EXPRESSION OF NEUROFILAMENT PROTEINS DURING DEVELOPMENT OF THE NERVOUS-SYSTEM IN THE SQUID LOLIGO-PEALEI

The squid nervous system includes various brain ganglia, optic lobes ( the visual center), and the stellate ganglia, the system of giant moto r fibers responsible for rapid jet-propelled escape behavior. The larg e caliber of giant fibers is due, in part, to the accumulation of squi d-specific neurofilaments (NFs) made up of a heavily phosphorylated NF 220 protein together with NF 70 and NF 60 subunits. Using antibodies prepared against known peptide sequences in these proteins, together w ith a mammalian-derived antibody that specifically recognizes phosphor ylated squid NF 220, we studied the localization of NFs in adult tissu es and during neural development. Immunoblot and immunohistochemical a nalyses showed that NFs were present in adult neural tissues, primaril y in selected fibers, with giant axons showing the most robust express ion. After the first neurons differentiated at stage 22, immunoblots s howed NF 60- and NF 70-immunoreactive proteins at all stages. The NF 2 20 subunit, however, was not detected in immunoblots at any developmen tal stage. Phosphorylated NF 220 immunoreactivity, although absent in immunoblots, was first seen in selected fibers of the stellate ganglia at stage 25, increasing thereafter in all giant fibers until hatching (stage 30). The stellate ganglion is the first neural tissue to acqui re a mature neurofilament complement (i.e., phosphorylated NF 220), sh ortly before the onset of jet-propelled escape behavior. The temporal pattern of expression of the NFs during development resembled that see n in vertebrates; i.e., the smaller NFs appeared before the larger sub unit in most neural tissues. In the squid, the expression pattern seem s to depend upon the post-transcriptional regulation of a single gene rather than upon transcriptional regulation of three independent genes as in vertebrates. (C) 1995 Wiiey-Liss, Inc.