An ontogenic series of chick embryo brains (4,6,9,12,14,16 and 18 days of incubation, hatching day: 21) was coronally or saggitally sectioned and investigated for expression of the arginine vasotocin (AVT)/mesotocin (MT) gene. To this end a 39mer oligonucleotide recognizing the AVTlMT encoding sequence of their respective mRNAs was constructed employing optimized codon usage and was used for in situ hybridization. AVTlMT mRNA-expressing neurons were first detected on embryonal day (E) 6 adjacent to the third ventricle. By E9 the periventricular nucleus had expanded in size but the hybridization signal was weaker. These results suggest a migration of cells in all directions away from the third ventricle into the diencephalon; some perikarya were even observed at the lateral pial surface above the optic chiasm. By E12, brain differentiation had advanced to distinct hypothalamo-neurohypophyseal nuclei (supraoptic and paraventricular nuclei) as well as to accessory groups expressing AVTlMT mRNA. Two cell types were then distinguishable in the paraventricular nucleus; the specific mRNA was expressed either as a weak or a strong hybridization signal.Comparison with other studies suggested that differentiation had almost attained adult level though cell growth and differentiation of supraoptic and paraventricular nuclei still occurred. This was complete by El8 when individual cells were larger and the intensity of the hybridization signal became very strong.RNase pretreatment depressed the signal by 100%. Northern blot hybridization of RNA extracted from newly hatched chicks verified the specificity of the probe. A single band was evident, indicating an mRNA of approximately 700 bases, which is only found in hypothalamus and not in muscle, liver or extra-hypothalamic brain, and corresponds in size closely with mammalian vasopressin mRNA.The data demonstrate a very early development (E6) of neurohypophyseal hormone gene expression in the chick embryo brain with important differentiation around E9. At El2 magnocellular neuronal arrangement resembled adult neurons but the gene expression signal increased in intensity until E18.Once the egg is shelled inside the hen and once it is layed, the chick embryo develops independently of maternal support. Thus, the chick embryo offers a number of excellent advantages over mammalian systems to study hypothalamo-neurohypophyseal development and function (1). In addition, embryonic tissue is easily accessible and the embryology is well defined. The similarity in the structures, and in part, in the function of neurohypophyseal hormones between mammals and the chicken, suggests that the chicken model could provide very useful information to assess the ontogenetic regulation of these genes and may pertain for all homeotherms.Arginine vasotocin (AVT) and mesotocin (MT) are the avian analogues to the mammalian neuropeptide hormones vasopressin and oxytocin, respectively. Throughout the vertebrates, these neurohypophyseal nonapeptides can be classified into two types according to t...

The expression of proopiomelanocortin (POMC) mRNA, which plays an important role in neural, endocrine, neuroendocrine and immune systems, was studied by in situ hybridization during the development of pituitary in the domestic pig. The POMC gene was activated as early as fetal day 30 (E30). The signal for POMC mRNA in the anterior lobe progressively increased from E30 to E80 and then remained at relatively constant level. In contrast, POMC transcripts in the intermediate lobe first appeared at E40 and steadily increased during development. POMC transcripts in the brain were first found at E40 and were scattered in the arcuate nucleus (AN) and nucleus medialis thalami (NMT). At E50 the extra-pituitary POMC mRNA was located not only in the AN and NMT but also in the fasciculus tegmenti and entorhinal cortex. In the posterior lobe, no signal was detected. The specific pattern of expression of the pig POMC gene in the pituitary and in specific regions of the central nervous system suggests important roles for POMC in fetal development. These results also suggest that POMC is excellent for studying the expression and regulation of pituitary hormone genes because of its tissue-specific regulation and developmental pattern.

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