The "Dsl1p complex" in Saccharomyces cerevisiae, consisting of Dsl1p and Tip20p, is involved in Golgi-ER retrograde transport and it is functionally conserved from yeast to mammalian cells. To further characterize this complex, we analyzed the function of Dsl3p, a protein that interacts with Dsl1p in yeast two hybrids screens. DSL3, recently identified in a genome wide analysis of essential genes as SEC39, encodes a cytosolic protein of 82 kDa that is peripherally associated with membranes derived from the ER. There is strong genetic interaction between DSL3 and other factors required for Golgi-ER retrograde transport. Size exclusion chromatography and affinity purification approaches confirmed that Dsl3p is associated with subunits of the "Dsl1p complex." The complex also includes the Q/t-SNARE proteins, Use1p, Sec20p, and Ufe1p, integral membrane proteins that constitute the trimeric acceptor for R/v-SNAREs on Golgi-derived vesicles at the ER. Using mutants, we performed a detailed analysis of interactions between subunits of the Dsl1p complex and the ER-localized SNARE proteins. This analysis showed that both Dsl1p and Dsl3p are required for the stable interaction of the SNARE Use1p with a central subcomplex consisting of Tip20p and the SNARE proteins Ufe1p and Sec20p. INTRODUCTIONThe protein trafficking pathway in the yeast S. cerevisiae is composed of several distinct membrane-bounded compartments, which interact via a bidirectional flow of membranebounded vesicles in a process referred to as vesicular transport (Kaiser and Schekman, 1990;Rothman and Orci, 1992;Ferro-Novick and Jahn, 1994;Rothman, 1994;Waters and Hughson, 2000). Briefly, secretory proteins destined for transport must be sorted away from resident proteins, packaged into the proper cargo vesicles, and subsequently, delivered to the correct target membrane (Palade, 1975). Each step of this process must be tightly regulated to ensure efficient secretion and maintenance of the distinct cellular compartments. Transport in the retrograde direction ensures further rounds of anterograde transport by recycling components of the transport machinery, recovering wayward proteins and maintaining the balance of lipids between the distinct compartments of the pathway.The cell makes use of a variety of coated vesicles to transport proteins, whose formation is nucleated by the action of small GTP-binding proteins. Specifically, vesicle budding in the retrograde direction from the Golgi to the ER involves a heptameric coat protein complex called COPI (Waters et al., 1991;Stenbeck et al., 1993;Letourneur et al., 1994;Barlowe, 2000). The COPI coat consists of coatomer, an ϳ700 -800 kDa protein complex comprised of an equimolar assembly of ␣-, ␤-, ␤'-, ␥-, ␦-, ⑀-, and -COP (Cop1[Ret1]p, Sec26p, Sec27p, Sec21p, Ret2p, Sec28p, and Ret3p, respectively, in yeast) and a small ras-like GTPase termed Arf (encoded by ARF1 or ARF2).Current models of vesicular transport propose that the vesicle coat is removed soon after vesicles are formed (although this has not been di...

The molecular mechanisms of regionalization of the medial pallium (MP), the anlage of the hippocampus, and transitional (cingulate and retrosplenial) cortices are largely unknown. Previous analyses have outlined an important role of the transcription factor (TF) Zbtb20 for hippocampal CA1 field specification (Nielsen et al. (2007) Development 134:1133-1140; Nielsen et al. (2010) Cereb Cortex 20:1904-1914; Xie et al. (2010) Proc Natl Acad Sci USA 107:6510-6515). Here, we present novel data showing that Zbtb20 exhibits a ventral(high)-to-dorsal(low) gradient of expression in MP progenitors as well as an expression in postmitotic cells at the transitional cortex/neocortex border. Our detailed pattern analysis revealed that in Zbtb20 loss-of-function the molecular borders between neocortical, transitional, and hippocampal fields are progressively shifted ventrally, leading to an ectopic positioning of all dorsal fields into the neighboring ventrally located areas. Thus, in addition to its known importance for the specification of the hippocampal CA1 sector, the graded expression of TF Zbtb20 in ventricular zone of MP appears to translate early positional information for establishment of all developing MP fields. Our data also suggest that the signaling factor Wnt3a is a putative molecular partner of TF Zbtb20 in this patterning process.

BackgroundDuring corticogenesis, genetic programs encoded in progenitor cells at different developmental stages and inherited in postmitotic neurons specify distinct layer and area identities. Transcription factor Zbtb20 has been shown to play a role for hippocampal development but whether it is implicated in mammalian neocortical morphogenesis remains unknown.ResultsHere, we report that during embyogenesis transcription factor Zbtb20 has a dynamic spatio-temporal expression pattern in mitotic cortical progenitors through which it modulates the sequential generation of cortical neuronal layer identities. Zbtb20 knock out mice exhibited enhanced populations of early born L6-L4 neuronal subtypes and a dramatic reduction of the late born L3/L2 neurons. This defect was due to a temporal misbalance in the production of earlier versus later born neurons, leading to a progressive diminishing of the progenitor pool for the generation of L3-L2 neurons. Zbtb20 implements these temporal effects in part by binding to promoter of the orphan nuclear receptor CoupTF1/Nr2f1. In addition to its effects exerted in cortical progenitors, the postmitotic expression of Zbtb20 in L3/L2 neurons starting at birth may contribute to their proper differentiation and migration.ConclusionsOur findings reveal Zbtb20 as a novel temporal regulator for the generation of layer-specific neuronal identities.Electronic supplementary materialThe online version of this article (doi:10.1186/s13041-016-0242-2) contains supplementary material, which is available to authorized users.

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