Sclerotome induction and differentiation.

Inductive events in the development of the sclerotome and their possible underlying mechanisms were reviewed from the primary literature. A brief review of morphological and anatomical aspects of sclerotome development was given. The importance of the notochord and neural tube in sclerotome induction and somite chondrogenesis in vivo and in vitro was established. The functions and patterns of expression of different sclerotome markers were discussed. Shh and Noggin were discussed as two molecules produced by the neural tube and notochord that appear to maintain and initiate the sclerotome, respectively. While the abilities of the axial organs and Shh and Noggin to induce sclerotome marker expression in the somite was not disputed, the exact nature of these inductions was discussed with regard to possible effects on gene expression, effects on cell survival, and physical effects on the cells and it was argued that the fundamental nature of inductive events in the sclerotome is still unknown.

Mentoring in biomedical science graduate programs: a student's perspective.

The traditional model for the mentoring of graduate students has been for the student to receive all formal mentoring from the thesis advisor, the laboratory principal investigator (PI). While this continues to be a successful model for some students, other students find that they need or desire additional mentors during their graduate career. Graduate programs have a responsibility to provide their students with increased mentoring opportunities. Three means that graduate programs could use to serve the diverse needs of students are discussed as well as the potential benefits to the program and the students.

Determination of sclerotome to the cartilage fate.

When the somite first forms the cells appear to be equivalent in potential. In order to understand the lineage diversification of the somite, the determination of sclerotome cells to the cartilage fate was tested using an in vivo challenge assay in which quail sclerotome fragments were grafted into a dorsal position in a chick host. Grafts containing undetermined cells were expected to differentiate into other tissues while grafts containing determined chondrocyte precursors were expected to consistently give rise to cartilage. We found that grafted sclerotome fragments from somite stages V-XX were capable of giving rise to integrated muscle and dermis and that it was not until fragments from stage XII somites were grafted that cartilage was consistently produced in the assay. Sclerotomal tissue from embryonic day 4-6 embryos remained as morphologically unintegrated mesenchyme when grafted into an embryonic day 2 host, but formed only cartilage when placed into an identically aged host. Vertebral body cartilage from embryonic day 7 and embryonic day 8 embryos formed exclusively ectopic cartilage in an embryonic day 2 host. We conclude that cells determined to the cartilage fate do not appear until somite stage XII, but that not all sclerotome cells are determined at this time. The effect of host age on the differentiation and morphogenetic behavior of sclerotome fragment grafts in this assay indicate the existence of developmental eras within the embryo.