Plant cytoplasmic male sterility (CMS) results from incompatibilities between the organellar and nuclear genomes and prevents self pollination, enabling hybrid crop breeding to increase yields. The Wild Abortive CMS (CMS-WA) has been exploited in the majority of 'three-line' hybrid rice production since the 1970s, but the molecular basis of this trait remains unknown. Here we report that a new mitochondrial gene, WA352, which originated recently in wild rice, confers CMS-WA because the protein it encodes interacts with the nuclear-encoded mitochondrial protein COX11. In CMS-WA lines, WA352 accumulates preferentially in the anther tapetum, thereby inhibiting COX11 function in peroxide metabolism and triggering premature tapetal programmed cell death and consequent pollen abortion. WA352-induced sterility can be suppressed by two restorer-of-fertility (Rf) genes, suggesting the existence of different mechanisms to counteract deleterious cytoplasmic factors. Thus, CMS-related cytoplasmic-nuclear incompatibility is driven by a detrimental interaction between a newly evolved mitochondrial gene and a conserved, essential nuclear gene.
A major challenge in stem-cell mediated regenerative medicine is the development of defined culture systems for the maintenance of clinical-grade human embryonic stem (hES) cells. Using a feedback system control scheme, we identified a unique combination of three small molecule inhibitors that enables the maintenance of hES cells on a fibronectin-coated surface through single cell passaging. After 20 passages, the undifferentiated state of the hES cells was confirmed by OCT4, SSEA4 and NANOG expressions, while their pluripotent potential and genetic integrity were demonstrated by teratoma formation and normal karyotype, respectively. Our study attests to the power of feedback system control scheme in quickly pinpointing optimal conditions for desired biological activities and provides a chemically defined, scalable and single cell passaging culture system for hES cells.
With their unique ability to differentiate into all cell types, embryonic stem (ES) cells hold great therapeutic promise. To improve the efficiency of embryoid body (EB)-mediated ES cell differentiation, we studied murine EBs on the basis of their size and found that EBs with an intermediate size (diameter 100 -300 m) are the most proliferative, hold the greatest differentiation potential, and have the lowest rate of cell death. In an attempt to promote the formation of this subpopulation, we surveyed several biocompatible substrates with different surface chemical parameters and identified a strong correlation between hydrophobicity and EB development. Using self-assembled monolayers of various lengths of alkanethiolates on gold substrates, we directly tested this correlation and found that surfaces that exhibit increasing hydrophobicity enrich for the intermediate-size EBs. When this approach was applied to the human ES cell system, similar phenomena were observed. Our data demonstrate that hydrophobic surfaces serve as a platform to deliver uniform EB populations and may significantly improve the efficiency of ES cell differentiation.hydrophobicity ͉ self-assembled monolayers ͉ serum-free differentiation T he potential of embryonic stem (ES) cells to differentiate into all specialized cell types has made them attractive models for studying the mechanisms of lineage commitment and has opened pathways for regenerative medicine (1). Various in vitro strategies have been developed for differentiation of ES cells into populations of specific cell types (2). Of these strategies, the formation of three-dimensional cell aggregates known as embryoid bodies (EBs) is a common and critical intermediate to the induction of lineage-specific differentiation (3, 4). In addition, lineage differentiation programs within the EB closely resemble lineage commitment in vivo in the developing embryo, further highlighting the importance of the ES cell-EB culture system (5-8).Although EBs can be generated through several methodologies, the suspension culture technique allows for easy access to the cultured EBs and can be scaled for expansion (9). In this method, EBs are formed when ES cells are removed from feeder contact and dispersed on low-attachment tissue culture plates, supplemented by culture medium absent of key factors necessary for the maintenance of undifferentiated ES cell growth. Lowattachment tissue culture plates typically use neutral, hydrophilic hydrogels to prevent protein adsorption and subsequent cell attachment, facilitating the initial aggregation of ES cells that is critical to EB formation (10). The cellular aggregates formed by this procedure will develop simple EBs that consist of an outer layer of endoderm cells within 2-4 days (3). At this point, two differentiation strategies can be applied. If suspension culture is continued, simple EBs will differentiate further to form cystic EBs that typically contain an inner layer of columnar ectodermlike cells and that accumulate fluid in the interior of the struct...
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