Cannot derive from UTexture2D

i made a custom class:
UCLASS()
class UMyTexture2D : public UTexture2D
{
GENERATED_BODY()

};

got link error:
Error LNK2001 unresolved external symbol “public: virtual void __cdecl UTexture2D::Serialize(class FArchive &)” (?Serialize@UTexture2D@@UEAAXAEAVFArchive@@@Z) CryptEditorPlugin F:\UE4\CryptEditorPlugin\Intermediate\ProjectFiles\Module.EditorCrypt.cpp.obj 1

it’s ok with UTexture,why?