Expression of Notch pathway genes in the embryonic mouse metanephros suggests a role in proximal tubule development

The interaction of neighboring cells via Notch signalling leads to cell fate determination, differentiation and patterning of highly organized tissues. Mice with targeted disruption of genes from the Notch signal transduction pathway display defects in the developing somites, neurogenic structures, blood vessels, heart and other organs. Recent studies have added requirements for Notch signalling during kidney, pancreas and thymus morphogenesis. Here, we describe the expression of all four receptors (Notch1-4), the five transmembrane ligands (Dll1, 3, 4, Jag1 and Jag2), intracellular effectors (the Hey genes) and extracellular modulators (Lfng, Mfng, Rfng) in the developing mouse metanephros. Our results point to a Lfng-dependent role for Notch signalling in the development of nephron segments, especially the proximal tubules.     

Expression analysis of the NLRP gene family suggests a role in human preimplantation development

Background

The NLRP (Nucleotide-binding oligomerization domain, Leucine rich Repeat and Pyrin domain containing) family, also referred to as NALP family, is well known for its roles in apoptosis and inflammation. Several NLRPs have been indicated as being involved in reproduction as well.

Methodology

We studied, using the unique human gametes and embryo materials, the expression of the NLRP family in human gametes and preimplantation embryos at different developmental stages, and compared the expression levels between normal and abnormal embryos using real-time PCR.

Principal Findings

Among 14 members of the NLRP family, twelve were detected in human oocytes and preimplantation embryos, whereas seven were detected in spermatozoa. Eight NLRPs (NLRP4, 5, 8, 9, 11, 12, 13, and 14) showed a similar expression pattern: their expression levels were high in oocytes and then decreased progressively in embryos, resulting in a very low level in day 5 embryos. However, NLRP2 and NLRP7 showed a different expression pattern: their expression decreased from oocytes to the lowest level by day 3, but increased again by day 5. The expression levels of NLRP5, 9, and 12 were lower in day 1 abnormal embryos but higher in day3 and day5 arrested embryos, when compared with normal embryos at the same stages. NLRP7 was down-regulated in day 1 and day 5 abnormal embryos but over-expressed in day3 arrested embryos.

Conclusions

According to our results, different NLRPs possibly work in a stage-dependent manner during human preimplantation development.     

Abdominal-B expression in a spider suggests a general role for Abdominal-B in specifying the genital structure.

We have cloned an Abdominal-B (Abd-B) orthologue from the spider Cupiennius salei and have analysed its expression pattern during embryogenesis. An early expression domain is seen in the posterior part of the embryo, with an initial border in the third opisthosomal segment and later in the fifth opisthosomal segment. During mid-stage of germ band extension, two additional spots of expression appear in the posterior parts of the limb buds on the second opisthosomal segment. These coincide with the position of the future genital opening and Cs-Abd-B remains expressed in these regions until the openings are formed. In view of the fact that Abd-B and its orthologous genes are also required for specifying the genitalia in Drosophila and vertebrates, we suggest that this function may constitute an independent and ancestral role of Abd-B that can be separated from its role in specifying the posterior part of the body region.     

Teratogenicity of 3-hydroxynorvaline in chicken and mouse embryos

Summary. 3-Hydroxynorvaline (HNV; 2-amino-3-hydroxypentanoic acid), a microbial L-threonine analogue, is toxic to mammalian cells and displays antiviral properties. In view of this, we investigated the toxicity and/or potential teratogenicity of HNV in developing chicken and mouse embryos. HNV was administered to chicken embryos (in ovo; dose 75–300 μmole/egg; 48 h post-incubation) and pregnant Hanover NMRI mice (per os; total dose 900–1800 mg/kg body mass; gestation days 7–9). Control animals received sterile saline solutions. Harvested embryos (chicken embryos, 10 days post-incubation; mouse embryos; gestation day 18) were fixed in glutaraldehyde and stereomicroscopically inspected for signs of dysmorphogenesis. Body mass, body and toe length and mortality of chicken embryos, and the body mass and mortality of mouse embryos were recorded. HNV exposure significantly increased the incidence of embryotoxic (growth retardation, toxic mortality) and congenital defects in both chicken and mouse embryos. All the observed effects were dose-dependent. In conclusion, HNV is an embryotoxic and teratogenic compound, which caused significant developmental delay and congenital defects in developing chicken and mouse embryos.     

Double knockout Nme1/Nme2 mouse model suggests a critical role for NDP kinases in erythroid development

Nm23/NDP kinases A and B encoded by the Nme1/Nme2 genes are multifunctional enzymes responsible for the majority of NDP kinase activity in mammals. This review summarizes recent studies on their physiological roles using a mouse model in which both Nme1 and Nme2 genes have been deleted. The double knockout mice are stunted in growth and die perinatally. Additionally, these mice display hematologic phenotypes, including severe anemia, abnormal erythroid cell development, loss of the iron transport receptor molecule TfR1, and reduced iron uptake by Nme1 ^?/? /Nme2 ^?/? erythroid cells. We hypothesize that Nm23/NDP kinases regulate TfR1 gene expression in erythroid cells in some manner, and that defective iron transport into these cells is responsible for the anemia and death. This Nme1/Nme2 mouse model also links nucleotide metabolism with erythropoiesis, suggesting alternative or additional mechanisms that may explain the observed phenomena.     

The role of calcium in DNA synthesis and development of mouse preimplantation embryos in vitro.

The effect of calcium upon embryonic growth was studied using cultured mouse preimplantation embryos. Both morphological development of the embryos and embryo DNA synthesis were shown to be dependent on the Ca2+ concentration in the medium in which the embryos were grown. Reduction of the calcium concentration below 10(-5) M completely blocked cell division and blastocyst formation in the cultured embryos, but only moderately inhibited embryo DNA synthesis. Trifluoperazine, a calmodulin antagonist, strongly inhibited the Ca(2+)-dependent DNA synthesis in the embryos. On the other hand, the drug only slightly affected the morphological development of the embryos. These results demonstrate that calcium independently affects two different aspects of the embryo development, i.e. DNA synthesis and cell division. It is suggested that the former effect is calmodulin-dependent, while the latter involves the calcium-dependence of metabolite transport through the cell membranes.     

Expression of the EMILIN-1 gene during mouse development.

Expression of EMILIN-1, the first member of a newly discovered family of extracellular matrix genes, has been investigated during mouse development. EMILIN-1 mRNA is detectable in morula and blastocyst by RT-PCR. First expression of the gene is found by in situ hybridization in ectoplacental cone in embryos of 6.5 days and in extraembryonic visceral endoderm at 7.5 days. The allantois is also labeled. Staining of ectoplacental cone-derived secondary trophoblast giant cells and spongiotrophoblast is strong up to 11.5 days and then declines. In the embryo, high levels of mRNA are initially expressed in blood vessels, perineural mesenchyme and somites at 8.5 days. Later on, intense labeling is identified in the mesenchymal component of organs anlage (i.e. lung and liver) and different mesenchymal condensations (i.e. limb bud and branchial arches). At late gestation staining is widely distributed in interstitial connective tissue and smooth muscle cell-rich tissues. The data suggest that EMILIN-1 may have a function in placenta formation and initial organogenesis and a later role in interstitial connective tissue.     

The role of Wnt genes in vertebrate development.

Over the past decade, many potential candidates for molecules involved in pattern formation in the vertebrate embryo have been identified. Manipulation of the expression of some of these factors has generated fascinating results that have allowed investigators to address their roles in embryogenesis. One such family consists of a group of putative cell signaling molecules related to the proto-oncogene Wnt-1. An accumulating body of evidence suggests that the Wnt-family plays a major role in several aspects of vertebrate development.     

Expression of the L14 lectin during mouse embryogenesis suggests multiple roles during pre- and post-implantation development.

A cDNA encoding L14, the lactose-binding, soluble lectin of relative molecular mass 14 x 10(3), has been isolated in a differential screen designed to identify genes that are regulated during the differentiation of murine embryonic stem cells in vitro. The expression patterns of the gene and of the encoded protein during mouse embryogenesis are consistent with the lectin playing a role at several stages of development. Firstly, it is initially synthesised in the trophectoderm of expanded blastocysts immediately prior to implantation, suggesting that it may be involved in the attachment of the embryo to the uterine epithelium. Secondly, in the postimplantation embryo, the lectin is abundantly expressed in the myotomes of the somites. This observation, when taken together with data indicating a role for the lectin in myoblast differentiation in culture, suggests that the protein is important in muscle cell differentiation. Finally, within the nervous system expression of this gene is activated early during the differentiation of a particular subset of neurones.     

The deaf mouse mutant whirler suggests a role for whirlin in actin filament dynamics and stereocilia development

Stereocilia, finger-like projections forming the hair bundle on the apical surface of sensory hair cells in the cochlea, are responsible for mechanosensation and ultimately the perception of sound. The actin cytoskeleton of the stereocilia contains hundreds of tightly cross-linked parallel actin filaments in a paracrystalline array and it is vital for their function. Although several genes have been identified and associated with stereocilia development, the molecular mechanisms responsible for stereocilia growth, maintenance and organisation of the hair bundle have not been fully resolved. Here we provide further characterisation of the stereocilia of the whirler mouse mutant. We found that a lack of whirlin protein in whirler mutants results in short stereocilia with larger diameters without a corresponding increase in the number of actin filaments in inner hair cells. However, a decrease in the actin filament packing density was evident in the whirler mutant. The electron-density at the tip of each stereocilium was markedly patchy and irregular in the whirler mutants compared with a uniform band in controls. The outer hair cell stereocilia of the whirler homozygote also showed an increase in diameter and variable heights within bundles. The number of outer hair cell stereocilia was significantly reduced and the centre-to-centre spacing between the stereocilia was greater than in the wildtype. Our findings suggest that whirlin plays an important role in actin filament packing and dynamics during postnatal stereocilium elongation.     

MORN1 has a conserved role in asexual and sexual development across the apicomplexa

The gene encoding the membrane occupation and recognition nexus protein MORN1 is conserved across the Apicomplexa. In Toxoplasma gondii, MORN1 is associated with the spindle poles, the anterior and posterior rings of the inner membrane complex (IMC). The present study examines the localization of MORN1 during the coccidian development of T. gondii and three Eimeria species (in the definitive host) and erythrocytic schizogony of Plasmodium falciparum. During asexual proliferation, MORN1 is associated with the posterior ring of the IMCs of the multiple daughters forming during T. gondii endopolygeny and schizogony in Eimeria and P. falciparum. Furthermore, the expression of P. falciparum MORN1 protein peaked in late schizogony. These data fit a model with a conserved role for MORN1 during IMC assembly in all variations of asexual development. An important new observation is the reactivity of MORN1 antibody with certain sexual stages in T. gondii and Eimeria species. Here MORN1 is organized as a ring-like structure where the microgametes bud from the microgametocyte while in mature microgametes it is present near the flagellar basal bodies and mitochondrion. These observations suggest a conserved role for MORN1 in both asexual and sexual development across the Apicomplexa.