A novel ATM-dependent X-ray-inducible gene is essential for both plant meiosis and gametogenesis

DNA damage in Arabidopsis thaliana seedlings results in upregulation of hundreds of genes. One of the earliest and highest levels of induction is displayed by a previously uncharacterized gene that we have termed X-ray induced 1 ( XRI1 ). Analysis of plants carrying a null xri1 allele revealed two distinct requirements for this gene in plant fertility. XRI1 was important for the post-meiotic stages of pollen development, leading to inviability of xri ⁻ pollen and abnormal segregation of the mutant allele in heterozygous xri1 ^+/− plants. In addition, XRI1 was essential for male and female meiosis, as indicated by the complete sterility of homozygous xri1 mutants due to extensive chromosome fragmentation visible in meiocytes. Abolition of programmed DNA double-strand breaks in a spo11-1 mutant background failed to rescue the DNA fragmentation of xri1 mutants, suggesting that XRI1 functions at an earlier stage than SPO11-1 does. Yeast two-hybrid studies identified an interaction between XRI1 and a novel component of the Arabidopsis MND1/AHP2 complex, indicating possible requirements for XRI1 in meiotic DNA repair.     

Allomyces neo-moniliformis gametogenesis

Summary InAllomyces neo-moniliformis meiosis takes place during resting sporangium germination. The meiospores are characteristically binucleate and biflagellate as described byEmerson (1938) andTeter (1944). A variation in the number of nuclei and flagella per meiospore from two is correlated with germination of the resting sporangia under reduced oxygen tension. The meiospores are extremely poor swimmers and are typically amoeboid. At encystment the gamma bodies of the cell are mobilized and appear involved in cyst wall synthesis. A single mitotic division of each nucleus gives rise to four nuclei. Gamete cleavage is as described for spore cleavage inBlastocladiella (Lessie andLovett 1968). The assembly of the nuclear cap and side body complex of the spore are extremely late processes in gametogenesis. The gametes are released when the single papilla dissolves. The gametes fuse in pairs and after zygote formation the cell is uninucleate with two flagella. The biflagellate zygote is an active swimming cell. The presence of homothallism or hetero-thallism inA. neo-moniliformis is discussed.     

Kinetics of gametogenesis

Cell and Tissue Research - In the rat (Wistar-WU) sexual differentiation of the gonads occurs between days 14 and 15 post conception (p.c.). At this time the oogonia and their parallel population...     

DNA methylation in mouse gametogenesis

DNA methylation is involved in many biological processes and is particularly important for both development and germ cell differentiation. Several waves of demethylation and de novo methylation occur during both male and female germ line development. This has been found at both the gene and all genome levels, but there is no demonstrated correlation between them. During the postnatal germ line development of spermatogenesis, we found very complex and drastic DNA methylation changes that we could correlate with chromatin structure changes. Thus, detailed studies focused on localization and expression pattern of the chromatin proteins involved in both DNA methylation, histone tails modification, condensin and cohesin complex formation, should help to gain insights into the mechanisms at the origin of the deep changes occurring during this particular period.     

Male gametogenesis without centrioles

The orientation of the mitotic spindle plays a central role in specifying stem cell-renewal by enabling interaction of the daughter cells with external cues: the daughter cell closest to the hub region is instructed to self-renew, whereas the distal one starts to differentiate. Here, we have analyzed male gametogenesis in DSas-4 Drosophila mutants and we have reported that spindle alignment and asymmetric divisions are properly executed in male germline stem cells that lack centrioles. Spermatogonial divisions also correctly proceed in the absence of centrioles, giving rise to cysts of 16 primary spermatocytes. By contrast, abnormal meiotic spindles assemble in primary spermatocytes. These results point to different requirements for centrioles during male gametogenesis of Drosophila. Spindle formation during germ cell mitosis may be successfully supported by an acentrosomal pathway that is inadequate to warrant the proper execution of meiosis.     

Current topics in organogenesis and gametogenesis

At the 49(th) Annual Drosophila Research Conference from April 3-8, 2008 in San Diego there were eight talks and over ninety posters in the section on Organogenesis and Gametogenesis. These covered a wide range of topics within the two broad categories of organ-specific stem cells (including germ cells) and organ-specific developmental programs. Here we discuss eleven of these presentations describing current research into the formation of the gonad, intestine, trachea, muscle and leg joint. The new insights presented advance our understanding of the molecular events that underlie interactions between stem cells and their niches as well as mechanisms underlying tissue-specific differentiation programs.     

Hormonal regulation of gametogenesis in insect

The review discusses the role of juvenile hormone (JH), ecdysone and brain in the regulation of oogenesis and spermatogenesis in insects. The early period of gametogenesis (gonial mitoses, the meiotic prophase) in both sexes is controlled mainly by ecdysone and neurosecretory cells of the brain. In periods of cytoplasmic growth of oocytes and vitellogenesis the main role in the regulation belongs to JH. The modern views on hormonal regulation of vitellogenin synthesis and follicular epithelium differentiation are under consideration with a special reference of the role of ecdysteroids in Diptera and Lepidoptera oogenesis.     

Aquaporins in gametogenesis of vertebrate animals

A review of the data on the presence, localization, and supposed role of aquaporin water channels in oocytes of Xenopus laevis, oogenesis and maturation of teleosts Sparus auratus and Oncorhynchus mykiss, oogenesis and oocyte maturation of rats and mice, and spermatogenesis of several mammalians.     

Spectrin in mouse gametogenesis and embryogenesis

Antibodies to nonerythroid alpha spectrin (p 230) were used to study the distribution of this polypeptide in mouse germ cells, zygote, and early embryonic cells. In the primordial germ cells, fetal oocytes, and spermatogonia, spectrin was found predominantly in the form of a narrow condensed subplasmalemmal band, as in all other somatic cells. During spermatogenesis, spectrin is condensed into the supraacrosomal cytoplasm and is lost during the reduction of the cytoplasm of the maturing spermatozoa. The postnatal growth of the oocyte is accompanied by a loss of the dense cortical band of spectrin and its redistribution in the cytoplasm. Zygotes also contain granular dispersed spectrin. Cortical condensation of spectrin filaments gradually reappears in the blastomeres at the two-cell stage and in the secondary polar body. Cortically condensed filaments represent thereafter the predominant form of spectrin in all preimplantation stage embryonic cells. Trophoblastic cells spreading out from explanted blastocysts are devoid of the cortically condensed spectrin and contain, instead, spectrin arrays in the cytoplasm. Trophoblastic cells, which surround the implanted embryo in vivo, also show diffuse cytoplasmic spectrin which subsequently undergoes subplasmalemmal condensation. These data show that spectrin is present in all stages of gametogenesis and embryogenesis, except in mature spermatozoa; and that it undergoes cytoplasmic redistribution during morphogenesis.     

Aquaporins in gametogenesis of vertebrate animals

A review of the data on the presence, localization, and supposed role of aquaporin water channels in oocytes of Xenopus laevis, oogenesis and maturation of teleosts Sparus auratus and Oncorhynchus mykiss, oogenesis and oocyte maturation of rats and mice, and spermatogenesis of several mammalians.     

FEARless in meiosis

Degradation of mitotic cyclins is critical for exit from mitosis. Recent studies in budding yeast address the role of cyclin degradation in meiosis. Cyclin stabilization in meiosis I interferes with anaphase I spindle disassembly but, surprisingly, does not halt progression into meiosis II.