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Female gametophyte development in Arabidopsis thaliana follows a well-defined program that involves many fundamental cellular processes. In this study, we report the involvement of the Arabidopsis thaliana MIDASIN1 (AtMDN1) gene during female gametogenesis through the phenotypic characterization of plants heterozygous for an insertional mdn1 mutant allele. The MDN1 yeast ortholog has previously been shown to encode a non-ribosomal protein involved in the maturation and assembly of the 60S ribosomal subunit. Heterozygous MDN1/mdn1 plants were semisterile and mdn1 allele transmission through the female gametophyte was severely affected. Development of mdn1 female gametophyte was considerably delayed compared to their wild-type siblings. However, delayed mdn1 female gametophytes were able to reach maturity and a delayed pollination experiment showed that a small proportion of the female gametophytes were functional. We also report that the Arabidopsis NOTCHLESS (AtNLE) gene is also required for female gametogenesis. The NLE protein has been previously shown to interact with MDN1 and to be also involved in 60S subunit biogenesis. The introduction of an AtNLE-RNA interference construct in Arabidopsis led to semisterility defects. Defective female gametophytes were mostly arrested at the one-nucleate (FG1) developmental stage. These data suggest that the activity of both AtMDN1 and AtNLE is essential for female gametogenesis progression.

A relatively small number of signaling pathways drive a wide range of developmental decisions, but how this versatility in signaling outcome is generated is not clear. In the Drosophila follicular epithelium, localized epidermal growth factor receptor (EGFR) activation induces distinct cell fates depending on its location. Posterior follicle cells respond to EGFR activity by expressing the T-box transcription factors Midline and H15, while anterior cells respond by expressing the homeodomain transcription factor Mirror. We show that the choice between these alternative outputs of EGFR signaling is regulated by antiparallel gradients of JAK/STAT and BMP pathway activity and that mutual repression between Midline/H15 and Mirror generates a bistable switch that toggles between alternative EGFR signaling outcomes. JAK/STAT and BMP pathway input is integrated through their joint and opposing regulation of both sides of this switch. By converting this positional information into a binary decision between EGFR signaling outcomes, this regulatory network ultimately allows the same ligand-receptor pair to establish both the anterior-posterior (AP) and dorsal-ventral (DV) axes of the tissue.

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The E2F family of transcription factors are evolutionarily conserved regulators of the cell cycle that can be divided into two groups based on their ability to either activate or repress transcription. In Drosophila, there is only one "activator" E2F, dE2F1, which provides all of the pro-proliferative activity of E2F during development. Interestingly, the de2f1 gene can be transcribed from multiple promoters resulting in six alternate transcripts. In this study, we sought to investigate the biological significance of the alternate transcriptional start sites. We focused on the de2f1 promoter region where tissue and cell-type specific enhancer activities were observed at the larval stage. While a genomic deletion of this region, de2f1(ΔRA), decreased the overall expression level of dE2F1, flies developed normally with no obvious proliferation defects. However, a detailed analysis of the de2f1(ΔRA) mutant eye imaginal discs revealed that dE2F1 is needed for proper cell cycle exit. We discovered that dE2F1 expression during G1 arrest prior to the differentiation process of the developing eye is important for maintaining cell cycle arrest at a later stage of the eye development. Overall, our study suggests that specific alternate transcripts of "activator" E2F, dE2F1, may have a dual function on cell cycle progression and cannot simply be viewed as a pro-proliferative transcription factor.

Solanum chacoense ovule receptor kinase 28 (ScORK28) was found among 30 receptor kinases from an ovule cDNA library enriched for weakly expressed mRNAs. This LRR-RLK displayed high level of tissue specificity at the RNA and protein levels and was predominantly expressed in female reproductive tissues. Protein expression analyses in planta revealed that ScORK28 was N-glycosylated and ScORK28::GFP fusion analyses showed that it was localized at the plasma membrane. Bacterial expression of ScORK28 catalytic domain followed by kinase activity assays revealed that ScORK28 is an active Mg 2+ -dependent protein kinase and that the juxtamembrane domain is necessary for kinase activity.

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