Mosaic Eggs Research Articles

Cytoplasmic localization and reorganization in ascidian eggs: role of postplasmic/PEM RNAs in axis formation and fate determination

Localization of maternal molecules in eggs and embryos and cytoplasmic movements to relocalize them are fundamental for the orderly cellular and genetic processes during early embryogenesis. Ascidian embryos have been known as 'mosaic eggs' because of their autonomous differentiation abilities based on localized cell fate determinants. This review gives a historical overview of the concept of cytoplasmic localization, and then explains the key features such as ooplasmic movements and cell lineages that are essential to grasp the process of ascidian development mediated by localized determinant activities. These activities are partly executed by localized molecules named postplasmic/PEM RNAs, originating from approximately 50 genes, of which the muscle determinant, macho-1, is an example. The cortical domain containing these RNAs is relocalized to the posterior-vegetal region of the egg by cytoskeletal movements after fertilization, and plays crucial roles in axis formation and cell fate determination. The cortical domain contains endoplasmic reticulum and characteristic granules, and gives rise to a subcellular structure called the centrosome-attracting body (CAB), in which postplasmic/PEM RNAs are highly concentrated. The CAB is responsible for a series of unequal partitionings of the posterior-vegetal cytoplasmic domain and the postplasmic/PEM RNAs at the posterior pole during cleavage. Some components of this domain, which is rich in granules, are eventually inherited by prospective germline cells with particular postplasmic/PEM RNAs such as vasa. The postplasmic/PEM RNAs are classified into two groups according to their final cellular destinations and localization pathways. Localization of these RNAs is regulated by specific nucleotide sequences in the 3' untranslated regions (3'UTRs).

Interspecies linkage analysis of mo, a Bombyx mori locus associated with mosaicism and gynandromorphism

The mo (hereditary mosaic) mutation is one of the most famous and interesting mutations of the silkworm, Bombyx mori. Females homozygous for mo generate mosaic and gynandromorphic offspring due to non-elimination of polar bodies and subsequent double fertilization events, irrespective of the genotype of the mated males. Although mo was first reported in 1927, the locus has not been mapped to linkage groups, as the mutation is unstable and appears to be sensitive to genetic background. In this study, linkage analysis of mo was performed using PCR-based markers on single nucleotide polymorphism linkage maps. Bombyx mandarina was used as the mating partner for the B. mori mo strain, as it is easier to identify polymorphic markers between B. mori and B. mandarina than within B. mori strains. Surprisingly, we identified two homozygous linkage groups (LGs) in all of the 12 B(1) (first backcross generation) moths that had deposited mosaic eggs. It was revealed that +( mo ) is located on the M chromosome of B. mandarina, which corresponds to two linkage groups of B. mori, LG 14 and 27. Based on further linkage analysis using B. mori as a mating partner, mo was mapped to LG 14. Additionally, we found that mo activity could be modified by a gene(s) on LG 17.

Pattern formation in insect embryogenesis: The evolution of concepts and mechanisms

This award lecture reviews concepts of embryonic pattern formation developed since the time when, early in this century, insect embryogenesis first became a topic of causal research. These concepts, considered here in their historical sequence, are: (1) preformed patterns of determinants in “mosaic eggs”; (2) “regulative” pattern formation directed by a differentiation centre; (3) pattern specification by antagonistic polar gradients; and (4) the complex interactions of developmental genes recently revealed by genetical and molecular methods. These methods have triggered an epoch-making breakthrough in developmental biology, but they also can reveal surprising evolutionary aspects.

PH in eggs of the ascidian Ciona intestinalis at fertilization and activation

AbstractUsing liquid ion exchanger microelectrodes, we have measured the intracellular pH of unfertilized ascidian eggs. The pH in these eggs ranges from 7.1 to 7.6 (similar to values for fertilized sea urchin eggs) and does not change during the first 7 minutes of activation, whether induced by spermatozoa or by the Ca2+ ionophore A23187. Factors regulating metabolic derepression in regulative and mosaic eggs are discussed.

The detection of mosaics and polyploids in a hereditary mosaic strain of the silk moth, Bombyx mori, using egg colour mutants

SummaryTo analyze abnormal fertilization in a hereditary mosaic strain (mo/mo) of Bombyx mori, the percentages of diploidy mosaic, polyploidy mosaic and polyploid eggs in a batch were estimated by using egg colour mutants (pe re). Among 48 890 eggs from crosses of pe + / + re, mo/mo females with pe re/pe re males, 9409 abnormal eggs were obtained; 4472 of them were diploidy mosaics (red-white eggs), 4038 were polyploids (black eggs) and 899 were polyploidy mosaics (566 black-white, 256 black-red and 77 black-white-red eggs). The total number of diploidy mosaic eggs was approximately equal to that of polyploid eggs. A significant correlation was detected between the diploidy mosaic and polyploid egg ratios within a batch. This suggests that diploidy mosaics are produced by double fertilization in which two genetically non-identical egg nuclei are fertilized in turn by a sperm, and polyploids are formed by the fertilization of a diploid, non-disjunctive egg nucleus gamete by a single sperm. Our results also indicated the presence of common factors modifying both mosaic and polyploid frequency. The concordance of the observed ratio of polyploidy mosaic eggs (1·84%) with the expected value (diploidy mosaic ratio × polyploidy ratio × 2 = 1·83%) suggests that the formation of mosaics occurs independently of the formation of polyploids in this abnormal fertilization process. We point out that it is necessary to modify Goldschmidt & Katsuki's general model to explain abnormal fertilization, and we propose several possible models.

Genotoxicity of metacid established through the somatic and germ line mosaic assays and the sex-linked recessive lethal test in Drosophila.

The mutagenic potential of metacid (methyl parathion), an anticholinesterase organophosphate pesticide, has been studied in the Drosophila eye, wing and female germ line assays and the sex-linked recessive lethal tests. Larvae 24 h, 48 h and 72 h old, heterozygous for various recessive genetic markers on the first and third chromosomes, were exposed to the LD50 and half of this dose for different periods of time. The eyes and wings were checked for the presence of mosaic spots and eggs laid by the females for germ line mosaicism. The M-5 technique was used to detect the induction of sex-linked recessive lethals. It is concluded that metacid is mutagenic in somatic and germ line cells of Drosophila and induces sex-linked recessive lethals in immature male germ cells.

Cytological studies on mixoploidy and embryonic development in mosaic silkworms induced by low temperature treatment

Mosaicism in silkworms is easily inducible by applying a cold shock to the hybrid eggs between two strains with different markers at the early developmental stage. When BF1 eggs from the cross between a tetraploid female (which had been induced from the cross between a red egg and a white egg strain) and a male of the red egg strain were exposed to a cold shock, hexaploid eggs and two types of mosaic eggs were obtained: black-black (BB-) mosaic eggs, which possessed two kinds of black serosa cells with different-sized nuclei, and black-red (BR-) mosaic eggs. Cytological studies on the embryos from these mosaic eggs revealed that the BB-mosaic type was a 3n/6n mixoploid, while the BR-mosaic type was mixoploid with n/2n/3n, n/3n, or 2n/6n constitution. The hatchability of BB- and BR-mosaic eggs was considerably lower than that of either n/2n or 2n/4n mixoploid eggs obtained by a cold treatment of diploid eggs. Since abnormal development was observed at a high frequency in the embryos from BB- and BR-mosaic eggs at the blastokinesis stage, it is speculated that the coexistence of hexaploid or triploid cells may be a factor in the induction of such abnormality in early embryogenesis.

Cytological studies on the mosaic silkworms induced by low temperature treatment

Mosaic silkworms were induced when the hybrid eggs of two strains with different egg color and larval markings were exposed to low temperature. Cytological studies were conducted to find out the relation between mosaic larval pattern and ploidy in reproductive cells along with demonstration of chromosomes in the mosaic embryos. — Mosaic eggs eith the characters of both the father and the hybrid were two types, one with large serosa nuclei (LN-mosaic) and the other with small serosa nuclei (SN-mosaic). The cytological studies demonstrated that LN-mosaic individuals were 2n/4n, while SN-mosaic ones were n/2n. In both types of silkworms, cell ploidy level in nuclei of synkaryon origin was two times that of androgenic ones. — From the results obtained in the present studies as well as in the previous studies, a possible mechanism of induction of mosaicism in silkworms by cold shock is contemplated.

Protein Pattern of Mosaic Eggs for Normal and Small Egg Charater in Bombyx mori

Protein Pattern of Mosaic Eggs for Normal and Small Egg Charater in Bombyx mori

Heteroploidy in mammals

1. Forty-two spontaneously heteroploid eggs have been found in the mouse (Mus musculus). 2. Haploid, triploid, tetraploid, hexaploid, diplo/polyploid mosaic, aneuploid and multiform aneuploid eggs have been identified. The commonest form of heteroploidy is triploidy. Up to three heteroploid eggs have been observed in the same female. 3. All but one of the heteroploid eggs were found in a particular laboratory stock (silver stock) which is associated with thesilver factor. 4. In any one mouse the triploid eggs contain on the average fewer nuclei than diploid eggs. 5. Heteroploid eggs are capable of apparently normal development up to the blastula stage, the latest stage at which they have so far been examined. The possibility of further development is being investigated. 6. The silver factor, or a closely linked factor, is probably responsible for the production of heteroploid eggs in silver stock. 7. As in germ cells, chromosomes in the pre-implantation mouse egg are rod-shaped and most if not all chromosomes have a subterminal centromere. 8. The origin and frequency of occurrence of these heteroploid eggs are discussed, and also some consequences which might attend any further viability.

THE LOCALIZATION OF ENZYMES IN CELLS

THE LOCALIZATION OF ENZYMES IN CELLS

On a spontaneous mosaicism observed in the silkworm egg

Among the larvae of silkworm spontaneous mosaicism is not a rare occurrence and it is known to be highly accererated by some agents such as X-rays, temperature shocks, centrifuging and other extreme treatments. In the egg of this insect, however, spontaneous mosaicism has never been recorded even though several colouring genes had been known. As was previously reported, the present author has succeeded to obtain mosaic eggs by means of high temperature shock. Since then, he paid constant attention to find out mosaics in thousands of eggs, and succeeded, fortunately.From a crossing of (Be2/Be2, re/re, Z+/W_??_×be2/be2, Re/Re, Zos/Zos_??_) F2 offspring is expected in a ratio of 9 black: 4 red: 3 brown. Among these F2 eggs two mosaics were found, which is shown in Fig. 1. As is clearly seen in the figure, anterior part of the egg was covered by red serosa cells and posterior by black cells, thus belong to an antero-posterior mosaic type. One of these two eggs (ms. 1) hatched out and completed its life cycle. The resulted caterpillar from this egg was a mosaic, whose left half of the body was os-translucent, while the other part was wholly normal. Therefore, it belongs to a bilateral type. The moth was, also, bilateral mosaic having black right and red left eyes. This individual was a female but laid no eggs after mating. As the plane of bilaterality of the embryo corresponds to the plane of symmetry of the egg, the antero-posterior mosaic egg ought to give rise to the same mosaic type in the caterpillar as well as in the moth. In the present case, however, the mosaic caterpillar and moth, resulted from the mosaic egg, was bilateral mosaic. Disaccordance of mosaic planes in the egg and later life remains unexplained.

Experimental formation of the mosaic eggs and criticism of the difusible substance in the silkworm

Experimental formation of the mosaic eggs and criticism of the difusible substance in the silkworm

EMBRYONIC DETERMINATION IN THE ANNELID, SABELLARIA VULGARIS

1. Isolation experiments on the egg of Sabellaria vulgaris demonstrate that the formation of the apical tuft in partial larvæ is dependent upon the presence of the first polar lobe and the C cell; that the post-trochal region develops only when the three polar lobes and the 1D cell are present; and that apical cilia form only if the A or B cell is included. 2. Form changes in isolated first and second polar lobes are described. The early changes are synchronous with the cleavages of the ovum, except that all events in the isolated lobe are delayed. 3. The results of the following transplantation experiments are reported: (a) Transplantation of polar lobes. (b) Transplantation of blastomeres to the whole egg. (c) Transplantation of blastomeres to E-PL1. (d) Fusions of half- and quarter-blastomeres. (e) Fusions of two eggs. In all combinations, complete self-differentiation of individual blastomeres occurs. Apical tufts develop only when C cells are present, post-trochal bristles are dependent upon the presence of D cells, and apical cilia form only when either the A or B cell is included. 4. The results of this investigation are compared with those from experiments on other mosaic eggs.