Fate-restricted neural progenitors in the mammalian cerebral cortex.

During development of the mammalian cerebral cortex, radial glial cells (RGCs) generate layer-specific subtypes of excitatory neurons in a defined temporal sequence, in which lower-layer neurons are formed before upper-layer neurons. It has been proposed that neuronal subtype fate is determined by birthdate through progressive restriction of the neurogenic potential of a common RGC progenitor. Here, we demonstrate that the murine cerebral cortex contains RGC sublineages with distinct fate potentials. Using in vivo genetic fate mapping and in vitro clonal analysis, we identified an RGC lineage that is intrinsically specified to generate only upper-layer neurons, independently of niche and birthdate. Because upper cortical layers were expanded during primate evolution, amplification of this RGC pool may have facilitated human brain evolution.

Reelin regulates cadherin function via Dab1/Rap1 to control neuronal migration and lamination in the neocortex.

Neuronal migration is critical for establishing neocortical cell layers and migration defects can cause neurological and psychiatric diseases. Recent studies show that radially migrating neocortical neurons use glia-dependent and glia-independent modes of migration, but the signaling pathways that control different migration modes and the transitions between them are poorly defined. Here, we show that Dab1, an essential component of the reelin pathway, is required in radially migrating neurons for glia-independent somal translocation, but not for glia-guided locomotion. During migration, Dab1 acts in translocating neurons to stabilize their leading processes in a Rap1-dependent manner. Rap1, in turn, controls cadherin function to regulate somal translocation. Furthermore, cell-autonomous neuronal deficits in somal translocation are sufficient to cause severe neocortical lamination defects. Thus, we define the cellular mechanism of reelin function during radial migration, elucidate the molecular pathway downstream of Dab1 during somal translocation, and establish the importance of glia-independent motility in neocortical development.

Identification and characterization of CRG-L2, a new marker for liver tumor development.

Liver cancer is very common worldwide and the rates of hepatocellular carcinoma (HCC) have increased by over 70% in the last 2 decades in the US. Late diagnosis, because of the lack of clinical symptoms, and decreased hepatic function, because of underlying hepatic disease, lead to the extremely high mortality rates associated with HCC. Clearly, the identification of markers that are expressed early in the development of HCC and that are easily detected in high-risk patients would aid in early diagnosis and increased survival. We present the cloning and characterization of a novel gene, CRG-L2 (Cancer related gene-Liver 2), which displays high expression in murine and human hepatocellular carcinomas. Using in situ hybridization, we show that CRG-L2 mRNA levels are increased early during the development of liver tumors in C3H/HeJ mice, and that in normal tissues CRG-L2 mRNA is restricted to the murine testis and human placenta. Its restricted expression in normal tissues and unique early upregulation during tumor development make CRG-L2 an excellent candidate as a new clinical marker of HCC.