| OCR Text |
Show 104 proliferating pool of progenitors, and that upon loss of HGF ligands, the muscle cells begin to differentiate, which is consistent with the timing of diaphragm myofiber differentiation. Distinguishing between these two hypotheses would require a Cre allele that specifically deletes Hgf in the PPFs, or alternatively, you could use PPF cultures to test the effects of HGF. Addition of HGF protein could distinguish whether it is required for increased proliferation and maintenance of the progenitor state or migration of resident muscle cells. The effects of HGF protein could also be tested in diaphragm explant cultures. While my Hgf expression time course strongly suggests that Hgf expression is required in the PPFs for muscularization of the diaphragm, this has not been explicitly shown. Deletion of Hgf in the PPFs using the Prx1Cre allele yielded a range of phenotypes from complete amuscularization of the diaphragm to partial muscularization. Surprisingly, only a small percentage of embryos with partially muscularized diaphragms had CDH. It is not clear from these results whether Prx1Cre is deleting Hgf before delamination or if it is required in the PPFs. If Hgf is required in the PPFs, mosaic recombination, characteristic of the Prx1Cre allele, may result in less severe phenotypes. While you could look earlier in development when Lbx1+ migratory muscle precursors are delaminating, the resulting phenotype would remain unknown. However, if delamination was inhibited in all mutant embryos then you could conclude that Prx1Cre is deleting Hgf too early to assess the requirement of Hgf in the PPFs. Deletion of Hgf in muscle did not result in diaphragm defects. I also tested whether Hgf was required in the PPFs using the tamoxifen- |
