Achondroplasia (ACH) is a representative skeletal disorder characterized by rhizomelic shortened limbs and short stature. ACH is classified as belonging to the fibroblast growth factor receptor 3 (FGFR3) group. The downstream signal transduction of FGFR3 consists of STAT1 and RAS/RAF/MEK/ERK pathways. The mutant FGFR3 found in ACH is continuously phosphorylated and activates downstream signals, resulting in abnormal proliferation and differentiation of chondrocytes in the growth plate and cranial base synchondrosis. A patient registry has been developed and has contributed to revealing the natural history of ACH patients. Concerning the short stature, the adult height of ACH patients ranges between 126.7–135.2 cm for men and 119.9–125.5 cm for women in many countries. Along with severe short stature, foramen magnum stenosis and spinal canal stenosis are major complications: the former leads to sleep apnea, breathing disorders, myelopathy, hydrocephalus, and sudden death, and the latter causes pain in the extremities, numbness, muscle weakness, movement disorders, intermittent claudication, and bladder-rectal disorders. Growth hormone treatment is available for ACH only in Japan. However, the effect of the treatment on adult height is not satisfactory. Recently, the neutral endopeptidase-resistant CNP analogue vosoritide has been approved as a new drug for ACH. Additionally in development are a tyrosine kinase inhibitor, a soluble FGFR3, an antibody against FGFR3, meclizine, and the FGF2-aptamer. New drugs will bring a brighter future for patients with ACH.

The pituitary gland is endocrine tissue composed of two distinct parts with different origins: the adenohypophysis (adenohypophyseal placode origin) and the neurohypophysis (neuroectoderm origin). Differentiation of endocrine cells in the pituitary gland leads to hormone synthesis, secretion into the capillary network, and transportation to target organs. In 1988, the discovery of the pituitary transcription factor PIT1 sparked research on endocrine cell differentiation. In the twenty-first century, the discovery that SOX2-positive stem/progenitor cells give rise to all types of pituitary endocrine cells advanced research on differentiation processes using diverse marker molecules. Lineage tracing using specific marker genes from early embryos revealed that during construction of the anterior pituitary from the adenohypophyseal placodal cells the developing anterior pituitary incorporates diverse cell types originating from the neural crest-derived and ectodermal-derived cells. Consequently, the postnatal anterior pituitary becomes a mosaic of terminally differentiated cells of different origin and with different life histories. It has also been revealed that most of the postnatal stem/progenitor cells form at least solid clusters in the parenchyma. Moreover, the classification and role of S100β-positive cells had been ambiguous, but now they are identified as a major component of postnatal stem/progenitor cells. This paper provides an updated overview of pituitary development.

Androgens play a vital role not only in promoting the development of male sexual characteristics but also in exerting diverse physiological effects, including the regulation of skeletal muscle growth and function. Given that the effects of androgens are mediated through androgen receptor (AR) binding, an understanding of AR functionality is crucial for comprehending the mechanisms of androgen action on skeletal muscles. Drawing from insights gained using conditional knockout mouse models facilitated by Cre/loxP technology, we review the cell-specific functions of AR in skeletal muscles. We focus on three specific cell populations expressing AR within skeletal muscles: skeletal muscle cells, responsible for muscle contraction; satellite cells, which are essential stem cells contributing to the growth and regeneration of skeletal muscles; and mesenchymal progenitors, situated in interstitial areas and playing a crucial role in muscle homeostasis. Furthermore, the indirect effects of androgens on skeletal muscle through extra-muscle tissue are essential, especially for the regulation of skeletal muscle mass. The regulation of genes by AR varies across different cell types and contexts, including homeostasis, regeneration and hypertrophy of skeletal muscles. The varied mechanisms orchestrated by AR collectively influence the physiology of skeletal muscles.

Bone secrets the hormone, fibroblast growth factor 23 (FGF23), as an endocrine organ to regulate blood phosphate level. Phosphate is an essential mineral for the human body, and around 85% of phosphate is present in bone as a constituent of hydroxyapatite, Ca₁₀(PO₄)₆(OH)₂. Because hypophosphatemia induces rickets/osteomalacia, and hyperphosphatemia results in ectopic calcification, blood phosphate (inorganic form) level must be regulated in a narrow range (2.5 mg/dL to 4.5 me/dL in adults). However, as yet it is unknown how bone senses changes in blood phosphate level, and how bone regulates the production of FGF23. Our previous data indicated that high extracellular phosphate phosphorylates FGF receptor 1 (FGFR1) in an unliganded manner, and its downstream intracellular signaling pathway regulates the expression of GALNT3. Furthermore, the post-translational modification of FGF23 protein via a gene product of GALNT3 is the main regulatory mechanism of enhanced FGF23 production due to high dietary phosphate. Therefore, our research group proposes that FGFR1 works as a phosphate-sensing receptor at least in the regulation of FGF23 production and blood phosphate level, and phosphate behaves as a first messenger. Phosphate is involved in various effects, such as stimulation of parathyroid hormone (PTH) synthesis, vascular calcification, and renal dysfunction. Several of these responses to phosphate are considered as phosphate toxicity. However, it is not clear whether FGFR1 is involved in these responses to phosphate. The elucidation of phosphate-sensing mechanisms may lead to the identification of treatment strategies for patients with abnormal phosphate metabolism.

Collision tumors involving the metastasis of malignant neoplasms to pituitary neuroendocrine tumors (PitNETs) are extremely rare. We herein report a case involving a patient with lung adenocarcinoma metastasis within a PitNET who exhibited relatively rapid progression of neurological symptoms. A 75-year-old man who underwent tumor resection 36 and 18 years prior to presentation for bladder and colon cancer, respectively, without recurrence presented with bitemporal hemianopsia, ptosis, and diplopia of the right eye. Subsequent magnetic resonance imaging (MRI) revealed a tumor 3.2 cm in diameter that extended from the anterior pituitary gland to the suprasellar region. Gadolinium-enhanced MRI of the tumor showed heterogeneous contrast enhancement. Considering the relatively rapid progression of neurological symptoms, semi-emergency endoscopic endonasal transsphenoidal surgery was performed. Histopathological examination revealed a group of thyroid transcription factor-1- and napsin A-positive papillary proliferating cells intermingled with α-subunit- and steroidogenic factor-1-positive PitNET cells. Thus, the patient was diagnosed with lung adenocarcinoma metastasis within a gonadotroph PitNET. Genetic testing revealed the presence of an EGFR (Ex-19del) mutation, after which chemotherapy was initiated. Additional stereotactic radiotherapy was performed for the residual tumor in the sella turcica. With continued chemotherapy, good control of both the primary and metastatic tumors was noted after 24 months after surgery. Cases of malignant neoplasm metastasis within a PitNET are difficult to diagnose. In the case of a sella turcica tumor with relatively rapid progression of neurological symptoms, early surgical intervention is recommended given the possibility of a highly proliferative tumor and the need to obtain pathologic specimens.