Inactivation of aPKCλ results in the loss of adherens junctions in neuroepithelial cells without affecting neurogenesis in mouse neocortex

Abstract

In developing mammalian telencephalon, the loss of adherens junctions and cell cycle exit represent crucial steps in the differentiation of neuroepithelial cells into neurons, but the relationship between these cellular events remains obscure. Atypical protein kinase C (aPKC) is known to contribute to junction formation in epithelial cells and to cell fate determination for Drosophila neuroblasts. To elucidate the functions of aPKCλ, one out of two aPKC members, in mouse neocortical neurogenesis, a Nestin-Cre mediated conditional gene targeting system was employed. In conditional aPKCλ knockout mice, neuroepithelial cells of the neocortical region lost aPKCλ protein at embryonic day 15 and demonstrated a loss of adherens junctions, retraction of apical processes and impaired interkinetic nuclear migration that resulted in disordered neuroepithelial tissue architecture. These results are evidence that aPKCλ is indispensable for the maintenance of adherens junctions and may function in the regulation of adherens junction integrity upon differentiation of neuroepithelial cells into neurons. In spite of the loss of adherens junctions in the neuroepithelium of conditional aPKCλ knockout mice, neurons were produced at a normal rate. Therefore, we concluded that, at least in the later stages of neurogenesis, regulation of cell cycle exit is independent of adherens junctions.

Loss of Cell Adhesion Causes Hydrocephalus in Nonmuscle Myosin II-B–ablated and Mutated Mice

“…The requirement of aPKC in cell-cell adhesion has been demonstrated both in cultured cells (Suzuki et al, 2001, Nunbhakdi-Craig et al, 2002 and neuroepithelial cells in the developing mouse brain (Manabe et al, 2002). As noted above, the importance of aPKC in maintaining adherens junctions in the neocortex was demonstrated by conditional loss of this enzyme, which also resulted in hydrocephalus, although at a much later time (P3) than we report here (Imai et al, 2006). This report on the role of the scaffolding properties of NM II raises important and intriguing questions.…”

“…A recent report by Imai et al (2006) showed that conditional ablation of aPKC in developing mouse brains resulted in the loss of adhesion junctions in the neuroepithelial cells lining the cerebral ventricles. We, therefore, used antibodies to aPKC to analyze for the presence of this kinase in the spinal cord at E12.5.…”

“…No evidence for MLC20 serine-19 phosphorylation could be detected in these cells by using MLC20 serine-19 phosphospecific antibodies (Figure 8a), although there is evidence for serine-19 phosphorylation in the nearby vasculature (arrows). These findings support the idea that, although NM II-B is required to maintain cell-cell adhesion at the apical border of the spinal canal, activation of its motor is not required.A recent report by Imai et al (2006) showed that conditional ablation of aPKC in developing mouse brains resulted in the loss of adhesion junctions in the neuroepithelial cells lining the cerebral ventricles. We, therefore, used antibodies to aPKC to analyze for the presence of this kinase in the spinal cord at E12.5.…”

Analysis of aPKCλ and aPKCζ reveals multiple and redundant functions during vertebrate retinogenesis

“…Homozygous aPKCζ -/-mice, however, show normal embryogenesis, suggesting that aPKCλ may compensate for loss of aPKCζ within those embryos (Leitges et al, 2001). Furthermore, conditional deletion of aPKCλ within the differentiating nervous system as mediated by Nestin-driven Cre recombinase resulted in loss of adherens junctions without affecting cell cycle exit or cortical cell-type patterning of late progenitors (Imai et al, 2006). Therefore aPKCζ may partially compensate for aPKCλ function within the differentiating cortex.…”

The microenvironment of the embryonic neural stem cell: Lessons from adult niches?

“…Such a mechanism provides a hypothetical explanation for the human microcephaly syndromes that result from mutations in genes encoding centrosomal proteins (Bond and Woods, 2006), one of which (ASPM) has been shown to regulate cleavage plane angle and neurogenesis directly (Fish et al, 2006). Loss of apical adhesion could result in displacement of the NSC into deeper cortical layers, generating a random distribution of cells (NSCs, basal progenitors, and differentiated cells) in the cortex and a possible increase in the number of intermediate progenitors and differentiated cells as seen in Rho-GTPase cdc42 mutants (Cappello et al, 2006) and aPKC (Imai et al, 2006). In contrast, loss of basal adhesion could result in migration defects leading to ectopias in the cortex as seen in mice deficient in laminin ␥1 (Halfter et al, 2002), ␣6 integrin (Georges-Labouesse et al, 1998;Haubst et al, 2006), and ␤1 integrin (Graus-Porta et al, 2001).…”