Brian Howell, PhD

RESEARCH ABSTRACT

Brain development is an exquisitely regulated phenomenon, whereby waves of differentiation produce diverse classes of neurons, oligodendrocytes and finally, astrocytes. Ultimately these cells, particularly the neurons, organize into functional networks that receive, integrate and transmit information. My lab studies how molecular signaling regulates the migration of neurons from their site of origin to destinations where they extend processes, form synapses and integrate into networks. One of our focuses is to investigate how the Reelin signaling pathway influences the positioning of distinct neuronal classes into stereotypical layers in the brain. Reelin, a secreted ligand, induces the tyrosine phosphorylation of the intracellular docking protein Dab1 by clustering the neuronal receptors ApoER2 and VLDLR and activating Src-family kinases. The tyrosine phosphorylation of Dab1 generates signaling complexes that includes the molecules Nckβ, Crk, CrkL and PI3K. These complexes regulate the behavior of neurons as they migrate, enabling them to settle into layers. We have shown that Reelin signaling influences the extension of the Golgi apparatus into neuronal dendrites and the ability of neurons to polarize. We are currently investigating how these cellular behaviors influence neuronal positioning and other neuronal properties regulated by Reelin signaling.

Figure 1. Reln is required for proper Golgi elongation and orientation in the hippocampus at birth. Hippocampal neurons identified by Ctip2 immunostaining typically have elongated GRASP65-positive Golgi that extend into the apical dendrite. On the contrary, in homozygous Reln mutant animals the Golgi apparatus is convoluted proximal to the nucleus.

Figure 2. Stk25, a genetic modifier of the phospho Tau phenotype in Dab1 mutant mice, influences neuronal migration. In contrast to constitutive Stk25 knockout, the acute inactivation of a conditional allele of Stk25 by GFP-Cre expression at E14.5 causes aberrant neuronal migration apparent by E17.5.

Figure 3. Knockdown of Stk25 causes anomalies in dendritogenesis. Expression of an Stk25 shRNA in the hippocampus at E16.5 results in reduced dendritic asymmetry between the apical and basal dendrites.

We have recently expanded our focus to include genetic causes of autism spectrum disorder (ASD); specifically RELN mutations, more than 40 of which have been identified in ASD patients. We have found that mutations are enriched in an Arg-X-Arg motif in the core of the Reelin subrepeat domains. The function of the paired Arg residues is unknown. Therefore, we are working to resolve the consequences of mutations in this motif in Reelin biosynthesis and signaling with the ultimate goal of determining how they contribute to ASD.

Selected Publications

Sütt S, Cansby E, Paul A, Amrutkar M, Nunez Duran E, Kulkarni NM, Ståhlman M, Borén J, Laurencikiene J, Howell BW, Enerbäck S, Mahlapuu M. STK25 regulates oxidative capacity and metabolic efficiency in adipose tissue. J Endocrinol. 2018 May 24. pii: JOE-18-0182. doi: 10.1530/JOE-18-0182. [Epub ahead of print]PMID:29794231

Lammert, D.B., Middleton, F.A., Pan, J., Olson, E.C. and Howell, B.W. (2017) The de novo Autism Spectrum Disorder RELN R2290C Mutation Reduces Reelin Secretion and Increases Protein Disulfide Isomerase Expression. J Neurochem. 142:89-102. doi: 10.1111/jnc.14045

Lammert DB, Howell BW. RELN Mutations in Autism Spectrum Disorder. Front Cell Neurosci. 2016 Mar 31;10:84. doi: 10.3389/fncel.2016.00084. eCollection 2016. Review.PMID:27064498

Abadesco AD, Cilluffo M, Yvone GM, Carpenter EM, Howell BW, Phelps PE. Novel Disabled-1-expressing neurons identified in adult brain and spinal cord. Eur J Neurosci. 2014 Feb;39(4):579-92. doi: 10.1111/ejn.12416. Epub 2013 Nov 19.PMID:24251407

Matsuki T, Chen J, Howell BW. Acute inactivation of the serine-threonine kinase Stk25 disrupts neuronal migration. Neural Dev. 2013 Nov 13;8:21. doi: 10.1186/1749-8104-8-21.PMID:24225308

Teixeira CM, Kron MM, Masachs N, Zhang H, Lagace DC, Martinez A, Reillo I, Duan X, Bosch C, Pujadas L, Brunso L, Song H, Eisch AJ, Borrell V, Howell BW, Parent JM, Soriano E. Cell-autonomous inactivation of the reelin pathway impairs adult neurogenesis in the hippocampus. J Neurosci. 2012 Aug 29;32(35):12051-65.PMID:22933789

Matsuki T, Zaka M, Guerreiro R, van der Brug MP, Cooper JA, Cookson MR, Hardy JA, Howell BW. Identification of Stk25 as a genetic modifier of Tau phosphorylation in Dab1-mutant mice. PLoS One. 2012;7(2):e31152. doi: 10.1371/journal.pone.0031152. Epub 2012 Feb 15.PMID:22355340

Matsuki T, Matthews RT, Cooper JA, van der Brug MP, Cookson MR, Hardy JA, Olson EC, Howell BW. Reelin and stk25 have opposing roles in neuronal polarization and dendritic Golgi deployment. Cell. 2010 Nov 24;143(5):826-36. doi: 10.1016/j.cell.2010.10.029.PMID:21111240

Matsuki T, Pramatarova A, Howell BW. Reduction of Crk and CrkL expression blocks reelin-induced dendritogenesis. J Cell Sci. 2008 Jun 1;121(11):1869-75. doi: 10.1242/jcs.027334. Epub 2008 May 13.PMID:18477607

Pramatarova A, Chen K, Howell BW. A genetic interaction between the APP and Dab1 genes influences brain development. Mol Cell Neurosci. 2008 Jan;37(1):178-86. Epub 2007 Sep 26.PMID:18029196

Pramatarova A, Ochalski PG, Lee CH, Howell BW. Mouse disabled 1 regulates the nuclear position of neurons in a Drosophila eye model. Mol Cell Biol. 2006 Feb;26(4):1510-7.PMID:16449660

Howell, B.W., Herrick, T.M., Hildebrand, J.D., Zhang, Y., Cooper, J.A. (2000).  Dab1 tyrosine  phosphorylation  sites  relay  positional signals  during  mouse brain  development. Current Biology 10: 877-885. PMID:10959835

Howell, B.W., Herrick, T., Cooper, J.A. (1999) Reelin-induced tyrosine phosphorylation of Disabled 1 during neuronal positioning. Genes Dev.13 (6):643-648

Howell, B.W., Hawkes, R., Soriano, P., and Cooper, J.A. (1997). Neuronal position in the developing brain is regulated by mouse disabled. Nature, 389: 733-737.