Signals from the edges: The cortical hem and antihem in telencephalic development

Abstract

The early cortical primordium develops from a sheet of neuroepithelium that is flanked by distinct signaling centers. Of these, the hem and the antihem are positioned as longitudinal stripes, running rostro-caudally along the medial and lateral faces, respectively, of each telencepahlic hemisphere. In this review we examine the similarities and differences in how these two signaling centers arise, their roles in patterning adjacent tissues, and the cells and structures they contribute to. Since both the hem and the antihem have been identified across many vertebrate phyla, they appear to be part of an evolutionary conserved set of mechanisms that play fundamental roles in forebrain development.

Pallio-Pallial Tangential Migrations and Growth Signaling: New Scenario for Cortical Evolution?

“…2 b) [Assimacopoulos et al, 2003;Subramanian et al, 2009]. The schema in figure 2 b shows that this territory at the back is also where the antihem and hem converge upon the boundaries of the prethalamic eminence and the hypothalamus, a point which is not always clear in the literature.…”

“…one step closer to the dorsal pallium target), we have the cortical hem and the antihem planar signal sources [Assimacopoulos et al, 2003;Campbell, 2003;O'Leary et al, 2007;O'Leary and Sahara, 2008;Subramanian et al, 2009]. The cortical hem area lies at the rim of the medial pallium, where the choroidal roof is inserted (topologically a dorsal alar position), and it releases morphogens of the Wnt and Bmp families [Grove et al, 1998] (Hem and Ch; fig.…”

“…The hem domain is regulated in size by the aforementioned peripheral signaling sources [Shimogori et al, 2004] and is well delimited from the rest of the medial pallium; for instance, Lhx2 expression, widely occurring in the pallium, does not extend into the hem, ending sharply at its limit. The Wnt morphogens are required for normal hippocampal patterning [Grove et al, 1998] but also generally affect the pallium [Assimacopoulos et al, 2003;Campbell, 2003;Subramanian et al, 2009]. Later on in development the hem becomes the bed of the hippocampal fimbria tract (fibers proceeding rostrally towards the hippocampal commissure and the fornix tract).…”

Tumor suppressor Nf2 limits expansion of the neural progenitor pool by inhibiting Yap/Taz transcriptional coactivators

“…We first examined the cortical hem, a signaling center that instructs hippocampus formation (Grove et al, 1998;Mangale et al, 2008;Subramanian et al, 2009). Using the hem marker Lmx1a, we found that the hem was significantly enlarged in mutant brains by E14.5, and by E15.5 it was about three times the size of that in control brains ( Fig.…”

Cajal–Retzius cells: Update on structural and functional properties of these mystic neurons that bridged the 20th century

“…The most important source of CRc is the cortical hem ( Fig. 3A; Meyer et al, 2002;Takiguchi-Hayashi et al, 2004;Yoshida et al, 2006), an area located at the caudomedial region of the developing neocortex and one of the major organizing centers in corticogenesis (Subramanian et al, 2009). Ablation experiments revealed that hemderived CRc represent the largest proportion of CRc (Yoshida et al, 2006).…”