The current study demonstrates to our knowledge for the first time that this protein is also markedly expressed in postnatal CNS tissue and therefore not restricted to muscle tissue. Western-blot Sipeimine analysis and quantitative PCR revealed a transient retinal MLP expression starting at E20, reaching a peak between P7 and P14 and absence in the adult retina. Immunohistochemical analysis confined 
MLP expression in cholinergicAC. These neurons are one of at least 26 distinguishable AC subtypes with the ability to produce the neurotransmitter acetylcholine and are involved in the maturation of postnatal retinaas well as motion sensation by the visual apparatus. In rodents, first AC are born at E8/E9, along with retinal ganglion cells, horizontal cells and cone photoreceptors. AC genesis peaks at E16/E17, but proceeds at least until P5/P7. Consistent with the data presented in the current study, cholinergic AC start to express choline acetyltransferaseat around E18 and therefore almost simultaneously to the observed induction of retinal MLP-expression. However, in contrast to the lifelong expression of ChAT, MLP is only expressed throughout the first 3 weeks after birth and 4-Aminohippuric Acid absent in adult AC. During this postnatal time period AC form dendrites, establish two well-separated cholinergic dendritic layers in the IPL and make synapses on RGCs and bipolar cells. This process also timely overlaps with the emergence of spontaneous acetylcholine dependent waves of excitatory activity between P0 and P11, which are important for the formation of synapses and the establishment of neural circuits between retinal neurons. The formation of specific synapses between cholinergic AC and direction-selective RGCs, known to be crucial for motion sensing, occurs in the second postnatal week and is therefore timely correlated with morphologic maturation of AC. Maturation of cholinergic AC is eventually accomplished at postnatal day 15, the time of eye openingand of detected decrease of MLP expression, suggesting a potential functional involvement of this protein in this context. Future studies still have to investigate the potential role of MLP during AC development. To this end the morphology of AC or other retinal cells as well as the visual function of MLP deficient and wild-type mice could be compared with each other to identify potential differences. In muscle tissue MLP is crucially involved in myogenesis and myocyte differentiation, requiring the localization of MLP in the nucleus, where it serves as transcriptional cofactor and modulates the expression of myocyte specific genes. In addition, MLP is also located in the cytoplasm where it might promote the assembly of cytoskeletal proteins along actin-based filaments. As MLP was only detected in the cytoplasm of AC it appears more likely that it is rather involved in the organization of cytoskeleton than regulation of gene expression in these neurons. In this context MLP may support the growth and stratification of dendrites or synapse formation. MLP has been shown to interact with a broad variety of proteins belonging to different functional classes in muscle tissue. In particular, interactions of MLP with aactin, actin-binding proteins like cofilin 2, spectrins or even metabolic enzymes like D-lactate dehydrogenasewere described. Therefore, the role of MLP in cholinergic AC might depend on the interaction with several partners. Further research is required to address these possibilities.