buds at the time of epitheliomesenchymal interactions. Endodermal cells (such as hepatocytes, oesophageal and tracheal epithelia) did not express detectable levels of c-myc at any time.

Our results reveal a time- and tissue-specific expression of c-myc during avian development. It is noteworthy that the expression of the c-myc protein often appears dissociated from cell proliferation as shown by the absence of the signal in endodennal cells at E3-E13 as well as its presence in postmitotic neurones.

Finally, although RNA and protein are simultaneously detected in some structures such as presumptive feather buds, their expression is dissociated in endodermal tissues, notably hepatocytes, where in situ hybridization detects a large number of RNA copies with no detectable protein signal.
The correlation between patterns of dye transfer through gap junctions and future developmental fate in Xenopus: the consequences of u.v. irradiation and lithium treatment
Authors: Nagajski D. J. , Guthrie S. C. , Ford C. C. , Warner A. E.
Published: April 2021

The correlation between cell-to-cell communication through gap junctions at the 32-cell stage and the subsequent patterning of the embryonic axis has been examined in Xenopus laevis embryos. Disturbances of embryonic axis formation were generated by exposure to u.v. irradiation at the vegetal pole before 0·6 in the cell cycle, which generates embryos with dorsal axial deficiencies. Alternatively embryos were treated with 100 mm-lithium chloride between the 2-cell and 32-cell stage, which generates embryos with ventral axial deficiencies. The cell-to-cell transfer of Lucifer Yellow was used to monitor junctional permeability. Injections were made into animal hemisphere cells, lying in tiers 1 and 2 of the 32-cell embryo, whose position relative to the future dorsoventral axis of the embryo was determined on the basis of differences in pigmentation. The frequency of Lucifer Yellow transfer in the future dorsal half of the animal hemisphere was compared with that in the future ventral half for control (untreated), u.v.-irradiated and Li-treated embryos. Injected embryos were subsequently scored for axial development for comparison with dye transfer frequencies.

In control embryos at the 32-cell stage, Lucifer Yellow transfer was both more frequent and more extensive in future dorsal regions than in future ventral regions, as observed previously. In embryos that had been u.v. irradiated before 0·6 in the first cell cycle, Lucifer transfer was the same in both light and dark regions of the animal hemisphere and at the low level characteristic of future ventral regions in normal embryos. These embryos developed with massive reductions in dorsal axial structures. Embryos irradiated after 0-8 in the first cell cycle, when u.v. irradiation no longer inhibits the cytoplasmic movements initiated at fertilization, showed a normal dorsoventral difference in Lucifer Yellow transfer and developed with normal dorsoventral polarity. Embryos exposed to 100mm-LiCl contained 1·4 mm-lithium at the end of the treatment period. The transfer of Lucifer Yellow between animal pole cells of 32-cell embryos previously treated with LiCl was the same in both light (dorsal) and dark (ventral) and at the high level characteristic of future dorsal regions in normal embryos. Such embryos subsequently developed with substantial ventral axis deficiencies. U.v.-irradiated embryos subsequently treated with lithium showed transfer rates in ventral regions equivalent to that in embryos treated with Li alone and developed with ventral axial deficiencies. We conclude that the frequency with which Lucifer Yellow transfers through gap junctions at the 32-cell stage indicates the future developmental fate of animal cells and can be used to predict the subsequent organization of the embryonic axis.
Evidence that elevated intracellular cyclic AMP triggers spore maturation in Dictyostelium
Authors: Kay Robert R.
Published: April 2021

Spore maturation occurs during normal development in Dictyostelium when environmental influences induce a migrating slug to transform into a fruiting body. As the amoeboid prespore cells turn into refractile spores there is a burst of enzyme accumulation, including UDP-galactose epimerase, and at a later stage the exocytosis of preformed components of the spore coat. Evidence is presented here that this process is triggered by an elevated intracellular cAMP concentration.

First, a number of rapidly developing (rde) mutants, whose cAMP metabolism had been investigated previously, are shown to be able to form spores in submerged monolayers, whereas wild-type strains are not. The phenotypes of these mutants are best explained by a derepression of the signal transduction pathway utilizing intracellular cAMP.

Second and more direct, it is shown that the permeant cAMP analogues 8-Br-cAMP and 8-chlorophenylthio-cAMP, but not cAMP itself, can rapidly induce spore differentiation in wild-type amoebae incubated in submerged monolayers. These analogues also stimulate accumulation of UDP-galactose epimerase in slug cells transferred to shaken suspension.

The ability to induce spore differentiation with Br-cAMP in wild-type strains provides a new technique that can be exploited in various ways. For instance, spore differentiation in strain V12M2 is induced by 8-Br-cAMP at very low cell densities, suggesting that neither cell contact nor additional soluble inducers are necessary in these conditions. In contrast NC4 cells may require an additional inducer. Spore differentiation is inhibited by the stalk-specific inducer DIF-1 suggesting that DIF-1 inhibits a target downstream of intracellular cAMP in the signal transduction pathway inducing spore differentiation.
The durations and compositions of cell cycles in embryos of the leech, Helobdella triserialis
Authors: Bissen Shirley T. , Weisblat David A.
Published: April 2021

When tritiated thymidine triphosphate ([3H]TTP) or its immunohistochemically detectable analogue, bromodeoxyuridine triphosphate (BrdUTP), is injected into blastomeres of leech embryos it passes throughout the entire embryo and is rapidly incorporated (within 2 min after injection) into nuclei of cells synthesizing DNA (S phase). In the same embryos a DNA-specific stain can be used to identify cells in mitosis (M phase) or nonreplicative interphase (G1 or G2 phase) on the basis of nuclear or chromosomal morphology. Using this procedure, we have determined the lengths and compositions of the mitotic cell cycles of identifiable cells in early embryos of the leech, Helobdella triserialis, and have analysed how the cell cycles change during the first seven stages of development. The relatively short cell cycles of the early blastomeres comprise not only phases of M and S, but also postreplicative gap (G2) phases. The lengthening of the cell cycles that occurs as development progresses is primarily accomplished by an increase in the length of G2 and secondarily by an increase in the length of S and, in some instances, the addition of a prereplicative gap (G1) phase; M phase remains relatively constant. These data suggest that the durations of the cell cycles of embryonic cells are regulated by a variety of mechanisms.
Identification of genes that interact with glp-1, a gene required for inductive cell interactions in Caenorhabditis elegans
Authors: Maine Eleanor M. , Kimble Judith
Published: April 2021

The glp-1 gene functions in two inductive cellular interactions and in development of the embryonic hypodermis of C. elegans. We have isolated six mutations as recessive suppressors of temperature-sensitive (ts) mutations of glp-1. By mapping and complementation tests, we found that these suppressors are mutations of known dumpy (dpy) genes; dpy genes are required for development of normal body shape. Based on this result, we asked whether mutations previously isolated in screens for mutants defective in body shape could also suppress glp-1 (ts). From these tests, we learned that unselected mutations of eight genes required for normal C. elegans morphogenesis, including the four already identified, suppress glp-l(ts). All of these suppressors rescue all three mutant phenotypes of glp-l(ts) (defects in embryonic induction of pharyngeal tissue, in embryonic hypodermis development, and in induction of germline proliferation). However, they do not rescue putative glp-1 null mutants and therefore do not bypass the requirement for glp-1 in development. In the light of current ideas about the molecular nature of the glp-1 and suppressor gene products, we propose an interaction between the glp-1 protein and components of the extracellular matrix and speculate that this interaction may impose spatial constraints on the decision between mitosis and meiosis in the germline.
l(1)pole hole is required maternally for pattern formation in the terminal regions of the embryo
Authors: Ambrosio Linda , Mahowald Anthony P. , Perrimon Norbert
Published: April 2021

Maternal expression of the l(l)pole hole (l(l)ph) gene product is required for the development of the Drosophila embryo. When maternal l(l)ph+ activity is absent, alterations in the embryonic fate map occur as visualized by the expression of segmentation genes fushitarazu and engrailed. If both maternal and zygotic activity is absent, embryos degenerate around 7h of development. If only maternal activity is missing, embryos complete embryogenesis and show deletions of both anterior and posterior structures. Anteriorly, structures originating from labral and acron head regions are missing. Posteriorly, abdominal segments A8, 9 and 10, the telson and the proctodeum are missing. Similar pattern deletions are observed in embryos derived from the terminal class of female sterile mutations. Thus, the maternal 1(1)ph+ gene product is required for the establishment of cell identities at the anterior and posterior poles of the Drosophila embryo.
The effects of phorbol ester on mouse blastomeres: a role for protein kinase C in compaction?
Authors: Bloom Theodora L.
Published: April 2021

The effects of phorbol myristate acetate (PMA) and other activators of protein kinase C on the cytoskeletal organization of mouse oocytes and early embryos have been examined. The effects observed depended on the developmental stage on exposure to PMA. PMA had little effect on the cytoskeletal or microvillous organization of unfertilized oocytes. Interphase cells from embryos prior to compaction showed limited disruption and loss of microvilli when exposed to PMA and foci of polymerized actin remained visible in the cytocortex of embryos up to the early 8-cell stage. When compacted late 8-cell embryos were exposed to PMA, most microvilli were lost and little polymerized actin remained in the cytocortex. PMA also caused loss of microtubules from compact 8-cell embryos under some experimental conditions. Intercellular flattening was both prevented and reversed. The relevance of these observations to the rearrangement of cell-cell contacts and cytoskeletal organization seen during compaction at the 8-cell stage is discussed and a possible role for protein kinase C in the generation of cell polarity proposed.
Analysis of competence: receptors for fibroblast growth factor in early Xenopus embryos
Authors: Gillespie L. L. , Paterno G. D. , Slack J. M. W.
Published: April 2021

Xenopus ectodermal cells have previously been shown to respond to acidic and basic FGF by differentiating into mesodermal tissue. In the present study, ectodermal explants from Xenopus blastulae were shown to have high affinity binding sites for 125I-aFGF (Kd = l·4× 10−10M). The total number of sites, determined by Scatchard analysis, was 3× 108 per explant (surface area of approximately 1mm2). Two putative receptors of relative molecular mass 130 000 and 140 000 were identified by chemical crosslinking to 125I-aFGF. Both acidic and basic FGF, but not TGFβ2, could compete for affinity labelling of these bands. The receptor density at the cell surface parallels the developmental competence of Xenopus animal pole cells to respond to FGF. Receptors are present at highest density in the marginal zone but are not restricted to cells in this region.
fushi tarazu protein expression in the cellular blastoderm of Drosophila detected using a novel imaging technique
Authors: Karr Timothy L. , Kornberg Thomas B.
Published: April 2021

The fushi tarazu (ftz) gene is essential for segmentation of the Drosophila embryo. This requirement is reflected at the cellular blastoderm stage of embryogenesis by seven transverse stripes of ftz expression. These stripes correspond to the missing segments of ftz mutant embryos. We describe here novel intermediate patterns of ftz protein expression which were detected in younger embryos by using anti-ftz antibodies and a sensitive fluorescence/immunoperoxidase technique (‘filtered fluorescence imaging’, FFI). Striped patterns of ftz protein evolved continuously, and the different stripes appeared in an ordered sequence, involving both anterior-posterior (A/P) and dorsal-ventral (D/V) progressions. Comparison of these patterns of ftz protein with those of ftz RNA suggests that these novel aspects of the patterning process involve post-transcriptional regulation in addition to the transcriptional control known to be involved in expression of this gene.
Abnormal flowers and pattern formation in floral development
Authors: Meyerowitz Elliot M. , Smyth David R. , Bowman John L.
Published: April 2021

“From our acquaintance with this abnormal metamorphosis, we are enabled to unveil the secrets that normal metamorphosis conceals from us, and to see distinctly what, from the regular course of development, we can only infer.”

- J. W. von Goethe (1790)
Characterization of proteins secreted by sheep oviduct epithelial cells and their function in embryonic development
Authors: Gandolfi F. , Brevini Tiziana A. L. , Richardson Louise , Brown C. R. , Moor R. M.
Published: April 2021

The role in early development of proteins secreted by oviduct epithelial cells has been investigated. Secreted proteins devoid of serum contamination have been produced by the surgical removal and immediate incubation of oviduct cells in [3sS]methionine-containing medium. After electrophoretic separation, secreted polypeptides could be divided into those that were secreted uniformly throughout the oestrous cycle and a second class that showed a cyclical pattern of secretion. The first class of proteins represented a small proportion of total output whilst the predominant second class was composed mainly of polypeptides of Mr 92 and 46×103, respectively. Both of these polypeptide species, referred to as sheep oviduct proteins 92 and 46 (SOP 92, SOP 46), are detected only during the first 4 to 5 days after oestrus when the embryos are located in the oviduct. Oviduct cells collected at oestrus and maintained thereafter in culture secrete the same pattern of proteins and follow the same time course as their counterparts in vivo.

The interaction between the oviduct proteins and the developing embryo was studied firstly by determining whether any of the secreted proteins bound to the zona pellucida. The results of iodination studies showed that two polypeptides of MT 92 and 46×103, respectively, were bound to the zona pellucida of eggs removed from the oviduct but were absent from eggs that had not had contact with the oviduct epithelium. That these newly acquired proteins represent SOP 92 and 46 is suggested by their electrophoretic mobility and their ability to bind to the zona of follicular eggs when added in vitro and by the fact that they both disappear from the zonae of embryos after exit from the oviduct. The collection of unlabelled secreted proteins enabled us to produce a monoclonal antibody, which was used in the second series of experiments on oviduct-embryo interactions. The results confirmed that SOP 92 binds to the zona pellucida and moreover showed that this protein crosses the zona and becomes associated with the individual blastomeres of the developing embryo. These findings provide evidence that the mammalian oviduct probably plays a direct role in supporting embryonic development through specific polypeptides produced by its epithelium.
The small nuclear RNAs for pre-mRNA splicing are coordinately regulated during oocyte maturation and early embryogenesis in the mouse
Authors: Dean Wendy L. , Seufert Andrea C. , Schultz Gilbert A. , Prather Randall S. , Simerly Calvin , Schatten Gerald , Pilch Duane R. , Marzluff William F.
Published: April 2021

The abundance and localization of snRNAs and snRNPs involved in processing and splicing of pre-mRNA has been studied during early mouse embryogenesis. The amount of U1, U2, U4, U5 and U6 RNA remains relatively constant between the postovulatory oocyte and 2-cell stage but increases three- to ten-fold in quantity between the 2-cell and blastocyst stages. Localization was examined by in situ hybridization with Ul, U2 and U6 riboprobes and immunofluorescence microscopy using a monoclonal antibody to snRNP antigens. The snRNAs and snRNPs are primarily localized to the germinal vesicle in the preovulatory oocyte but are released and diluted within the cytoplasm of the oocyte during germinal vesicle breakdown and meiotic maturation. They subsequently relocalize to both pronuclei following fertilization and the nuclei of the 2-cell embryo following the first cleavage division. Since the amount of snRNA is constant during the first cleavage, the small amount of pre-mRNA that is synthesized at the time of transcriptional activation in the 2-cell embryo may be spliced and processed by snRNPs of maternal origin.
Transcription of the Spec 1-like gene of Lytechinus is selectively inhibited in response to disruption of the extracellular matrix
Authors: Wessel Gary M. , Zhang Wei , Tomlinson Craig R. , Lennarz William J. , Klein William H.
Published: April 2021

The influence of the extracellular matrix (ECM) on differential gene expression during sea urchin develop­ment was explored using cell-type-specific cDNA probes. The ECM of three species of sea urchins, Strongylocen- trotus purpuratus, Lytechinus variegatus and Lytechinus pictus, was disrupted with the lathrytic agent /5-amino- propionitrile (BAPN), which inhibits collagen deposition in the ECM and arrests gastrulation (Wessel & McClay, Devi Biol. 121: 149, 1987). The levels of several mRNAs (Spec 1, Spec 2, Cylla actin, Cyllla actin and collagen in S. purpuratus, and metallothionine, ubiquitin and LpS3 in L. pictus and L. variegatus) were compared in BAPN- treated and control embryos. These mRNAs accumu­lated normally during BAPN treatment, even though the embryos did not gastrulate. To determine if the ex­pression of any gene product is sensitive to ECM disruption, a differential cDNA screen compared poly (A+) RNA from BAPN-arrested and control embryos in Lytechinus. A cDNA clone was isolated from this screen that represented a 2Ί kb mRNA that did not accumulate during BAPN treatment. Removal of BAPN resulted in the accumulation of this transcript coincident with the onset of gastrulation. This cDNA clone encodes a L. variegatus homologue of LpSl, recently demonstrated to be an ancestral homologue of the aboral ectoderm- specific Spec 1-Spec 2 gene family in S. purpuratus. Nuclear run-on assays in L. pictus suggested that transcriptional activity of LpSl was selectively inhibited by BAPN treatment. Thus, although the accumulation of many gene products occurred independently of the embryonic collagenous matrix, the accumulation of LpSl and LvSl appeared to be mediated by the ECM.
Poly(A) shortening accompanies the activation of translation of five mRNAs during spermiogenesis in the mouse
Authors: Kleene Kenneth C.
Published: April 2021

I have compared the quantity and the length of the poly(A) tracts of five haploid-expressed mRNAs in the polysomal and nonpolysomal fractions of round and elongating spermatids in mice: transition proteins 1 and 2, protamines 1 and 2, and an unidentified mRNA of about 1050 bases. Postmitochondrial supernatants of highly enriched populations of round and elongating spermatids (early and late haploid spermatogenic cells) were sedimented on sucrose gradients, and the size and amount of each mRNA in gradient fractions were analyzed in Northern blots. In round spermatids, all five mRNAs are restricted to the postpolysomal fractions, but in elongating spermatids about 30–40% of each mRNA is associated with the polysomes. The distribution of these mRNAs in sucrose gradients suggests that all five mRNAs are stored in a translationally repressed state in round and early elongating spermatids, and that they become translationally active in middle and late elongating spermatids. The translationally repressed forms of all five mRNAs are long and homogenous in size, whereas the polysomal forms are shorter and more heterogenous due to shortening of their poly (A) tracts. The relationship between translational activity and poly(A) size exemplified by these five mRNAs may be typical of mRNAs which are translationally repressed in round spermatids and translationally active in elongating spermatids.
Differential localization of villin and fimbrin during development of the mouse visceral endoderm and intestinal epithelium
Authors: Ezzell Robert M. , Chafel Mark M. , Matsudaira Paul T.
Published: April 2021

The apical surface of transporting epithelia is specially modified to absorb nutrients efficiently by amplifying its surface area as microvilli. Each microvillus is supported by an underlying core of bundled actin filaments. Villin and fimbrin are two actin-binding proteins that bundle actin filaments in the intestine and kidney brush border epithelium. To better understand their function in the assembly of the cytoskeleton during epithelial differentiation, we examined the pattern of villin and fimbrin expression in the developing mouse using immunofluorescence and immunoelectron microscopy. Villin is first detected at day 5 in the primitive endoderm of the postimplantation embryo and is later restricted to the visceral endoderm. By day 8-5, villin becomes redistributed to the apical surface in the visceral endoderm, appearing in the gut at day 10 and concentrating in the apical cytoplasm of the differentiating intestinal epithelium 2–3 days later. In contrast, fimbrin is found in the oocyte and in all tissues of the early embryo. In both the visceral endoderm and gut epithelium, fimbrin concentrates at the apical surface 2–3 days after villin; this redistribution occurs when the visceral endoderm microvilli first contain organized microfilament bundles and when microvilli first begin to appear in the gut. These results suggest a common mechanism of assembly of the absorptive surface of two different tissues in the embryo and identify villin as a useful marker for the visceral endoderm.
Exclusionary dendritic interactions in the retina of the goldfish
Authors: Hitchcock Peter F.
Published: April 2021

The retina of the goldfish grows throughout its life, in part, by the addition of new neurons at the margin. New ganglion cells added at the margin tend not to grow their dendritic arbors into the older, central retina. Hitchcock and Easter (J. Neurosci. 6, 1037-1050 (1986)) proposed that the dendrites of the new cells were prevented from extending centrally within the inner plexiform layer by the dendrites of the previous generations of cells. This proposal was tested by first killing existing ganglion cells with a retrogradely transported neurotoxin (propidium iodide; PI), and then observing the orientation and branching pattern of the dendrites of ganglion cells added subsequently at the margin. Dendrites were stained in retinal wholemounts by intracellular injections of Lucifer yellow. The data showed that cells added subsequent to the PI treatment grew their dendritic arbors preferentially toward central retina consistent with the hypothesis. It is concluded that interactions among adjacent ganglion cells regulates dendritic growth.
Glial interactions with neurons during Drosophila embryogenesis
Authors: Fredieu John R. , Mahowald Anthony P.
Published: April 2021

A monoclonal antibody (Mab5B12) demonstrating speci-ficity for glial cells within the central and peripheral nervous systems of Drosophila has been used in combi-nation with neural-specific antibodies to study the early organization of the Drosophila embryo. The embryonic central nervous system of Drosophila contains cells within the ventral midline that are recognized by mono-clonal antibody 5B12. These cells are not recognized by either a polyclonal antiserum to horse radish peroxidase, which recognizes several antigens on the surface of Drosophila neurons, or Mab22C10, which recognizes an antigen specific to the peripheral nervous system. Mab5B12-positive cells lie dorsal both to the developing anterior and posterior commissures in each thoracic and abdominal segment and to the supraoesophageal com-missure. They ensheath these commissures in later stage embryos. Other Mab5B12-positive cells lie dorsolateral to the CNS and send processes laterally to the lateral sensilla during axonogenesis in the PNS. These cells surround the axons of the intersegmental and segmental nerves. Other cells that line the advancing ectoderm during dorsal closure and surround the anal pads also express the Mab5B12 antigen. Neuronal cell cultures derived from Drosophila gastrulae contain cells express-ing the Mab5B12 antigen. These cells can be found separate or in close association with neuronal clusters and their axons.
Mouse homeo-genes within a subfamily, Hox-1.4, -2.6 and -5.1, display similar anteroposterior domains of expression in the embryo, but show stage- and tissue-dependent differences in their regulation
Authors: Gaunt Stephen J. , Krumlauf Robb , Duboule Denis
Published: April 2021

By use of in situ hybridization experiments on mouse embryo sections, we compare the transcript patterns of three homeo-genes from the Hox-1.4 subfamily (Hox- 1.4, -2.6 and -5.1). Genes within a subfamily are true homologues, present in the genome as a result of duplication of an ancestral homeo-gene cluster.

We show that Hox-1.4, -2.6 and -5.1 are similar, although apparently not identical, in the limits of their transcript domains along the anteroposterior axis. Within the prevertebral column of the day embryo, for example, the anterior boundary of transcripts for each of the three genes was most obvious at the junction of the first and second prevertebrae. Similarly, all three genes showed an anterior boundary of transcripts within the central nervous system that was located in the midmyelencephalon of the hindbrain. Both in the prevertebral column and hindbrain, however, Hox-2.6 and Hox-5.1 transcripts extended slightly anterior to the anteriormost limits detected for Hox-1.4.

In spite of close similarities in the positions of their transcript domains, Hox-1.4, -2.6 and -5.1 displayed striking stage- and tissue-dependent differences in the relative abundance of their transcripts. For example, Hox-5.1 transcripts were abundant within mesoderm and ectoderm of early stages ( and days), yet were detected only weakly in mesodermal components of the lung and stomach at days, and were apparently absent from these tissues at days. In contrast, Hox-1.4 and Hox-2.6 transcripts were relatively weakly detected at and days, but were abundant within the lung and stomach at days. Our findings suggest, but do not prove, that genes within the Hox-1.4 subfamily might be coordinately regulated in their expression.

We discuss the patterns of mouse homeo-gene expression now observed in terms of models originally devised for Drosophila. We also propose how our new findings may help to explain any selective advantage to the vertebrates of homeo-gene duplication to form subfamilies.
Regionalisation of the mouse embryonic ectoderm: allocation of prospective ectodermal tissues during gastrulation
Authors: Tam Patrick P. L.
Published: April 2021

The regionalisation of cell fate in the embryonic ectoderm was studied by analyzing the distribution of graft-derived cells in the chimaeric embryo following grafting of wheat germ agglutinin-gold-labelled cells and culturing primitive-streak-stage mouse embryos. Embryonic ectoderm in the anterior region of the egg cylinder contributes to the neuroectoderm of the prosencephalon and mesencephalon. Cells in the distal lateral region give rise to the neuroectoderm of the rhombencephalon and the spinal cord. Embryonic ectoderm at the archenteron and adjacent to the middle region of the primitive streak contributes to the neuroepithelium of the spinal cord. The proximal-lateral ectoderm and the ectodermal cells adjacent to the posterior region of the primitive streak produce the surface ectoderm, the epidermal placodes and the cranial neural crest cells. Some labelled cells grafted to the anterior midline are found in the oral ectodermal lining, whereas cells from the archenteron are found in the notochord. With respect to mesodermal tissues, ectoderm at the archenteron and the distal-lateral region of the egg cylinder gives rise to rhomben-cephalic somitomeres, and the embryonic ectoderm adjacent to the primitive streak contributes to the somitic mesoderm and the lateral mesoderm. Based upon results of this and other grafting studies, a map of prospective ectodermal tissues in the embryonic ectoderm of the full-streak-stage mouse embryo is constructed.
Developmental stages of fetal-type Leydig cells in prepubertal rats
Authors: Kuopio T. , Tapanainen J. , Pelliniemi L. J. , Huhtaniemi I.
Published: April 2021

Fetal Leydig cells were studied in rats during and after the perinatal-neonatal period by comparing changes in morphology, number and volume with changes in testicular steroids and serum luteinizing hormone (LH) concentration. Stereologic examination indicated regression of fetal Leydig cells in testis by showing that their total volume as well as the average cell volume decreased between prenatal day 20 and postnatal day 3. The total number and total volume of cells both increased between postnatal days 3 and 11 but the average cell volume did not change during the same time period. Determination of serum LH showed a close correlation between an increase in LH concentration and increases in total number and volume of cells. The combined number of fetal- and adult-type Leydig cells on day 20 was more than 20 times the number of fetal cells at 3 days of age. Electron microscopic analysis showed that fetal Leydig cells after birth formed conspicuous clusters, which were surrounded by a layer of envelope cells and extracellular material. Occasional dividing fetal Leydig cells and possible precursors of fetal or adult Leydig cells were observed. Mitoses of spindle-shaped pericordal cells were frequent during the neonatal period. During and after the second postnatal week fetal Leydig cells again showed signs of regression, indicated by disintegration of the cell clusters, a decrease in cell size, accumulation of collagen between the cells and a decrease in steroid content per cell. The cytoplasm showed no degenerative changes, but the shape of the nuclei changed from spherical into irregular.

The present results suggest that the perinatal regression of fetal Leydig cells is followed by an LH-induced phase of growth. This growth period precedes a second phase of regression that coincides with early development of adult-type cells reported earlier. Contrary to the present concept of a biphasic pattern of Leydig cell development in rat, we suggest three consecutive stages: fetal (fetal cells in fetal testis), early juvenile (fetal cells during neonatal-early juvenile life) and juvenile-adult (adult cells before and after puberty). The regression of the fetal cells suggests that they have only a minor role in testicular hormone production after the appearance of adult-type Leydig cells prior to puberty.
Fibroblast growth factor (FGF) induces different responses in lens epithelial cells depending on its concentration
Authors: McAvoy J. W. , Chamberlain C. G.
Published: April 2021

We reported previously that epithelial cells in expiants from neonatal rat lenses, when cultured in the presence of fibroblast growth factor (FGF), showed increased proliferation, cell migration and fibre differentiation; moreover, fibre differentiation in response to the basic form of FGF (bFGF) was virtually completely blocked by an anti-bFGF antibody. In the present study, we report a detailed analysis of the effects of bFGF on cells in the central region of lens epithelial explants. Proliferation in explants was assessed by measuring [3H]thymi-dine incorporation. Cell migration was measured by labelling cells in explants with fluorescein isothiocyanate (FITC)-dextran and monitoring them by UV fluorescence microscopy. Fibre differentiation in explants was assessed on the basis of β-crystallin accumulation. This study showed that half maximal activities for the three responses, proliferation, migration and fibre differentiation, were achieved at different concentrations of bFGF, namely, 0·15, 3 and 40 ng ml-1, respectively. Thus, the response of lens epithelial cells to bFGF varied qualitatively, as well as quantitatively, as the concentration increased. Monitoring FITC-dextran injected cells for up to 5 days after exposure to bFGF allowed analysis of the interrelation between various responses to bFGF in individual cells. As expected some cells divided in response to FGF, mainly within the first three days. However, whether or not they divided, all labelled cells responded to FGF by migrating and elongating. Maximal migration occurred during the first day of culture and maximal elongation was achieved by day 4. It was also found that [3H]thymidine incorporation and cell migration were substantially inhibited (90–93 %) by the anti-bFGF antibody shown previously to inhibit fi-crystallin accumulation, providing strong support for the conclusion that FGF is the molecule responsible for inducing all three responses. All these findings lead us to suggest that variations in FGF concentration in the different ocular media may be involved in controlling and maintaining lens polarity and lens growth patterns.
Cellular insertion of primary and secondary myotubes in embryonic rat muscles
Authors: Duxson M. J. , Usson Y.
Published: April 2021

Mammalian muscles develop from two populations of myotubes; primary myotubes appear first and are few in number; secondary myotubes appear later and form most of the muscle fibres. We have made an ultrastructural study to investigate how primary and secondary myotubes in embryonic rat muscles transmit tension during the period of their development. Primary myotubes extend from end to end of the muscle from the earliest times, and attach directly to the tendon. In contrast, newly formed secondary myotubes are short cells which insert solely into the primary myotubes by a series of complex interdigitating folds along which adhering junctions occur. As the secondary myotubes lengthen and mature, their insertion is progressively transferred from the primary myotube to the tendon proper. We suggest that this variable insertion of immature secondary myotubes, combined with complex patterns of innervation and electrical coupling in developing muscle, makes it difficult to predict the overall contribution of secondary myotubes to muscle tension development. This work extends other studies showing the unique relationship between a primary myotube and its associated secondary myotubes, indicating that these may constitute a developmental compartment.
Cell lines with developmental potential restricted to mesodermal lineages isolated from differentiating cultures of pluripotential P19 embryonal carcinoma cells
Authors: Rudnicki Michael A. , Reuhl Kenneth R. , McBurney Michael W.
Published: April 2021

Embryonal carcinoma (EC) cells are developmentally pluripotential cells which can be induced to differentiate in cell culture to form a wide variety of cell types. To investigate the lineage relationships between cells of different types, we set out to isolate cell lines with multiple but restricted developmental potentials from differentiating cultures of P19 cells, a line of EC. By selecting for differentiated cells capable of anchorage independent growth, we isolated cell lines which differentiated in high density cultures to form at least two cell types; myocytes that resembled fetal skeletal muscle cells and loose connective tissue cells that secreted large amounts of type I collagen. These results suggest that skeletal myocytes and connective tissue share a common precursor and that stem cells with limited but multiple developmental potentials can be isolated from differentiating cultures of P19 cells.
Ontogeny and tissue distribution of leukocyte-common antigen bearing cells during early development of Xenopus laevis
Authors: Ohinata Hiroshi , Tochinai Shin , Katagiri Chiaki
Published: April 2021

To analyze the ontogenic emergence of leukocytes during early development, a mouse monoclonal antibody (IgG1), designated as XL-1, was produced against the peritoneal macrophages of adult Xenopus laevis. The XL-1 determinant was expressed on all types of leukocytes, including lymphocytes, granulocytes, thrombocytes and macrophages, but not on erythrocytes of either larvae or adults. Immunohistochemical observations of the hemopoietic organs revealed that the XL-1+ cells with granulocyte and/or macrophage morphology appeared at st.36–37 in the liver, at st.44–45 in the mesonephric and the thymus rudiments, and at st.47 in the spleen. The XL-1 determinant was expressed on the precursor cells of T lymphocytes in the thymus rudiments at st.46–47, on the pre-B cells in the liver rudiments at st.47, and on lymphocytes in the spleen at st.48–49. A few XL-1+ cells were present in the ventral blood island of the st.35/36 embryos, where differentiating erythrocytes had predominated since st.28. XL-1+ cells with a macrophage-like morphology were found in several locations of the mesenchyme in the st.32 embryos, before the establishment of vascularization at st.33/34 and far earlier than the emergence of lymphocytes.
Bone formation following intrarenal transplantation of isolated murine chondrocytes: chondrocyte-bone cell transdifferentiation?
Authors: Moskalewski Stanislaw , Malejczyk Jacek
Published: April 2021

Isolated syngeneic epiphyseal chondrocytes transplanted into a muscle formed cartilage in which matrix resorption and endochondral ossification began at the end of the second week after transplantation. After 56 days cartilage was converted into an ossicle. In 7-day-old intrarenal transplants, epiphyseal chondrocytes formed nodules of cartilage. In 10-day-old transplants, islands of bone appeared. Slight resorption of cartilage was first noted in 14-day-old transplants of chondrocytes. After eight weeks, transplants contained mainly bone. Intramuscularly transplanted rib chondrocytes formed cartilage which did not ossify. Nevertheless, bone islands appeared in intrarenal transplants of rib chondrocytes. Bone was not formed in allogeneic intrarenal transplants of epiphyseal or rib chondrocytes, but appeared in such transplants in animals immunosuppressed by anti-thymocyte serum and procarbazine. When spleen cells from animals immunized with allogeneic chondrocytes were transferred to immunosuppressed chondrocyte recipients two weeks after intrarenal chondrocyte transplantation, the majority of osteocytes in bone islands was dead. On the other hand, endochondral bone formed in intramuscular transplants of allogenic epiphyseal chondrocytes in immunosuppressed recipients was not damaged by sensitized spleen cells. This suggested that bone in 10- to 14-day-old intrarenal transplants of chondrocytes arose from injected cells and not by induction. To see whether bone was formed by chondrocytes or by some cells contaminating the chondrocyte suspension, the superficial layer of rib cartilage was removed by collagenase digestion and only more central chondrocytes were used for transplantation. Intrarenal transplants of these chondrocytes also yielded bone. Furthermore, in some experiments intrarenal transplants of syngeneic rib chondrocytes were stained in toto by Alcian blue and Alizarin red S 7 and 14 days after transplantation and examined under a dissecting microscope. In 7-day-old transplants only cartilage nodules could be found while in the older ones cartilage and bone or only bone islands were present. These results strongly suggest that in intrarenal transplants epiphyseal and rib chondrocytes transdifferentiated into bone cells. It also seems that chondrocytes first formed cartilage matrix which, after their transdifferentiation, was substituted by bone matrix.
Cell lineage and pattern formation in the earthworm embryo
Authors: Storey Kate G.
Published: April 2021

The pattern of segmental contribution of teloblasts in the earthworm embryo was examined by injection of the lineage tracer HRP and by studying the timing and symmetry of the first few divisions in each teloblast bandlet . The changing spatial relationship of the ectoteloblasts during development was also used to assess segmental contributions. A mathematical method for determining the cell cycle time of each teloblast is presented. The teloblasts and their immediate progeny, the blast cells, were found to undergo unique and highly stereotyped patterns of division which lead to equally stereotyped patterns of contribution in the segments apparent in the later embryo.
Delayed determination of claw laterality in lobsters following loss of target
Authors: Govind C. K. , Pearce Joanne
Published: April 2021

Lateralization of the paired claws into a major crusher and a minor cutter type is determined during the 4th and 5th stages of juvenile development of the lobster, Homarus americanus. Loss of both claws during this critical period delays the determination of laterality until the 6th stage when regenerate claws are present. Continued loss into the 6th stage, and beyond, however, suppresses laterality, resulting in lobsters with paired cutter claws.

The critical period for determining claw laterality may therefore be extended for a brief time to cater for claw loss, which is especially common in these early juvenile stages.