Effects of diapause on lethal yellow (Ay/Ay) mouse embryos.

One of the problems in studying early acting recessive lethal genes is recognizing the homozygotes prior to their demise. Molecular probes can assist in this task, but their use generally requires removal of cells and consequent damage to the embryo, which may compromise its subsequent development. The present study was undertaken in an attempt to distinguish intact, living, lethal yellow (Ay/Ay) embryos from Ay/ae and ae/ae littermates before implantation by placing them in implantation delay or diapause. After 2 days in the reproductive tract of prepubertal females, the great majority of presumptive lethal Ay/Ay embryos has failed to hatch from the zona pellucida and they exhibited a marked deficiency of cells relative to controls, particularly in the inner cell mass. This argues against a stage-specific role for the gene in implantation.     

Lysozymes in insects: what role do they play in nitrogen metabolism?

Abstract. Lysozymes are widely distributed in many organisms as one of the components of defence mechanisms. In herbivores, when nitrogen is not contained in sufficient amounts in the diet, bacteria lysed by stomach lysozymes are used as sources of nitrogen. In ruminants, lysozymes function as digestive enzymes in the true stomach. A convergence of amino acid sequence has been shown between the stomach lysozymes of different ruminants, and similar lysozymes have recently been reported in the gut or salivary gland of insects. In this mini review, the enzymatic and ecological functions of lysozymes in insects, particularly in termites, are introduced, together with future studies that are needed in this field.     

Distribution of hyaluronan in the mouse endometrium during the periimplantation period of pregnancy

The tissue distribution of stromal hyaluronan (HA) in the periimplantation mouse uterus was studied histochemically using a biotin-labelled HA-binding complex from cartilage proteoglycan. HA is present around proliferating stromal cells in both the pregnant and pseudopregnant mouse uterus prior to their differentiation into the decidualized phenotype. Decidualization is accompanied by clearance of HA from the extracellular matrix (ECM). This clearing is part of an intrinsic developmental program of the differentiating deciduum. A specific embryonic signal from the implanting conceptus is not required for this phenomenon to occur, since a similar response could be induced in deciduoma produced by artificial stimulation of a receptive uterus. Clearing of HA from the antimesometrial stroma is consistent with the hypothesis that the HA-negative decidual cell may be involved in restricting the invasion of trophoblast cells during embryo implantation. Retention of HA within angiogenic regions of the decidua basalis implies a functional role for this molecule in placental vascularization.     

Diapause of mouse blastocysts transferred to oviducts of immature mice

Mouse blastocysts transferred to the oviducts of immature females entered a period of diapause from which they could be activated by culture in vitro or by transfer to pseudopregnant recipients. In the tract of immature females, embryos hatched from the zona pellucida, increased cell number to a maximum that is comparable to that of blastocysts delayed by ovariectomy, and some moved to the uterus. Viability of blastocysts retained in the non-progestational, immature tract remained high for 4 days but dropped after 5 or 6 days. This new method of producing a delay in implantation offers precision in determining survival and viability rates and in determining the requirements of diapausing embryos.     

A Triple-Arginine Motif in the Amino-Terminal Domain and Oligomerization Are Required for HIV-1 Inhibition by Human MX2

We have employed molecular genetic approaches to understand the domain organization of the HIV-1 resistance factor myxovirus resistance 2 (MX2). First, we describe an essential triple-arginine motif in the amino-terminal domain. Second, we demonstrate that this 91-residue domain mediates antiviral activity when appended to heterologous proteins, and we provide genetic evidence that protein oligomerization is required for MX2 function. These insights will facilitate future work aiming to elucidate MX2''s mechanism of action.