On 2014 Feb 20, Markus Meissner commented:

Thank you very much for your feedback and the constructive criticism regarding our paper. We agree with some of the criticism regarding the nature of the localisation of TgStx6. Based on the co-localisation data with proM2AP, VP1 and GRASP we were initially convinced that Stx6 is localising to early endosomes, similar to the situation in ophistokonts. However, EM and IEM analysis did not result in the identification of EE but rather it appears that Stx6 is localising to the TGN as mentioned in the manuscript. However, we do not rule out that EEs exist and propose it as a hypothesis that apicomplexans have a more plant-like configuration.

With respect to other co-localisations with Rab5 or GalNac, we had some technical problems with these assays. As described in Kremer et al., 2013 overexpression of Rab5A (and Rab5C) leads to significant defects in the secretory system and therefore colocalisation analysis of parasites (over-) expressing both markers turned out to be not reliable. However, we agree that colocalisation with GalNac on transgenic parasites expressing endogenously tagged Stx6 would add additional information and should be performed in the future.

As you point out there is currently much confusion in the field if we can call something endosomal or endosomal-like. As one anonymous reviewer put it:” The authors are very generous in their use of the tern “endosome” in an organism where no form of endocytosis has even been seen. It might be better to define the process studied here as post-golgi membrane trafficking. “ We believe that unless one is very familiar with the terminology surrounding vesicular trafficking in Toxoplasma, the literature is very confusing. Therefore it might be the time where we have to agree on a common nomenclature based on the localisation of known markers, so that everyone has a clearer idea of the endomembrane system.

On 2014 Feb 19, Vernon B Carruthers, PhD commented:

Our group reviewed this paper for journal club recently. The group appreciated the novelty and importance of the study in defining new players in the elaborate vesicular transport system of the parasite. The main point raised was the unclear basis for stating that the study provided no "conclusive evidence for early endosomes in the parasite" and that the parasite likely harbors a fused TGN-EE similar to plants. The study did not attempt to look for early endosomes. It is widely acknowledged that there is limited published evidence that T. gondii can internalize exogenous material into its endocytic system. Nonetheless, Rab5, which is a classic marker for early endosomes has been used in several studies to define a mid-apical compartment that is associated with other markers of endosome-like compartments. Likewise, a previously characterized marker for the TGN, UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferase or GalNac for short, was not tested. Comparing the localization of TgStx6 with these markers would help clarify the issue of a merged or separate TGN-EE in T. gondii.

On 2014 Feb 19, Vernon B Carruthers, PhD commented:

Our group reviewed this paper for journal club recently. The group appreciated the novelty and importance of the study in defining new players in the elaborate vesicular transport system of the parasite. The main point raised was the unclear basis for stating that the study provided no "conclusive evidence for early endosomes in the parasite" and that the parasite likely harbors a fused TGN-EE similar to plants. The study did not attempt to look for early endosomes. It is widely acknowledged that there is limited published evidence that T. gondii can internalize exogenous material into its endocytic system. Nonetheless, Rab5, which is a classic marker for early endosomes has been used in several studies to define a mid-apical compartment that is associated with other markers of endosome-like compartments. Likewise, a previously characterized marker for the TGN, UDP-GalNAc:polypeptide N-acetylgalactosaminyltransferase or GalNac for short, was not tested. Comparing the localization of TgStx6 with these markers would help clarify the issue of a merged or separate TGN-EE in T. gondii.