RPL18aB helps maintain suspensor identity during early embryogenesis

During embryogenesis, plants are thought to use a mechanism that allows the suspensor to maintain its identity. Here, we reported that RPL_18aB is involved in this mechanism in Arabidopsis thaliana. The suspensor cells proliferated in rpl_18aB and formed a multicellular structure rather than undergo programmed cell death, as in wild type. Suspensors of rpl_18aB expressed the embryo proper marker, DRN::GFP, but not the suspensor marker, WOX8::GFP. In addition, auxin accumulated throughout the suspensors of rpl_18aB proembryos. Suspensor-specific expression of RPL_18aB could rescue the cell proliferation defects in rpl_18aB suspensors. These findings supported a role for RPL_18aB in maintaining suspensor identity.     

Step-wise specification of retinal stem cells during normal embryogenesis

The specification of embryonic cells to produce the retina begins at early embryonic stages as a multi-step process that gradually restricts fate potentials. First, a subset of embryonic cells becomes competent to form retina by their lack of expression of endo-mesoderm-specifying genes. From these cells, a more restricted subset is biased to form retina by virtue of their close proximity to sources of bone morphogenetic protein antagonists during neural induction. During gastrulation, the definitive RSCs (retinal stem cells) are specified as the eye field by interactions with underlying mesoderm and the expression of a network of retina-specifying genes. As the eye field is transformed into the optic vesicle and optic cup, a heterogeneous population of RPCs (retinal progenitor cells) forms to give rise to the different domains of the retina: the optic stalk, retinal pigmented epithelium and neural retina. Further diversity of RPCs appears to occur under the influences of cell-cell interactions, cytokines and combinations of regulatory genes, leading to the differentiation of a multitude of different retinal cell types. This review examines what is known about each sequential step in retinal specification during normal vertebrate development, and how that knowledge will be important to understand how RSCs might be manipulated for regenerative therapies to treat retinal diseases.     

Arrested apoptosis of nurse cells during Hydra oogenesis and embryogenesis

During Hydra oogenesis, an aggregate of germ cells differentiates into one oocyte and thousands of nurse cells. Nurse cells display a number of features typical of apoptotic cells and are phagocytosed by the growing oocyte. Yet, these cells remain unchanged in morphology and number until hatching of the polyp, which can occur up to 12 months later. Treatments with caspase inhibitors can block oocyte development during an early phase of oogenesis, but not after nurse cell phagocytosis has taken place, indicating that initiation of nurse cell apoptosis is essential for oocyte development. The genomic DNA of the phagocytosed nurse cells in the oocyte and embryo shows large-scale fragmentation into 8- to 15-kb pieces, but there is virtually none of the internucleosomal degradation typically seen in apoptotic cells. The arrested nurse cells exhibit high levels of peroxidase activity and are prevented from entering the lysosomal pathway. After hatching of the polyp, apoptosis is resumed and the nurse cells are degraded within 3 days. During this final stage, nurse cells become TUNEL-positive and enter secondary lysosomes in a strongly degraded state. Our results suggest that nurse cell apoptosis consists of caspase-dependent and caspase-independent phases. The independent phase can be arrested at an advanced stage for several months, only to resume after the primary polyp hatches.     

Synchronization of somatic embryogenesis in a carrot cell suspension culture

Synchronization of somatic embryogenesis was achieved in a carrot (Daucus carota L. cv. “Kurodagosun”) suspension culture by sieving the initial heterogeneous cell population, by density gradient centrifugation in Ficoll solutions, and by subsequent repeated centrifugations at a low speed (50g) for a short time (5 seconds), followed by transferring the cell clusters obtained, which were composed of 3 to 10 cells, to a medium containing zeatin (0.1 micromolar) but no auxin. The frequency of embryo formation reached more than 90%, and synchrony of the embryogenetic process was observed at least in the early stages of the process. The system established in the present work provides a useful system for biochemical research into the mechanisms of somatic embryogenesis.     

14-3-3 isoforms and pattern formation during barley microspore embryogenesis

The members of the 14-3-3 isoform family have been shown to be developmentally regulated during animal embryogenesis, where they take part in cell differentiation processes. 14-3-3 isoform-specific expression patterns were studied in plant embryogenic processes, using barley (Hordeum vulgare L.) microspore embryogenesis as a model system. After embryogenesis induction by stress, microspores with enlarged morphology showed higher viability than non-enlarged ones. Following microspore culture, cell division was only observed among the enlarged microspores. Western blot and immunolocalization of three barley 14-3-3 isoforms, 14-3-3A, 14-3-3B and 14-3-3C were carried out using isoform-specific antibodies. The level of 14-3-3C protein was higher in enlarged microspores than in non-enlarged ones. A processed form of 14-3-3A was associated with the death pathway of the non-enlarged microspores. In the early embryogenesis stage, 14-3-3 subcellular localization differed among dividing and non-dividing microspores and the microspore-derived multicellular structures showed a polarized expression pattern of 14-3-3C and a higher 14-3-3A signal in epidermis primordia. In the late embryogenesis stage, 14-3-3C was specifically expressed underneath the L(1) layer of the shoot apical meristem and in the scutellum of embryo-like structures (ELSs). 14-3-3C was also expressed in the scutellum and underneath the L(1) layer of the shoot apical meristem of 21 d after pollination (DAP) zygotic embryos. These results reveal that 14-3-3A processing and 14-3-3C isoform tissue-specific expression are closely related to cell fate and initiation of specific cell type differentiation, providing a new insight into the study of 14-3-3 proteins in plant embryogenesis.     

Skeletal muscle satellite cells appear during late chicken embryogenesis.

The emergence of avian satellite cells during development has been studied using markers that distinguish adult from fetal cells. Previous studies by us have shown that myogenic cultures from fetal (Embryonic Day 10) and adult 12-16 weeks) chicken pectoralis muscle (PM) each regulate expression of the embryonic isoform of fast myosin heavy chain (MHC) differently. In fetal cultures, embryonic MHC is coexpressed with a ventricular MHC in both myocytes (differentiated myoblasts) and myotubes. In contrast, myocytes and newly formed myotubes in adult cultures express ventricular but not embryonic MHC. In the current study, the appearance of myocytes and myotubes which express ventricular but not embryonic MHC was used to determine when adult myoblasts first emerge during avian development. By examining patterns of MHC expression in mass and clonal cultures prepared from embryonic and posthatch chicken skeletal muscle using double-label immunofluorescence with isoform-specific monoclonal antibodies, we show that a significant number of myocytes and myotubes which stain for ventricular but not embryonic MHC are first seen in cultures derived from PM during fetal development (Embryonic Day 18) and comprise the majority, if not all, of the myoblasts present at hatching and beyond. These results suggest that adult type myoblasts become dominant in late embryogenesis. We also show that satellite cell cultures derived from adult slow muscle give results similar to those of cultures derived from adult fast muscle. Cultures derived from Embryonic Day 10 hindlimb form myocytes and myotubes that coexpress ventricular and embryonic MHCs in a manner similar to cells of the Embryonic Day 10 PM. Thus, adult and fetal expression patterns of ventricular and embryonic MHCs are correlated with developmental age but not muscle fiber type.