INTRODUCTION

The pituitary gland is one of the most critical endocrine glands in mammals, and it can be divided into the anterior lobe and posterior lobe. The anterior pituitary gland comprises the pars distalis, pars tuberalis, and pars intermedia. The endocrine functions of the anterior pituitary gland are precisely regulated by hypothalamic neurons, which secrete releasing hormones into the hypothalamic‐hypophyseal portal system. These hormones modulate five major cell populations in the anterior pituitary: corticotropes (ACTH), somatotropes (GH), lactotropes (PRL), thyrotropes (TSH), and gonadotropes (LH and FSH). During development, the differentiation of these cell types is governed by specific transcription factor cascades: PIT1 directs the differentiation of somatotropes, lactotropes, and thyrotropes; TPIT determines corticotrope differentiation; and SF‐1 regulates gonadotrope differentiation. 1 , 2 , 3 Through the secretion of various hormones, anterior pituitary cells orchestrate essential physiological processes such as growth, development, behavior, and reproduction. They also influence internal homeostasis and regulate other endocrine organs. The dynamic balance of their secretory activity is fundamental to maintaining endocrine homeostasis and is closely associated with multiple major endocrine disorders. 4

In recent years, secretagogin (SCGN), a calcium‐binding protein, has garnered significant attention for its role in neuroendocrine regulation. As a member of the EF‐hand superfamily, SCGN is a highly conserved protein containing six EF‐hand domains. It is highly expressed in pancreatic β‐cells but is also found in the central nervous system and gastrointestinal enteroendocrine cells. 5 , 6 , 7 Recent studies indicate that SCGN regulates secretory granules dynamics by interacting with the core exocytotic SNARE protein SNAP‐25 and β‐actin, thereby serving as a key regulator in the vesicular secretion of hormones such as insulin, corticotropin‐releasing hormone, and oxytocin. 8 , 9 , 10 , 11 , 12

Accumulating evidence shows that SCGN is expressed in various neuronal and non‐neuronal cell types with exocytotic activity, including pituitary adenohypophyseal cells, hypothalamic cells, pancreatic, intestinal and thyroid cells. 13 , 14 , 15 However, its expression and function within the anterior pituitary gland remain largely unexplored. Therefore, this study aims to identify the cell types expressing SCGN in the anterior pituitary gland across different species (including mice, rats, pigs and humans) by employing scRNA‐seq analysis and immunostaining, and to provide a comparative expression atlas of SCGN that may help to assess whether its expression is evolutionarily conserved in the anterior pituitary and to what extent its function might be species‐restricted.