Cloning and characterization of a new gene from the PAT protein family, in a marsupial, the stripe-faced dunnart (Sminthopsis macroura)

The Principal Forces of Oocyte Polarity Are Evolutionary Conserved but May Not Affect the Contribution of the First Two Blastomeres to the Blastocyst Development in Mammals

Oocyte polarity and embryonic patterning are well-established features of development in lower species. Whether a similar form of pre-patterning exists in mammals is currently under hot debate in mice. This study investigated this issue for the first time in ovine as a large mammal model. Microsurgical trisection of unfertilized MII-oocytes revealed that cortical cytoplasm around spindle (S) contained significant amounts of total maternal mRNAs and proteins compared to matched cytoplast hemispheres that were located either near (NS) or far (FS) -to-spindle. RT-qPCR provided striking examples of maternal mRNA localized to subcellular substructures S (NPM2, GMNN, H19, PCAF, DNMT3A, DNMT1, and STELLA), NS (SOX2, NANOG, POU5F1, and TET1), and FS (GCN) of MII oocyte. Immunoblotting revealed that specific maternal proteins DNMT3A and NANOG were asymmetrically enriched in MII-spindle-half of the oocytes. Topological analysis of sperm entry point (SEP) revealed that sperm preferentially entered via the MII-spindle-half of the oocytes. Even though, the topological position of first cleavage plane with regard to SEP was quite stochastic. Spatial comparison of lipid content revealed symmetrical distribution of lipids between 2-cell blastomeres. Lineage tracing using Dil, a fluorescent dye, revealed that while the progeny of leading blastomere of 2-cell embryos contributed to more cells in the developed blastocysts compared to lagging counterpart, the contributions of leading and lagging blastomeres to the embryonic-abembryonic parts of the developed blastocysts were almost unbiased. And finally, separated sister blastomeres of 2-cell embryos had an overall similar probability to arrest at any stage before the blastocyst (2-cell, 4-cell, 8-cell, and morula) or to achieve the blastocyst stage. It was concluded that the localization of maternal mRNAs and proteins at the spindle are evolutionarily conserved between mammals unfertilized ovine oocyte could be considered polar with respect to the spatial regionalization of maternal transcripts and proteins. Even though, the principal forces of this definitive oocyte polarity may not persist during embryonic cleavages.

As the fat flies: The dynamic lipid droplets of Drosophila embryos

Research into lipid droplets is rapidly expanding, and new cellular and organismal roles for these lipid-storage organelles are continually being discovered. The early Drosophila embryo is particularly well suited for addressing certain questions in lipid-droplet biology and combines technical advantages with unique biological phenomena. This review summarizes key features of this experimental system and the techniques available to study it, in order to make it accessible to researchers outside this field. It then describes the two topics most heavily studied in this system, lipid-droplet motility and protein sequestration on droplets, discusses what is known about the molecular players involved, points to open questions, and compares the results from Drosophila embryo studies to what it is known about lipid droplets in other systems.

Lipid-rich blastomeres in the two-cell stage of porcine parthenotes show bias toward contributing to the embryonic part

This study was designed to determine the fate of the blastomeres in two-cell porcine parthenotes that display uneven size (larger vs. smaller) or cytoplasmic brightness (darker vs. brighter) during development to the blastocyst stage. For the non-invasive tracing of cell lineage, lipophilic fluorescence dye DiI (red) and DiD (blue) was randomly microinjected into each of two different blastomeres in each embryo. In blastocysts derived from the two-cell parthenotes with unevenly-sized blastomeres, no biased contribution was found in the progeny of either blastomere. However, in the blastocysts derived from the two-cell parthenote having different cytoplasmic brightnesses, the progeny of darker (more lipid-rich cytoplasm) blastomeres were more than two-fold more likely to form the embryonic part (43.6%; 17/39) than they were to form the abembryonic part (17.9%; 7/39), while the contribution of brighter blastomeres (less lipid) was just the opposite. The expressions of four marker genes involved in lineage allocation (Cdx2, Tead4, Oct4 and Carm1) were also analyzed in darker and brighter blastomeres of two-cell parthenotes using quantitative RT-PCR. The expression of Carm1 that encodes arginine methyltransferase 1 and that promotes inner cell mass (ICM) differentiation was significantly higher (P<0.05) in darker blastomeres. The ICM marker Oct4 also tended to be more highly expressed in the darker blastomeres, while Cdx2 and the TE marker Tead4 showed comparably higher expressions in the brighter blastomeres. However, in all cases, the marginal differences in the expression levels of Oct4, Cdx2 and Tead4 were not statistically significant (P>0.05). Our findings indicate that expression of genes related to early differentiation, especially Carm1, are partially associated with lipid droplet distribution in the two-cell porcine parthenote and may lead to biased embryonal axis formation.

A novel marsupial pri-miRNA transcript has a putative role in gamete maintenance and defines a vertebrate miRNA cluster paralogous to the miR-15a/miR-16-1 cluster

Successful maintenance, survival and maturation of gametes rely on bidirectional communication between the gamete and its supporting cells. Before puberty, factors from the gamete and its supporting cells are necessary for spermatogonial stem cell and primordial follicle oocyte maintenance. Following gametogenesis, gametes rely on factors and nutrients secreted by cells of the reproductive tracts, the epididymis and/or oviduct, to complete maturation. Despite extensive studies on female and male reproduction, many of the molecular mechanisms of germ cell maintenance remain relatively unknown, particularly in marsupial species. We present the first study and characterisation of a novel primary miRNA transcript, pri-miR-16c, in the marsupial, the stripe-faced dunnart. Bioinformatic analysis showed that its predicted processed miRNA – miR-16c – is present in a wide range of vertebrates, but not eutherians. In situ hybridisation revealed dunnart pri-miR-16c expression in day 4 (primordial germ cells) and day 7 (oogonia) pouch young, in primary oocytes and follicle cells of primordial follicles but then only in follicle cells of primary, secondary and antral follicles in adult ovaries. In the adult testis, pri-miR-16c transcripts were present in the cytoplasm of spermatogonial cells. The oviduct and the epididymis both showed expression, but not any other somatic tissues examined or conceptuses during early embryonic development. This pattern of expression suggests that pri-miR-16c function may be associated with gamete maintenance, possibly through mechanisms involving RNA transfer, until the zygote enters the uterus at the pronuclear stage.