Apparent mitochondrial asymmetry in <i>Xenopus</i> eggs

Володина, Наталья; Denegre, James M.; Mowry, Kimberly L.

doi:10.1002/dvdy.10275

Cited by 9 publications

(6 citation statements)

References 48 publications

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“…For immunoprecipitations, 5-μl anti-hnRNP I, anti-Vg1RBP/vera ( Zhang et al, 1999 ; Git and Standart, 2002 ), anti-myc (9E10; Sigma-Aldrich), or control (anti-VP67; Volodina et al, 2003 ) antibodies were incubated overnight at 4°C with 10 μl protein G–Sepharose beads (Amersham Biosciences) in 1 ml YSS. FLAG immunoprecipitations were performed using 10 μl anti-FLAG beads (Sigma-Aldrich).…”

Section: Methodsmentioning

confidence: 99%

Nuclear RNP complex assembly initiates cytoplasmic RNA localization

Kress

Yoon

Mowry

2004

The Journal of Cell Biology

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108

168

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Cytoplasmic localization of mRNAs is a widespread mechanism for generating cell polarity and can provide the basis for patterning during embryonic development. A prominent example of this is localization of maternal mRNAs in Xenopus oocytes, a process requiring recognition of essential RNA sequences by protein components of the localization machinery. However, it is not yet clear how and when such protein factors associate with localized RNAs to carry out RNA transport. To trace the RNA–protein interactions that mediate RNA localization, we analyzed RNP complexes from the nucleus and cytoplasm. We find that an early step in the localization pathway is recognition of localized RNAs by specific RNA-binding proteins in the nucleus. After transport into the cytoplasm, the RNP complex is remodeled and additional transport factors are recruited. These results suggest that cytoplasmic RNA localization initiates in the nucleus and that binding of specific RNA-binding proteins in the nucleus may act to target RNAs to their appropriate destinations in the cytoplasm.

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Section: Methodsmentioning

confidence: 99%

Nuclear RNP complex assembly initiates cytoplasmic RNA localization

Kress

Yoon

Mowry

2004

The Journal of Cell Biology

Self Cite

108

168

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“…A bottleneck has been proposed based on the observation that mitochondrial genomes in each individual are largely homoplasmic, despite their high mutation rate [41] – [43] . In oocytes of many organisms two populations of mitochondria can be distinguished: one population is aggregated in the Bb and enters the embryo PGCs during development [7] , [21] , [34] , while the remaining mitochondria spread in the oocyte and are transmitted to the somatic lineage [44] – [46] . For this reason, the Bb mitochondrial population or a part of it may actually represent the mitochondrial bottleneck [47] .…”

Section: Introductionmentioning

confidence: 99%

Doubly Uniparental Inheritance of Mitochondria As a Model System for Studying Germ Line Formation

et al. 2011

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BackgroundDoubly Uniparental Inheritance (DUI) of mitochondria occurs when both mothers and fathers are capable of transmitting mitochondria to their offspring, in contrast to the typical Strictly Maternal Inheritance (SMI). DUI was found in some bivalve molluscs, in which two mitochondrial genomes are inherited, one through eggs, the other through sperm. During male embryo development, spermatozoon mitochondria aggregate in proximity of the first cleavage furrow and end up in the primordial germ cells, while they are dispersed in female embryos.Methodology/Principal FindingsWe used MitoTracker, microtubule staining and transmission electron microscopy to examine the mechanisms of this unusual distribution of sperm mitochondria in the DUI species Ruditapes philippinarum. Our results suggest that in male embryos the midbody deriving from the mitotic spindle of the first division concurs in positioning the aggregate of sperm mitochondria. Furthermore, an immunocytochemical analysis showed that the germ line determinant Vasa segregates close to the first cleavage furrow.Conclusions/SignificanceIn DUI male embryos, spermatozoon mitochondria aggregate in a stable area on the animal-vegetal axis: in organisms with spiral segmentation this zone is not involved in cleavage, so the aggregation is maintained. Moreover, sperm mitochondria reach the same embryonic area in which also germ plasm is transferred. In 2-blastomere embryos, the segregation of sperm mitochondria in the same region with Vasa suggests their contribution in male germ line formation. In DUI male embryos, M-type mitochondria must be recognized by egg factors to be actively transferred in the germ line, where they become dominant replacing the Balbiani body mitochondria. The typical features of germ line assembly point to a common biological mechanism shared by DUI and SMI organisms. Although the molecular dynamics of the segregation of sperm mitochondria in DUI species are unknown, they could be a variation of the mechanism regulating the mitochondrial bottleneck in all metazoans.

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“…Axis formation depends largely on maternal and zygotic genes and involves a series of inductive cell interactions. In the fly, the frog and the zebrafish, an animal-vegetal (AV) polarity emerges upon localization of maternal components, including transcripts, proteins, cytoskeleton or mitochondria, to distinct cytoplasmic parts of the egg (Cheng and Bjerknes, 1989;Gard et al, 1997;Howley and Ho, 2000;Rand and Yisraeli, 2001;Volodina et al, 2003). Cells are endowed with different sets of these determinants and acquire their fates according to their position.…”

Section: Introductionmentioning

confidence: 99%

Maternal control of vertebrate dorsoventral axis formation and epiboly by the POU domain protein Spg/Pou2/Oct4

2006

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Dorsoventral (DV) axis formation of the vertebrate embryo is controlled by the maternal genome and is subsequently refined zygotically. In the zygote, repression of ventralizing Bmp activity on the dorsal side through chordin and noggin is crucial for establishment of a dorsally located organizer. This interplay generates a zygotic Bmp activity gradient that defines distinct positional values along the DV axis. The maternal processes that control expression of the zygotic genes implicated in DV patterning are largely unknown. spiel-ohne-grenzen (spg/pou2) is a maternally and zygotically expressed zebrafish gene that encodes the POU domain transcription factor Pou2, an ortholog of mammalian Oct4/Pou5f1. We show that embryos that are genetically depleted of both maternal and zygotic pou2 function (MZspg) exhibit extreme DV patterning defects and, independently, a blastoderm-specific arrest of epiboly. Dorsal tissues expand to the ventral side at the expense of ventrolateral tissue in MZspg embryos. Dorsally expressed Bmp-antagonists, such as Chd and Nog1, and Gsc are ectopically activated at ventral levels in MZspg. Lack of ventral specification is apparent very early, suggesting that maternal processes are affected in MZspg. Indeed, maternal pou2 function is necessary to initiate zygotic expression of ventrally expressed genes such as bmp2b and bmp4, and for proper activation of bmp7, vox, vent and eve1. A constitutively active Alk8-TGF␤-receptor can ectopically induce bmp2b and bmp4 and rescues the dorsalization of MZspg. This indicates that pou2 acts upstream of Alk8, a maternally provided receptor implicated in the activation of zygotic bmp2b and bmp4 transcription. Consistent with this possibility, Bmp gene misexpression can rescue MZspg embryos, indicating that TGF␤-mediated signal transduction itself is intact in absence of Pou2. Inhibition of Fgf signaling, another pathway with early dorsalizing activity, can also restore and even ventralize MZspg embryos. The requirement for pou2 to initiate bmp2b expression can therefore be bypassed by releasing the repressive function of Fgf signaling upon bmp2b transcription. In transplantation experiments, we find that dorsalized cells from prospective ventrolateral regions of MZspg embryos are non cellautonomously respecified to a ventral fate within wild-type host embryos. Analysis of pou2 mRNA injected MZspg embryos shows that pou2 is required on the ventral side of cleavage stage embryos. Based on the maternal requirement for pou2 in ventral specification, we propose that ventral specification employs an active, pou2-dependent maternal induction step, rather than a default ventralizing program.

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Apparent mitochondrial asymmetry in Xenopus eggs

Cited by 9 publications

References 48 publications

Nuclear RNP complex assembly initiates cytoplasmic RNA localization

Nuclear RNP complex assembly initiates cytoplasmic RNA localization

Doubly Uniparental Inheritance of Mitochondria As a Model System for Studying Germ Line Formation

Maternal control of vertebrate dorsoventral axis formation and epiboly by the POU domain protein Spg/Pou2/Oct4

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