Regression and shortening of the primitive streak in the explanted chick blastoderm

Abstract

Since the time of Dursy (1866) who first extensively investigated the development of the primitive streak in the chick, embryologists have been interested in the manner of origin and growth in length of the streak and its relationship to the developing embryo. The recent experiments of TVillier and his students on blastoderms of the head-process and definitive primitive streak stages have shown that many organforming areas have a definite spatial arrangement about the anterior end of the streak (see Willier and Rawles, '35, and Rawles, '36). Whether a similar relationship may be found at still earlier stages of development of the streak is a problem of considerable importance.The purpose of this study is twofold: (1) to determine the approximate positions of some of the organ-forming regions in blastoderms of pre-and early streak stages, and (2) to esamine the relationship of these regions to the primitive streak as it arises and grows in length. The approach used is that of testing the potency of isolated anterior and posterior pieces of blastoderms to undergo development in vitro upon the surface of a blood plasma clot. The behavior of such isolates at different stages of development has a direct bearing upon I am grateful for the excellent facilities provided a t the University of Rochester where this investigation was begun. G9

Primitive and definitive erythropoiesis in the yolk sac: a birds eye view

“…Fates of mesoderm precursors in the primitive streak vary depending on the stages. Generally speaking, posterior part (1/2 to 1/3) of the primitive streak continues to give rise to extraembryonic fated mesoderm from HH2 to at least HH9 (Murray, 1932;Nakazawa et al, 2006;Nocolet, 1970;Peebles, 1898;Psychoyos and Stern, 1996;Rawles, 1936;Rosenquist, 1966;Rudnick, 1938;Sawada and Aoyama, 1999;Schoenwolf et al, 1992;Spratt, 1942;Spratt, 1946;Spratt, 1947;Spratt and Haas, 1965). Relative to more axially located mesoderm lineages (the axial, paraxial, intermediate and lateral plate mesoderm), extraembryonic mesoderm precursors are of the ventralmost fate and populate the lateralmost regions of the developing embryo.…”

Embryology of myelomeningocele and anencephaly

“…3). Results of earlier mapping studies 56 suggested that the prospective neuroectoderm is organized in a linear, craniocaudal sequence, so that prospective forebrain cells are located more cranially than prospective midbrain cells. In more recent studies, however, a different organization is suggested.…”

“…In the chick, the notochordal process grows largely by the latter mechanism. 56 In mammals, analysis of the available evidence suggests that the situation is much more complex and may involve both mechanisms. 60 The mechanism of notochord elongation in humans is unknown.…”

Second messenger regulation of occlusion of the spinal neurocoel in the chick embryo

“…Two hundred forty-seven dozen embryos were used in the pharmacological study, 15 dozen and 9 dozen for the determination of the amount of CAMP and calmodulin, respectively, in the neural tube during occlusion. The embryos were excised from the yolks, the vitelline membrane was removed, and the embryos were aseptically transferred to small Petri dishes containing either modified Spratt agar substrate (Spratt, 1947) or liquid medium (physiological saline, Hank's salt, or medium 199).…”