Referee 2's Review:

Direct Islation, Culture and Transplantation of Mouse Skeletal Muscle Derived Endothelial Cells with Angiogenic Potential

The work describes the isolation of the cells and demonstrates their angiogenic potential after injection or implantation within a matrigel pad.

The analytical data and the results presented are over all of good quality. Major criticism are the poor description of the isolation procedure, in particular the setting of the sorting conditions for the enrichment of the EC subtypes specified. In addition the quality of the qRT-PCR should be improved and statistical variations included. This is in particular interesting because the non-quantitative RT-PCR data shown in the same figure do not reflect the observed trends.

In the transplantation experiments the major concern is, wether the seeding of new vessels is soley derived from the transplanted material or also from endogenous sources. The visualization of transplanted cell material should be superimposed with staining for overall newly formed vessels in the tissue. I also would suggest to compare the effects of selected muscle EC with mock injections and injections of cell material not enriched for EC.

Other corrections:

Figure 1: This figure is quite complicated and not easily understandable. This should be improved, in particular to make the selection (gate setting) better understandable for readers.

Figure 2: This figure should demonstrat the overlap of the various markers used, I can only see a clear overlap for CD34 and CD31 all the others is more like a guess. May be there are figures available that make the co-expression of the markers more clear. Or focus on potential distinct cell types within the tissue that express different markers.

Minor corrections: there are some incomplete sentences:
e.g. Abstract line 6.

**********
N.B. These are the comments made by the referee when reviewing an earlier version of this paper. Prior to publication the manuscript has been revised in light of these comments and to address other editorial requirements.