3-Dimensional Examination of the Adult Mouse Subventricular Zone Reveals Lineage-Specific Microdomains

Abstract

Recent studies suggest that the subventricular zone (SVZ) of the lateral ventricle is populated by heterogeneous populations of stem and progenitor cells that, depending on their exact location, are biased to acquire specific neuronal fates. This newly described heterogeneity of SVZ stem and progenitor cells underlines the necessity to develop methods for the accurate quantification of SVZ stem and progenitor subpopulations. In this study, we provide 3-dimensional topographical maps of slow cycling “stem” cells and progenitors based on their unique cell cycle properties. These maps revealed that both cell populations are present throughout the lateral ventricle wall as well as in discrete regions of the dorsal wall. Immunodetection of transcription factors expressed in defined progenitor populations further reveals that divergent lineages have clear regional enrichments in the rostro-caudal as well as in the dorso-ventral span of the lateral ventricle. Thus, progenitors expressing Tbr2 and Dlx2 were confined to dorsal and dorso-lateral regions of the lateral ventricle, respectively, while Mash1+ progenitors were more homogeneously distributed. All cell populations were enriched in the rostral-most region of the lateral ventricle. This diversity and uneven distribution greatly impede the accurate quantification of SVZ progenitor populations. This is illustrated by measuring the coefficient of error of estimates obtained by using increasing section sampling interval. Based on our empirical data, we provide such estimates for all progenitor populations investigated in this study. These can be used in future studies as guidelines to judge if the precision obtained with a sampling scheme is sufficient to detect statistically significant differences between experimental groups if a biological effect is present. Altogether, our study underlines the need to consider the SVZ of the lateral ventricle as a complex 3D structure and define methods to accurately assess neural stem cells or progenitor diversity and population sizes in physiological or experimental paradigms.

Adding a spatial dimension to postnatal ventricular-subventricular zone neurogenesis

“…2B). Stereological estimates of active NSCs in the young adult mouse V-SVZ range between 600 and 750 cells (Azim et al, 2012c), a number that is in line with recent quantifications performed using V-SVZ whole-mount preparations (Ponti et al, 2013). Quantification of other proliferative cell populations, i.e.…”

“…The methodological biological variability is particularly relevant when quantifying the V-SVZ cellular content, since the precision of cell number estimations is highly sensitive to regional fluctuations in cell density within a single animal, as well as to cell motility, a characteristic of germinal regions such as the V-SVZ. As mentioned above, the number and the density of NSCs exhibit significant variations along the dorsoventral and rostrocaudal axis, with the presence of neurogenic hotspots (Mirzadeh et al, 2008;Azim et al, 2012c;Falcao et al, 2012) (Fig. 2B).…”

“…In agreement with their developmental origin, pallial markers [Emx1, Pax6, Tbr2 (Eomes), Tbr1, Ngn2 (Neurog2)] are expressed in the dorsalmost regions of the neonatal and adult LV, whereas subpallial [Dlx1/2/5, Gsx1/2 (Gsh1/2), Mash1 (Ascl1), Nkx2.1, Nkx6.2] and septal (Zic1/3) markers are expressed in the lateral and medial walls of the LV, respectively (Fig. 4B) (Kohwi et al, 2007;Winpenny et al, 2011;Azim et al, 2012c;Lopez-Juarez et al, 2013;Merkle et al, 2014). These probably represent a mere fraction of the TFs that are regionally expressed in the postnatal V-SVZ.…”

“…Several attempts have been made to quantify these cell types in the postnatal V-SVZ (Encinas and Enikolopov, 2008;Azim et al, 2012c;Falcao et al, 2012;Ponti et al, 2013). However, owing to its thinness, irregular shape and, most importantly, the dynamic nature and heterogeneous distribution of NSCs and their progeny, the V-SVZ is a complex structure, and performing such quantitative studies is challenging.…”

“…For example, although NSCs are sessile, their number and density vary markedly along the dorsoventral and rostrocaudal axes, with the presence of neurogenic hotspots (Mirzadeh et al, 2008;Azim et al, 2012c;Falcao et al, 2012) (Fig. 3A).…”