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Ontogeny of parathyroid hormone-related protein in the ovine parathyroid gland
R J MacIsaac1, I W Caple, J A Danks
1St. Vincent's Institute of Medical Research, Fitzroy, Victoria, Australia.
Insights
Parathyroid hormone-related protein (PTHrP) is present in developing ovine parathyroid glands, suggesting its role in fetal and neonatal calcium regulation. This study investigated PTHrP ontogeny in sheep, finding it in fetal and lamb glands but not maternal ones.
Area of Science:
- Endocrinology
- Developmental Biology
- Calcium Metabolism
Background:
- Parathyroid hormone-related protein (PTHrP) is known to play a role in calcium regulation during fetal development.
- The specific ontogeny and localization of PTHrP within the parathyroid gland during mammalian fetal and neonatal life require further elucidation.
Purpose of the Study:
- To examine the ontogeny of PTHrP in ovine parathyroid glands from fetal to neonatal stages.
- To determine the presence and localization of immunoreactive PTHrP in ovine parathyroid glands using various immunological techniques.
Main Methods:
- Immunohistochemistry was employed to visualize PTHrP in parathyroid gland sections from fetal, neonatal lambs, and maternal ewes.
- Western blot analysis and Radioimmunoassay (RIA) were utilized to detect and quantify PTHrP in parathyroid gland extracts.
- Antisera against different fragments of human PTHrP (hPTHrP) were used for specific detection.
Main Results:
- Positive PTHrP immunostaining was observed in fetal (gestation day 116) and neonatal lamb parathyroid glands, but not in maternal glands, using PTHrP(50-69) antiserum.
- Western blot and RIA detected PTHrP in newborn lamb parathyroid extracts, identifying a substance of 14.4K molecular weight similar to hPTHrP(1-84).
- Newborn lamb parathyroid glands contained significantly higher levels of PTHrP (0.35 ng/micrograms) compared to maternal glands (0.035 ng/micrograms).
Conclusions:
- The detection of immunoreactive PTHrP in developing ovine parathyroid glands supports its involvement in fetal and neonatal calcium homeostasis.
- PTHrP is likely produced within the parathyroid gland itself and plays a crucial role in regulating calcium metabolism during mammalian development.
Abstract:
PTH-related protein (PTHrP) has been implicated in calcium regulation during fetal life. In this study the ontogeny of PTHrP was examined in ovine parathyroid glands. Immunohistochemical techniques, Western blot analysis, and a RIA with antisera raised against synthetic fragments of human (h) PTHrP (i.e. 1-34, 1-40, 50-69, and 107-141) were used to detect the presence of immunoreactive PTHrP in parathyroid glands from fetal and neonatal lambs and maternal ewes. Positive immunostaining for PTHrP was observed in fetal (from 116 days of gestation) and lamb (up to 180 days post birth) but not maternal parathyroid glands with the PTHrP(50-69) antiserum. Fetal and lamb parathyroid glands consisted entirely of one cell type in which PTHrP immunoreactivity to PTHrP(50-69) antiserum was found. In contrast, immunoreactivity to PTHrP could not be detected in sections of fetal, lamb, or maternal parathyroid glands with antisera raised against PTHrP(1-34) or PTHrP(107-141). However, PTHrP immunoreactivity in urea/acid extracts of newborn lamb parathyroid glands could be detected by Western blot analysis and RIA with antisera raised against the N-terminal portion of PTHrP. Western blot analysis with the PTHrP(1-34) antisera revealed that urea/acid extracts of newborn lamb parathyroid glands contained a substance with a mol wt of 14.4K, which corresponded in size to that of hPTHrP(1-84). Newborn lamb parathyroid glands contained 0.35 ng PTHrP/micrograms extract, whereas maternal parathyroid glands contained only 0.035 ng PTHrP/micrograms extract when tested in a RIA employing recombinant hPTHrP(1-84) as standard and an antibody raised against hPTHrP(1-40). The detection of immunoreactive PTHrP in the developing ovine parathyroid gland provides further evidence to support the suggestion that PTHrP produced in the parathyroid gland is involved in the normal hormonal regulation of calcium metabolism in the mammalian fetus and neonate.