Clonal analysis reveals granule cell behaviors and compartmentalization that determine the folded morphology of the cerebellum

Abstract

The mammalian cerebellum consists of folds of different sizes and shapes that house distinct neural circuits. A crucial factor underlying foliation is the generation of granule cells (gcs), the most numerous neuron type in the brain. We used clonal analysis to uncover global as well as folium size-specific cellular behaviors that underlie cerebellar morphogenesis. Unlike most neural precursors, gc precursors divide symmetrically, accounting for their massive expansion. We found that oriented cell divisions underlie an overall anteroposteriorly polarized growth of the cerebellum and gc clone geometry. Clone geometry is further refined by mediolateral oriented migration and passive dispersion of differentiating gcs. Most strikingly, the base of each fissure acts as a boundary for gc precursor dispersion, which we propose allows each folium to be regulated as a developmental unit. Indeed, the geometry and size of clones in long and short folia are distinct. Moreover, in engrailed 1/2 mutants with shorter folia, clone cell number and geometry are most similar to clones in short folia of wild-type mice. Thus, the cerebellum has a modular mode of development that allows the plane of cell division and number of divisions to be differentially regulated to ensure that the appropriate number of cells are partitioned into each folium.

Allometric Analysis Detects Brain Size-Independent Effects of Sex and Sex Chromosome Complement on Human Cerebellar Organization

“…Because scaling relationships between regional and global brain volumes can be profoundly nonlinear in humans, scaling (or allometric) norms provide a critical framework for valid comparison of regional anatomy between males and females or any other groups that differ in brain size Reardon et al, 2016). Securing a detailed map of regional cerebellar allometry in humans is also important for our basic understanding of cerebellar morphogenesis, and is well motivated by both phylogenetic (Finlay and Darlington, 1995;Clark et al, 2001;Balsters et al, 2010;Charvet et al, 2013) and developmental (Sudarov and Joyner, 2007;Legué et al, 2015) evidence that the factors that determine global and regional cerebellar size are partially dissociable from those determining overall brain size.…”

A Mathematical Model of Granule Cell Generation During Mouse Cerebellum Development

“…1). Gcps undergo symmetric division in the EGL during cerebellum development (Espinosa & Luo, 2008; Legué et al , 2015). Proliferation occurs in the outer EGL (oEGL), where a gcp generates two daughter gcp cells with each division.…”

“…At t=0 there are no differentiated granule cells (N i (0) = N g (0) = 0), but there are gcp cells (N o (0) > 0). The time t=0 was assumed to be one day before birth (Legué et al , 2015). The experimental data were measured in postnatal days (P2, P6, P10 and P14), so t=0 in the model is actually “P−1”.…”

“…Conversion between cell numbers and tissue areas was made using the following simple formula: $${\mathrm{N}}_{\mathrm{normalo},\mathrm{normali}}=\frac{{\mathrm{A}}_{\mathrm{normalo},\mathrm{normali}}\times L}{v_c}$$ where v c is the volume of a granule cell, assumed to be 300-μm 3 (Mares et al, 1970; Seil & Herndon, 1970; Altman & Bayer, 1997), and L is the medial-lateral width (measured in μm) of the vermis (central cerebellum), containing lobule III from which we measured the data. Both histological and MRI studies have shown that L is relatively constant over the early postnatal developmental period, with most of the growth of the cerebellum occurring in the anterior-posterior direction, along the length of each of the lobules (Legué et al , 2015, Szulc et al , 2015). From MRI data (Szulc et al , 2015), we estimated L (measured along the medial-lateral outer contour of the vermis) to be 1775-μm (± 20%) between P2 and P14.…”

“…Furthermore, the folded morphology of the postnatal cerebellum develops similarly in all mammalian species, with 10 major lobules in the midline of mice that are further foliated in higher mammals, including humans. At the cellular level, the gcps and granule cells in mice have been studied extensively for close to 50 years (Fujita, 1967; Haddara & Nooreddin, 1966; Mares et al , 1970; Seil & Herndon, 1970; Hatten et al , 1982; Goldowitz et al , 1997), including recent reports using the most advanced genetic cell labeling and tracking tools, providing important new data from clonal analysis (Espinosa & Luo, 2008; Legué et al , 2015). Finally, a number of genetic factors have been identified, including SHH, that are involved in cerebellum growth and patterning, and many genetically engineered mouse models of abnormal cerebellum development have been produced and are available for in vivo studies (Joyner et al , 1991; Goldowitz et al , 1997; Goodrich et al, 1997; Corrales et al , 2006; Cheng et al , 2010).…”