Distribution of cytoplasmic determinants in unfertilized eggs of the ascidian Halocynthia roretzi

1996 ◽  
Vol 206 (5) ◽  
pp. 297-304 ◽  
Author(s):  
A. Yamada ◽  
Hiroki Nishida
Keyword(s):  
Halocynthia Roretzi ◽  
Cytoplasmic Determinants

Localized regions of egg cytoplasm that promote expression of endoderm-specific alkaline phosphatase in embryos of the ascidian Halocynthia roretzi

Development ◽  
1993 ◽  
Vol 118 (1) ◽  
pp. 1-7 ◽  
Author(s):  
H. Nishida
Keyword(s):  
Alkaline Phosphatase ◽  
Histochemical Staining ◽  
Halocynthia Roretzi ◽  
Endoderm Differentiation ◽  
Initial Event ◽  
Cytoplasmic Factors ◽  
Early Embryos ◽  
Vegetal Pole ◽  
Cytoplasmic Determinants ◽  
Cytoplasmic Transfer

Embryogenesis in ascidians is known to be of the mosaic type, a property that suggests the presence of cytoplasmic factors in the egg which are responsible for specification of the developmental fates of early blastomeres. Endoderm cells are present in the trunk region of tadpole larvae, and these cells specifically express alkaline phosphatase (AP). Endoderm cells originate exclusively from blastomeres of the vegetal hemisphere of early embryos. To obtain direct evidence for cytoplasmic determinants of endoderm specification, we carried out cytoplasmic-transfer experiments by fusing blastomeres and cytoplasmic fragments from various regions. Initially, presumptive-epidermis blastomeres (blastomeres from the animal hemisphere) were fused to cytoplasmic fragments from various regions of blastomeres of 8-cell embryos of Halocynthia roretzi, and development of endoderm cells was monitored by histochemical staining for AP. AP activity was observed only when presumptive-epidermis blastomeres were fused with cytoplasmic fragments from the presumptive-endoderm blastomeres. The results suggest that cytoplasmic factors that promote the initial event of endoderm differentiation (endoderm determinants) are present in endoderm-lineage blastomeres. Next, to examine the presence and localization of endoderm determinants in the egg, cytoplasmic fragments from various regions of unfertilized and fertilized eggs were fused with the presumptive-epidermis blastomeres. The results suggest that endoderm determinants are already present in unfertilized eggs, and that they are segregated by movements of the ooplasm after fertilization. Initially, these determinants move to the vegetal pole of the egg. Then, prior to the first cleavage, their distribution extends in the equatorial direction, namely, to the entire vegetal hemisphere from which future endoderm-lineage blastomeres are formed.

Regionality of egg cytoplasm that promotes muscle differentiation in embryo of the ascidian, Halocynthia roretzi

Development ◽  
1992 ◽  
Vol 116 (3) ◽  
pp. 521-529 ◽  
Author(s):  
H. Nishida
Keyword(s):  
Muscle Cells ◽  
Muscle Differentiation ◽  
Posterior Region ◽  
Second Phase ◽  
Halocynthia Roretzi ◽  
Early Embryos ◽  
Vegetal Pole ◽  
Restricted Region ◽  
Ooplasmic Segregation ◽  
Cytoplasmic Determinants

Development of ascidians occurs in typical mosaic fashion: blastomeres isolated from early embryos differentiate into tissues according to their normal fates, an indication that cytoplasmic determinants exist in early blastomeres. To provide direct evidence for such cytoplasmic determinants, we have devised methods for fusing blastomeres and cytoplasmic fragments from various regions. (1) Presumptive-epidermis blastomeres were fused to cytoplasmic fragments from various regions of blastomeres of 8-cell embryos of Halocynthia roretzi and development of muscle cells was monitored by an antibody to ascidian myosin. Muscle differentiation was observed only when presumptive-epidermis blastomeres were fused with fragments from the posterior region of B4.1 (posterior-vegetal) blastomeres, the normal progenitor of muscle cells. The results indicate that muscle determinants are present and localized in the cytoplasm that enters muscle-lineage cells. (2) To investigate the presence and localization of muscle determinants in the egg, cytoplasmic fragments from various regions of unfertilized and fertilized eggs were fused with the presumptive- epidermis blastomeres, and formation of muscle cells was assessed by monitoring myosin, actin and acetylcholinesterase expression. These proteins were expressed only when cytoplasm from a restricted region of the eggs, i.e. the vegetal region, after the first phase of ooplasmic segregation, and posterior region, after the second phase of segregation, were fused. Based on these experiments, it is suggested that muscle determinants are segregated by ooplasmic movements after fertilization. They move initially to the vegetal pole of the egg and, prior to first cleavage, to the posterior region from whence future muscle-lineage blastomeres are formed. The inferred movements of muscle determinants correspond to those of the myoplasm, a microscopically visible portion of the egg cytoplasm.

Expression of endostyle-specific genes in the ascidian Halocynthia roretzi

1996 ◽  
Vol 206 (3) ◽  
pp. 227-235 ◽  
Author(s):  
M. Ogasawara ◽  
Kimio J. Tanaka ◽  
Kazuhiro W. Makabe ◽  
Noriyuki Satoh
Keyword(s):  
Halocynthia Roretzi

scholarly journals Effect of emetine, a protein synthesis inhibitor, on larval tail resorption in the ascidian Halocynthia roretzi

2006 ◽  
Vol 23 (2) ◽  
pp. 43-46
Author(s):  
Kiyotaka Matsumura ◽  
Manami Nagano ◽  
Sachiko Tsukamoto ◽  
Haruko Kato ◽  
Nobuhiro Fusetani
Keyword(s):  
Protein Synthesis ◽  
Protein Synthesis Inhibitor ◽  
Synthesis Inhibitor ◽  
Halocynthia Roretzi

Localization of egg cytoplasm that promotes differentiation to epidermis in embryos of the ascidian Halocynthia roretzi

Development ◽  
1994 ◽  
Vol 120 (2) ◽  
pp. 235-243 ◽  
Author(s):  
H. Nishida
Keyword(s):  
Specific Antigen ◽  
Equatorial Region ◽  
Epidermal Cells ◽  
Second Phase ◽  
Halocynthia Roretzi ◽  
Cytoplasmic Factors ◽  
Early Embryos ◽  
Ooplasmic Segregation ◽  
Anucleate Cell ◽  
Cell Fragments

Embryogenesis in ascidians is of the mosaic type. This property suggests the presence of cytoplasmic factors in the egg that are responsible for specification of the developmental fates of early blastomeres. The epidermal cells that surround the entire tadpole larva originate exclusively from blastomeres of the animal hemisphere of early embryos. To obtain direct evidence for cytoplasmic determinants of epidermis fate, we carried out cytoplasmic transfer experiments by fusing blastomeres and anucleate cell fragments from various regions of eggs and embryos. Initially, presumptive non-epidermis blastomeres (blastomeres from the vegetal hemisphere) were fused to cytoplasmic fragments from various regions of blastomeres of 8-cell embryos of Halocynthia roretzi, and development of epidermal cells was monitored by following the expression of an epidermis- specific antigen, as well as by observations of morphology and the secretion of larval tunic materials. Formation of epidermis was observed when vegetal blastomeres were fused with cytoplasmic fragments from the presumptive epidermis blastomeres. The results suggested that cytoplasmic factors that promoted epidermis differentiation (epidermis determinants) were present in epidermis progenitors. Vegetal blastomeres only manifested this change in fate when fused with cytoplasmic fragments of roughly equal or larger size. Next, to examine the presence and localization of epidermis determinants in the uncleaved egg, cytoplasmic fragments from various regions of unfertilized and fertilized eggs were fused with the vegetal blastomeres. The results suggested that epidermis determinants were already present in unfertilized eggs and that they were segregated by movements of the ooplasm after fertilization. After the first phase of ooplasmic segregation, these determinants were widely distributed, with the highest activity being located in the equatorial region. There were no indications of regional differences in the activity within the equatorial region of eggs at this stage. After the second phase of ooplasmic segregation, prior to the first cleavage, the activity moved in the animal direction, namely, to the animal hemisphere, from which future epidermis-lineage blastomeres are normally formed.

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