The Role And Mechanism Of Geminin In Hindbrain Patterning In Zebrafish

Geminin(Gem)is a small multifunctional protein,which is localized predominantly in the nucleus.It plays an important role in regulating cell proliferation, cell differentiation,embryonic development and cancer.And its existance in the nucleus is strongly dependent on the cell cycle phase.Geminin suppresses DNA re-replication during the cell cycle to maintain the genetic stability and promotes the G₂/M phase. Through the interaction with homeobox proteins such as Hox and Six3,geminin coordinates cell proliferation and differentiation,thus regulating embryonic development.The expression pattern of geminin is developmentally different.It can play both inductive and inhibitory roles in different developmental of cellular context. Kroll et al.have found that overexpressed geminin in Xenopus embryos led to an expansion of the neural plate.In our work,we first find that the dysfunctional geminin led to severe defects of hindbrain development.The hindbrain is the only part in the central nervous system development,which has a segmental pattem.By the time the posterior end of the neural tube closes,the hindbrain becomes subdivided into 7 parts along the anterior-posterior axis,termed rhombomeres.Using foxd3:GFP and islet1:GFP transgenic lines,we find that the knock down of geminin leads to defective migration of the hindbrain neural crest cell and misprojection of hindbrain neurons.The bone staining experiment indicates that the loss of geminin results in severe defects of branchial arch catilage derived from hindbrain neural crest.3A10 antibody staining shows that geminin is critical for the projection and cross of Mauthner neurons from rhombomere 4 of the hindbrain.All these results demonstrate that geminin plays an important part in hindbrain patterning during development.Further cell transplantation assay shows that the role of geminin in hindbrain patterning is cell non-autonomous.Using whole mount in situ hybridization,we fred that geminin is a negative regulator of FGF8,which is expressed in the isthmus,the midbrain-hindbrain boundary,and critical for the hindbrain patterning.In summary,geminin regulates hindbrain patterning through FGF8,thus regulating the hindbrain neuron projection and catilage development.