Biomedical subjects

Stacey S Huppert

Publications and source records attributed to Stacey S Huppert.

4 recordsLinked to original sources

PubMed2005

Analysis of transmembrane domain mutants is consistent with sequential cleavage of Notch by gamma-secretase.

gamma-Secretase is a lipid-embedded, intramembrane-cleaving aspartyl protease that cleaves its substrates twice within their transmembrane domains (TMD): once near the cytosolic leaflet (at S3/epsilon) and again in the middle of the TMD (at S4/gamma). To address whether this unusual process occurs in two independent or interdependent steps, we investigated how mutations at the S3/epsilon site in Notch1-based substrates impact proteolysis. We demonstrate that such mutations greatly inhibit not only gamma-secretase-mediated cleavage at S3 but also at S4, independent of their impact on NICD stability. These results, together with our previous observations, suggest that hydrolysis at the center of the Notch transmembrane domain (S4/gamma) is dependent on the S3/epsilon cleavage. Notch (and perhaps all gamma-secretase substrates) may be cleaved by sequential proteolysis starting at S3.

Amyloid Precursor Protein Secretases↗

PubMed2005

Analysis of Notch function in presomitic mesoderm suggests a gamma-secretase-independent role for presenilins in somite differentiation.

The role of Notch signaling in general and presenilin in particular was analyzed during mouse somitogenesis. We visualize cyclical production of activated Notch (NICD) and establish that somitogenesis requires less NICD than any other tissue in early mouse embryos. Indeed, formation of cervical somites proceeds in Notch1; Notch2-deficient embryos. This is in contrast to mice lacking all presenilin alleles, which have no somites. Since Nicastrin-, Pen-2-, and APH-1a-deficient embryos have anterior somites without gamma-secretase, presenilin may have a gamma-secretase-independent role in somitogenesis. Embryos triple homozygous for both presenilin null alleles and a Notch allele that is a poor substrate for presenilin (N1(V-->G)) experience fortuitous cleavage of N1(V-->G) by another protease. This restores NICD, anterior segmentation, and bilateral symmetry but does not rescue rostral/caudal identities. These data clarify multiple roles for Notch signaling during segmentation and suggest that the earliest stages of somitogenesis are regulated by both Notch-dependent and Notch-independent functions of presenilin.

Amyloid Precursor Protein Secretases↗

PubMed2004

A requirement for Notch1 distinguishes 2 phases of definitive hematopoiesis during development.

Notch1 is known to play a critical role in regulating fates in numerous cell types, including those of the hematopoietic lineage. Multiple defects exhibited by Notch1-deficient embryos confound the determination of Notch1 function in early hematopoietic development in vivo. To overcome this limitation, we examined the developmental potential of Notch1(-/-) embryonic stem (ES) cells by in vitro differentiation and by in vivo chimera analysis. Notch1 was found to affect primitive erythropoiesis differentially during ES cell differentiation and in vivo, and this result reflected an important difference in the regulation of Notch1 expression during ES cell differentiation relative to the developing mouse embryo. Notch1 was dispensable for the onset of definitive hematopoiesis both in vitro and in vivo in that Notch1(-/-) definitive progenitors could be detected in differentiating ES cells as well as in the yolk sac and early fetal liver of chimeric mice. Despite the fact that Notch1(-/-) cells can give rise to multiple types of definitive progenitors in early development, Notch1(-/-) cells failed to contribute to long-term definitive hematopoiesis past the early fetal liver stage in the context of a wild-type environment in chimeric mice. Thus, Notch1 is required, in a cell-autonomous manner, for the establishment of long-term, definitive hematopoietic stem cells (HSCs).

Animals↗

PubMed2004

Notch pathway is dispensable for adipocyte specification.

In the past decade we have witnessed an epidemic of obesity in developed countries. Therefore, understanding the mechanisms involved in regulation of body weight is becoming an increasingly important goal shared by the public and the scientific community. The key to fat deposition is the adipocyte, a specialized cell that plays a critical role in energy balance and appetite regulation. Much of our knowledge of adipogenesis comes from studies using preadipocytic cell lines that have provided important information regarding molecular control of adipocyte differentiation. However, they fall short of revealing how naive cells acquire competence for adipogenesis. Studies in preadipocytes indicate that the Notch pathway plays a role in regulating adipogenesis (Garces et al.: J Biol Chem 272:29729-29734, 1997). Given the known biological functions of Notch in mediating cell fate decisions (Artavanis-Tsakonas et al.: Science 284:770-776, 1999), we wished to test the hypothesis that the Notch pathway is required for this cellular program by examining adipogenesis in several genetic loss-of-function models that encompass the entire pathway. We conclude that the "canonical" Notch signaling pathway is dispensable for adipocyte specification and differentiation from either mesenchymal or epithelial progenitors.

Adipocytes↗