User:Kim radford/sandbox

Neurulation is defined as morphogenic movements within the primitive streak to form an enclosed neural tube.1 Morphogens can be defined as intracellular signals. These signals have the capability to inhibit or activate cell growth. In mice, the primitive streak extension begins on day 6.5.2 The primitive streak can be defined as cell growth to form the midline anterior-posterior axis of an embryo.2 Here, anterior and posterior are words that represent the future head and tail sites.

The anterior tip of the embryo denotes where head development will occur. To begin neurulation, the neural plate needs to develop. The neural plate will become the neural tube later on in development. To create the neural tube, the anterior cells within the primitive streak need to replicate. In order for the correct cells to replicate, an important mass of morphogens need to be inhibited.1 The inhibition morphogens are exported by a signaling center called the node. This correct cell replication causes a thickening in that region. The thickening grows into a U shape. In mice, this occurs on day 7.5 of development.2

Next, the U-shaped mass of cells needs to extend. The U-shaped mass becomes thinner and longer within the anterior region. In order to form a closed tube, the U-shaped mass needs to fold. The neural plate U is induced to fold. Morphogens are secreted by the notochord, which lay underneath the neural plate. Hinge regions are created within the neural plate and assist in the fold. The folding occurs during day 9-10 of embryo development.3 The folding that occurs due to the hinge regions allow the both ends of the neural-U, or neural folds, to touch along the dorsal midline of the neural plate.2 Fusion begins once the neural folds touch. And the neural plate is now a neural tube.

1.    Colas, JF; Schoenwolf, GC; (2001) “Towards a cellular and molecular understanding of neurulation”. Developmental Dynamics, 221: 117-145.

2.    Slack, JMW, ed. (2013). Essential Developmental Biology (3. Ed.). Wiley-Blackwell: John Wiley & Sons. IBSN 978-0-470-92351-1

3.    Ybot-Gonzalez, P; Gaston-Massuet, C; Girdler, G; Klingensmith, J; Arkell, R; Greene, NDE; Copp, AJ; (2007) “Neural plate morphogenesis during mouse neurulation is regulated by anayagonism of Bmp signaling”. Development and Disease, 134: 3203-3211. Doi: 10.1242/dev.008177.

4.    Tam, PPL; Behringer, RR; (May 2007) “Mouse gastrulation: the formation of a mammalian body plan”. Mechanisms of Development, 68: 3-25.

Like coordinates on a map, a developing embryo needs axis. Certain morphogens, or cell signals, direct cells when and where to replicate. Replication of specific cells create a head-tail axis, also known as the anterior-posterior axis; as well as the ventral-dorsal axis and left-right axis. Because embryos grow outwards as well as 2-dimnesionally – 3 axis need to be established.

Many of the morphens, or signaling cells, are excreted by the node in mice. To help establish the anterior-posterior axis. A posterior (or tail-end) extension signal is excreted, called FGF.1

1.    Oginuma, M; Moncuquet, P; Xiong, F; Karoly, E; Chal, J; Guevorkian, K; Pourquie, O; (2017) “A gradient of glycolytic activity coordinates Fgf and Wnt signaling during elongation of the body axis in amniote embryos” Developmental Cell 40: 342-353. Doi:10.1016/j.devcel.2017.02.001.