Hox Genes in Bombyx mori: From Segment Identity to Silk‑Gland Differentiation
Priyangana Chetia
Department of Sericulture, Forest College and Research Institute, Tamil Nadu Agricultural University, Mettupalayam-641 301, India.
Pramod K.
Department of Sericulture, Forest College and Research Institute, Tamil Nadu Agricultural University, Mettupalayam-641 301, India.
Pulak Rabha
CSB-REC, Lakhimpur-787 031, Assam, India.
Kongkon Jyoti Bora
Department of Entomology, Assam Agricultural University, Jorhat-785013, Assam, India.
Murthy S.
Department of Sericulture, Forest College and Research Institute, Tamil Nadu Agricultural University, Mettupalayam-641 301, India.
Rubi Sut *
Department of Sericulture, Forest College and Research Institute, Tamil Nadu Agricultural University, Mettupalayam-641 301, India.
*Author to whom correspondence should be addressed.
Abstract
Homeobox and Hox genes are conserved transcriptional regulators involved in insect segment identity, appendage patterning and tissue differentiation. This review examines the organisation and functional diversification of these genes in the silkworm, Bombyx mori, by integrating classical genetic observations with genomic, expression and functional studies. Genome analyses have identified 102 homeobox genes, including a structurally distinctive Hox cluster on chromosome 6 with a split arrangement and tandem homeobox duplications. Research on the E homeotic complex links variation in Ubx, abd-A and Abd-B activity to abdominal identity and proleg development. Studies of the Nc, Wes and Edl mutants, together with RNA-interference investigations, further implicate Antennapedia and Distal-less in thoracic and distal appendage formation. Beyond segment patterning, homeodomain regulators participate in silk-gland specification and compartmental regulation. Scr is associated with embryonic gland development, whereas Antp regulates sericin and other silk-protein genes in the middle silk gland. The LIM-homeodomain factor Awh contributes to fibroin-gene activation in the posterior silk gland. Taken together, these findings support a context-dependent role for Hox and related homeobox factors in both developmental patterning and silk-gland gene expression. Unresolved questions concern the regulatory elements underlying homeotic variation, Hox–Dll interactions and tissue-specific transcriptional mechanisms. Targeted genome editing and spatially resolved molecular approaches may help address these questions.
Keywords: Bombyx mori, Hox genes, homeobox, homeotic mutation, Antennapedia, Ultrabithorax, abdominal-A, proleg, silk gland, silk protein, developmental regulation