Determinants of Neocortical Development and Function

1.       Regulation of the proliferation and differentiation of cortical progenitors

Katrin Gerstmann (PhD Student), Daniel Pensold and Dr. Geraldine Zimmer

The phylogenetic evolution of the six-layered mammalian neocortex can only be understood in the light of ontogenetic development. During evolution the neocortex was subjected to an enormous expansion of its size and complexity correlating with the extraordinary human cognitive abilities.  Another hallmark is the increase of the relative size of the supragranular layers. Thus, revealing the developmental mechanisms controlling the number of cortical progenitor cells may provide insights into evolutionary advances as well as in the pathogenesis for neuropsychiatric disorders.

Excitatory cortical neurons are generated in transient proliferative regions at the ventricular surface of the dorsal embryonic telencephalon. Postmitotic neurons migrate radially into the developing cortex and form successively the cortical layers. Thereby, neurons destined for the infragranular layers are born first, while supragranular neurons are born at later stages. Various key molecules have already been identified to orchestrate developmental processes like neurogenesis, cell cycle exit, neuronal differentation and migration, including proneural genes, transcription factors and guidance molecules. Members of the Eph/Ephrin-system are expressed in cortical progenitors of the developing neocortex. Ephrins and their receptors were already identified to regulate developmental processes like proliferation, axonal guidance and migration. Therefore, one focus of research is to reveal the role of membrane‑bound ephrins and their cognate receptors in the regulation of differentiation and proliferation of cortical progenitors during corticogenesis in mice.

Figure 1: A, DAPI stained hemisphere of an E13 coronal brain section. B, Pax6 is a transcription factor expressed by apical progenitors of the ventricular zone (VZ), while Tbr2 is a marker for basal progenitors located in the subventricular zone (SVZ). C, The mode of division (symmetrical and asymmetrical cell division) can be visualized by combined DAPI (blue) and ASPM (red) staining. D, Cell cycle kinetics can be investigated by the sequential application of different thymidine analoga (BrdU and IdU). Ctx=cortex, MGE=medial ganglionic eminence, LGE=lateral ganglionic eminence.

2.       Epigenetic regulation of cortical interneuron development and function

Daniel Pensold (Diploma Student), Katrin Gerstmann (PhD Student), Julia Pissang (Bachelor Student), Diane Penndorf (Bachelor Student), Lisa Blüml (Bachelor Student), Judit Symmank (Master Student) and Dr. Geraldine Zimmer

Shaping excitatory responses of pyramidal neurons by the very diverse group of GABAergic interneurons falling into 20 highly diverse subpopulations is crucial for cortical circuits, plasticity and higher cognitive functions. Abnormalities in interneuron number, composition and function of cortical interneurons have been implicated in a wide range of neurological disorders and in age‑related decline of cognitive capabilities. Thus, deciphering the developmental determinants that sculpt and maintain their physiological diversity seems critical in any attempt to understand the logic behind their integration into cortical circuits, as well as causes for cortical dysfunction. A paucity of specific interneuron subtype markers further complicates investigations on the molecular mechanisms underlying the generation of cortical interneuron heterogeneity.

It has become clear that different classes of cortical interneurons are generated in a temporally regulated fashion within distinct domains of the basal telencephalon, from where they migrate over long distances along predefined routes to the cortex. This temporal and spatial origin of cortical interneurons seems predictive for their intrinsic properties in respect to their mature function. Epigenetic mechanisms, like DNA methylation in particular, are known to govern cell fate decisions during development. Thus, this project intends to reveal the contribution of epigenetic transcriptional regulation to interneuron subtype development and cortical function.

Methodologically we approach our scientific questions with a variety of technologies covering the cellular and systemic level of analysis. This includes functional in vitro and in vivo assays, immunohistochemical and molecular techniques, live-cell imaging, confocal microscopy, transcriptome analysis as well as mouse genetics (knockout and transgenic animals) and behavioural experiments.

Figure 2: A, Schematic illustration of the migratory routes of postmitotic cortical interneurons dependent on their site of origin. B, Calbindin immunostaining at E14 labels migrating interneurons generated in the POA and MGE. C, POA-cells that were electroporated with a GFP construct, as illustrated by the white circle in B, are dissociated for manual isolation using a micromanipulator, shown in D. E, F, Characterization of subsets of cortical interneurons with subtype specific markers (parvalbumin in E and calretinin in F). Ctx=cortex, MGE=medial ganglionic eminence, LGE=lateral ganglionic eminence, POA=preoptic area.

Master Projects available!!!!

Master and Bachelor Students:

Judit Symmank

Diane Penndorf

Julia Pissang

Lisa Blümel

Publications:

Zimmer G, Rudolph J, Landmann J, Gerstmann K, Steinecke A, Gampe C and Bolz J (2011) Bidirectional ephrinB3/EphA4 signaling mediates the segregation of MGE‑and POA derived interneurons in the deep and superficial migratory stream. J Neurosci: 31(50):18364-18380

Rudolph J, Zimmer G, Steinecke A, Barchmann S, Bolz J (2010) Ephrins guide migrating cortical interneurons in the basal telencephalon. Cell Adh Migr 4.

Zimmer G, Schanuel SM, Burger S, Weth F, Steinecke A, Bolz J, Lent R (2010) Chondroitin Sulfate Acts in Concert with Semaphorin 3A to Guide Tangential Migration of Cortical Interneurons in the Ventral Telencephalon. Cerebral Cortex (10):2411-22

Zimmer G, Garcez P, Rudolph J, Niehage R, Weth F, Lent R, Bolz J (2008) Ephrin-A5 acts as a repulsive cue for migrating cortical interneurons. Eur J Neurosci 28:62-73.

Zimmer G, Kastner B, Weth F, Bolz J (2007) Multiple effects of ephrin-A5 on cortical neurons are mediated by SRC family kinases. J Neurosci 27:5643-5653.