Nitric oxide stimulates human neural progenitor cell migration via cGMP-mediated signal transduction

Neuronal migration is one of the most critical processes during early brain development. The gaseous messenger nitric oxide (NO) has been shown to modulate neuronal and glial migration in various experimental models. Here, we analyze a potential role for NO signaling in the migration of fetal human neural progenitor cells. Cells migrate out of cultured neurospheres and differentiate into both neuronal and glial cells. The neurosphere cultures express neuronal nitric oxide synthase and soluble guanylyl cyclase that produces cGMP upon activation with NO. By employing small bioactive enzyme activators and inhibitors in both gain and loss of function experiments, we show NO/cGMP signaling as a positive regulator of migration in neurosphere cultures of early developing human brain cells. Since NO signaling regulates cell movements from developing insects to mammalian nervous systems, this transduction pathway may have evolutionary conserved functions.     

Faithful chaperones

This review describes the properties of some rare eukaryotic chaperones that each assist in the folding of only one target protein. In particular, we describe (1) the tubulin cofactors, (2) p47, which assists in the folding of collagen, (3) α-hemoglobin stabilizing protein (AHSP), (4) the adenovirus L4-100 K protein, which is a chaperone of the major structural viral protein, hexon, and (5) HYPK, the huntingtin-interacting protein. These various-sized proteins (102–1,190 amino acids long) are all involved in the folding of oligomeric polypeptides but are otherwise functionally unique, as they each assist only one particular client. This raises a question regarding the biosynthetic cost of the high-level production of such chaperones. As the clients of faithful chaperones are all abundant proteins that are essential cellular or viral components, it is conceivable that this necessary metabolic expenditure withstood evolutionary pressure to minimize biosynthetic costs. Nevertheless, the complexity of the folding pathways in which these chaperones are involved results in error-prone processes. Several human disorders associated with these chaperones are discussed.     

甜玉米

甜玉米(学名为 Zea Mays L.)属于禾本科(禾本科植物),在世界大多数讲英语国家的人们,称做玉米 maize,只有北美叫谷粒 corn。在法国,它叫 mais;而在西班牙称 maiz。甜玉米是玉米 maize 的几种类型之一,即大家知道的软玉米类型,有时被称做糖质玉米或皱纹玉米。与其它玉米类型相比较,甜玉米以它较高的含糖量(在乳熟和蜡熟早期阶段)和它     

不同胚乳遗传型的甜玉米在吸胀期间代谢物的浸析

高糖基因型皱缩—2(sh_2)与含直链淀粉增加(ae)、粗胚乳(du)和蜡质胚乳(wx)组合的三倍体作隐性基因型的甜玉米(Zea mags L.)杂种。由于先天性种籽品质低劣,已限制商品生产,这些杂种的种籽重量轻,比普通甜玉米含糖(sn)基因型玉米皱缩得多,且杂种后代不稳定,植株幼苗生活力差。本研究采用浸析法,高糖甜玉米种籽在吸胀期间其代谢产物浸析出来,代谢物浸析充分与否跟甜玉米基因型及其种籽本身先天性品质低劣有关。本研究选择三个有代表性的甜玉米基因类型,即 Iochief(su)、美国佛罗里达州甜支柱(sh_2)和 Penn-fresh ADX(ae、du、wx),测定在吸胀期间代谢物的浸析是通过本身电子传导和吸胀以后在不同的时间间隔里可溶性蛋白质数量测量的。高糖基因类型的种籽比含糖的(su)种籽传导率高,在24—48小时的吸胀时间里,ae du wx 种籽本身的传导率比其他两个类型的高。在吸胀期间,高糖基因类型的种籽可溶性蛋白质的浸析也比含糖的(su)种籽高。在不同基因类型的种籽中,最初析出的可溶性蛋白质数量[蛋白质(毫克)/种籽(克)]没有显著的差异。但是,高糖基因类型的种籽由于种籽品质差,每粒种籽可溶蛋白质比 su 类型要少得多,对于 sh_2和 ae duwx 的种籽,在吸胀期间,蛋白质浸析似乎与果皮破裂和高膜渗透性有关。这些研究说明高糖基因型玉米种籽果皮和薄膜表层对收获和干燥期间损伤的反应比含糖的(su)可能更为敏感。为了生产高质量高糖基因型种籽,必须特别细心。     

太阳周期长度:太阳活动性与气候紧密联系的一个“指示器”

科学家进行了许多尝试,力图探讨CO_2大量释放到大气中后对气候的影响。从现实情况考虑,在全球范围进行实验是不可能的,物理学理论的证据就是依赖模型模拟和观察。模型模拟需要某种假设,而获得大量基本数据则需长时间的观察。太阳辐射是与地球气候相关的一个最基本因素。这是无法准确知道的一个参数。埃迪(Eddy)指出,太阳活动性与全球气候的某些“指示器”之间的长期关系可能是由太阳辐照度的变化所引起的。但是,只有在当今人造卫星时代,才能测得有关太阳辐照度的可靠