mRNA coding for oxytocin is present in axons of the hypothalamo-neurohypophysial tract.

Abstract

Neuronal mRNA is thought to be restricted to perikaryal and dendritic compartments containing rough endoplasmic reticulum. We have used both in situ hybridization and DNA polymerase chain reaction methods to determine the precise intracellular distribution of oxytocin mRNA. Using light-and electron-microscopic detection of in situ hybridization with 5'-bromo-2'-deoxyuridine-labeled oligonucleotide probes, we found oxytocin mRNA in axons and Herring bodies in the lateral and ventral hypothalamus, the median eminence, and the posterior lobe of the pituitary in postpartum lactating rats. Southern blot analysis of the amplification products confirmed the presence of oxytocin mRNA in all three tissue samples. The present findings indicate that oxytocin mRNA can be transported axonally. Such transport could reflect an adventitious compartmentalization or a functional storage in Herring bodies for subsequent secretion. In the mammalian brain, specific intradendritic mRNAs are seen consistently (1,8,9). On the other hand, Guitteny and Bloch (10), using autoradiographic detection of vasopressin mRNA hybridization by both light and electron microscopy, reported that hybridization was restricted to perinuclear cytoplasm. Nevertheless, the micrographs presented in this study do not exclude the possibility that vasopressin mRNA is present in more distal neuronal processes. McCabe et al. (11) reported the presence of vasopressin mRNA in extracts of the posterior lobe by using solution hybridization. Although they did not directly determine the cellular origin of this mRNA, they suggested that it might arise from pituicytes (11), the major cell type in the posterior pituitary other than the vascular elements.We recently developed an immunocytochemical method for in situ hybridization with BrdUrd-labeled oligonucleotide probes (12). This sensitive nonradioactive method also provides resolution of hybridization sites by electron microscopy. In a recent light microscopy study, we found that oxytocin mRNA hybridization was present in neuronal processes at some distance from neuronal perikarya (13). Therefore, we initiated these studies to apply this method to an evaluation of possible intraaxonal localization of the mRNA for oxytocin in the posterior pituitary. The neurohypophysial magnocellular system is ideal for analysis ofthe intraneuronal compartmentalization of neuropeptide mRNAs as its cell bodies are concentrated within the hypothalamus, while the axons of these neurons are concentrated in neuron-free sites in the median eminence and neurophypophysis. Early lactating animals were chosen for these experiments to take advantage of their high rates of oxytocin synthesis (14) accompanied by high levels of oxytocin mRNA (15). Our results indicate that in this physiological state, the oxytocin mRNA can indeed be detected in the axons of oxytocincontaining neurons in the median eminence and the posterior pituitary by both light microscopy and ultrastructural in situ hybridization as well as in RNA samples from the poste...

Medium weight neurofilament mRNA in goldfish Mauthner axoplasm

“…In conclusion, the discovery of NF-M mRNA within the goldfish M-axon increases the number of known axonally localized mRNAs, including oxytocin mRNA in the rat hypothalamoneurohypophyseal tract [9], caudodorsal cell hormone mRNA in the central nervous system of the mollusc Lymnea stagnalis [5], kinesin mRNA in the squid giant axon [6], and arginine vasopressin precursor mRNA in rat hypothalamo magnocellular neurons [19]. The presence of mRNA in the M-axon is particularly significant given previous reports of tRNA, rRNA, polyribosomes, and protein synthesis in the M-axon [13][14][15].…”

“…The M-axon is a particularly advantageous preparation because more basic components of the translational machinery (transfer RNA (tRNA), ribosomal RNA (rRNA), and ribosomes) have been identified in the M-axon [13][14][15] compared to any other vertebrate axon. However, no direct evidence has been published for any mRNAs that could function as templates for protein synthesis in M-axoplasm, although mRNAs have been reported in other vertebrate axons [9,19] for which the presence of translational machinery …”

Fragile X Mental Retardation Protein: Nucleocytoplasmic Shuttling and Association with Somatodendritic Ribosomes

“…Although axons do not contain ribosomes, they do contain many mRNAs (Perrone-Capano et al, 1987). Some mRNA species have been identified that appear to be specifically targeted to axons, including those for ␤-actin (Olink-Coux and Hollenbeck, 1996), vasopressin (Trembleau et al, 1994;Mohr et al, 1995), oxytocin (Jirikowski et al, 1990), and BC1 (Tiedge et al, 1993). The lack of axonal ribosomes has led to an assumption that translation does not occur in axons, however, some evidence for axonal protein synthesis is beginning to accumulate (reviewed in Van Minnen, 1994).…”

“…The lack of axonal ribosomes has led to an assumption that translation does not occur in axons, however, some evidence for axonal protein synthesis is beginning to accumulate (reviewed in Van Minnen, 1994). It has also been hypothesized that axonal targeting of mRNA down-regulates protein synthesis by removing these mRNAs from the translating ribosomes (Jirikowski et al, 1990;Mohr et al, 1995). Whether FMRP has any functional significance in the axon still remains to be elucidated; however, it may play a role in the localization or regulation of some axonal mRNAs.…”

Effect of hypoosmolality on the abundance, poly(A) tail length and axonal targeting of arginine vasopressin and oxytocin mRNAs in rat hypothalamic magnocellular neurons

“…Interestingly, this is accompanied by an elongation of their poly(A) tails although the physiological significance remains to be determined [4][5][6]. Both AVP and OT mRNAs are subject to axonal targeting [7][8][9] and hyperosmolar stimuli give rise to a differential increase in the level of AVP (17-fold) and OT (3-fold) mRNAs in the axonal compartment [8,[10][11][12]. The axonal transcripts exhibit shorter poly(A) tracts than their counterparts in the cell bodies [2], and a poly(A) tail polymorphism following osmotic challenge is not observed for these transcripts [12].…”