Dll3 pudgy mutation differentially disrupts dynamic expression of somite genes

Mutations in the notch ligand delta-like 3 have been identified in both the pudgy mouse (Dll3(pu); Kusumi et al.: Nat Genet 19:274-278, 1998) and the human disorder spondylocostal dysostosis (SCD; Bulman et al.: Nat Genet 24:438-441, 2000), and a targeted mutation has been generated (Dll3(neo); Dunwoodie et al.: Development 129:1795-1806, 2002). Vertebral and rib malformations deriving from defects in somitic patterning are key features of these disorders. In the mouse, notch pathway genes such as Lfng, Hes1, Hes7, and Hey2 display dynamic patterns of expression in paraxial mesoderm, cycling in synchrony with somite formation (Aulehla and Johnson: Dev Biol 207:49-61, 1999; Forsberg et al.: Curr Biol 8:1027-1030, 1998; Jouve et al.: Development 127:1421-1429, 2000; McGrew et al.: Curr Biol 8:979-982, 1998; Nakagawa et al.: Dev Biol 216:72-84, 1999). We report here that the Dll3(pu) mutation has different effects on the expression of cycling (Lfng and Hes7) and stage-specific genes (Hey3 and Mesp2). This suggests a more complex situation than a single oscillatory mechanism in somitogenesis and provides an explanation for the unique radiological features of the human DLL3-type of SCD.     

Targeting gene expression in the mouse somite: adenovirus-mediated gene delivery and whole embryo culture

We report here a novel approach to direct gene expression in the mouse somite based on the combined application of adenovirus-mediated gene delivery and whole embryo ex vivo culture. As proof of principle, we show functional analysis of somites microinjected with an engineered virus expressing an activated form of Smoothened, the signaling receptor for Sonic Hedgehog (SHH). As adenovirus can infect many embryonic tissues in the mouse, this method may provide an effective alternative to conventional transgenesis for targeted spatial and temporal gene expression.     

南极鱼两种寄生海蛭的研究

从南极海纽喀姆湾(南纬66°17′,东经110°32′)的南极鱼属Notothenia鱼体上得到两个海蛭标本。经鉴定为多皱海蛭Pontobdella rugosa Moore,1938和椎蛭属Notobdella的一新种。前者的环带后区环的分割明显并因许多大、小结节变得崎岖不平。在一完全体节(ⅫⅠ-ⅩⅫⅠ)里环的通常大小关系是8_2(?)a_1>b_5=b_(60)扭椎蛭新种Notobdella streptocheles sp.nov.呈S形弯曲井从稍膨大的中部向两端渐渐变细。在前吸盘上没有眼。尾吸盘与躯干部的最大体宽相等。在—完全体节(Ⅹ-ⅩⅩⅣ)里环的通常大小关系是a_1=a_2>b_3=b_(60)嗉囊有6对盲囊和一个后嗉囊盲囊。     

Hox genes in time and space during vertebrate body formation

Vertebrae display distinct morphological features at different levels of the body axis. Links between collinear Hox gene activation and the progressive mode of body axis elongation have provided a fascinating blueprint of the mechanisms for establishing these morphological identities. In this review, we first discuss the regulation and possible role of collinear Hox gene activation during body formation and then highlight the direct role of Hox genes in controlling cellular movements during gastrulation, therefore contributing to body formation. Additional related research aspects, such as imaging of chromatin regulation, roles of micro RNAs and evolutional findings are also discussed.     

脊椎动物胚胎骨骼肌的生成

肌肉发生的起始和生肌节的形成是胚胎肌肉发育中的两个关键事件。研究表明,肌肉发生的起始有赖于体节周围组织所产生的分泌因子的影响。这些组织包括体轴结构,侧板中胚层及体节正上方的外胚层,代表性的分子有Ｗｎｔｓ家族的一些成员以及Ｓｈｈ和ＢＭＰ－４;而生肌节的形成则首先依赖与分节化相关的基因,如ｄｅｌｔａ,ｈｅｒ１等的正常功能,分节之后也同样需在周围环境的作用之下形成生肌节。两栖类非洲爪蟾的肌肉发生有其特殊性。本文对这一领域中最近的研究进展作一综合介绍。     

Differential Distribution of Retinoic Acid Synthesis in the Chicken Embryo as Determined by Immunolocalization of the Retinoic Acid Synthetic Enzyme, RALDH-2

Retinaldehyde dehydrogenase type 2 (RALDH-2) is a major retinoic acid generating enzyme in the early embryo. Here we report the immunolocalization of this enzyme (RALDH-2-IR) in stage 6-29 chicken embryos; we also show that tissues that exhibit strong RALDH-2-IR in the embryo contain RALDH-2 and synthesize retinoic acid. RALDH-2-IR indicates dynamic and discrete patterns of retinoic acid synthesis in the embryo, particularly within the somitic mesoderm, lateral mesoderm, kidney, heart, and spinal motor neurons. Prior to somitogenesis, RALDH-2-IR is present in the paraxial mesoderm with a rostral boundary at the level of the presumptive first somite; as the somites form, they exhibit strong RALDH-2-IR. Cervical presomitic mesoderm exhibits RALDH-2-IR but thoracic presomitic mesoderm does not. Neural crest cells do not express detectable levels of RALDH-2, but migrating crest cells are associated with RALDH-2 expressing mesoderm. The developing limb mesoderm expresses little RALDH-2-IR; however, RALDH-2-IR is strongly expressed in tissues adjacent to the limb. The most lateral, earliest-projecting motor neurons at all levels of the spinal cord exhibit RALDH-2-IR. Subsequently, many additional motor neurons in the brachial and lumbar cord regions express RALDH-2-IR. Motor neuronal expression of RALDH-2-IR is present in the growing axons as they extend to the periphery, indicating a potential role of retinoic acid in nerve influences on peripheral differentiation. With the exception of a transient expression in the facial/vestibulocochlear nucleus, cranial motor neurons do not express detectable levels of RALDH-2-IR.     

A transgenic Tbx6;CreERT2 line for inducible gene manipulation in the presomitic mesoderm

The rhythmic segmentation process of the presomitic mesoderm (PSM) orchestrates the formation of somites, the fundamental units for the vertebrate axial body plan. To aid the investigation of molecular components governing the conversion from PSM into somites, we generated a transgenic mouse line that expresses a tamoxifen (tmx) inducible CreER(T2) under the control of a 2.5 kb enhancer element of Tbx6, a gene essential for PSM formation and somite patterning. Combined with Cre reporters, this Tbx6;CreER(T2) line displays robust tmx-inducible Cre activity in the PSM at various embryonic stages. This tool should be useful for studying gene function during somitogenesis by either conditional inactivation or mis-expression, and potentially coupled with cell marking.