Hbp1 regulates the timing of neuronal differentiation during cortical development by controlling cell cycle progression

Abstract

In the developing mammalian brain, neural stem cells (NSCs) initially expand the progenitor pool by symmetric divisions. NSCs then shift from symmetric to asymmetric division and commence neurogenesis. Although the precise mechanisms regulating the developmental timing of this transition have not been fully elucidated, gradual elongation in the length of the cell cycle and coinciding accumulation of determinants that promote neuronal differentiation might function as a biological clock that regulates the onset of asymmetric division and neurogenesis. We conducted gene expression profiling of embryonic NSCs in the cortical regions and found that expression of high mobility group box transcription factor 1 (Hbp1) was upregulated during neurogenic stages. Induced conditional knockout mice of Hbp1, generated by crossing with Nestin-CreER T2 mice, exhibited a remarkable dilatation of the telencephalic vesicles with a tangentially expanded ventricular zone and a thinner cortical plate containing reduced numbers of neurons. In these Hbp1-deficient mouse embryos, neural stem/ progenitor cells continued to divide with a shorter cell cycle length. Moreover, downstream target genes of the Wnt signaling, such as cyclin D1 (Ccnd1) and c-jun (Jun), were upregulated in the germinal zone of the cortical regions. These results indicate that Hbp1 plays a crucial role in regulating the timing of cortical neurogenesis by elongating the cell cycle and that it is essential for normal cortical development.

Chd8 Mutation Leads to Autistic-like Behaviors and Impaired Striatal Circuits

“…In particular, we examined both the number of cortical progenitors as well as the cell cycle length in embryonic day 15.5 (E15.5) embryos. We performed intraperitoneal injections of BrdU and Edu in pregnant dams 120 and 30 minutes prior to euthanasia (Figure S3C) (Mairet-Coello et al, 2012; Watanabe et al, 2015). Examination of brain sections showed no increase in the number of cortical progenitor cells as measured by BrdU incorporation within the somatosensory cortex of Chd8 +/− mice compared to wild-type littermates [WT (n = 6) 240 ± 10 BrdU + cells SEM; Chd8 +/− (n = 6) 241 ± 9 BrdU + cells SEM, two-tailed t-test p-value = 0.990](Figure S3D).…”

“…To estimate the cell cycle length, we conducted a dual-pulse-labeling of DNA synthesis using 5-bromo-2′-deoxyuridine (BrdU; Sigma-Aldrich) and 5-ethynyl-2′-deoxyuridine (EdU; Molecular Probes) as previously described (Mairet-Coello et al, 2012; Watanabe et al, 2015). Timed pregnant C57BL/6 females, crossed with Chd8 +/− males, received one intraperitoneal injection of BrdU (50 mg/kg) and Edu (12.5 mg/kg) 120 and 30 minutes before sacrifice, respectively, and the ratios of cells that incorporated either or both BrdU and EdU were analyzed to estimate the cell cycle length.…”

“…At least 1000 cells were counted per section, 3–4 mid-cortex sections per genotype were counted. For cell cycle estimation was performed as previously described (Mairet-Coello et al, 2012; Watanabe et al, 2015). Briefly, all Ki67 cells present in the ROI were counted and the existence of co-staining with BrdU and/or Edu was noted.…”

Transcription factor HMG box‐containing protein 1 (HBP1) modulates mitotic clonal expansion (MCE) during adipocyte differentiation

“…In cancer cells, ectopic overexpression of HBP1 can result in growth arrest, apoptosis, or differentiation, suggesting HBP1's possible role in tumor suppression (Chen et al, ; Kim et al, ; Lee et al, ; Yao, Works, Romagnoli, & Austin, ). Meanwhile, HBP1 also plays a crucial role in tissue differentiation, including muscle (Shih et al, ), myeloid (Yao et al, ), skin (Borrelli et al, ), and nervous cells (Watanabe, Kageyama, & Ohtsuka, ). Elevated HBP1 expression has been shown to determine the differentiation timing of erythroid, megakaryocyte and keratinocyte, and cortical neurogenesis (Borrelli et al, ; Watanabe et al, ).…”

“…Meanwhile, HBP1 also plays a crucial role in tissue differentiation, including muscle (Shih et al, ), myeloid (Yao et al, ), skin (Borrelli et al, ), and nervous cells (Watanabe, Kageyama, & Ohtsuka, ). Elevated HBP1 expression has been shown to determine the differentiation timing of erythroid, megakaryocyte and keratinocyte, and cortical neurogenesis (Borrelli et al, ; Watanabe et al, ). However, the expression of HBP1 blocks muscle cell differentiation (Shih et al, ).…”