bluuebunny/crossref_metadata_2025 huggingface dataset:
Desmin and titin expression in early postimplantation mouse embryos
Authors: Schaart G. , Viebahn C. , Langmann W. , Ramaekers F.
Published: April 2021

The expression of the intermediate filament (IF) constituents desmin, vimentin and keratin, as well as the striated-muscle-specific marker titin, was studied in mouse embryos of 8.0 to 9.5 days post coitum (d.p.c.), using the indirect immunofluorescence technique in combination with polyclonal and monoclonal antibodies. During the development of the embryo, desmin was first detected at 8.25 d.p.c. in the ectoderm, where it was transiently coexpressed with keratin and vimentin. At later stages, the ectoderm contained only keratin and to a certain extent also vimentin IF. At 8.5 d.p.c., desmin was found exclusively in the heart rudiment, and remained present with increasing intensity in the myocardial cells during later cardiogenesis. Striation of desmin in the heart muscle cells was observed in 9.5 d.p.c. embryos. At these stages (8.5–9.5 d.p.c.), triple expression of the IF proteins desmin, vimentin and keratin was evident in these cells. From 9.0 d.p.c. onwards, desmin could be detected in the myotomes as well. Immunoblotting studies of 9.5 d.p.c. mouse embryos confirmed the immunohistochemical data.

Titin was found in the early heart anlage at stage 8.25 d.p.c., when no desmin expression was observed in this tissue. At this stage the titin appeared in a punctate pattern, similar to that observed in cardiac myofibrils of early chicken embryos (Tokuyasu and Maher, 1987; J. Cell Biol. 105, 2781–2793). In 8.5 d.p.c. mouse embryos, this punctate titin staining pattern was still observed, while, at this stage, a filamentous staining reaction could be seen with the desmin antibodies. During further development, cross-striation was detected within myocardial cells using the polyclonal titin antibody from 9.0 d.p.c. onwards, i.e. before such striation could be detected with the desmin antibodies.

From these data, we conclude that titin synthesis may anticipate desmin expression in the developing mouse myocard, although the level of expression of the former protein remains low until 9.0 d.p.c.
Spatial aspects of neural induction in Xenopus laevis
Authors: Jones E. A. , Woodland H. R.
Published: April 2021

A monoclonal antibody, 2G9, has been identified and characterised as a marker of neural differentiation in Xenopus. The epitope is present throughout the adult central nervous system and in peripheral nerves. Staining is first detected in embryos at stage 21 in the thoracic region. By stage 29 it stains the whole central nervous system, except the tail tip. The epitope is present in a 65K Mr protein, and includes sialic acid. The antibody also reacts with neural tissue in mice and axolotls and newts. 2G9 was used to show that both notochord and somites are capable of neural induction, and the stimulus is present as late as stage 22. Attempts to demonstrate the induction of nervous system by developing nervous system (homoiogenetic induction) were unsuccessful. The view that the lateral extent of the nervous system might be determined by that of the inductive stimulus is discussed. Neural induction was detected as early as stage 10 and occurs in embryos without gastrulation and without cell division from stage .
Pre-existing neuronal pathways in the leg imaginal discs of Drosophila
Authors: Tix Simone , Bate Michael , Technau Gerhard M.
Published: April 2021

Injection of a cell lineage tracer (HRP) into Drosophila embryos before cellularization provides a way of selectively labelling cells at later stages that have undergone only a few mitoses. All cells born and differentiating during embryogenesis become labelled, whereas further proliferation and growth during postembryonic development causes an almost complete dilution of the marker in the adult cell complement. Early born neurons visualized in this way are good candidates for executing a pioneering function during postembryonic differentiation of the adult nervous system.

In all three pairs of leg imaginal discs, a stereotyped set of larval sense organs becomes selectively labelled. Their axons fasciculate with a larval nerve, which connects the leg disc with the central nervous system. Larval sense organs are not present in the other imaginal discs.

Larval neurons are not present in the transformed antennal discs of Antp 73B flies. Nonetheless adult axons successfully navigate to the base of these discs as they differentiate to form ectopic legs. We conclude that embryonically formed larval nerves are not essential for the guidance of adult axons within the leg discs.
Steroid hormone receptor homologs in development
Authors: Oro Anthony E. , Umesono Kazuhiko , Evans Ronald M.
Published: April 2021

The steroid/thyroid receptor superfamily are liganddependent transcription factors which consist of distinct functional domains required for transcriptional control of a network of genes. Members of this superfamily are beginning to be studied for their contribution to embryogenesis. Two human receptors for the vertebrate morphogen retinoic acid have been isolated and further characterized on model promoters. Moreover, the presence of homologs of these receptors in Drosophila reveals that members of this superfamily predate the divergence of the vertebrates and Invertebrates. One locus is knirps-related (knrl), whose product is closely related to that of the gap segmentation gene knirps (kni). knrl is one of the most diverged steroid receptor-like molecules and displays a spatially restricted blastoderm pattern.
Segmental polarity and identity in the abdomen of Drosophila is controlled by the relative position of gap gene expression
Authors: Lehmann Ruth , Frohnhöfer Hans Georg
Published: April 2021

The establishment of the segmental pattern in the Drosophila embryo is directed by three sets of maternal genes: the anterior, the terminal and the posterior group of genes. Embryos derived from females mutant for one of the posterior group genes lack abdominal segmentation. This phenotype can be rescued by transplantation of posterior pole plasm into the abdominal region of mutant embryos. We transplanted posterior pole plasm into the middle of embryos mutant either for the posterior, the anterior and posterior, or all three maternal systems and monitored the segmentation pattern as well as the expression of the zygotic gap gene Kriippel in control and injected embryos. We conclude that polarity and identity of the abdominal segments do not depend on the relative concentration of posterior activity but rather on the position of gap gene expression. By changing the pattern of gap gene expression, the orientation of the abdomen can be reversed. These experiments suggest that maternal gene products act in a strictly hierarchical manner. The function of the maternal gene products becomes dispensable once the position of the zygotically expressed gap genes is determined. Subsequently the gap genes will control the pattern of the pair-rule and segment polarity genes.
The decapentaplegic gene: a TGF-β homologue controlling pattern formation in Drosophila
Authors: Gelbart William M.
Published: April 2021

The type β transforming growth factor (TGF-β) family of secreted factors encompasses a wide range of structurally related proteins that control the state of determination or differentiation in a wide variety of cell types. For all members of the family that have been studied at the protein level, the active moieties arise as dimers of the C-terminal ∼110 amino acid fragment derived from much longer precursor polypeptides. The hallmark of the family is a series of 7 completely conserved cysteine residues in the C-terminus; other conserved amino acid sequences generally cluster in the vicinity of 6 of these 7 cysteines. This report focuses on our current understanding of the genetic structure and developmental role of the decapentaplegic (dpp) gene in Drosophila, the only member of the TGF-β family thus far identified in invertebrates. The dpp polypeptide bears a sufficiently close relationship to two bone morphogenesis proteins (BMP-2A and BMP-2B) identified in mammals (Wozney et al. 1988, Science 242, 1528-1534) to warrant the suggestion that dpp and the BMP-2s are the descendants of a common ancestral gene. The protein-coding information for dpp is contained within a 6 kb DNA segment. An elaborate cis-regulatory apparatus, encompassing a >55 kb DNA segment, has evolved to control expression of the dpp gene, which is required for determination of dorsal ectoderm in the early embryo, for normal distal outgrowth of the adult appendages, and for sundry other developmental events, which are currently less well-defined. Studies of chimeric individuals and observations of transcript accumulation in situ have demonstrated that the dpp gene is expressed along the A/P boundary of the imaginai disks. A possible role of dpp in elaborating positional information in imaginai disk development is discussed.
Early determination in the C. elegans embryo: a gene, cib-1, required to specify a set of stem-cell-like blastomeres
Authors: Schnabel Ralf , Schnabel Heinke
Published: April 2021

The early somatic blastomeres founding the tissues in the C. elegans embryo are derived in a stem-cell-like lineage from the P cells. We have isolated maternal effect lethal mutations defining the gene cib-1 in which the P cells, Pi-P3, skip a cell cycle and acquire the fates of only their somatic daughters. Therefore, the cib-1 gene is required for the specification of the stem-cell-like fate of these cells.

The analysis of the development of these mutants suggests that the clock controlling the cell cycles in the early embryo is directly coupled to the fate of a cell and that there must be another developmental clock that activates the determinative inventory for the early decision-making.
Immunological, biochemical and physiological analyses of cardioacceleratory peptide 2 (CAP2) activity in the embryo of the tobacco hawkmoth Manduca sexta
Authors: Broadie Kendal S. , Sylwester Andrew W. , Bate Michael , Tublitz Nathan J.
Published: April 2021

The cells In the embryonic CNS of the tobacco hawkmoth, Manduca sexta, that synthesize a cardioacceleratory peptide 2 (CAP2)-llke antigen were identified using immunohistochemical techniques. Two distinct neurosecretory cell types were present in the abdominal ventral nerve cord (VNC) that contain CAP2-like immunoreactivity during late embryogenesis: a pair of large (diameter range 15–20 μm) cells lying along the posterior, dorsal midline of abdominal ganglia A4–A8, and a bilateral set of four smaller (diameter range 6–11 μm) neurons which lie at the base of each ventral root in abdominal ganglia A2–A8. CAP2-like accumulation appeared to follow independent patterns in the two cell types. CAP2-like immunoreactivity began at 60% of embryo development (DT) in the medial cells, accumulated steadily throughout embryogenesis, and dropped markedly during hatching. Lateral cells synthesized the CAP2-like antigen later in development (70 % DT) and showed a sharp drop in antigen levels between 75 % and 80 % of embryonic development.

Extracts from developing M. sexta embryos were found to contain a cardioactive factor capable of accelerating the contraction frequency of the pharate adult moth heart in a fashion similar to CAP2. Immunoprecipitation with a monoclonal antibody that specifically recognizes the two endogenous Manduca cardioacceleratory peptides and purification using high pressure liquid chromatography identified this factor as cardioac-celeratory peptide 2 (CAP2). Using an in vitro heart bioassay, the levels of this cardioactive neuropeptide were traced during the development of the M. sexta embryo. As with the immunohistochemical results, two periods during embryogenesis were identified in which the level of CAP2 dropped markedly: between 75 % and 80 % development, and at hatching. Embryo bioassays of CAP2 activity were used to identify possible target tissues for physiological activity during these two putative release times. CAP2 was found to accelerate contraction frequency in the embryonic heart and hindgut of Manduca in a dose-dependent fashion. Of these two possible targets, the hindgut proved to be more sensitive to CAP2, having a lower response threshold and a longer duration of response to a given concentration of the exogenously applied peptide.

Based on these immunocytochemical, pharmacological and biochemical results, and on a previously published detailed analysis of Manduca embryogenesis, we conclude that CAP2 is probably released from a specific set of identified neurosecretory cells in the abdominal VNC to modulate embryonic gut activity at 75–80 % of embryo development during ingestion of the extra-embryonic yolk.
Spatial and temporal patterns of neurogenesis in the embryo of the locust (Schistocerca gregaria)
Authors: Shepherd D. , Bate C. M.
Published: April 2021

Embryonic neurogenesis in the ventral nerve cord of the locust Schistocerca gregaria was studied using toluidine blue (TB) staining and birthdating of cells by incorporation of bromodeoxyuridine (BUdR). In the thorax, the neuroblasts (NBs) start dividing at the 28 % stage and neurogenesis continues until 90%. In the abdomen, neurogenesis starts at about 30 % and continues until 70 %. Every NB appears to have its own fixed period of division before disappearing. Thus a specific spatial and temporal pattern of NB degeneration can be seen in every segment. This pattern is identical in each of the three thoracic ganglia. We have traced the fate of each of the original complement of NBs in the mesothoracic neuromere and specified the stage of development at which each NB ends its lineage and disappears. The abdominal segments A2 to A7 share an identical pattern of NB death, which is not comparable to the thoracic pattern. The progress of neurogenesis is marked by a gradual decrease in the number of NBs, with NBs in the thoracic ganglia persisting longer than their abdominal homologues. The differences between the thoracic and abdominal NBs are also reflected in the rates at which they divide, thoracic NBs dividing at almost twice the rate of the abdominal NBs.
Specific spatial and temporal distribution of retinoic acid receptor gamma transcripts during mouse embryogenesis
Authors: Ruberte Esther , Dolle Pascal , Krust Andree , Zelent Arthur , Morriss-Kay Gillian , Chambon Pierre
Published: April 2021

Retinoic acid (RA), a putative morphogen in vertebrates, has profound effects on development during embryogenesis, chondrogenesis and differentiation of squamous epithelia. The distribution of the transcripts of the retinoic acid receptor gamma (RAR-γ) gene has been studied here by in situ hybridization during mouse development from days 6.5 to 15.5 post-coitum (p.c.). RAR-γ transcripts are detected as early as day 8 p.c. in the presomitic posterior region. Between days 9.5 and 11.5 p.c., the transcripts are uniformly distributed in the mesenchyme of the frontonasal region, pharyngeal arches, limb buds and sclerotomes. At day 12.5 p.c., RAR-γ transcripts are found in all precartilaginous mesenchymal condensations. From day 13.5 p.c., the transcripts are specifically localized in all cartilages and differentiating squamous keratinizing epithelia, irrespective of their embryological origin. RAR-γ transcripts are also found in the developing teeth and whisker follicles. The developmental pattern of expression of the RAR-γ gene suggests that RAR-γ plays a crucial role for transducing RA signals at the level of gene expression during morphogenesis, chondrogenesis and differentiation of squamous epithelia.
Transition of myosin isozymes during development of human masseter muscle: Persistence of developmental Isoforms during postnatal stage
Authors: Soussi-Yanicostas N. , Barbet J. P. , Laurent-Winter C. , Barton P. , Butler-Browne G. S.
Published: April 2021

Previous results have shown that the adult human masseter muscle contains myosin isoforms that are specific to early stages of development in trunk and limb muscles, i.e. embryonic and fetal (neonatal) myosin heavy chains (MHC) and embryonic myosin light chain (MLC1emb). We wanted to know if this specific pattern is the result of a late maturation or of a distinct evolution during development.

We show here that the embryonic and the fetal MHC and the MLC1emb are expressed throughout perinatal and postnatal masseter development. Our results also demonstrate that MLC1emb accumulation increases considerably during the postnatal period. In addition, both the slow MLCs and the slow isoform of tropomyosin are expressed later in the masseter than quadriceps and the fast skeletal muscle isoform MLC3 is not detected during fetal and early postnatal development in the masseter whereas it is expressed throughout fetal development in the quadriceps.

Our results thus confirm previous histochemical data and demonstrate that the masseter muscle displays a pattern of myosin and tropomyosin isoform transitions different to that previously described in trunk and limb muscles. This suggests that control of masseter muscle development involves mechanisms distinct from other body muscles, possibly as a result of either its craniofacial innervation or of a possibly different embryonic origin.
Developmental expression of the putative transcription factor Egr-1 suggests that Egr-1 and c-fos are coregulated in some tissues
Authors: Mcmahon Andrew P. , Champion Janet E. , Mcmahon Jill A. , Sukhatme Vikas P.
Published: April 2021

We have investigated developmental expression of the gene Egr-1, which encodes a protein containing three zinc fingers. Egr-1 like c-fos is a serum inducible, early response gene, which is co-induced with c-fos in a variety of quite different situations. A single 3.7-kb RNA was detected throughout fetal mouse development, which increased in absolute levels in total fetal RNA from 9.5 to 12.5 days post coitum (p.c.). In situ hybridization to 14.5- and 17.5-day p.c. fetal tissues demonstrated Egr-1 accumulation at several specific sites. These included mesenchymal components of the developing tooth germs and salivary and nasal glands; an ectodermally derived component of the whisker pad and developing muscle, cartilage, and bone. Expression of Egr-1 in cartilage and bone showed a strikingly similar expression to previously published reports of c-fos in these tissues. High levels of Egr-1 RNA was observed at the perichondrial interface of opposing cartilaginous elements and in interstitial cells that lie in between. Bone expression was observed in membranous bone of the head, alveolar bone around the tooth germs, and at periosteal and endochondral ossification sites in the limb bones. Our data support the idea that Egr-1 and c-fos may be coregulated in vivo and together may regulate normal development of the skeleton.
The role of the dorsal lip in the induction of heart mesoderm in Xenopus laevis
Authors: Sater Amy K. , Jacobson Antone G.
Published: April 2021

We have examined the tissue interactions responsible for the expression of heart-forming potency during gastrulation. By comparing the specification of different regions of the marginal zone, we show that heart-forming potency is expressed only in explants containing both the dorsal lip of the blastopore and deep mesoderm between 30° and 45° lateral to the dorsal midline. Embryos from which both of these 30°-45° dorsolateral regions have been removed undergo heart formation in two thirds of cases, as long as the dorsal lip is left intact. If the dorsal lip is removed along with the 30° – 45° regions, heart formation does not occur. These results indicate that the dorsolateral deep mesoderm must interact with the dorsal lip in order to express heart-forming potency. Transplantation of the dorsal lip into the ventral marginal zone of host embryos results in the formation of a secondary axis; in over half of cases, this secondary axis includes a heart derived from the host mesoderm. These findings suggest that the establishment of heart mesoderm is initiated by a dorsalizing signal from the dorsal lip of the blastopore.
Pathways of trunk neural crest cell migration in the mouse embryo as revealed by vital dye labelling
Authors: Serbedzija George N. , Fraser Scott E. , Bronner-Fraser Marianne
Published: April 2021

Analysis of neural crest cell migration in the mouse has been difficult due to the lack of reliable cell markers. Recently, we found that injection of Dil into the chick neural tube marks premigratory neural crest cells whose endfeet are in contact with the lumen of the neural tube (Serbedzija et al. Development 106, 809-819 (1989)). In the present study, this technique was applied to study neural crest cell migratory pathways in the trunk of the mouse embryo. Embryos were removed from the mother between the 8th and the 10th days of development and Dil was injected into the lumen of the neural tube. The embryos were then cultured for 12 to 24 h, and analyzed at the level of the forelimb. We observed two predominant pathways of neural crest cell migration: (1) a ventral pathway through the rostral portion of the somite and (2) a dorsolateral pathway between the dermamyotome and the epidermis. Neural crest cells were observed along the dorsolateral pathway throughout the period of migration. The distribution of labelled cells along the ventral pathway suggested that there were two overlapping phases of migration. An early ventrolateral phase began before E9 and ended by E9.5; this pathway consisted of a stream of cells within the rostral sclerotome, adjacent to the dermamyotome, that extended ventrally to the region of the sympathetic ganglia and the dorsal aorta. A later ventromedial phase was apparent after E9.5 and continued through E10.5; this pathway consisted of a thin strand of Dil-labelled cells along the lateral surface of the neural tube which later protruded into the rostral sclerotome to form the dorsal root ganglia and Schwann cells. Those embryos injected at later stages contained labelled cells only in dorsal derivatives, suggesting that neural crest derivatives are populated in a ventral-to-dorsal order. While the overall pattern and order of neural crest migration was similar to that previously observed in avians and rats, some details of the timing and trajectories apparently differed, most notably the timing of neural crest migration along the dorsolateral pathway.
The role of gap junctions in patterning of the chick limb bud
Authors: Allen Francesca , Tickle Cheryll , Warner Anne
Published: April 2021

The role of gap junctional communication during patterning of the chick limb has been investigated. Affinity-purified antibodies raised against rat liver gap junctional proteins were used to block communication between limb mesenchyme cells. Co-injection of the antibodies and Lucifer yellow Into mesenchyme cultures demonstrated that communication was inhibited almost immediately. When antibodies were loaded into mesenchyme tissue by DMSO permeabilisation, [3H]nucleotide transfer was prevented for at least 16 h.

Polarising region tissue from the posterior limb bud margin causes digit duplications when grafted to the anterior margin. Quail polarising region cells were loaded with gap junction antibody and grafted into chick wing buds. The antibody had no effect on growth or survival of the grafted cells. As very few polarising region cells are required to initiate duplications, the number of polarising region cells in the grafts was reduced by diluting 1:9 with anterior mesenchyme tissue.

When either polarising region or anterior mesenchyme tissue in the graft was loaded separately with antibody, there was little effect on respecification of the digit pattern. However, loading both tissues in the graft caused a significant decrease in duplications. This indicates that a major role of gap junctions in limb patterning may be to enable polarising region cells to communicate directly with adjacent anterior mesenchyme. A role for gap junctional communication between anterior mesenchyme cells cannot be excluded. The results are discussed in relation to the role of retinoic acid as a putative morphogen.
Thyroxine-dependent modulations of the expression of the neural cell adhesion molecule N-CAM during Xenopus laevis metamorphosis
Authors: Levi Giovanni , Broders Florence , Dunon Dominique , Edelman Gerald M. , Thiery Jean Paul
Published: April 2021

During amphibian metamorphosis, a complete remodeling of the phenotype takes place under complex hormonal control whose final effectors are thyroid hormones. This process implies the activation of coordinated programs of cell death, proliferation, migration, adhesion and differentiation. Inasmuch as the neural cell adhesion molecule N-CAM is thought to play a central role in the control of morphogenetic processes, we have studied by immunohistofluorescence and immunoblots the patterns of expression of N-CAM at different stages of Xenopus laevis metamorphosis. A scan was made of all major organs and appendages.

Before the metamorphic climax, all neuronal cell bodies and processes express high levels of N-CAM. During the metamorphic climax, N-CAM expression decreases sharply on the cell bodies and processes of the peripheral nervous system (PNS) but remains high in the central nervous system (CNS). Towards the end of metamorphosis, the PNS and spinal nerves are virtually negative for N-CAM while the CNS is still positive. The optic and olfactory nerves, although myelinated, are still strongly positive for N-CAM. The lens and olfactory epithelia express N-CAM throughout metamorphosis. In the brain, N-CAM is present at all times as three polypeptides of 180, 140, and 120X103Mr; before metamorphosis some of the N-CAM is in its polysialylated form. During metamorphosis and the subsequent growth of the animal, the amount of N-CAM decreases gradually. In all polypeptides, the polysialylated form is the first to disappear.

Cardiac muscle expresses high level of N-CAM from its first formation throughout metamorphosis; in contrast, the level of N-CAM in skeletal muscle is high in newly formed muscles, but decreases rapidly after myoblast fusion.

The liver of adult Xenopus contains large amounts of a 160 xlO3 polypeptide that is recognized by polyclonal and monoclonal antibodies against N-CAM. cDNA probes of Xenopus brain N-CAM recognize major transcripts of 9.2, 3.8 and 3.3 kb in Xenopus liver mRNA; these bands are different in size from those recognized in brain mRNA (9.5, 4.2 and 2.2 kb).

Premetamorphic liver does not express the 160xlO3 form of N-CAM, which can be first detected at stage 59 and persists then through all the life of the animal. Expression of N-CAM in the liver can be induced in premetamorphic animals (stage 51-52) by a 48 h treatment with thyroxine. All hepatocytes are responsive.

The thyroxine-dependent induction of the expression of N-CAM in the liver provides the first example of hormonally induced expression of a cell adhesion molecule. These results are discussed in terms of the potential morphogenetic roles of the various forms of N-CAM in development and metamorphosis.
How imprinting is relevant to human disease
Authors: Hall Judith G.
Published: April 2021

Genomic imprinting appears to be a ubiquitous process in mammals involving many chromosome segments whose affects are dependent on their parental origin. One of the challenges for clinical geneticists is to determine which disorders are manifesting imprinting effects and which families are affected. Re-evaluation of cases of chromosomal abnormalities and family histories of disease manifestations should give important clues. Examination of the regions of human chromosomes homologous to mouse imprinted chromosomal regions may yield useful information. Cases of discordance in monozygous twins may also provide important insights into imprinted modification of diseases.
Variation and inheritance of cytosine methylation patterns in wheat at the high molecular weight glutenin and ribosomal RNA gene loci
Authors: Flavell R. B. , O’Dell M.
Published: April 2021

Chromosome marking by cytosine methylation has been examined in two gene systems in wheat - at the loci encoding high molecular weight (BMW) glutenin sub-units (seed proteins) and ribosomal RNA. Variation in cytosine methylation occurs between progeny in highly inbred lines around the BMW glutenin locus. The variation is inherited through meiosis to F1 and F2 generations but occasionally a new variant arises. Specific cytosine residues lose their methyl group in the seed, the organ where the genes are expressed.

Within the multigene family of ribosomal RNA genes, several subsets of genes can be defined based upon the cytosine methylation patterns. High activity of a ribosomal RNA gene locus is correlated with loss of methylation at specific cytosine residues, especially in the promoter and upstream regulatory regions. A model is described in which the subset of genes selected to be used are those to which specific regulatory proteins and transcription complexes bind most favourably. Binding of such proteins inhibits cytosine methylation and so marks the subset of genes for expression in subsequent cell generations. Examples are described where new types of RNA genes are introduced via sexual crosses that result in changes to the methylation patterns of the ribosomal RNA genes. The processes determining the changes begin, it is believed, in the fertilised egg.
Autosomal and X-chromosome imprinting
Authors: Cattanach Bruce M. , Beechey Colin V.
Published: April 2021

Mouse genetic studies using Robertsonian and reciprocal translocations have shown that certain autosomal regions of loci are subject to a parental germ line imprint, which renders maternal and paternal copies functionally inequivalent in the embryo or later stages of development. Duplication of maternal or paternal copies with corresponding paternal/maternal deficiencies in chromosomally balanced zygotes causes various effects. These range from early embryonic lethalities through to mid-fetal and neonatal lethalities, and in some instances viable young with phenotypic effects are obtained. Eight to nine chromosomal regions that give such imprinting effects have been identified. Six to seven of these regions are located in only three chromosomes (2, 7 and 17). The two other regions are located in chromosomes 6 and 11. Maternal and paternal disomies for each of four other chromosomes (1, 5, 9 and 14) have been recovered with different frequencies, but the possibility that this may be due to imprinting has yet to be supported by follow-up studies on regions of the chromosomes concerned. No clear evidence of genetic-background modifications of the imprinting process have been observed in these mouse genetic experiments.

The mammalian X chromosome is also subject to imprinting, as demonstrated by the non-random, paternal X-inactivation in female mouse extra-embryonic tissues and in the somatic cells of marsupial females. There is also the opposite bias towards inactivation of the maternal X in the somatic cells of female mice. On the basis that both X-chromosome inactivation and autosomal chromosome imprinting may be concerned with gene regulation, it is suggested that evidence from X-chromosome inactivation studies may help to elucidate factors underlying the imprinting of autosomes. The relevant aspects of X-inactivation are summarized.
The DDK inbred strain as a model for the study of interactions between parental genomes and egg cytoplasm in mouse preimplantation development
Authors: Babinet Charles , Richoux Véronique , Guénet Jean-Louis , Renard Jean-Paul
Published: April 2021

The DDK strain of mice has unusual genetic properties. When females of this strain are crossed to males of other strains, they generally exhibit a very low fertility, whereas reciprocal crosses are fully fertile as are the intrastrain crosses. The observed low fertility results from early embryonic lethality, the F1 embryos dying around the late morula-early blastocyst stage. Nuclear transplantation experiments between hybrid eggs of BALB/c and DDK strains has shown that failure of F1 (DDK♀ × BALB/CC♂) embryos to develop is not due to the combination per se of maternal (DDK) and paternal (BALB/c) genomes but rather to an incompatibility between paternal (BALB/c) genomic contribution and DDK cytoplasm. This incompatibility does not occur between a female BALB/c pronucleus and the DDK cytoplasm, suggesting the involvement of a differential imprinting of parental genomes. Introduction of cytoplasts isolated from DDK 1- to 8-cell embryos into BALB/c♀ xBALB/c♂ or BALB/c♀ xDDK♂ embryos of the corresponding developmental stage demonstrate that the cytoplasm of DDK embryos prevents the formation of normal blastocysts through a specific interaction with the paternal component of the BALB/c diploid nucleus. Genetic and molecular studies are underway to try and isolate the gene(s) responsible for the failure of (DDK♀ BALB/C♂)F1 embryos. These experiments should help in our understanding of nucleocytoplasmic interactions and the respective roles of parental genomes in early embryonic development.
KTF-1, a transcriptional activator of Xenopus embryonic keratin expression
Authors: Snape A. M. , Jonas E. A. , Sargent T. D.
Published: April 2021

Nuclear extracts from embryos of Xenopus laevis were shown to contain a protein activity, KTF-1, which binds in vitro to the promoter of the embryonic, epidermisspecific keratin gene, XK81A1. Mobility shift assays, methylation interference and footprinting analysis were used to show that the KTF-1 binding site contains an imperfect, palindromic sequence, ACCCTGAGGCT. This sequence occurs once in the XK81A1 promoter, 152-162 base pairs upstream of the transcription start site. A construct of the keratin gene in which this sequence was altered so that it no longer binds KTF-1 in vitro showed severely reduced transcription levels upon injection into Xenopus embryos, but retained epidermal specificity. Addition of KTF-1 binding sites also enhanced epidermal and non-epidermal activity of a heterologous promoter, Xenopus /J-globin, in embryos. These results suggest that KTF-1 is a general activator of embryonic keratin transcription, which acts in concert with other factors to produce high levels of epidermisspecific expression.
Expression of basic fibroblast growth factor in the nervous system of early avian embryos
Authors: Kalcheim Chaya , Neufeld Gera
Published: April 2021

Basic fibroblast growth factor (bFGF) promotes the survival of a subpopulation of non-neuronal cells developing from trunk neural crest (Kalcheim, Devi Biol. 134, 1-10, 1989). It was therefore important to determine whether this factor is present in the nervous system at early developmental stages. Immunocytochemistry using specific polyclonal and monoclonal antibodies was combined with three highly sensitive assays: bFGF-induced proliferation of bovine adrenal cortex-derived capillary endothelial cells (ACE), a radioimmunoassay for bFGF (RIA) and Western blot analysis. bFGF immunoreactivity was localized to the cytoplasm of neuroepithelial cells derived from embryonic day 2 (E2) quail neural tubes and cultured for one day in a chemically defined medium. Specific staining was observed in young sensory neurons in cultures of neural crest clusters as well as in a subpopulation of non-neuronal cells. In cultured E7 dorsal root ganglia, immunostaining was confined to neuronal cell bodies and fibers. In situ, staining of spinal cord and ganglionic neurons appeared on E6 and increased In intensity towards E10. Various mesoderm-derived structures such as the limb buds, the mesenchyme dorsal to the neural tube, the vertebral muscles and cartilage showed specific staining patterns in addition to neural tissue. In agreement with the results of immunocytochemical studies, 1.4 ng bFGF per mg protein was detected in spinal cord extracts by RIA as early as E3, its concentration increased to 8.0ng mg−1 on ES and then to a maximum of 18.0 ng mg−1 protein on E10, this was followed by a subsequent decrease in concentration in older embryos. On the other hand, high levels of bFGF were present in vertebral tissues from E10 onwards. Extracts of immunopositive tissues were subjected to heparin-Sepharose affinity chromatography and eluted in a stepwise salt gradient. Fractions that eluted from the columns at 2 M NaCl contained a bFGF-like protein as revealed by their ability to stimulate the proliferation of ACE cells and by Western blot analysis. These data demonstrate that bFGF is expressed during early nervous system development in both central and peripheral neurons.
A study of meiosis in chimeric mouse fetal gonads
Authors: Dolci Susanna , Felici Massimo De
Published: April 2021

The influence of somatic environment on the onset and progression of meiosis in fetal germ cells was studied in chimeric gonads produced in vitro by dissociationreaggregation experiments. Germ cells isolated from testes or ovaries of 11.5-13.5 days post coitum (dpc) CD-1 mouse embryos were loaded with the fluorescent supravital dye 5-6 carboxyfluorescein diacetate succinimyl ester (CFSE) and mixed with a cell suspension obtained by trypsin-EDTA treatment of gonads of various ages and of the same or opposite sex. Whereas 11.5 dpc donor germ cells appeared unable to survive in the chimeric gonads obtained, about 76 % of the CFSElabeled female germ cells obtained from 12.5 dpc donor embryos (premeiotic germ cells) found viable within host ovarian tissues showed a meiotic nucleus. In contrast, a smaller number (about 19 %) were in meiosis in chimeric testes. None or very few of donor male germ cells entered meiosis in testes or ovarian host tissues. Aggregation of meiotic 13.5 dpc female germ cells with testis tissues from 13.5 to 14.5 dpc embryos resulted in inhibition of meiotic progression and pyknosis in most donor germ cells.

These results support the existence of a meiosis-preventing substance or a factor causing oocyte degeneration in the fetal mouse testis, but not of a meiosisinducing substance in the fetal ovary.
Distribution of insulin-like growth factor peptides in the developing chick embryo
Authors: Ralphs J. R. , Wylie L. , Hill D. J.
Published: April 2021

Growth factors are likely to be of major significance in developmental biology. Here, the distribution of insulin-like growth factor (IGF) peptides is described during development of the chick embryo. IGF was immunolocalised using a polyclonal antibody to human IGF I detected with a modified Vectastain ABC procedure. Under the conditions used, the antibody binds strongly to IGF I and weakly to IGF II; thus the distribution of IGF peptide, rather than the individual factors, is described.

Muscle, peripheral nerve and the notochord were labelled whenever present. Muscle label was associated with the myotubes and neural labelling with neurons; Schwann cells were unlabelled. IGF distribution changed during differentiation of connective tissues. Regions of mesenchyme destined to form cartilage labelled weakly or not at all, and cartilage condensations were unlabelled. In the limb, chondrocytes became labelled once cartilage rudiments had formed; however, in later development, label was absent in zones of rounded and flattened chondrocytes and appeared strongly at the onset of hypertrophy. Early osteogenic mesenchyme was also unlabelled, although later bone cells were strongly stained. In the neural tube, label was associated with differentiating neuroblasts and cell bodies and with axons, especially in the developing dorsolateral tracts.

These results show a possible correlation between IGF label and cell division in early mesenchyme; cartilage condensations, which have reduced mitotic indices, do not label. In other tissues, notably muscle and nerve but also later connective tissues, label is associated with differentiating, rather than dividing, cells.
Expression and function of the homoeotic genes Antennapedia and Sex combs reduced in the embryonic midgut of Drosophila
Authors: Reuter Rolf , Scott Matthew P.
Published: April 2021

Drosophila homoeotic genes control the formation of external morphological features of the embryo and adult, and in addition affect differentiation of the nervous system. Here we describe the morphogenetic events in the midgut that are controlled by the homoeotic genes Sex combs reduced (Scr) and Antennapedia (Antp). The midgut is composed of two cell layers, an inner endoderm and an outer visceral mesoderm that surround the yolk. Scr and Antp are expressed in the visceral mesoderm but not in the endoderm. The two genes are required for different aspects of the midgut morphogenesis. In Scr null mutant embryos the gastric caeca fail to form. Scr is expressed in the visceral mesoderm cells posterior to the primordia of the gastric caeca and appears to be indirectly required for the formation of the caeca. Antp is expressed in visceral mesoderm cells that overlie a part of the midgut where a constriction will form, and Antp null mutant embryos fail to form this constriction. An ultrastructural analysis of the midgut reveals that the visceral mesoderm imposes the constriction on the endoderm and the yolk. The mesodermal tissue contracts within the constriction and thereby penetrates the layer of the midgut endoderm. Microtubules participate in the morphological changes of the visceral mesoderm cells. The analysis of the expression of Scr in Antp mutant embryos revealed a case of tissue-specific regulation of Scr expression by Antp. In the epidermis, Antp has been shown to negatively regulate Scr, but it positively regulates Scr in the visceral mesoderm.
Target-independent regulation of a novel growth associated protein in the visual system of the chicken
Authors: Schlosshauer Burkhard , Dütting Dieter , Wild Monika
Published: April 2021

Using an immunosuppression technique, the monoclonal antibody 2A1 has been generated specific for a 140 ×103Mr cytoplasmic-membrane-associated protein as shown by subcellular fractionation and Western blot analysis. The antigen is initially confined to perikarya of postmitotic migratory ganglion cells of the embryonic chick retina as revealed by bromodeoxyuridine labeling. During the subsequent period of axon outgrowth, the antigen becomes restricted to ganglion cell axons but disappears during the innervation of the tectum opticum, suggesting a tectal inhibition of antigen expression in retinal axons. To analyse whether the tectum suppresses 2Al-antigen expression, optic nerves of chick embryos were severed to prevent tectal innervation. 2Al-immunoreactivity was determined in deflected axons in comparison to control axons. In addition, retinal axons were grown in vitro on a substratum consisting of alternating stripes of laminin and tectal membranes, in order to investigate whether retinal axons become devoid of the 2Al-antigen once they cross from laminin to tectal membranes. However, neither prevention of target innervation by optic nerve transection in vivo nor exposure of retinal axons to soluble or particulate tectal components in vitro modify 2Al-antigen regulation in ganglion cell axons, suggesting a retina inherent-control of gene expression. Antigen expression is essentially restricted to the period of axonal outgrowth and therefore the 2Al-protein is likely to be involved in processes essential for neurite extension, independent of the synaptic target.
Cytoskeletal protein and mRNA accumulation during brush border formation in adult chicken enterocytes
Authors: Fath Karl R. , Obenauf Steven D. , Burgess David R.
Published: April 2021

We have explored the development of the brush border in adult chicken enterocytes by analyzing the cytoskeletal protein and mRNA levels as enterocytes arise from crypt stem cells and differentiate as they move toward the villus. At the base of the crypt, a small population of cells contain a rudimentary terminal web and a few short microvilli with long rootlets. These microvilli appear to arise from bundles of actin filaments which nucleate on the plasma membrane. The microvilli apparently elongate via the addition of membrane supplied by vesicles that fuse with the microvillus and extend the membrane around the actin core. Actin, villin, myosin, tropomyosin and spectrin, but not myosin I (previously called 110 kD; see Mooseker and Coleman, J. Cell Biol. 108, 2395-2400, 1989) are already concentrated in the luminal cytoplasm of crypt cells, as seen by immunofluorescence. Using quantitative densitometry of cDNA-hybridized RNA blots from cells isolated from crypts, villus middle (mid), or villus tip (tip), we found a 2- to 3-fold increase in villin, calmodulin and tropomyosin steady-state mRNA levels; an increase parallel to morphological brush border development. Actin, spectrin and myosin mRNA levels did not change significantly. ELISA of total crypt, mid and tip cell lysates show that there are no significant changes in actin, myosin, spectrin, tropomyosin, myosin I, villin or α-actinin protein levels as the brush border develops. The G-/F-actin ratio also did not change with brush border assembly. We conclude that, although the brush border is not fully assembled in immature enterocytes, the mgjor cytoskeletal proteins are present in their full concentration and already localized within the apical cytoplasm. Therefore brush border formation may involve reorganization of a pool of existing cytoskeletal proteins mediated by the expression or regulation of an unidentified key protein(s).
Vertebral Malformation in the Mouse Foetus Caused by Maternal Hypoxia During Early Stages of Pregnancy
Authors: Murakami Ujihiro , Kameyama Yoshiro
Published: April 2021

The ddN strain of mice were kept in a chamber with reduced atmospheric pressure (225 mmHg) for 5 hours on their eighth (group A), ninth (group B), tenth (group C), eleventh (group D) or twelfth (group E) day of pregnancy and examined both for external malformations and for skeletal changes in the foetuses. For skeletal examinations they were cleared by the Dawson method. In group A, besides two cases of atlanto-occipital fusions, malformations of upper cervical vertebrae were seen. In group B, cervical vertebrae were chiefly involved in malformations, but the thoraco-lumbar ones were also disturbed. In group C, besides a few cervical involvements, lower thoracic and lumbar malformations were the most striking. In group D, malformations shifted to the sacro-caudal level, while in group E the malformations ranged from the lumbar to the caudal level, though they were low in frequency. These changes were fusion, adhesion, bifurcation, absence, reduction in size, asymmetry of the primordial posterior rami, disordered segmentation, etc. The primordium of the vertebral body was also involved. At the thoracic level ribs were also involved in deformities when their corresponding vertebrae were affected. In the lowest part of the thoracic level, the absence or vestigial of the rib was often seen in group C. In an overall picture, a clear-cut head-to-tail gradient shift of malformations occurs as the developmental stage of oxygen deficiency advances. This sequence is in good agreement with that shown by Ingalls et al. and by Degenhardt. Atlanto-occipital fusions and abnormalities in the upper cervical region recall the conditions seen in iniencephalia, Klippel-Feil syndrome and platybasia in human beings. Some of the malformations in the vertebrae at other levels resembled those in vertebral rachischisis in man.