bluuebunny/crossref_metadata_2025 huggingface dataset:
Genomic imprinting and allelic exclusion
Authors: Holliday Robin
Published: April 2021

In diploid cells, allelic exclusion reduces genes to functional haploidy, because only one of two alleles is active. It is best known in cells producing immunoglobulins, but other examples also exist. X-chromosome inactivation in female mammals is related to allelic exclusion, but in this case the dosage compensation mechanism extends to the whole chromosome. Functional hemizygosity in some mammalian cell lines is probably also due to allelic exclusion, where one autosomal allele is active and the other is methylated and inactive.

In early development, it may be important to have only one functional copy of specific regulatory genes. If one considers the possible mechanisms whereby genes are switched from an active to an inactive form, or vice versa, complications arise if the same type of switch operates in two homologous chromosomes segregating independently at mitosis. This complication is avoided if one of the genes is totally inactive. It is therefore suggested that important regulatory genes are subject to allelic exclusion and that this provides a basis for genomic imprinting. Male or female gametes complement in the zygote, because they may have different inactive genes, and the active allele in each case is then functionally haploid in the zygote and developing embryo. These haploid genes would be those involved in critical switches of gene activity during the developmental process. Allelic exclusion imposed by imprinting might be based on the heritable DNA methylation of the regulatory regions of silent genes.
Preferential X-chromosome inactivation, DNA methylation and imprinting
Authors: Monk Marilyn , Grant Mark
Published: April 2021

Non-random X-chromosome inactivation in mammals was one of the first observed examples of differential expression dependent on the gamete of origin of the genetic material. The paternally-inherited X chromosome is preferentially inactive in all cells of female marsupials and in the extra-embryonic tissues of developing female rodents. Some form of parental imprinting during male and female gametogenesis must provide a recognition signal that determines the nonrandomness of X-inactivation but its nature is thus far unknown. In the mouse, the imprint distinguishing the X chromosomes in the extra-embryonic tissues must be erased early in development since X-inactivation is random in the embryonic cells. Random X-chromosome inactivation leads to cellular mosaicism in expression and differential methylation of active and inactive X-linked genes. Transgene imprinting shares many features with X-inactivation, including differential DNA methylation.

In this paper we consider when methylation differences in early development affecting X-chromosome activity and imprinting are established. There are processes of methylation and demethylation occurring in early development, as well as changes in the activity of the DNA methylase itself. Methylation of a specific CpG site associated with activity of the X-linked PGK-1 gene has been studied. This site is already methylated on the Inactive X chromosome by 6·5 days’ gestation, close to the time of X-inactivation. However, differential methylation of this site is not the primary imprint marking the paternal X chromosome for preferential inactivation in the extra-embryonic membranes.

A consideration of factors influencing both X-chromosome inactivation and imprinting suggests that a process of communication and comparison between nonidentical alleles might by the basis for the differential modification and expression patterns observed.
A transgene insertional mutation at an imprinted locus in the mouse genome
Authors: DeLoia Julie A. , Solter Davor
Published: April 2021

Genetic imprinting in mice results in functional differences in the oocyte and spermatocyte genomes, as evidenced by both genetic and pronuclear transfer experiments. To gain insights into the molecular mechansims involved in the imprinting process, researchers have studied methylation phenotypes and expression of hemizygous transgenes associated with parental origin. In this report, we describe a transgenic mouse lineage in which expression of both the transgene and an endogenous gene at the insertion site are determined by the parent of origin. The mutation caused by transgene insertion shows variable expressivity and incomplete penetrance in addition to a modified dominant pattern of inheritance.
Disuse and passive stretch cause rapid alterations in expression of developmental and adult contractile protein genes in skeletal muscle
Authors: Loughna Paul T. , Izumd Seigo , Goldspink Geoffrey , Nadal-Ginard Bernado
Published: April 2021

Contractile proteins exist as a number of isoforms that show a developmental and tissue-specific pattern of expression. Using gene-specific cDNA probes, the expression of the sarcomeric myosin heavy chain (MHC) multi-gene family and of cardiac (foetal) α -actin was analysed in three different rat hindlimb muscles immobilised for 5 days in either the shortened or lengthened positions. For each of the MHC genes normally expressed in adult muscle (slow, DA and IIB), the effect of disuse alone (immobilisation in the shortened position) upon expression was markedly different to that of passive stretch (immobilisation in the lengthened position) in each of the three muscles. However, the same adult sarcomeric myosin heavy chain gene can be affected in a different, or even opposite, manner by either disuse or passive stretch depending on the muscle in which it is being expressed. The fast IIB MHC gene, for example, exhibits a rapid induction in the slow postural soleus muscle, in response to disuse but no such induction occurs in the faster plantaris and gastrocnemius muscles. Furthermore, the induction of this gene in the soleus was prevented by passive stretch. The MHC gene, normally only expressed in embryonic skeletal muscle, showed a similar response in all three muscles and was reinduced in adult muscle in response to passive stretch but not by disuse alone. In contrast, the isoform of α -actin which is normally only present in significant quantities in embryonic skeletal muscle and which is reduced postnatally, is not reinduced by passive stretch but is reduced still further by immobilisation in the shortened position.
The effects of protease inhibitors on axon growth through astrocytes
Authors: Fawcett James W. , Housden Elizabeth
Published: April 2021

We have shown in a previous paper (Devi Biol. 135, 449, 1989) that axons regenerating from postnatal neurons are unable to penetrate three-dimensional cultures of mature astrocytes, while axons from embryonic dorsal root ganglia (DRGs) and retina will grow through such cultures for considerable distances. We have now investigated the role of proteases in the penetration of three--dimensional astrocyte cultures by axons from embryonic DRGs. Embryonic DRGs were grown in association with three-dimensional astrocyte cultures, with astrocyte monolayers, and with-air dried collagen. The effects of inhibitors of the three families of proteases that have been shown to be involved in tumour cell invasion were investigated. The serine protease inhibitors EACA and Trasylol both reduced growth in three-dimensional astrocyte cultures to around 50% of control, but had little effect on growth on astrocyte monolayers or on collagen. TIMP, which inhibits collagenases, had no effect on growth on two- or three-dimensional cultures. Cbz-gly-phen-amide, an inhibitor of enteroproteases, reduced growth in all three types of culture.
Retinoid-binding protein distribution in the developing mammalian nervous system
Authors: Maden M. , Ong D. E. , Chytil F.
Published: April 2021

We have analysed the distribution of cellular retinol-binding protein (CRBP) and cellular retinoic acidbinding protein (CRABP) in the day 8.5–day 12 mouse and rat embryo. CRBP is localised in the heart, gut epithelium, notochord, otic vesicle, sympathetic ganglia, lamina terminalis of the brain, and, most strikingly, in a ventral stripe across the developing neural tube in the future motor neuron region. This immunoreactivity remains in motor neurons and, at later stages, motor axons are labelled in contrast to unlabelled sensory axons. CRABP is localised to the neural crest cells, which are particularly noticeable streaming into the branchial arches. At later stages, neural crest derivatives such as Schwann cells, cells in the gut wall and sympathetic ganglia are immunoreactive. An additional area of CRABP-positive cells are neuroblasts in the mantle layer of the neural tube, which subsequently appear to be the axons and cell bodies of the commissural system. Since retinol and retinoic acid are the endogenous ligands for these binding proteins, we propose that retinoids may play a role in the development and differentiation of the mammalian nervous system and may interact with certain homoeobox genes whose transcripts have also been localised within the nervous system.
Mouse Hox-3.4: homeobox sequence and embryonic expression patterns compared with other members of the Hox gene network
Authors: Gaunt S. J. , Coletta P. L. , Pravtcheva D. , Sharpe P. T.
Published: April 2021

A putative mouse homeobox gene (Hox-3.4) was previously identified 4 kb downstream of the Hox-3.3 (Hox-6.1)* gene (Sharpe et al. 1988). We have now sequenced the Hox-3.4 homeobox region. The predicted amino acid sequence shows highest degree of homology in the mouse with Hox-1.3 and -2.1. This, together with similarities in the genomic organisation around these three genes, suggests that they are comembers of a subfamily, derived from a common ancestor. Hox-3.4 appears to be a homologue of the Xenopus Xlhbox5 and human cpll genes (Fritz and De Robertis, 1988; Simeone et al. 1988). Using a panel of mouse-hamster somatic cell hybrids we have mapped the Hox-3.4 gene to chromosome 15.

From the results of in situ hybridization experiments, we describe the distribution of Hox-3.4 transcripts within the day mouse embryo, and we compare this with the distributions of transcripts shown by seven other members of the Hox gene network. We note three consistencies that underlie the patterns of expression shown by Hox-3.4. First, the anterior limits of Hox-3.4 transcripts in the embryo are related to the position of the Hox-3.4 gene within the Hox-3 locus. Second, the anterior limits of Hox-3.4 expression within the central nervous system are similar to those shown by subfamily homologues Hox-2.1 and Hox-1.3, although the tissuespecific patterns of expression for these three genes show many differences. Third, the patterns of Hox-3.4 expression within the spinal cord and the testis are very similar to those shown by a neighbouring Hox-3 gene (Hox-3.3), but they are quite different from those shown by Hox-1 genes (Hox-1.2, -1.3 and -1.4).
Developmental regulation of expression of the lactate dehydrogenase (LDH) multigene family during mouse spermatogenesis
Authors: Thomas Kelwyn , Mazo Jesus Del , Eversole Pam , Bellvé Anthony , Hiraoka Yukihiro , Li Steven S. L. , Simon Melvin
Published: April 2021

Expression of the Lactate Dehydrogenase (LDH) genes during various stages of spermatogenesis was studied by using a combination of Northern blot analyses and in situ hybridization techniques. These studies have indicated that developmentally programmed expression of all three functional LDH genes occurs during differentiation of germ cells. The LDH/C (ldh-3) gene was expressed exclusively during meiosis and spérmiogenesis, beginning in leptotene/zygotene spermatocytes and continuing through to the elongated spermatids. LDH/C (ldh-3) gene expression was accompanied by transient expression of the LDH/A (ldh-1) gene in pachytene spermatocytes and round spermatids. The LDH/B (Idh-2) gene was expressed mainly in Sertoli and spermatogonia! cells. By using somatic cell hybrids, the LDH/C (ldh-3) gene has been mapped to mouse chromosome 7, establishing that it is syntenic with the LDH/A (ldh-1) gene locus. Experimental observations made in this study provide new insight into the order and sequence of events involved in the regulation of gene expression of the LDH gene family during spermatogenesis.
Electrical Potential Differences Across the Foetal Membranes of the Rabbit
Authors: Krespi V. , Davies J.
Published: April 2021

The chemical composition of the foetal fluids in the rabbit was studied by Davies & Routh (1957). These investigators showed that the amniotic and exocoelomic fluids resembled extracellular fluid in their ionic composition whereas the allantoic fluid more closely resembled intracellular fluid. These findings were confirmed by Dickerson & McCance (1957).
The Effects of Vitamin A and Citral on Epithelial Differentiation in vitro 1. The Chick Tracheal Epithelium
Authors: Aydelotte Margaret B.
Published: April 2021

Differentiation of the tracheal epithelium of embryonic chicks was studied in organ cultures in a normal medium and in media containing added vitamin A and citral. In normal medium, the tracheal epithelium differentiated well, but usually fewer mucous cells developed than in the intact chick. High concentrations of vitamin A alcohol inhibited the differentiation of mucous cells and favoured that of ciliated cells. Citral, in fairly low concentrations, had opposite effects: it stimulated mucus-secretion and inhibited the differentiation of ciliated cells. In higher concentrations it stimulated division of the basal cells, and the epithelium became stratified and sometimes keratinized. Vitamin A and citral added together to the culture medium produced a citral effect, which varied in intensity according to the proportions of the two compounds, but was always milder than that resulting from treatment with the same concentration of citral alone. These results suggest that citral inhibits both the natural vitamin A in the plasma and the added synthetic vitamin A, thus producing changes in the tracheal epithelium characteristic of vitamin A deficiency. The results indicate that secretion of mucus by the tracheal epithelium is maximal at a lower concentration of vitamin A than that to which it is normally exposed in the body. It is suggested that vitamin A may influence epithelial differentiation partly by affecting the mitotic rate.
The Effect of Chloroacetophenone on the Development of Planorbis (Indoplanorbis) exustus (Deshayes)
Authors: Mulherkar Leela , Sherbet Gajanan V.
Published: April 2021

The effect of chloroacetophenone (CAP) on the developmental stages of Planorbis (Indoplanorbis) exustus (Deshayes) has been studied. Treatment with the substance caused (a) exogastrulation, (b) inhibition of cytoplasmic and nuclear division of the big endoderm cells, (c) arrest of development accompanied by enlargement of blastomeres or delay in development, (d) a reversal of the flattening which normally follows cleavage, and (e) a secondary fusion of the micro- and megameres. The phase of development from the second cleavage to the fourth cleavage seemed to be CAP-susceptible and the period between the third cleavage and the third cleavage-flattened stages seemed to be critical from the point of view of production of exogastrulae. The exogastrulae which had developed for 77 hours showed some differentiation. The effect of CAP on the vegetative hemisphere was striking. The CAP-susceptible phase in general coincides with the process of ooplasmic segregation taking place in the cleaving egg, and the critical phase, in particular, coincides with the establishment of the -SH rich ectoplasm. The other abnormalities caused by the substance are interrelated and are explained on the basis of a probable –SH and –SS– balance existing in the cortical region of the blastomeres. The results have been interpreted to indicate that integrity of –SH groups is important in the morphogenesis of the species studied.
A Study of the Developmental Relationship Between Enterochromaffin Cells and the Neural Crest
Authors: Andrew Ann
Published: April 2021

Explants were made of blastoderm of chick embryos from definitive primi-tive streak-to 22-somite stages. Definitive and potential neural crest and neural plate were excluded from experimental expiants, and included in controls. The expiants were cultured as chorio-allantoic grafts for a total of 17 to 18 days ; the grafts were, therefore, of 18 to 20 days’ total incubation age on their final retrieval. This period was more than adequate for the differentiation of enterochromaffin cells. The elimination of neural crest cells from experimental expiants, and their inclusion in control ones, was confirmed by the absence of known neural crest derivatives from the former, and their presence in the latter. Differentiation of intestine in grafts, adequate for the appearance of entero-chromaffin cells, was assessed according to criteria based on the histology of normal chick embryo gut at, and soon after, the first appearance of enterochromaffin cells. Enterochromaffin cells occurred in well-differentiated gut, whether in control or experimental grafts. They appeared to be present in numbers at least as great as in normal gut. It is concluded that enterochromaffin cells are not derived from the neural crest. Evidence purporting to support their origin from other sources is discussed and found to be inconclusive.
An Immunoembryological Study of the Chick Iris
Authors: Maisel Harry , Harmison Charles
Published: April 2021

Using immunological techniques it has been shown that in all major vertebrate species the lens, iris and pigment retina of the eye share common antigens (Langman & Prescott, 1959; Maisel & Langman, 1961; Flickinger & Stone, 1960; Maisel, 1962). These data are of particular interest since in certain animals the iris has the ability to form a lens or lens cells in the absence of the original lens. Indeed, lens regeneration from the dorsal iris is well documented in the genus Triturus (Stone, 1952; Reyer, 1954). Although McKeehan (1961) and Woerdeman (1962) did not record lens regeneration in the chick embryo in vivo, other observers have reported on the formation of lens cells from embryonic chick pigment retina and iris explanted in vitro (Dorris, 1938; van Deth, 1940; Reinhold, 1958).
Homograft Implants of Young Testes, Ovaries and Ovotestes in the Intact Female Chick
Authors: Erickson Alan E. , Pincus Gregory
Published: April 2021

Attempts to control differentiation of the reproductive system of vertebrates have been made by use of hormone treatment, grafting, and parabiosis of embryos, larvae and neonates (for reviews, see Domm, 1939; Burns, 1949; Willier, 1952; Witschi, 1961; Burns, 1961). True sex reversal by use of steroid compounds has been accomplished only in certain amphibians (Witschi & Chang, 1950; Chang & Witschi, 1955) and in more primitive forms. Among birds and mammals such manipulations have modified components of the reproductive system but have not resulted in ovulation and fertilization of ova from the cortex of feminized gonads of the male. Spermatogenesis in the hypertrophied right rudiment of a small percentage of hens ovariotomized prior to 30 days has been reported by Domm (1929) but in only rare instances has it occurred in birds similarly treated at an older age (Domm, 1927). No chicks have hatched from eggs of hens artificially inseminated with sperm derived from such experimentally modified birds.
The Induction of Deciduomata in the Rat
Authors: Finn C. A. , Keen P. M.
Published: April 2021

One of the main steps in the elucidation of the mechanism of ovum implantation is to determine how the blastocyst stimulates the uterus to undergo a decidual reaction. The extent of this reaction varies between species but is particularly marked in rodents, and normal ovum implantation does not occur without it. It has been known for several years, however, that the uterus of a suitably primed rodent can be stimulated to produce decidual cells in the absence of a blastocyst simply by traumatization of the uterus. The so-called deciduoma which results is thought to be analogous to the decidual reaction of normal implantation because (a) it is histologically similar (Krehbiel, 1937), and (b) the hormonal requirements for its formation are similar to those for implantation. Thus the deciduoma is a useful model on which to investigate factors which may be important in the initiation of the decidual response. It is also of interest as an example of extremely rapid cellular proliferation (the uterus may increase its weight four-fold in 72 hours) and so may provide information about cellular growth in general. If the deciduoma is analogous to the decidual reaction it is a reasonable assumption that the mechanisms by which the two responses are initiated have at least a final stage in common.
Immunochemical Investigation of the Serum Proteins in Chick Embryos
Authors: Peetoom F. , Kraijenhoff Sloot W. J. A. TH. , Woerdeman M. W.
Published: April 2021

In this paper, experiments which were performed to investigate the possible presence of serum proteins in blood cells of young stage chick embryos are described. From the results we conclude that serum proteins are not present in primitive blood cells at a time shortly before their disintegration. Our findings are not in accordance with those of Schechtman & Hoffman (1952) who postulated that the appearance of a- and β-globulins in the blood-stream is a result of the liberation of these globulins during the destruction of primitive blood cells. We are of the opinion that the maturation of blood cell-forming tissue, which results in the formation of a new blood cell population, goes parallel or coincides with the functional development of protein-forming tissues.
Anti-mesodermal Activity of a Nitrogen Mustard Derivative
Authors: Jurand A.
Published: April 2021

Amongst the numerous derivatives of nitrogen mustard that have been tested for their anti-tumour activity on Walker carcinoma by Danielli and his collaborators (1961), (Cl—CH2—CH2)2:N—C6H4—O—CO—NH—C6H4—COOH, i.e., p-(7V7V-Di-2-chloroethyloamino)-phenyl - N-(p-carboxyphenyl) - carbamate (later referred to as I.C. 140), has been found to be particularly promising. To check its cytotoxic activity for embryos, and to find out, if possible, whether I.C. 140 has any specific selectivity for particular embryonic tissues, chick and mouse embryos were treated during the early stages of development.
Tenascin is accumulated along developing peripheral nerves and allows neurite outgrowth in vitro
Authors: Wehrle Bernhard , Chiquet Matthias
Published: April 2021

The extracellular matrix protein, tenascin, appears in a restricted pattern during organ morphogenesis. Here we studied the expression of tenascin along developing peripheral nerves in chick embryos and tested its activity as a substrate for cultured neurons. Motor axons grow out through the tenascin-rich, anterior part of the sclerotome. Shortly after, tenascin surrounds axon fascicles of ventral roots. At the limb levels, outgrowing axons accumulate in the tenascin-containing girdle region forming a plexus. In the limb, tenascin first appears in bracket-like structures that surround the precartilage cell condensations of the femur and humerus, respectively. These regions coincide with the channels along which axons first grow in from the girdle plexus to form the limb nerves. Later, the major tenascin staining is associated with the cartilage and tendon primordia, and not with the limb nerves. We used tenascin as a substrate for cultured neural explants and single cells in order to test for its function in neurite outgrowth. Dissociated embryonic neurons of various types attached to mixed polylysineμenascin substrates and sprouted rapidly after a lag of several hours. Outgrowth was inhibited and neurites were detached by anti-tenascin antibodies. On substrates coated with tenascin alone, neurite out-growth was achieved from 3 day spinal cord explants. Whereas growth cones were well spread and rapidly moving, the neurites were poorly attached, straight and rarely branched. We speculate that in vivo tenascin allows axonal outgrowth, but inhibits branching and supports fasciculation of newly formed axons.
Differential cytokeratin gene expression reveals early dorsal-ventral regionalization in chick mesoderm
Authors: Charlebois Timothy S. , Henryt Jonathan J. , Grainger Robert M.
Published: April 2021

The induction and spatial patterning of early mesoderm are known to be critical events in the establishment of the vertebrate body plan. However, it has been difficult to define precisely the steps by which mesoderm is initially subdivided into functionally discrete regions. Here we present evidence for a sharply defined distinction between presumptive dorsal and presumptive ventral regions in early chick mesoderm. Northern blot and in situ hybridization analyses reveal that transcripts corresponding to CKsel, a cytokeratin gene expressed during early development, are present at high levels in the presumptive ventral mesoderm, but are greatly reduced or undetectable in the future dorsal region of mesoderm, where the formation of axial structures occurs later in development. This distinction is present even while the mesoderm layer is being formed, and persists during the extensive cellular movements and tissue remodeling associated with morphogenesis. These results point to an early step in which two fundamentally distinct states are established along the presumptive dorsal-ventral axis in the mesoderm, and suggest that determination in this germ layer occurs in a hierarchical manner, rather than by direct specification of individual types of histological differentiation. The differential expression of Cksel represents the earliest molecular index of dorsoventral regionalization detected thus far in the mesoderm.
A mesoderm-inducing factor produced by WEHI-3 murine myelomonocytic leukemia cells is activin A
Authors: Albano R. M. , Godsave S. F. , Huylebroeck D. , Nimmen K. Van , Isaacs H. V. , Slack J. M. W. , Smith J. C.
Published: April 2021

The first inductive interaction in amphibian development is mesoderm induction, during which a signal from the vegetal hemisphere of the blastula-staged embryo induces mesoderm from overlying equatorial cells. Recently, a number of ‘mesoderm-inducing factors’ (MIFs), which may be responsible for this interaction, have been discovered. Examples of these MIFs include members of the fibroblast growth factor family as well as members of the TGF-β superfamily such as TGF-β2. In addition to these purified factors, several new sources of mesoderm-inducing activity have been described. One of the most potent of these is the murine myelomonocytic leukemia cell line WEHI-3. Even at high dilutions, conditioned medium from WEHI-3 cells induces isolated Xenopus animal pole regions to form a variety of mesodermal cell types. In this paper we show by several criteria, including N-terminal amino acid sequencing, Northern blotting and various functional assays, that the WEHI-MIF is activin A. Activins are known to modulate the release of follicle-stimulating hormone from cultured anterior pituitary cells and to cause the differentiation of two erythroleukemia cell lines. Our results, along with recent data from other laboratories, indicate that these molecules may also act in early development in the formation of the mesoderm.
A point mutation in the proteolipid protein gene of the ‘shaking pup’ interrupts oligodendrocyte development
Authors: Nadon Nancy L. , Duncan Ian D. , Hudson Lynn D.
Published: April 2021

The differentiation of the oligodendrocyte from its bipotential progenitor culminates in the production of the myelin-specific proteins and the elaboration of membrane processes that ensheath the axon. Mutations in proteolipid protein (PLP) and its alternatively spliced isoform DM-20, the major protein constituents of central nervous system myelin, are characterized by a significant reduction in the number of mature oligoden-drocytes, resulting in severe hypomyelination, tremor and early death. The canine shaking pup carries such a mutation, a single base change that substitutes a proline for a histidine near the first transmembrane region of PLP and DM-20. This mutation hinders oligodendrocyte differentiation, as evidenced by a splicing pattern at the PLP locus characteristic of immature oligodendrocytes. The spliced transcript expressed earliest in development, DM-20, continues to be overexpressed in shaking pup oligodendrocytes. The disruption of the normal maturation schedule in these X-linked dysmyelinating disorders suggests that PLP or DM-20 plays a fundamental role in oligodendrocyte development. We propose that, while the more abundant PLP is the primary structural component of myelin, DM-20 may be critical to oligodendrocyte maturation.
Primary structure and embryonic expression pattern of the mouse Hox-4.3* homeobox gene
Authors: Izpisùa-Belmonte Juan-Carlos , Dollé Pascal , Renucci Armand , Zappavigna Vincenzo , Falkenstein Hildegard , Duboule Denis
Published: April 2021

We report the cloning, genomic localization, primary structure and developmental expression pattern of the novel mouse Hox-4.3 gene. This gene is located within the HOX-4(5) complex, at a position which classifies it as a member of the Hox-3.1 and -2.4 subfamily, the DNA and predicted protein sequences further confirmed this classification. Hox-4.3 has a primary structure characteristic of a Hox gene but, in addition, contains several monotonic stretches of amino acids, one of the ‘paired’-like type. As expected from its presence and position within the complex, Hox-4.3 is developmentally expressed in structures of either mesodermal or neurecto-dermal origin located or derived from below a precise craniocaudal level. However, a very important offset between anteroposterior boundaries within neuroectoderm versus mesoderm derivatives is observed. Like other genes of the HOX-4(5) complex, Hox-4.3 is expressed in developing limbs and gonads, suggesting that ‘cluster specificity’ could be a feature of the HOX network.
Combinatorial control of cell differentiation by cAMP and DIF-1 during development of Dictyostelium discoideum
Authors: Berks Mary , Kay Robert R.
Published: April 2021

At least three distinct types of cell arise from a population of similar amoebae during Dictyostelium development: prespore, prestalk A and prestalk B cells. We report evidence suggesting that this cellular diversification can be brought about by the combinatorial action of two diffusible signals, cAMP and DIF-1. Cells at different stages of normal development were transferred to shaken suspension, challenged with various combinations of signal molecules and the expression of cell-type-specific mRNA markers measured 1 –2 h later. pDd63, pDd56 and D19 mRNAs were used for prestalk A, prestalk B and prespore cells respectively. We find the following results. (1) Cells first become responsive to DIF-1 for prestalk A differentiation and to cAMP for prespore differentiation at the end of aggregation, about 2h before these cell types normally appear. (2) At the first finger stage of development, when the rate of accumulation of the markers is maximal, the expression of each is favoured by a unique combination of effectors: prespore differentiation is stimulated by cAMP and inhibited by DIF-1; prestalk A differentiation is stimulated by both cAMP and DIF-1 and prestalk B differentiation is stimulated by DIF-1 and inhibited by cAMP. (3) Half-maximal effects are produced by 10-70 nM DIF-1, which is in the physiological range. (4) Ammonia and adenosine, which can affect cell differentiation in other circumstances, have no significant pathway-specific effect in our conditions. These results suggest that cell differentiation could be brought about in normal development by the localized action of cAMP and DIF-1.
A Drosophila growth factor homolog, decapentaplegic, regulates homeotic gene expression within and across germ layers during midgut morphogenesis
Authors: Panganiban Grace E. F. , Reuter Rolf , Scott Matthew P. , Hoffmann F. Michael
Published: April 2021

The decapentaplegic (dpp) gene product, a member of the transforming growth factor-β family, is required in Drosophila embryos for normal gastrulation and the establishment of dorsal-ventral polarity in the embryo. dpp is also expressed at specific positions in the visceral mesoderm along the developing midgut. We find that mutations that eliminate the visceral mesoderm expression of dpp lead to defects in midgut morphogenesis and alter the spatially localized expression of the homeotic genes Sex combs reduced (Scr), Ultrabithorax (Ubx), and Antennapedia (Antp) in the visceral mesoderm. The extracellular dpp protein migrates from the visceral mesoderm across the apposing endodermal cell layer in a region of the endoderm that expresses the homeotic gene labial (lab). Mesodermal expression of dpp is required for the expression of lab in these endodermal cells indicating that dpp mediates an inductive interaction between the two germ layers. We propose that extracellular dpp protein regulates gut morphogenesis, in part, by regulating homeotic gene expression in the visceral mesoderm and endoderm of the developing midgut.
Insect epidermis: polarity patterns after grafting result from divergent cell adhesions between host and graft tissue
Authors: Nübler-Jung K. , Mardini B.
Published: April 2021

Insect epidermal cells display planar polarity (i.e. polarity in the plane of the cell sheet) by secreting oriented cuticular denticles and bristles before each moult. We investigate how cell polarities in an abdominal segment are uniformly oriented towards the posterior of the animal.

Recently we have shown for the cotton bug Dysdercus that, in 180°-rotated grafts pretreated with colchicine, graft cells tend to adopt the orientation prevailing in surrounding host cells via an intermediate stage with outward oriented denticles (Nübler-Jung and Grau, 1987). Here we show that, in untreated grafts that were transposed along the anteroposterior segment axis, the denticles also always tend to point outwards. This independence of the polarity pattern from the direction of transposition is compatible neither with a gradient model for polarity control, nor with the assumption that epidermal cells orient according to the local sequence of distinctly differentiated cells. Instead we found that outward orientation of graft denticles correlates with an elongation of epidermal cells along a host–graft border with divergent cell adhesiveness. We therefore propose that outward orientation in a graft results from a combination of two factors: epidermal cells stretch along an interface with divergent cell adhesiveness, and they form a denticle perpendicular to their long axis. By analogy, the normal anteroposterior orientation of denticles in a segment may result because epidermal cells tend to elongate parallel to the segment boundary and to form denticles perpendicular to this mediolateral cell elongation, i.e. along the anteroposterior segment axis.
Survival in vitro of motoneurons identified or purified by novel antibodybased methods is selectively enhanced by muscle-derived factors
Authors: Bloch-Gallego E. , Huchet M. , M’hamdi H. El , Xie F.-K. , Tanaka H. , Henderson C. E.
Published: April 2021

Motoneurons were identified in vitro by a new method using the SCI monoclonal antibody. They constituted up to 30 % of total neurons in cultures of whole spinal cord from 4.5-day chicken embryos, and survived for at least 5 days in the presence of muscle extract, but not in its absence. By contrast, other neurons and floor-plate cells survived without muscle-derived factors. Motoneurons were purified to homogeneity by ‘panning’ on dishes coated with SCI antibody; they developed rapidly even in the absence of other spinal cells. Concentrations of muscle extract required for half-maximal motoneuron survival were indistinguishable in pure and mixed cultures, suggesting that muscle-derived factors act directly on motoneurons. Other purified growth factors tested, including ciliary neurotrophic factor, did not have the survival-promoting activity of muscle.
Retinoic acid-binding protein, rhombomeres and the neural crest
Authors: Maden M. , Hunt P. , Eriksson U. , Kuroiwa A. , Krumlauf R. , Summerbell D.
Published: April 2021

We have investigated by immunocytochemistry the spatial and temporal distribution of cellular retinoic acid-binding protein (CRABP) in the developing nervous system of the chick embryo in order to answer two specific questions: do neural crest cells contain CRABP and where and when do CRABP-positive neuroblasts first arise in the neural tube? With regard to the neural crest, we have compared CRABP staining with HNK-1 staining (a marker of migrating neural crest) and found that they do indeed co-localise, but cephalic and trunk crest behave slightly differently. In the cephalic region in tissues such as the frontonasal mass and branchial arches, HNK-1 immunoreactivity is intense at early stages, but it disappears as CRABP immunoreactivity appears. Thus the two staining patterns do not overlap, but are complementary. In the trunk, HNK-1 and CRABP stain the same cell populations at the same time, such as those migrating through the anterior halves of the somites. In the neural tube, CRABP-positive neuroblasts first appear in the rhombencephalon just after the neural folds close and then a particular pattern of immunoreactivity appears within the rhombomeres of the hindbrain. Labelled cells are present in the future spinal cord, the posterior rhombencephalon up to rhombomere 6 and in rhombomere 4 thus producing a single stripe pattern. This pattern is dynamic and gradually changes as anterior rhombomeres begin to label. The similarity of this initial pattern to the arrangement of certain homeobox genes in the mouse stimulated us to examine the expression of the chicken Hox-2.9 gene. We show that at stage 15 the pattern of expression of this gene is closely related to that of CRABP. The relationship between retinoic acid, CRABP and homeobox genes is discussed.
The effect of a heterochronic mutation, Teopod2, on the cell lineage of the maize shoot
Authors: Dudley Mark , Poethig R. Scott
Published: April 2021

Teopod2 (Tp2) is a semi-dominant mutation of maize that prolongs the expression of characteristics normally confined to the juvenile phase of development. Two of the many dramatic morphological effects of this mutation are an increase in the number of vegetative nodes, and a reduction in the overall size of the shoot. To determine the cellular basis of these phenotypes, the technique of clonal analysis was used to compare the cell division patterns of wild-type and Tp2 plants. Our results indicate that Tp2 increases the number of vegetative nodes produced by the apicahnost cells in the meristem but does not affect the cell lineage of the basal, juvenile, part of the shoot. This result demonstrates that Tp2 does not act uniquely in a ‘juvenile’ domain of the meristem, but instead causes cells that are normally destined to produce adult structures to express juvenile traits inappropriately. Clonal analysis also demonstrates that Tp2 does not affect the size of the meristem prior to germination, nor does it affect the cell lineage of the basic structural unit of the stem, the phytomer. Thus the effects of this mutation on the size of the shoot are the result of changes in cell fate late in development.
The surface glycoprotein Thy-1 is excluded from growing axons during development: a study of the expression of Thy-1 during axogenesis in hippocampus and hindbrain
Authors: Xue G. P. , Rivero B. Pliego , Morris R. J.
Published: April 2021

Thy-1 is a developmentally regulated surface glycoprotein expressed on a number of tissues, including nerve where it is a major surface component of mature neurons. During neural development in the rat and mouse, expression of Thy-1 protein does not necessarily follow appearance of its mRNA, but additionally requires completion of the initial phase of axonal growth. Where there is a substantial lag phase between initial elongation and final axonal outgrowth into a terminal field (e.g. pontine projection to the cerebellum), Thy-1 protein appears at the cell body and dendrites of the neurons, but is excluded from their axons until the terminal phase of axonal growth is completed. In the more complex case of the vestibular ganglion neurons, whose axons project primarily to the vestibular nuclei in the brainstem before birth, and then 1–2 weeks later into the cerebellum, Thy-1 enters the proximal axonal regions where growth is completed, but not the distal growing ends. Thus complex controls govern the initial expression and distribution of Thy-1 so as to exclude it from growing regions of axons.
Inductive differentiation of two neural lineages reconstituted in a microculture system from Xenopus early gastrula cells
Authors: Mjtani Shohei , Okamoto Harumasa
Published: April 2021

Neural induction of ectoderm cells has been reconstituted and examined in a microculture system derived from dissociated early gastrula cells of Xenopus laevis. We have used monoclonal antibodies as specific markers to monitor cellular differentiation from three distinct ectoderm lineages in culture (N1 for CNS neurons from neural tube, Mel for melanophores from neural crest and F.3 for skin epidermal cells from epidermal lineages).

CNS neurons and melanophores differentiate when deep layer cells of the ventral ectoderm (VE, prospective epidermis region; 150 cells/culture) and an appropriate region of the marginal zone (MZ, prospective mesoderm region; 5—150 cells/culture) are co-cultured, but not in cultures of either cell type on their own; VE cells cultured alone yield epidermal cells as we have previously reported. The extent of inductive neural differentiation in the co-culture system strongly depends on the origin and number of MZ cells initially added to culture wells. The potency to induce CNS neurons is highest for dorsal MZ cells and sharply decreases as more ventrally located cells are used. The same dorsoventral distribution of potency is seen in the ability of MZ cells to inhibit epidermal differentiation. In contrast, the ability of MZ cells to induce melanophores shows the reverse polarity, ventral to dorsal. These data indicate that separate developmental mechanisms are used for the induction of neural tube and neural crest lineages.

Co-differentiation of CNS neurons or melanophores with epidermal cells can be obtained in a single well of co-cultures of VE cells (150) and a wide range of numbers of MZ cells (5 to 100). Further, reproducible differentiation of both neural lineages requires intimate association between cells from the two gastrula regions; virtually no differentiation is obtained when cells from the VE and MZ are separated in a culture well. These results indicate that the inducing signals from MZ cells for both neural tube and neural crest lineages affect only nearby ectoderm cells.
Intracellular pH and intracellular free calcium responses to protein kinase C activators and inhibitors in Xenopus eggs
Authors: Grandin Nathalie , Charbonneau Michel
Published: April 2021

Cell activation during fertilization of the egg of Xenopus laevis is accompanied by various metabolic changes, including a permanent increase in intracellular pH (pHi) and a transient increase in intracellular free calcium activity ([Ca2+]1,). Recently, it has been proposed that protein kinase C (PKC) is an integral component of the Xenopus fertilization pathway (Bement and Capeo, J. Cell Biol. 108, 885-892, 1989). Indeed, activators of PKC trigger cortical granule exocytosis and cortical contraction, two events of egg activation, without, however, releasing the cell cycle arrest (blocked in second metaphase of meiosis). In the egg of Xenopus, exocytosis as well as cell cycle reinitiation are supposed to be triggered by the intracellular Ca2+ transient. We report here that PKC activators do not induce the intracellular Ca2+ transient, or the activation-associated increase in pHi. These results suggest that the ionic responses to egg activation in Xenopus do not appear to depend on the activation of PKC. In addition, in eggs already pretreated with phorbol esters, those artificial activators that act by releasing Ca2+ intracellularly, triggered a diminished increase in pHi. Finally, sphingosine and staurosporine, two potent inhibitors of PKC, were found to trigger egg activation, suggesting that a decrease in PKC activity might be an essential event in the release of the metaphase block, in agreement with recent findings on the release of the prophase block in Xenopus oocytes (Varnold and Smith, Development 109, 597–604, 1990).
Desmosome biogenesis in the mouse preimplantation embryo
Authors: Fleming Tom P. , Garrod David R. , Elsmore Andrew J.
Published: April 2021

The molecular processes underlying the formation of the first desmosomes in the mouse early embryo have been examined by immunocytochemical and biochemical techniques using antibody probes recognising desmosomal proteins 1 and 2 (dp1+2, desmoplakins), dp3 (plakoglobin), desmosomal glycoprotein 1 (dgl, desmoglein) and dg2+3 (desmocollins). Immunofluorescence labelling of staged intact embryos and synchronised cell clusters indicates that dp1+2, dgl and dg2+3 are first detectable on the lateral membrane contact sites between trophectoderm cells in early cavitating blastocysts, coincident with the onset of desmosome formation as seen in ultrastructural preparations. Membrane localisation of these antigens is predominantly punctate in appearance, occurs after division to the 32-cell stage and appears to be coincident with blastocoele formation since non-cavitated embryos/cell clusters of equivalent age/ cell cycle are usually unlabelled. In contrast, dp3 is first detectable at the 32-cell stage at all internal membrane contact sites (including those with inner cell mass cells) in a continuous linear pattern, and appears in both cavitated and non-cavitated specimens. Subsequently during blastocyst expansion, dp3 localisation becomes punctate and restricted to trophectodermal membranes. Immunoprecipitation of desmosomal antigens following metabolic labelling indicates that synthesis of dp3 is underway from at least compaction in the 8-cell embryo, while dp1 + 2 synthesis is first evident in 16-cell morulae. Synthesis of dgl and dg2+3 is not detectable until the early blastocyst stage. These results suggest that desmosome biogenesis in the preimplantation embryo might be regulated by transcription or translation of desmosomal glycoproteins and by maturational changes in the trophectoderm layer associated with blastocoele formation. The earlier expression and wider distribution of dp3 at cell contact areas may reflect non-desmosomal sites (eg, adherens junctions) for this protein and a possible role for dp3 in the development of intercellular junctions.