Reg-1α Promotes Differentiation of Cortical Progenitors via Its N-Terminal Active Domain

Abstract

Reg-1α belongs to the Reg family of small, secreted proteins expressed in both pancreas and nervous system. Reg-1α is composed of two domains, an insoluble C-type lectin domain and a short soluble N-terminal peptide, which is released from the molecule upon proteolytic N-terminal processing, although the biological significance of this proteolysis remains unclear. We have previously shown that binding of Reg-1α to its receptor Extl3 stimulates axonal outgrowth. Reg-1α and Extl3 genes are expressed in the developing cortex but their expression decreases in adulthood, pointing to a possible function of this signaling system at the early developmental stages. Here, we demonstrate that recombinant Reg-1α increases migration and differentiation of cultured embryonic rat telencephalic progenitors via the activation of GSK-3β activity. In vivo overexpression of Reg-1α by in utero electroporation, has a similar effect, favoring premature differentiation of cortical progenitors. Notably, the N-terminal soluble domain, but not the C-type lectin domain, is largely responsible for Reg-1α effects on cortical neuronal differentiation. We thus conclude that Reg-1α via its proteolytically generated N-terminal domain is required for basic development processes.

Reg-1α, a New Substrate of Calpain-2 Depending on Its Glycosylation Status

“…Considering our previous results on the role of Reg-1α in the central nervous system, the study of the impact of Reg-1α cleavage by calpain-2 appears pertinent for a better understanding of the structure–function relationship of Reg-1α in both physiological and pathological contexts. Indeed, we previously showed that during development the whole molecule was able to promote neurite outgrowth, and that this was the fact of the undecapeptide action [ 6 , 48 ]. In situations where the amount of glycosylation is altered and calpains overactivated, such as neurodegenerative diseases or diabetes, calpain cleavage of Reg-1α would generate two new entities: i.e., a peptide of only four amino acids, and the Reg-1α ΔN1−4 fragment.…”

“…The particularity of these members is the presence of a C-type lectin domain linked to a short N-terminal peptide. The latter can be generated by trypsin hydrolysis and was shown to be essential to the inhibitory activity of the protein on CaCO 3 crystal growth [ 5 ], or the differentiation of rodent telencephalic neuronal precursors during brain development [ 6 ]. Moreover, biochemical studies have revealed that Reg-1α is O-glycosylated on a unique site located in this specific part of the molecule, Thr 5 [ 7 , 8 ].…”