On the mechanisms of neural development in the ventral telencephalon

The time of arrival of interneurons and oligodendrocytes to the neocortex is critical for proper functional brain development. Aberrances in this sequence can be detrimental, and involved in different developmental diseases. Thus, understanding the mechanisms for temporal control of the genesis and migration of neural cells is crucial. The aim of this study was to focus on the ventral telencephalon, a major source of interneurons and oligodendrocytes, in more detail. A more sensitive method was developed for detecting and quantifying oligodendrocyte precursor cells, e.g. Olig2. The device decloaking chamber was compared to the microwave oven-based heat-induced epitope retrieval (HIER) method by studying the labeling of Olig2 marker in paraffin-embedded sections from embryonic mouse brain. The results demonstrated that the decloaking chamber-based HIER method is the most suitable technique for the detection of single Olig2-labeled cells in the ventral telencephalon. This qualitative result was reflected in the quantitative analyses: more Olig2-labeled cells were quantifiable with the decloaking chamber- than with the microwave oven-approach. Thus, the decloaking chamber-based HIER method constitutes a sensitive technique for the detection of oligodendrocyte precursor cells, and therefore for its quantification in the developing ventral telencephalon. The development of telencephalon depends on fundamental processes, which include proliferation and migration of neural cells. The Na-K-Cl cotransporter isoform 1 (NKCC1) is an important protein for the process of volume regulation, and has been implicated in cell division. Within the developing brain, the ventral telencephalon showed the highest expression of NKCC1. This expression corresponded to neural progenitor cells in the lateral ganglionic eminence (LGE). Using NKCC1 knockout mice, it was demonstrated that NKCC1 influenced cell cycle reentry. Consequently, mice lacking NKCC1 have impaired Sp8-expressing interneurons and Olig2-labeled cells. Thus, NKCC1 is crucial in vivo for cell cycle decision, thereby altering the production of oligodendrocyte and interneuron progenitor cells in the LGE. Once interneurons are born, they migrate to the neocortex. The implication of syndecan-3 was assessed in their tangential migration. The results showed that the Glial cell line-derived neurotrophic factor GDNF interacts with syndecan-3 to promote the tangential migration of calbindin-expressing interneurons within the telencephalon. Consistently, mice lacking syndecan-3 have an accumulation of migrating interneurons in the LGE. In summary, two important mechanisms were found for temporal and spatial control of cortical oligodendrocytes and interneurons.Aivojen kehitys on äärimmäisen monimutkainen prosessi. Interneuronit ja oligodendrosyytit ovat hermosolutyyppejä, joiden kehityksenaikainen siirtyminen kehittyvään aivojen kuorikerrokseen on aivojen kehityksen kannalta olennainen tapahtuma. Häiriöt kyseisessä tapahtumaketjussa johtavat vaikeisiin kehityksellisiin häiriöihin. Näin ollen on erittäin tärkeää ymmärtää mekanismeja, jotka hallitsevat kehittyvien hermosolujen kulkeutumista. Tässä työssä olemme tutkineet ventralista telenkefalonia, aivojen aluetta, joka on kehityksen aikana interneuronien ja oligodendrosyyttien tärkein lähde. Oligodendrosyyttien esiasteiden havaitsemiseksi olemme käyttäneet aiempaa herkempää menettelytapaa, jonka avulla voidaan Olig2- positiivisia soluja löytää ventraalisesta telenkefalonista paremmin kuin perinteisellä menetelmällä. Vertailu perinteiseen menetelmään osoitti, että uusi menetelmä soveltuu oligodendrosyyttien esiasteiden havaitsemiseen ja siten kehittyvän ventraalisen telenkefalonin tutkimiseen. Telenkefalonin kehitys vaatii hermosolujen onnistunutta kulkeutumista. Na-K-Cl kotransportteri 1 (NKCC1) on proteiini, jonka tehtävänä on hermosolujen tilavuuden säätely; proteiini säätelee myös solujen jakautumista kehityksen aikana. Kehittyvissä aivoissa suurin määrä NKCC1- proteiinia löytyy ventralisesta telenkefalonista. Tämä NKCC1:n ilmentymisen alue vastaa aluetta, jossa hermosolujen esiasteet esiintyvät. Olemme osoittaneet NKCC1- poistogeenisissä hiirissä, että NKCC1 proteiini säätelee solusykliä ja vaikuttaa oligodendrosyyttien ja interneuronien tuotantoon. Kun interneuronit ovat syntyneet, ne kulkeutuvat kehittyvälle aivokuorelle. Olemme tutkineet Syndecan 3- proteiinin roolia tässä tapahtumassa. Tulokset osoittavat, että GDNF (glial derived neurotrophic factor) ja syndecan 3- proteiinin yhteistoiminta säätelee interneuronien kulkeutumista telenkefalonissa. Syndecan-3- poistogeenisissä hiirissä interneuronien kulkeutuminen oli häiriintynyt. Yhteenvetona, tutkimuksemme on tuottanut tärkeää tietoa kahdesta olennaisesta mekanismista, jotka säätelevät interneuronien ja oligodendrosyyttien kehitystä

Heparan sulfate proteoglycan syndecan-3 is a novel receptor for GDNF, neurturin, and artemin

Syndecan-3 may act alone or as a coreceptor with RET to promote cell spreading, neurite outgrowth, and migration of cortical neurons by GNDF, NRTN, and ARTN

NKCC1-deficiency results in abnormal proliferation of neural progenitor cells of the lateral ganglionic eminence

The proliferative pool of neural progenitor cells is maintained by exquisitely controlled mechanisms for cell cycle regulation. The Na-K-Cl cotransporter NKCC1 is important for regulating cell volume and the proliferation of different cell types in vitro. NKCC1 is expressed in ventral telencephalon of embryonic brains suggesting a potential role in neural development of this region. The ventral telencephalon is a major source for both interneuron and oligodendrocyte precursor cells. Whether NKCC1 is involved in the proliferation of these cell populations remains unknown. In order to assess this question, we monitored several markers for neural, neuronal, and proliferating cells in wild-type and NKCC1 knockout mouse brains. We found that NKCC1 was expressed in neural progenitor cells from the lateral ganglionic eminence (LGE) at E12.5. Mice lacking NKCC1 expression displayed reduced PH3-labeled mitotic cells in the ventricular zone and reduced cell cycle reentry. Accordingly, we found a significant reduction of Sp8-labeled immature interneurons migrating from the dorsal LGE in NKCC1-deficient mice at a later developmental stage. Interestingly, at E14.5, NKCC1 regulated also the formation of Olig2-labeled oligodendrocyte precursor cells. Collectively, these findings show that NKCC1 serves in vivo as a modulator of the cell cycle decision in the developing ventral telencephalon at the early stage of neurogenesis. These results present a novel mechanistic avenue to be considered in the recent proposed involvement of chloride transporters in a number of developmentally related diseases such as epilepsy, autism, and schizophrenia