Bihormonal control of oogenesis in the freshwater prawn, Macrobrachium kistnensis

The hormonal control of oogenesis has been investigated in the freshwater prawn, Macrobrachium kistnensis. Experiments using bilateral eyestalk ablation and injection of eyestalk extract supported the presence of a gonad inhibiting factor in the eyestalk of female prawns. Injections of brain and thoracic ganglion extract in normal female prawns and in those subjected to bilateral eyestalk ablation revealed the presence of a gonad stimulating factor in the central nervous tissue.     

Cell cycle regulators control centrosome elimination during oogenesis in Caenorhabditis elegans

In many animals, the bipolar spindle of the first zygotic division is established after the contribution of centrioles by the sperm at fertilization. To avoid the formation of a multipolar spindle in the zygote, centrosomes are eliminated during oogenesis in most organisms, although the mechanism of this selective elimination is poorly understood. We show that cki-2, a Caenorhabditis elegans cyclin-dependent kinase (Cdk) inhibitor, is required for their appropriate elimination during oogenesis. In the absence of cki-2, embryos have supernumerary centrosomes and form multipolar spindles that result in severe aneuploidy after anaphase of the first division. Moreover, we demonstrate that this defect can be suppressed by reducing cyclin E or Cdk2 levels. This implies that the proper regulation of a cyclin E-Cdk complex by cki-2 is required for the elimination of the centrosome that occurs before or during oogenesis to ensure the assembly of a bipolar spindle in the C. elegans zygote.     

Molecular control of lymphangiogenesis

The lymphatic vasculature plays a critical role in the regulation of body fluid volume and immune function. Extensive research into the molecular mechanisms that control blood vessel growth has led to identification of molecules that also regulate development and growth of the lymphatic vessels. This is generating a great deal of interest in the molecular control of the lymphatics in the context of embryogenesis, lymphatic disorders and tumor metastasis. Studies in animal models carried out over the past three years have shown that the soluble protein growth factors, vascular endothelial growth factor (VEGF)-C and VEGF-D, and their cognate receptor tyrosine kinase, VEGF receptor-3 (VEGFR-3), are critical regulators of lymphangiogenesis. Furthermore, disfunction of VEGFR-3 has recently been shown to cause lymphedema. The capacity to induce lymphangiogenesis by manipulation of the VEGF-C/VEGF-D/VEGFR-3 signaling pathway offers new opportunities to understand the function of the lymphatic system and to develop novel treatments for lymphatic disorders.     

Actin in oogenesis

Summary

The laser-scanning confocal microscope employed in conjunction with various specific agents and antibodies conjugated to fluorescent dyes reveals details of the actin scaffolding of developing oocytes and the nuclei of attendant cells. The employment of DNase I followed by anti-DNase I antibody has been particularly useful in revealing otherwise cryptic actin-containing structures. The cortical cytoskeleton of developing moth eggs was found to bind both poly (A)+RNA and RNA Pol II. Exposure to cytochalasin D disrupted the actin of the cortex, and at the same time caused redistribution of the proteins and RNA associated with the cytoskeleton. Cytochalasin also had dramatic effects on the structure of nuclei of nurse and follicle cells. Taken in context of the actin network in nuclei uncovered by DNase-anti-DNase treatment, these results suggest that actin plays a major structural and perhaps functional role in insect nuclei.     

Counting in oogenesis

The determination of a precise number of cells within a structure and of a precise number of cellular structures within an organ is critical for correct development in animals and plants. However, relatively little is known about the molecular mechanisms that ensure that these numbers are achieved. We discuss counting mechanisms that operate during ovarian development and oogenesis.     

Molecular control of neuronal migration

Our understanding of neuronal migration has been advanced by multidisciplinary approaches. At the cellular level, tangential and radial modes of neuronal migration contribute to different populations of neurons and have differential dependence on glial cells. At the molecular level, extracellular guidance cues have been identified and intracellular signal transduction pathways are beginning to be revealed. Interestingly, mechanisms guiding axon projection and neuronal migration appear to be conserved with those for chemotactic leukocytes.     

Molecular control of neutrophil apoptosis

Human neutrophils constitutively undergo apoptosis and this process is critical for the resolution of inflammation. Whilst neutrophil apoptosis can be modulated by a wide variety of agents including GM-CSF, LPS and TNF-alpha, the molecular mechanisms underlying neutrophil death and survival remain largely undefined. Recent studies have shown the involvement of members of the Bcl-2 protein family (especially Mcl-1 and A1) and caspases in the regulation and execution of neutrophil apoptosis. Cell surface receptors and protein kinases, particularly mitogen-activated protein kinases, also play critical roles in transducing the signals that result in neutrophil apoptosis or extended survival. This review summarises current knowledge on the molecular mechanisms and components of neutrophil apoptosis.     

Molecular biology of weed control

The vast commercial effort to utilize chemical and molecular tools to solve weed control problems has had a major impact on the basic biological sciences as well as benefits to agriculture, and the first generation of transgenic products has been successful, while somewhat crude. More sophisticated products are envisaged and expected. Biotechnologically-derived herbicide-resistant crops have been a considerable benefit, yet in some cases there is a risk that the same useful transgenes may introgress into related weeds, specifically the weeds that are hardest to control without such transgenic crops. Biotechnology can also be used to mitigate the risks. Molecular tools should be considered for weed control without the use of, or with less chemicals, whether by enhancing crop competitiveness with weeds for light, nutrients and water, or via allelochemicals. Biocontrol agents may become more effective as well as more safe when rendered hypervirulent yet non-spreading by biotechnology. There might be ways to disperse deleterious transposons throughout weed populations, obviating the need to modify the crops. This revised version was published online in August 2006 with corrections to the Cover Date.     

Molecular control of angiopoietin signalling

The angiopoietins act through the endothelial receptor tyrosine kinase Tie2 to regulate vessel maturation in angiogenesis and control quiescence and stability of established vessels. The activating ligand, Ang1 (angiopoietin-1), is constitutively expressed by perivascular cells, and the ability of endothelial cells to respond to the ligand is controlled at the level of the Ang1 receptor. This receptor interacts with the related protein Tie1 on the cell surface, and Tie1 inhibits Ang1 signalling through Tie2. The responsiveness of endothelium to Ang1 is determined by the relative levels of Tie2 and the inhibitory co-receptor Tie1 in the cells. Tie1 undergoes regulated ectodomain cleavage which is stimulated by a range of factors including VEGF (vascular endothelial growth factor), inflammatory cytokines and changes in shear stress. Ectodomain cleavage of Tie1 relieves inhibition of Tie2 and enhances Ang1 signalling. This mechanism regulates Ang1 signalling without requiring changes in the level of the ligand and allows Ang1 signalling to be co-ordinated with other signals in the cellular environment. Regulation of signalling at the level of receptor responsiveness may be an important adaptation in systems in which an activating ligand is normally present in excess or where the ligand provides a constitutive maintenance signal.     

Molecular control of facial morphology

We present a developmental perspective on the concept of phylotypic and phenotypic stages of craniofacial development. Within orders of avians and mammals, a phylotypic period exists when the morphology of the facial prominences is minimally divergent. We postulate that species-specific facial variations arise as a result of subtle shifts in the timing and the duration of molecular pathway activity (e.g., heterochrony), and present evidence demonstrating a critical role for Wnt and FGF signaling in this process. The same molecular pathways that shape the vertebrate face are also implicated in craniofacial deformities, indicating that comparisons between and among animal species may represent a novel method for the identification of human craniofacial disease genes.     

Molecular control of rodent spermatogenesis

Spermatogenesis is a complex developmental process that ultimately generates mature spermatozoa. This process involves a phase of proliferative expansion, meiosis, and cytodifferentiation. Mouse models have been widely used to study spermatogenesis and have revealed many genes and molecular mechanisms that are crucial in this process. Although meiosis is generally considered as the most crucial phase of spermatogenesis, mouse models have shown that pre-meiotic and post-meiotic phases are equally important. Using knowledge generated from mouse models and in vitro studies, the current review provides an overview of the molecular control of rodent spermatogenesis. Finally, we briefly relate this knowledge to fertility problems in humans and discuss implications for future research. This article is part of a Special Issue entitled: Molecular Genetics of Human Reproductive Failure.     

Insect vitellogenin/lipophorin receptors: Molecular structures, role in oogenesis, and regulatory mechanisms

Insect vitellogenin and lipophorin receptors (VgRs/LpRs) belong to the low-density lipoprotein receptor (LDLR) gene superfamily and play a critical role in oocyte development by mediating endocytosis of the major yolk protein precursors Vg and Lp, respectively. Precursor Vg and Lp are synthesized, in the majority of insects, extraovarially in the fat body and are internalized by competent oocytes through membrane-bound receptors (i.e., VgRs and LpRs, respectively). Structural analysis reveals that insect VgRs/LpRs and all other LDLR family receptors share a group of five structural domains: clusters of cysteine-rich repeats constituting the ligand-binding domain (LBD), epidermal growth factor (EGF)-precursor homology domain that mediates the acid-dependent dissociation of ligands, an O-linked sugar domain of unknown function, a transmembrane domain anchoring the receptor in the plasma membrane, and a cytoplasmic domain that mediates the clustering of the receptor into the coated pits. The sequence analysis indicates that insect VgRs harbor two LBDs with five repeats in the first and eight repeats in the second domain as compared to LpRs which have a single 8-repeat LBD. Moreover, the cytoplasmic domain of all insect VgRs contains a LI internalization signal instead of the NPXY motif found in LpRs and in the majority of other LDLR family receptors. The exception is that of Solenopsis invicta VgR, which also contains an NPXY motif in addition to LI signal. Cockroach VgRs still harbor another motif, NPTF, which is also believed to be a functional internalization signal. The expression studies clearly demonstrate that insect VgRs are ovary-bound receptors of the LDLR family as compared to LpRs, which are transcribed in a wide range of tissues including ovary, fat body, midgut, brain, testis, Malpighian tubules, and muscles. VgR/LpR mRNA and the protein were detected in the germarium, suggesting that the genes involved in receptor-endocytotic machinery are specifically expressed long before they are functionally required.     

Cell functions inDrosophila oogenesis

We are studyingDrosophila oogenesis by analysing at genetic and molecular levels several female-sterile mutations. Some (hold up, wavoid-like andabnormal oocyte) have been isolated by L. Sandler in region 32 of the second chromosome; others have been isolated by us and their phenotype is presented for the first time in this paper. We performed chromosome walking in 32D-32E-F (250 Kb) and 32A-B (100 Kb) and in the last years we molecularly identified several genes with specific maternal expression patterns. We will review here our studies on two of these genes: the Vitelline Membrane Protein gene 32E and the gene coding for a receptor form of Guanylate Cyclase.     

Karyosphere in oogenesis]

The purpose of this review is to draw attention to the peculiar phenomenon during gametogenesis: the formation of the karyosphere. This phenomenon is characterized by concentration of all chromosomes in the limited area of the nucleus and may be considered as alternative of the genome in the state of lumpbrush chromosomes. The formation of the karyosphere is a widely spread phenomenon during oogenesis of different animal classes. The karyosphere can be developed during different stages of oogenesis in different organisms; but as a rule the chromosomes of diploten stage of meiosis take part in its formation. As to functional identity of the karyosphere in different species, special investigations are to be done, but contemporary knowledge of the karyosphere formation reveals some common feature:1) in the karyosphere the chromosomes are in a relatively spiral state as demonstrated by the positive Feulgen reaction; 2) there is a low level of RNA synthesis or the absence of it in the karyosphere; 3) during the karyosphere formation the nucleus is enriched by the acid proteins and a lot of protein granules and structures appearing in a close contact with the karysphere. The more typical examples of the karyosphere formation can be observed in the insect oocytes belonging to the nutrimentary type of oogenesis. In the oocytes of some animals the peculiar protein substances are formed around the chromosome knot and appear as a fibrillar zone. Such karyosphere appears to be a kind of capsule inside the nucleus. The capsules are developed as a result of complex interaction between the main nuclear structures; chromosomes, nucleoli, and nuclear membrane as it is manifested by the analysis of some recent ultrastructural date obtained in some insect and amphibian oocytes. The function of the karyosphere capsule and the role of the nuclear structure (sinaptonemal complex, extrachromosomal DNA, and nuclear membrane) in formation of the capsule, are discussed as well as the ultrastructural and cytochemical similarity between the karyosphere capsule of oocytes and nuclear bodies of somatic cells.