Staufen1, Kinesin1 and microtubule function in cyclin B1 mRNA transport to the animal polar cytoplasm of zebrafish oocytes

Spatiotemporal regulation of maternal mRNAs during vertebrate oocyte meiotic maturation

Vertebrate oocytes face a particular challenge concerning the regulation of gene expression during meiotic maturation. Global transcription becomes quiescent in fully grown oocytes, remains halted throughout maturation and fertilization, and only resumes upon embryonic genome activation. Hence, the oocyte meiotic maturation process is largely regulated by protein synthesis from pre-existing maternal messenger RNAs (mRNAs) that are transcribed and stored during oocyte growth. Rapidly developing genome-wide techniques have greatly expanded our insights into the global translation changes and possible regulatory mechanisms during oocyte maturation. The storage, translation, and processing of maternal mRNAs are thought to be regulated by factors interacting with elements in the mRNA molecules. Additionally, posttranscriptional modifications of mRNAs, such as methylation and uridylation, have recently been demonstrated to play crucial roles in maternal mRNA destabilization. However, a comprehensive understanding of the machineries that regulate maternal mRNA fate during oocyte maturation is still lacking. In particular, how the transcripts of important cell cycle components are stabilized, recruited at the appropriate time for translation, and eliminated to modulate oocyte meiotic progression remains unclear. A better understanding of these mechanisms will provide invaluable insights for the preconditions of developmental competence acquisition, with important implications for the treatment of infertility. This review discusses how the storage, localization, translation, and processing of oocyte mRNAs are regulated, and how these contribute to oocyte maturation progression.

RNA localization to the mitotic spindle is essential for early development and is regulated by kinesin-1 and dynein

Mitosis is a fundamental and highly regulated process that acts to faithfully segregate chromosomes into two identical daughter cells. Localization of gene transcripts involved in mitosis to the mitotic spindle might be an evolutionarily conserved mechanism to ensure that mitosis occurs in a timely manner. We identified many RNA transcripts that encode proteins involved in mitosis localized at the mitotic spindles in dividing sea urchin embryos and mammalian cells. Disruption of microtubule polymerization, kinesin-1 or dynein results in lack of spindle localization of these transcripts in the sea urchin embryo. Furthermore, results indicate that the cytoplasmic polyadenylation element (CPE) within the 3'UTR of the Aurora B transcript, a recognition sequence for CPEB, is essential for RNA localization to the mitotic spindle in the sea urchin embryo. Blocking this sequence results in arrested development during early cleavage stages, suggesting that RNA localization to the mitotic spindle might be a regulatory mechanism of cell division that is important for early development.

m6A reader Igf2bp3 enables germ plasm assembly by m6A-dependent regulation of gene expression in zebrafish

Bucky ball (Buc) is involved in germ plasm (GP) assembly during early zebrafish development by regulating GP mRNA expression via an unknown mechanism. The present study demonstrates that an m⁶A reader Igf2bp3 interacts and colocalizes with Buc in the GP. Similar to the loss of Buc, the genetic deletion of maternal igf2bp3 in zebrafish leads to abnormal GP assembly and insufficient germ cell specification, which can be partially restored by the injection of igf2bp3 mRNA. Igf2bp3 binds to m⁶A-modified GP-organizer and GP mRNAs in an m⁶A-dependent manner and prevents their degradation. These findings indicate that the functions of Igf2bp3, a direct effector protein of Buc, in GP mRNA expression and GP assembly involve m⁶A-dependent regulation; these results emphasize a critical role of m⁶A modification in the process of GP assembly.

RNA-binding motif protein 43 (RBM43) suppresses hepatocellular carcinoma progression through modulation of cyclin B1 expression

RNA-binding proteins play key roles in the posttranscriptional regulation of mRNA during cancer progression. Here, we show that RNA-binding motif protein 43 (RBM43) is significantly downregulated in human tumors, and its low expression is correlated with poor prognosis in patients with HCC. Overexpression of RBM43 suppressed cell proliferation in culture and resulted in the growth arrest of tumor xenografts, whereas downregulating RBM43 played an opposite role. We have also demonstrated that overexpression or knockdown of RBM43 affects the cell-cycle progression of liver cancer cells. Mechanistically, RBM43 directly associated with the 3'UTR of Cyclin B1 mRNA and regulated its expression. Moreover, loss of Rbm43 in mice promoted liver carcinogenesis and HCC development after diethylnitrosamine (DEN)-carbon tetrachloride (CCl4) treatment. Taken together, our data indicate that RBM43 is a tumor suppressor that controls the cell cycle through modulation of Cyclin B1 expression, providing evidence that RBM43 is particularly important in HCC.

The maternal coordinate system: Molecular-genetics of embryonic axis formation and patterning in the zebrafish

Axis specification of the zebrafish embryo begins during oogenesis and relies on proper formation of well-defined cytoplasmic domains within the oocyte. Upon fertilization, maternally-regulated cytoplasmic flow and repositioning of dorsal determinants establish the coordinate system that will build the structure and developmental body plan of the embryo. Failure of specific genes that regulate the embryonic coordinate system leads to catastrophic loss of body structures. Here, we review the genetic principles of axis formation and discuss how maternal factors orchestrate axis patterning during zebrafish early embryogenesis. We focus on the molecular identity and functional contribution of genes controlling critical aspects of oogenesis, egg activation, blastula, and gastrula stages. We examine how polarized cytoplasmic domains form in the oocyte, which set off downstream events such as animal-vegetal polarity and germ line development. After gametes interact and form the zygote, cytoplasmic segregation drives the animal-directed reorganization of maternal determinants through calcium- and cell cycle-dependent signals. We also summarize how maternal genes control dorsoventral, anterior-posterior, mesendodermal, and left-right cell fate specification and how signaling pathways pattern these axes and tissues during early development to instruct the three-dimensional body plan. Advances in reverse genetics and phenotyping approaches in the zebrafish model are revealing positional patterning signatures at the single-cell level, thus enhancing our understanding of genotype-phenotype interactions in axis formation. Our emphasis is on the genetic interrogation of novel and specific maternal regulatory mechanisms of axis specification in the zebrafish.

Repositioning Flubendazole for Spinal Cord Injury

We previously reported the serendipitous observation that fenbendazole, a benzimidazole anthelmintic, improved functional and pathological outcomes following thoracic spinal cord contusion injury in mice when administered pre-injury. Fenbendazole is widely used in veterinary medicine. However, it is not approved for human use and it was uncertain if only post-injury administration would offer similar benefits. In the present study we evaluated post-injury administration of a closely related, human anthelmintic drug, flubendazole, using a rat spinal cord contusion injury model. Flubendazole, administered i.p. 5 or 10 mg/kg day, beginning 3 h post-injury and daily thereafter for 2 or 4 weeks, resulted in improved locomotor function after contusion spinal cord injury (SCI) compared with vehicle-treated controls. Histological analysis of spinal cord sections showed that such treatment with flubendazole also reduced lesion volume and improved total tissue sparing, white matter sparing, and gray matter sparing. Flubendazole inhibited the activation of glial fibrillary acidic protein (GFAP); suppressed cyclin B1 expression and Bruton tyrosine kinase activation, markers of B cell activation/proliferation and inflammation; and reduced B cell autoimmune response. Together, these results suggest the use of the benzimidazole anthelmintic flubendazole as a potential therapeutic for SCI.